Jared G. Breyley and Brian R. Lindman
· Significant mitral or aortic valve disease is common and occurs in >10% of patients over 75 years old.
· History and physical examination play a prominent role in these patients as they often have physical findings long before the onset of symptoms.
· Primary care physicians are frequently the first doctors to recognize the physical findings in these patients. It is important to recognize cardiac murmurs that require further evaluation versus those that are benign flow murmurs (see Fig. 9-1).1 It is also important to know when to refer these patients to cardiac specialists.
Figure 9-1 Evaluation of heart murmurs. (Modified from Bonow RO, Carabello BA, Chatterjee K, et al. 2008 Focused Update Incorporated Into the ACC/AHA 2006 Guidelines for the Management of Patients With Valvular Heart Disease. J Am Coll Cardiol 2008;52:e1–e142.)
· The onset of symptoms (e.g., fatigue, increased dyspnea with exertion) in valvular heart disease is often quite insidious with a long period of asymptomatic progression in many patients.
· Advances in surgical and catheter-based techniques will provide additional, less invasive options for the treatment of severe valve disease.
· Determining whether and when to repair or replace a heart valve requires an integration of information about the severity of the valve disease, patient symptoms, and risk stratification.
Aortic Stenosis
GENERAL PRINCIPLES
· Aortic stenosis (AS) is usually present for many years before patients become symptomatic.
· There is a long latency with an excellent prognosis until chest pain, syncope, or heart failure develops.
· The operative mortality of isolated aortic valve replacement (AVR) is quite low in patients with isolated AS, normal left ventricular (LV) function, and relatively few comorbidities (<2% in experienced centers).1
· Treatment of high-risk and inoperable patients has been modified with the introduction of transcatheter aortic valve replacement (TAVR).
Pathophysiology
· AS results from an active valvular biology that leads to valve fibrosis and calcification; it occurs in 2% to 7% of patients >65 years of age.
· A bicuspid aortic valve occurs in 1% to 2% of the population and is associated with severe calcific AS at an earlier age (50s to 60s). It accounts for about 50% of valve replacements for AS.
· Maintenance of cardiac output in AS imposes a pressure overload on the LV, which leads to hypertrophic remodeling, diastolic dysfunction, increased myocardial oxygen demand, increased filling pressures, and eventually systolic dysfunction.
DIAGNOSIS
Clinical Presentation
History
· Generally, until the AS becomes severe, patients will not have symptoms directly attributable to the valve abnormality. Many patients with severe AS will be asymptomatic. Providers should be alert to the common scenario in which affected elderly patients subconsciously reduce activity and therefore report no symptoms.
· With the development of symptoms (e.g., angina, dizziness, syncope, heart failure), it is critical that these patients be seen and offered valve replacement expeditiously as the mean survival is 2 to 3 years for symptomatic severe AS.
· Risk factors for faster progression or a worse outcome include an elevated brain natriuretic peptide, abnormal exercise test, increased valve calcification, rapid increase in transvalvular gradient, higher transvalvular gradient, increased LV hypertrophic remodeling, diastolic dysfunction, and pulmonary hypertension.
Physical Examination
· The physical examination will reveal a harsh crescendo-decrescendo murmur heard over the aortic area and often radiating to the carotids.
· As the severity increases, the murmur peaks later and the aortic second sound (A2) becomes softer.
· The carotid upstroke becomes weaker and is delayed as the significance of AS increases (pulsus parvus et tardus).
Diagnostic Testing
Electrocardiography
· Electrocardiogram often reveals LV hypertrophy with strain.
Imaging
· Echocardiography:
o The development of quantitative Doppler echocardiography has revolutionized the care of these patients. The aortic valve area (AVA) and the peak jet across the valve can now be determined with accuracy (Table 9-1).
TABLE 9-1 Severity of Aortic Stenosis
Modified from Bonow RO, Carabello BA, Chatterjee K, et al. 2008 Focused Update Incorporated Into the ACC/AHA 2006 Guidelines for the Management of Patients With Valvular Heart Disease. J Am Coll Cardiol 2008;52:e1–e142.
o Any patient with a significant murmur (≥grade 3) in the aortic region should undergo echocardiography.
o Exercise testing may be beneficial in asymptomatic patients to unmask symptoms and further risk-stratify patients.
o Patients with an AVA <1 cm2 but low gradients due to low flow and low ejection fraction (EF) benefit from a dobutamine echocardiogram to clarify the severity of the AS and assess for contractile reserve.
· Cardiac MRI: Detection of myocardial fibrosis by MRI has been associated with increased mortality in patients with AS and may be helpful in risk stratification.
· Cardiac catheterization: Because of the high prevalence of coronary disease in patients with AS, all patients with chest pain and/or planned AVR should undergo coronary angiography.
TREATMENT
Medications
· There is no medical therapy specifically targeting AS that has been shown to improve clinical outcomes.
· It is important to treat any associated cardiovascular comorbidities (hypertension, coronary artery disease, atrial fibrillation, and heart failure) with appropriate medical therapy.
· In particular, hypertension is quite common in patients with AS and often undertreated due to concerns about inducing hypotension. Inadequately treated hypertension adds an additional detrimental load on the LV beyond the valvular stenosis.
Surgical Management
· AVR is the definitive treatment for AS and improves survival and quality of life, even in very elderly patients (>80 years of age).
· AVR is indicated for symptomatic patients with severe AS, asymptomatic patients with an EF < 50%, or those with moderate or severe AS undergoing cardiac surgery for another reason.
Percutaneous Management
· TAVR is a rapidly evolving, less invasive therapeutic alternative to surgical AVR for patients with severe AS.
· Patients at high risk or ineligible for surgical AVR may be candidates for TAVR. They should be evaluated by a multidisciplinary heart team (cardiologist, cardiac surgeon) to determine the best management strategy.
· The PARTNER Trial showed that TAVR is noninferior to surgical AVR in high-risk patients and TAVR is superior to standard therapy in inoperable patients.2
· Additional trials to evaluate these techniques are underway as are ongoing device modifications.
MONITORING/FOLLOW-UP
· In patients with AS, the AVA decreases 0.1 cm2/year on average, but there is significant variability from patient to patient in the rate of progression.
· Echocardiography is recommended every 3 years for mild AS, every 1 to 2 years for moderate AS, and at least yearly for severe AS.
· Patients with severe AS should be seen at least every 6 months to monitor clinically for the development of symptoms.
Aortic Regurgitation
GENERAL PRINCIPLES
Pathophysiology
· Mild aortic regurgitation (AR) is frequently documented by Doppler echocardiography, but severe AR requiring operative therapy is relatively uncommon.
· AR can result from intrinsic valve disease (e.g., bicuspid aortic valve, rheumatic heart disease, endocarditis, trauma, lupus, and other connective tissue disease).
· Dilatation of the aortic root can also cause severe AR (e.g., Marfan syndrome, aortic dissection, long-standing hypertension, ankylosing spondylitis, and syphilitic aortitis).
· Severe acute AR leads to marked increase in LV pressure since the LV is not compliant enough to accommodate the regurgitant volume. This may lead to pulmonary edema and/or cardiogenic shock.
· Since severe AR usually develops over years, the LV is allowed to dilate and accommodate the large regurgitant volume and maintain normal LV pressures. Over time, these compensatory mechanisms fail and the LV becomes markedly dilated, systolic function diminishes, and LV pressures increase.
DIAGNOSIS
Clinical Presentation
History
· Patients with acute severe AR are almost always symptomatic and often critically ill.
· Patients with chronic severe AR may be asymptomatic for years (compensated state) before developing symptoms, which are most commonly fatigue, dyspnea on exertion, palpitations, and heart failure.
Physical Examination
· Physical examination reveals bounding pulses, a wide pulse pressure, displaced PMI, and a diastolic decrescendo murmur often heard with the patient sitting up or bending forward.
· An Austin-Flint murmur can sometimes be heard at the apex as a low-pitch diastolic murmur due to regurgitant flow through the aortic valve that impedes opening of the anterior mitral valve leaflet and obstructs flow through the mitral valve.
Diagnostic Testing
Electrocardiography
· Electrocardiogram reveals LV hypertrophy and often left atrial enlargement.
Imaging
· Any patient with a diastolic murmur should undergo echocardiography.
· The echocardiogram should document the severity of AR, whether the valve is bicuspid, the size of the LV in systole and diastole, and the size of the aortic root.
· Transesophageal echo may be helpful to clarify whether there is a bicuspid valve and more accurately measure the dimension of the aorta.
TREATMENT
Medications
· Hypertension should be treated in patients with severe AR according to established guidelines.
· In the absence of hypertension, vasodilators may be considered as a chronic treatment for patients with symptomatic severe AR and reduced EF when surgery is not recommended or asymptomatic patients with severe AR and LV dilation with normal EF.
· Vasodilators may also be used in the acute setting in patients with severe HF symptoms as a bridge to AVR.
Surgical Management
· AVR is indicated for symptomatic patients with severe AR and for asymptomatic patients with EF <50% or severe LV dilatation (LV end-systolic dimension >50 to 55 mm; LV end-diastolic dimension >70 to 75 mm).
· Operative mortality is generally quite low and should be strongly considered even if the EF is markedly reduced.
· Concomitant surgery to repair/replace the aortic root is indicated in patients with an aortic root >4.5 to 5.0 cm with a bicuspid aortic valve or Marfan syndrome or >5.0 to 5.5 cm in the absence of those conditions. Operative therapy is also indicated for an increase of 0.5 cm/year in the aortic diameter.
MONITORING/FOLLOW-UP
· Patients with mild-to-moderate AR should be followed yearly with an echocardiogram performed every 2 to 3 years.
· Severe AR with normal LV function should be monitored clinically every 6 months with an echo usually once a year.
· Any change in symptoms warrants immediate evaluation.
· First-degree relatives of patients with Marfan syndrome or a bicuspid aortic valve should be screened with imaging.
Mitral Stenosis
GENERAL PRINCIPLES
Etiology
· Rheumatic heart disease is the most common cause of mitral stenosis (MS), particularly in young women. Mean age for severe MS is the fifth to sixth decades of life.
· With the decrease in rheumatic heart disease, the prevalence of MS has dropped dramatically in developed countries.
· Other causes of MS are rare (e.g., congenital) or less often progress to severe MS (e.g., mitral annular calcification).
Pathophysiology
· Leaflet and subvalvular thickening and calcification results in a decrease in the mitral valve orifice and the development of a diastolic transmitral pressure gradient.
· The transmitral pressure gradient depends on the severity of the obstruction (mitral valve area), flow across the valve (cardiac output), diastolic filling time (heart rate), and the presence of effective atrial contraction.
· Significant MS can lead to elevation of left atrial, pulmonary venous, and pulmonary artery pressures, which can lead to pulmonary vascular remodeling and right ventricular dysfunction.
DIAGNOSIS
Clinical Presentation
History
· The latency or delay between rheumatic fever and significant MS is typically decades; symptom onset can be insidious.
· In addition to dyspnea and/or fatigue, patients may present with cough and sometimes hemoptysis; symptoms of right heart failure may also occur.
· Symptoms may develop suddenly in the setting of fever, new-onset atrial arrhythmia, hyperthyroidism, or pregnancy due to an increased transvalvular gradient.
· Thirty to forty percent of patients with MS develop an atrial arrhythmia.
Physical Examination
· Physical examination reveals a loud S1 and an opening snap in diastole followed by a middiastolic rumble heard best at the apex with the bell of a stethoscope with the patient in left lateral decubitus position.
· A right ventricular heave, loud P2, and/or signs of right heart failure may also be present.
Diagnostic Testing
Electrocardiography
· Electrocardiogram often shows left atrial enlargement and right ventricular hypertrophy.
Imaging
· Echocardiography can frequently quantify the severity of MS (transvalvular gradient, valve area) and consequences of MS (elevated pulmonary pressures, MR, left atrial enlargement, right ventricular dysfunction).
· Stress echocardiography can be helpful in some cases to assess transmitral gradient and pulmonary artery pressures during exercise.
· If valvuloplasty is considered, transesophageal echocardiography should be performed to evaluate for any associated mitral regurgitation, left atrial clot, and significant calcification/tethering of the mitral valve and subvalvular apparatus.
TREATMENT
Medications
· Therapy is primarily aimed at rate control and prevention of thromboembolism.
· β-Blockers or nondihydropyridine calcium channel blockers (CCBs) tend to be more effective than digoxin for tachycardia associated with exertion.
· Anticoagulation is indicated for atrial arrhythmia (paroxysmal, persistent, or permanent), prior embolic event (even in sinus rhythm), and left atrial thrombus.
· Rhythm control strategies often fail in patients with significant MS.
Percutaneous Management
· Patients with moderate or severe MS with symptoms or associated pulmonary hypertension (at rest or with exercise) should be considered for percutaneous or surgical intervention.
· Patients with rheumatic MS are potentially candidates for percutaneous mitral balloon valvuloplasty (PMBV), whereas patients with calcific MS are not.
· Based on transesophageal echocardiography, patients with extensive calcification/fusion of the mitral leaflets and/or subvalvular apparatus, moderate or greater mitral regurgitation, or left atrial clot are not candidates for PMBV.
· PMBV is the procedure of choice in patients with rheumatic MS without these exclusions; these patients generally have an excellent result from PMBV that may last several years.
Surgical Management
· Those patients needing an intervention on their valve who are not candidates for PMBV should generally undergo valve replacement; valve repair is rarely an option for fibrotic, calcified valves.
MONITORING/FOLLOW-UP
· Asymptomatic patients with moderate to severe MS should be evaluated clinically every 6 months with an echo at least yearly or as clinically indicated.
· In asymptomatic patients, consideration should be given to performing periodic exercise stress tests to evaluate for exercise-induced pulmonary hypertension.
· Holter monitor should be considered in patients with palpitations to monitor for atrial arrhythmias.
Degenerative Mitral Regurgitation
GENERAL PRINCIPLES
Etiology
· Degenerative mitral valve disease refers to those processes that affect the mitral valve leading to regurgitation (myxomatous degeneration, mitral valve prolapse, rheumatic disease, and endocarditis).
· Mitral valve prolapse (MVP) occurs in 1% to 2% of the population and is characterized by prolapse of one or both mitral valve leaflets into the left atrium >2 mm in midsystole.
Pathophysiology
· In patients with acute severe MR (e.g., endocarditis, torn chordae), the sudden large-volume load from the ventricle into a noncompliant left atrium leads to increased pressures that are transmitted to the pulmonary vasculature, causing pulmonary congestion and edema. Forward cardiac output is reduced, and there is compensatory tachycardia to attempt to maintain forward flow.
· As the severity of chronic MR worsens over time, LV function can be maintained and the increased volume load accommodated at normal filling pressures by LV dilation and eccentric hypertrophy.
· As compensatory mechanisms fail, the LV and LA progressively dilate, LV dysfunction occurs, and atrial fibrillation and pulmonary hypertension can develop.
DIAGNOSIS
Clinical Presentation
History
· Patients with acute severe MR can present suddenly and be critically ill.
· Many patients with chronic severe MR are asymptomatic before they present with subtle dyspnea on exertion and fatigue.
· Patients may symptomatically decompensate with the development of atrial fibrillation.
Physical Examination
· Physical examination reveals a holosystolic murmur radiating to the axilla. Prolapse of the posterior and anterior leaflets may produce radiation of the murmur to the chest wall or back, respectively.
· A murmur may not be audible in the setting of acute severe MR, but does not rule out the diagnosis.
Diagnostic Testing
Electrocardiography
· Electrocardiogram may reveal left atrial enlargement and LV hypertrophy; in more end-stage cases, right ventricular hypertrophy may be present.
Imaging
· Chest radiography may reveal cardiomegaly, left atrial enlargement, and pulmonary vascular redistribution.
· Echocardiography:
o Transthoracic echocardiography should be used to evaluate the severity of mitral regurgitation, mechanism of leak, LV dimensions and function, left atrial size, and pulmonary artery pressures. It is important to incorporate quantitative measurements of MR severity, particularly in those with moderate or severe MR.
o Exercise stress evaluation with an echocardiogram should be considered to clarify whether symptoms are present in patients with severe MR and/or to evaluate for exercise-induced pulmonary hypertension.
o Transesophageal echocardiogram should be performed to clarify the severity and mechanism of the MR and assess the feasibility of valve repair.
TREATMENT
Medications
· There are no medical therapies that have been demonstrated to improve clinical outcomes (e.g., delay the time to surgery) in patients with degenerative MR and normal LV function.
· Treat other cardiovascular comorbidities (e.g., hypertension and coronary artery disease) according to appropriate guidelines.
· Patients with severe acute MR may be bridged to definitive therapy (valve surgery) with vasodilators or a balloon pump to maximize forward flow and minimize pulmonary congestion.
· Patients with MVP with a history of TIAs should take ASA (75 to 325 mg), and those with palpitations should avoid/minimize the use of tobacco, alcohol, and caffeine as these may worsen symptoms.
Surgical Management
· Acute severe MR must be treated promptly with surgery.
· For chronic severe MR, surgery is indicated for symptoms or, in the absence of symptoms, when there is LV dilation (LV end-systolic dimension ≥4 cm) or EF <60%. Surgery should also be considered in asymptomatic patients with the onset of an atrial arrhythmia and pulmonary hypertension (resting or exercise induced) or when the likelihood of successful valve repair is >90%.
· Mitral valve repair is preferable to mitral valve replacement for degenerative mitral valve disease and should be performed by a high-volume valve repair surgeon.
· Patients with a concomitant atrial arrhythmia should be considered for a surgical maze procedure at the time of valve repair.
MONITORING/FOLLOW-UP
· Patients with severe MR should be monitored very closely for the onset of symptoms, LV dysfunction, LV dilation, atrial arrhythmia, or pulmonary hypertension.
· Echocardiography should be done every 1 to 2 years in patients with moderate MR and at least yearly in those with severe MR. Periodic assessment for exercise-induced pulmonary hypertension is also recommended.
Functional Mitral Regurgitation
GENERAL PRINCIPLES
· Functional MR may occur in patients with LV dysfunction and dilation. The regurgitation results from annular dilatation and papillary muscle displacement due to LV enlargement and remodeling, which causes tenting of the leaflets and inadequate coaptation.
· It may occur in the setting of nonischemic or ischemic dilated cardiomyopathy.
· Functional MR often leads to more severe regurgitation (MR begets MR) as the increased volume load leads to further adverse LV remodeling and dilation, more leaflet tenting, and more inadequate coaptation.
DIAGNOSIS
Clinical Presentation
· Patients have a history of LV dysfunction and often a history of myocardial infarction and/or heart failure preceding the development of MR.
· Patients with moderate to severe functional MR usually have an audible holosystolic murmur heard best at the apex radiating to the axilla; when LV dysfunction is severe, the murmur may be relatively soft.
Diagnostic Testing
Electrocardiography
· Electrocardiogram may reveal left atrial enlargement, LV enlargement, atrial arrhythmia, right ventricular hypertrophy, and/or pathologic Q waves depending on the severity and chronicity of disease and etiology of LV dysfunction.
Imaging
· Chest radiography may reveal cardiomegaly, left atrial enlargement, and pulmonary vascular redistribution.
· Transthoracic echocardiography should be used to evaluate the severity of mitral regurgitation, mechanism of leak, severity of leaflet tethering, LV dimensions and function, and pulmonary artery pressures. It is important to incorporate quantitative measurements of MR severity, particularly in those with moderate or severe MR.
TREATMENT
Medications
· Patients with functional MR have LV dysfunction, so treatment with all the medications indicated for LV dysfunction and heart failure is appropriate for these patients, including ACE inhibitors, β-blockers, aldosterone antagonists, diuretics, and cardiac resynchronization therapy.
· These therapies can lead to favorable reverse remodeling of the LV, which can reduce the severity of functional MR.
Surgical Management
· Whether and when to perform mitral valve surgery for patients with functional MR is controversial as there is conflicting evidence regarding the presence of any survival and/or quality-of-life benefit from surgical intervention.
· Unlike surgery for degenerative MR, it is not clear whether valve repair or replacement is preferable for functional MR.
Percutaneous Management
· A variety of devices are being developed and investigated as potentially less invasive alternatives to surgery for the reduction of functional MR.
· The mitral clip has been evaluated in the EVEREST Trial, and ongoing clinical trials are testing it in patients with functional MR who are at increased operative risk.
Endocarditis Prophylaxis
· In 2007, the American Heart Association (AHA) released its most recent guidelines regarding infective endocarditis (IE) prophylaxis; it contains major changes compared with prior guidelines.3 There is a notable lack of data supporting the use of antibiotic prophylaxis in the setting of dental, gastrointestinal, and genitourinary procedures, and evidence of causation is circumstantial. The guidelines suggest that there be greater emphasis on oral health in individuals with high-risk cardiac conditions.
· The guidelines conclude that antibiotic prophylaxis is reasonable in a few clinical situations. Prophylaxis is now recommended only for patients undergoing certain dental procedures with cardiac conditions associated with the highest risk of adverse outcome (Table 9-2).
TABLE 9-2 Cardiac Conditions with the Highest Risk of Adverse Outcome from Infective Endocarditis
Modified from Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: guidelines from the American Heart Association. Circulation 2007;116:1736–1754.
· Only dental procedures that involve manipulation of the gingival tissue or the periapical region (i.e., near the roots) of teeth or perforation of the oral mucosa warrant prophylaxis. Tooth extractions and cleanings are included. In these instances, prophylactic antibiotics should be directed against viridans streptococci. The recommended regimens for dental procedures are shown in Table 9-3.3
· For procedures on infected skin, skin structures, or musculoskeletal tissue, it is reasonable that treatment of the infection itself should be active against staphylococci and β-hemolytic streptococci (e.g., antistaphylococcal penicillin or cephalosporin). For patients unable to tolerate penicillins or who are suspected or known to have an oxacillin-resistant Staphylococcus aureus (ORSA) infection, vancomycin or clindamycin may be used.
TABLE 9-3 AHA Guidelines—Regimens for a Dental Procedure
a Or other first- or second-generation oral cephalosporin in equivalent adult or pediatric dosage.
bCephalosporins should not be used in an individual with a history of anaphylaxis, angioedema, or urticaria with penicillins or ampicillin.
From Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: guidelines from the American Heart Association. Circulation 2007;116:1736–1754; with permission.
Anticoagulation
· Patients with mechanical prosthetic valves require long-term anticoagulation (Table 9-4).
· Long-term ASA is indicated for all heart valves.
· Patients with mechanical valves and atrial fibrillation or prior emboli should receive heparin as a bridge when warfarin is stopped for surgery.
· In general, warfarin is stopped for 72 hours prior to surgery and heparin is initiated when INR is <2.0. Low molecular weight heparin has been used as a bridge in small studies, but no large randomized studies have been performed, so no official recommendation has been made.
TABLE 9-4 Antithrombotic Therapy for Patients with Prosthetic Heart Valves
From Godara H, Hirbe, A, Nassif M, et al., eds. The Washington Manual of Medical Therapeutics, 34th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2014, with permission.
REFERENCES
1.Bonow RO, Carabello BA, Chatterjee K, et al. 2008 Focused Update Incorporated Into the ACC/AHA 2006 Guidelines for the Management of Patients With Valvular Heart Disease. J Am Coll Cardiol2008;52:e1–e142.
2.Leon MB, Smith CR, Mack M, et al. Transcatheter aortic-valve implantation for aortic stenosis in patients who cannot undergo surgery. N Engl J Med 2010;363:1597–1607.
3.Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis guidelines from the American Heart Association. Circulation 2007;116:1736–1754.
10Arrhythmia and yncope
Jason D. Meyers and Timothy W. Smith
GENERAL APPROACH TO ARRHYTHMIAS
· The primary care physician will frequently be the first to encounter or suspect an arrhythmia and will continue to care for the patient once the arrhythmia is diagnosed. This chapter focuses on arrhythmia diagnosis and management with an emphasis on issues arising in the primary care setting.
· The initial approach to any ongoing arrhythmia includes obtaining vital signs and a 12-lead electrocardiogram (ECG). If the patient is unstable (i.e., hypotensive, hypoxic, experiencing chest pain or dyspnea), immediate treatment according to ACLS (advanced cardiac life support) algorithms is necessary.
· Frequently, the clinician is faced with a patient whose symptoms are intermittent. If no ECG tracing from a previous event is available, an arrhythmia can be suspected but not definitively diagnosed. Efforts to confirm or detect the arrhythmia are a large part of the clinical approach.
· If an arrhythmia is suspected, a thorough history and physical exam should be performed.
· Symptoms of arrhythmias are frequently nonspecific and include palpitations, light-headedness, chest pain, presyncope/syncope, dyspnea, and a sense of anxiety. At the same time, many serious arrhythmias are frequently asymptomatic.
· The utility of the history and physical exam is to detect other signs of underlying cardiovascular disease. Fortunately, once an ECG or rhythm monitor recording of the arrhythmia is obtained, a diagnosis can often be made.
· In a few cases, such as preexcitation, the nature of the arrhythmia is evident on a baseline ECG. However, this is the exception, and often, other tools must be used to obtain a recording of the arrhythmia.
DIAGNOSTIC TOOLS
Several options are available for the diagnosis of arrhythmias and the correlation of arrhythmia with a patient’s symptoms.
· Holter monitor: an ambulatory ECG monitor that records continuously for 24 or 48 hours. The entire time period is then reviewed for arrhythmias. This approach is useful only in patients with daily symptoms.
· Event monitor or loop recorder: an ambulatory ECG monitor that records continuously but saves data only when triggered, either by the patient in accordance with symptoms or by predefined criteria such as heart rate. Events are then transmitted via a transtelephonic system for interpretation. This is often the most cost-effective method of identifying arrhythmias and correlating them with symptoms.
· Implantable event monitor: for relatively rare events, an implantable device can be placed.
CLASSIFICATION
· The categorization of arrhythmias is complex and can include categories based on the underlying electrophysiologic mechanisms (reentry, triggered activity, enhanced automaticity), rate, site of origin, and ECG features.
· Although there are some inconsistencies, a practical taxonomy for arrhythmias is based on rate and prominent ECG features. Tachyarrhythmias are those with a rate >100 beats per minute (bpm), whereas bradyarrhythmias have a rate typically <50 bpm. The terms tachycardia and tachyarrhythmia or bradycardia and bradyarrhythmia are essentially synonymous and will be used interchangeably in this chapter.
· Figure 10-1 provides an overview of the traditional classification of arrhythmias.
Figure 10-1 Arrhythmia classification. AVB, atrioventricular block; AVNRT, atrioventricular nodal reentrant tachycardia; AVRT, atrioventricular reentrant tachycardia; bpm, beats per minute; SVT, supraventricular tachycardia; VT, ventricular tachycardia.
TACHYARRHYTHMIAS
· Tachyarrhythmias exhibit a heart rate >100 bpm and can arise from either supraventricular or ventricular origins.
· Although the appropriate management is dictated by the origin and the mechanism (increased automaticity, reentry, or triggered activity), these details are often not immediately evident.
· For practical purposes, a distinction is often made between narrow-complex and wide-complex tachycardias (WCTs) on the basis of a QRS complex < or >120 ms.
NARROW-COMPLEX TACHYCARDIA
· Narrow-complex tachyarrhythmias invariably originate above or at the atrioventricular (AV) node with a resultant narrow QRS complex that reflects normal activation along the His-Purkinje system.
· Narrow-complex tachycardias are further divided based on the regularity of the rhythm.
· These arrhythmias include sinus tachycardia, atrial fibrillation (AF), atrial flutter, atrial tachycardias, and various reentrant arrhythmias (e.g., atrioventricular reentrant tachycardia [AVRT], atrioventricular nodal reentrant tachycardia [AVNRT]).
Initial Approach
· The first priority is to check the patient’s vital signs and initiate the appropriate ACLS protocol if the patient is unstable.
· In the stable patient, obtain a 12-lead ECG. However, correct identification of the arrhythmia is often difficult with rapid heart rates.
· A helpful approach to tachyarrhythmias is to promote vagal (parasympathetic) activity with either carotid massage or administration of adenosine (Table 10-1). This serves to slow down AV nodal conduction, decreasing the rate and frequently allowing identification of the rhythm. In addition, reentrant rhythms that require the AV node for maintenance will be terminated by these maneuvers.
· Carotid sinus massage
o In the absence of carotid bruits, apply circular pressure to one carotid sinus for 5 seconds.
o Use caution in patients at risk for myocardial ischemia or cerebrovascular accident.
· Adenosine (Table 10-1)
o Give 6-mg rapid IV push. Adenosine has a half-life of approximately 9 seconds, so the full dose must be pushed and flushed rapidly. A second dose of 12 mg can be used if the first dose has no effect.
o Adenosine will cause complete heart block, although typically brief; appropriate resuscitation equipment and personnel should be available.
o The patient should be warned that adenosine will cause a transient unpleasant feeling of presyncope.
o Rarely, adenosine can cause severe bronchospasm and severe respiratory distress.
TABLE 10-1 Antiarrhythmic Medications
AF, atrial fibrillation; ANA, antinuclear antibody; AV, atrioventricular; AVB, atrioventricular block; AVNRT, atrioventricular nodal reentrant tachycardia; CAD, coronary artery disease; HF, heart failure; CNS, central nervous system; CrCl, creatinine clearance; GI, gastrointestinal; HTN, hypertension; K, potassium; NAPA, n-acetyl procainamide; SLE, systemic lupus erythematosus; SVT, supraventricular tachycardia.
Sinus Tachycardia
GENERAL PRINCIPLES
· Although not an arrhythmia per se, it is important to consider sinus tachycardia when confronted with a rapid, narrow-complex tachycardia.
· Sinus tachycardia is almost invariably a response to an underlying condition such as fever, hypovolemia, pain, anemia, thyrotoxicosis, pulmonary disease, heart failure (HF), caffeine, illicit drug use/withdrawal, or anxiety.1
· In rare cases, however, the sinus tachycardia is genuinely inappropriate and may be due to a reentrant arrhythmia within the sinoatrial (SA) node.2
DIAGNOSIS
· Heart rate is typically 150 to 200 bpm. There is usually a slow increase and decrease in heart rate, not abrupt onset and termination.
· ECG will demonstrate P waves with a normal axis and morphology.
· Laboratory evaluation should include underlying causes such as anemia, thyrotoxicosis, and drug intoxication (either prescribed or illicit).
TREATMENT
· Treatment is focused on the underlying cause.1
· Treatment aimed solely at slowing the heart rate (e.g., β-blockers or calcium channel blockers [CCBs]) is rarely appropriate and should be pursued only if the underlying cardiac disease (e.g., valvular disease, coronary artery disease [CAD], HF) results in intolerance of the elevated heart rate. The increased heart rate frequently represents a compensatory response, which is necessary to maintain cardiac output.
· It should be emphasized that an inappropriate sinus tachycardia is a rare condition and should be considered only after a rigorous exclusion of secondary causes of tachycardia.
Atrial Fibrillation
General Principles
· AF is the most common sustained arrhythmia with an incidence of about 1% in the general population and about 10% in those >80.1
· It is most commonly associated with valvular disease, advanced age, hypertension, HF, CAD, and mechanical dilatation of the atria.1,3
· Hyperthyroidism is the most common noncardiac, treatable cause of AF.
· Frequently described as “lone” (i.e., occurring in the absence of other cardiac diseases), “first episode,” “recurrent,” “paroxysmal” (i.e., recurrent episodes that typically self-terminate), “persistent” (i.e., requiring electrical or chemical cardioversion), and “permanent” (i.e., cannot be converted to normal sinus rhythm).
· AF results in three distinct consequences.
o The loss of AV synchrony with a resultant decrease in cardiac output due to the lack of the atrial contraction
o Increased thromboembolic risk due to blood stasis in the noncontractile atrium
o Decreased cardiac output and increased myocardial oxygen demand due to the increased ventricular rate
· The underlying electrical substrate for AF remains under investigation, although the role of the pulmonary veins as a site of initiation has led to new treatment options (see Treatment section below).
Diagnosis
· ECG demonstrates chaotic atrial activity without evidence of P waves, although some coarse fibrillation waves may be evident in coarse AF (Fig. 10-2).
· Ventricular rate is typically 140 to 180 bpm but varies substantially depending on rapidity of AV nodal conduction.
· Laboratory evaluation should include tests of thyroid function.
Figure 10-2 Atrial fibrillation. Note the irregular rhythm and lack of P waves.
Treatment
· Despite the intuitive appeal of treatment, which maintains sinus rhythm, several studies have shown that this strategy is unsuccessful at reducing the morbidity and mortality associated with AF, most likely reflecting the poor success rate of current therapies at maintaining sinus rhythm.4–6 Therefore, current therapy focuses on addressing individually the adverse consequences of AF.
· The two general treatment strategies are often referred to as “rate control,” in which the AF rhythm is accepted, but the rate is controlled and “rhythm control,” in which efforts are made to maintain sinus rhythm. As discussed below, both strategies frequently require anticoagulation.6
Control of Ventricular Rate
· Ventricular rate is controlled with medications that slow down AV nodal conduction.
· β-Blockers and CCBs are first-line agents for control of ventricular rate. Choice of specific agents is often determined by other indications or contraindications in a given patient.
· Digoxin can also provide control of resting ventricular rate, although it is less effective at reducing ventricular rate during exertion. In addition, digoxin is associated with more side effects than are other agents (Table 10-1). Its ideal use is in a patient with left ventricular (LV) dysfunction whose ventricular function also benefits from digoxin.
· In some cases, pharmacologic control of ventricular rate proves impossible. In these patients, invasive radio-frequency AV node ablation (resulting in complete heart block) with implantation of a permanent pacemaker is an option.
Maintenance of Sinus Rhythm
· Restoration and maintenance of sinus rhythm is a tempting goal but not always readily achievable. How aggressively sinus rhythm is pursued is dictated by the patient’s overall cardiac function and the degree to which they can tolerate AF.
· Initial termination of AF is accomplished by synchronized direct current cardioversion (DCCV) with a success rate of ≥80%. DCCV requires sedation and hemodynamic monitoring and should be carried out in facility with emergency resuscitation and airway support available.
· Several medications may result in pharmacologic cardioversion, increase the success rate of DCCV, and improve maintenance of sinus rhythm once cardioversion is accomplished.1
· For patients with structural heart disease, preferred agents include amiodarone, sotalol, and dofetilide (Table 10-1).
· For patients without structural heart disease, preferred agents include amiodarone, flecainide, and propafenone (Table 10-1).
· Amiodarone (Table 10-1) is typically well tolerated but has several significant long-term side effects. It is, therefore, less favored for use in young patients who may require decades of therapy.7
· Initiation or adjustment of these medications frequently requires inpatient cardiac monitoring and should be performed in consultation with a cardiac electrophysiologist.
Atrial Fibrillation Ablation/Surgical Treatment Options
· New techniques of catheter-based AF ablation are becoming increasingly successful.
· Should noninvasive attempts to maintain sinus rhythm fail in a patient who does not tolerate AF well, invasive ablation techniques can be considered to restore the sinus rhythm.6
· Historically, the surgical Cox maze procedure was designed to eliminate AF by creating a pattern of scar lines in the atrium that interrupts the fibrillation. However, this technique is now more commonly performed in conjunction with other cardiac operations.
· Minimally invasive catheter-based techniques (such as electrical isolation of the pulmonary veins) may be a more suitable option for patients not requiring cardiac surgery with a success rate of 60% to 80% at experienced centers.
· The details of these techniques continue to undergo rapid development and are beyond the scope of this chapter.
· Consultation with a cardiac electrophysiologist is warranted for any patient with poorly tolerated AF.
Thromboembolic Risk
· Although, in theory, restoration of sinus rhythm obviates the need for anticoagulation, several studies have shown that the risk of stroke from atrial thrombi is essentially unchanged by pharmacologic attempts to maintain sinus rhythm.4,5 However, given the risks of anticoagulation, attempts have been made to identify which patients are at high enough risk to justify warfarin therapy.
· Several different indices of thromboembolic risk have been developed. In general, patients with advanced age, HF, a history of stroke, diabetes, or hypertension are at greater risk of stroke in the context of AF.4
· It is essential to ensure the absence of left atrial thrombus prior to DCCV in any patient with AF lasting longer than 48 hours. This can be accomplished with transesophageal echocardiography with visualization of the left atrial appendage; transthoracic echocardiography is not adequate. Alternatively, the patient can be anticoagulated for a period of at least 3 to 4 weeks prior to cardioversion.4
· Importantly, the risk of embolic events is highest in the several weeks following cardioversion, even if it is successful. It is therefore essential to continue therapeutic anticoagulation for at least 4 weeks following cardioversion.
o In recent years, a number of new agents have been approved for thromboembolism prevention in nonvalvular AF. The choice of a particular therapeutic anticoagulant should be tailored to each patient individually (see Chapter 14).
o The role of transesophageal echocardiogram (TEE) to exclude thrombus prior to DCCV when therapeutically anticoagulated with an agent other than warfarin has not been well established.
· It should be emphasized that AF is typically a chronic/recurrent condition. The presumption is, therefore, that the patient requires permanent anticoagulation unless (a) a contraindication to anticoagulation exists or (b) the patient is clearly at low risk for embolic events.
AF and Preexcitation (Wolff-Parkinson-White Syndrome)
· AF in a patient with an AV bypass tract poses a special risk. In the normal heart, the maximal ventricular rate in AF is limited by the slow conduction of the AV node. When conduction occurs through a bypass tract, the ventricular rate can match the AF rate (400 to 700 bpm) resulting in degeneration into ventricular fibrillation (VF) and cardiovascular collapse.
· The ECG in preexcited AF is characterized by an irregularly irregular rate with varying morphologies of a wide-complex QRS.
· Treatment options include procainamide, amiodarone, or DCCV. AV nodal blocking agents including adenosine, CCBs, β-blockers, and digoxin should be avoided as they can cause acceleration of the bypass tract conduction. Expert consultation is required for definitive treatment and ablation of the bypass tract (Table 10-1).
Perioperative AF
· AF is common in the postoperative patient, especially after cardiac surgery and most specifically valvular surgery. Most episodes are self-limiting but in the interim pose the same risks as any other episode of AF. Because of the potential complications of anticoagulation, prompt DCCV within the first 48 hours of AF is recommended.
· Perioperative treatment with β-blockers has been shown to reduce the incidence of AF.8
· In addition, amiodarone (Table 10-1) is frequently used as either prophylactic treatment or once the AF has occurred.8
· The need for continued therapy should be reevaluated by a cardiologist several months after the operation.
Atrial Flutter
GENERAL PRINCIPLES
· Atrial flutter is sustained reentry within the atria, causing rapid fluttering of the atria.
· Although it is more electrically organized than AF, the atrial transport of blood is still less efficient than normal; flutter thus also has a risk of thromboembolism.
· Many of the same factors that predispose to AF are also related to atrial flutter. It is not uncommon for patients to have both rhythms and transition from one to the other.
DIAGNOSIS
· ECG demonstrates sawtooth flutter waves. In typical flutter, these sawtooth waves are most evident in the inferior leads (Fig. 10-3). Typical flutter waves have a negative vector in the inferior leads (II, III, aVF) while positive in the anterior precordium (V1, V2). In other forms of flutter, various appearances of the flutter waves are possible.
· Flutter waves are typically at a rate of 240 to 340 bpm; 300 bpm is classic.
· Ventricular rate is usually at a 2:1, 3:1, or 4:1 ratio with the atrial rate. Although the ventricular rate may be irregular due to variable conduction block, it is more typically regular with a fixed ratio to the atrial activity.
Figure 10-3 Atrial flutter. This is an example of 3:1 atrial flutter. Note sawtooth-shaped flutter waves (arrows).
TREATMENT
· Medical treatment of atrial flutter is essentially identical to management of AF: control of ventricular rate, management of stroke risk with anticoagulation, and, when possible, maintenance of sinus rhythm.
· The stereotypical circuit in typical atrial flutter is readily amenable to catheter ablation techniques with a success rate of approximately 90%. However, a significant number of patients subsequently develop AF.6
Reentrant Supraventricular Tachycardia
GENERAL PRINCIPLES
· Although the term supraventricular tachycardia (SVT) would technically include all rhythms arising above the AV node, it is conventionally applied to a specific group of reentrant rhythms.9,10
· SVTs are divided into two main groups based on the anatomy of the reentrant circuit.
o AVNRT: The entire reentrant circuit is contained in the AV node and the immediate surrounding tissue.
o AVRT: The reentrant circuit includes atrial tissue, the AV node, ventricular tissue, and an accessory bypass tract.
· Common features of reentrant rhythms include one branch of the circuit with rapid conduction (and a long refractory period) and another branch with slow conduction (and a short refractory period). With this anatomy, an appropriately timed premature impulse can trigger the reentry and result in continuous cycling of electrical activity in this circuit.
· Different forms of AVRT and AVNRT are characterized by whether the antegrade impulse (forward, i.e., atrial to ventricular) occurs over the fast or slow pathway. The retrograde impulse (backward, i.e., ventricular to atrial) occurs over the other pathway.
· SVTs result in retrograde P waves as the retrograde signal stimulates the atrium. These rhythms can therefore be further divided into long RP in which the (retrograde) P wave occurs significantly after the QRS complex, reflecting retrograde conduction over a slow pathway, or short RP in which the (retrograde) P wave occurs rapidly after the QRS.
· AVRT and AVNRT typically occur in patients without other underlying cardiac diseases.
DIAGNOSIS
· Clinical presentations include palpitations, dyspnea, syncope, and angina/HF in patients with underlying cardiac disease.
· Accurate diagnosis of reentrant arrhythmias is frequently possible from the ECG.
· Reentrant rhythms typically have an abrupt onset and termination, in contrast to sinus tachycardia and AF, and exhibit heart rates in the range of 150 to 250 bpm.
· All reentrant SVTs exhibit retrograde P waves, which are negative in leads II, III, and aVF, reflecting activation of the atrium in a reverse, caudal-to-cranial direction.
· AVNRT represents approximately 70% of SVTs with AVRT constituting the remainder.1
· ECG features of common SVTs are summarized in Figure 10-4.
· Typical AVNRT (50% to 90% of AVNRTs): Antegrade conduction occurs over the slow pathway and retrograde conduction over the fast pathway. As a result, the retrograde P wave occurs within 100 ms of the QRS, making this a “short RP” rhythm. In fact, the RP interval is so brief that typically the P waves are obscured by the QRS or visible only as a pseudo-R in lead V1 or pseudo-S in lead II or III.
· Atypical AVNRT: Antegrade conduction occurs over the fast pathway and retrograde conduction over the slow pathway. As a result, the retrograde P wave is visible between the QRS complexes with a long RP interval.
· Orthodromic AVRT (95% of AVRTs): Antegrade conduction occurs via the AV node and retrograde conduction over the accessory pathway. Most commonly, the RP interval is short due to a fairly rapidly conducting accessory tract. However, a slowly conducting accessory tract is also possible and gives rise to a long RP tachycardia.
· Antidromic AVRT: This is a WCT but mentioned here for contrast with orthodromic AVRT. Antegrade conduction occurs over the accessory pathway with a resultant wide QRS complex.
· AVNRT may be visualized as reentry within the AV node. As a result, the tachycardia can continue regardless of events in the atria or ventricles, such as premature ventricular contractions (PVCs), premature atrial contractions (PACs), or bundle-branch block. In AVRT, the atrium and ventricle are part of the circuit. Atrial and ventricular events will therefore affect the tachycardia.
· AVRT requires the existence of an accessory tract. Accessory pathways may be “manifest,” that is, visible as preexcited delta waves on the baseline ECG (Wolff-Parkinson-White pattern), or concealed, that is, lacking evidence of antegrade conduction but capable of retrograde conduction and therefore support of AVRT. A manifest pathway can result in either orthodromic or antidromic AVRT, whereas a concealed pathway is capable only of orthodromic AVRT.
Figure 10-4 Supraventricular tachycardia. Above, SVT with a long RP interval; note inverted retrograde P waves in lead II (arrows). Below, SVT with a short RP interval; note inverted retrograde P waves in lead II (arrows).
TREATMENT
· The initial approach to a stable patient with a narrow-complex tachycardia is the use of vagal maneuvers such as the Valsalva maneuver or carotid sinus massage or the administration of adenosine, as discussed above (Table 10-1). This will usually result in the termination of the arrhythmia in the case of AVRT and AVNRT.
· Medical treatment consists of AV node blockade with β-blockers, CCBs, and digoxin (Table 10-1).
· DCCV usually terminates the arrhythmia and is required in unstable patients.
· The high success rate (>95%) of catheter ablation makes definitive invasive treatment of these rhythms equally first line with medical management.9
Atrial Tachycardia
· Atrial tachycardias encompass various intra-atrial arrhythmias, including intra-atrial reentry, automatic tachycardias, and triggered tachycardias.
· These rhythms are almost invariably associated with underlying cardiac disease, chronic obstructive pulmonary disease (COPD), electrolyte imbalances, or digoxin toxicity (Table 10-1).1
· ECG features of atrial tachycardia
o P-wave axis and morphology are different from sinus rhythm.
o Rhythm is typically regular.
o QRS is usually identical to normal sinus rhythm.
o An electrophysiology (EP) study is usually required to fully characterize the atrial arrhythmia.
· Medical treatment options are focused on treatment of the underlying abnormalities.
· For clinically significant atrial tachycardias, radiofrequency catheter ablation is often the treatment of choice.
Multifocal Atrial Tachycardia
· Multifocal atrial tachycardia (MAT) is almost invariably associated with COPD or HF.11
· The underlying electrophysiologic mechanism likely involves increased automaticity or triggered activity.
· ECG features of MAT
o Three or more different P-wave morphologies associated with different PR intervals (Fig. 10-5)
o Atrial rate typically 100 to 130 bpm
· Treatment is focused on the underlying disease with little role for antiarrhythmic medications.
· In cases where treatment is necessary, CCBs and amiodarone (Table 10-1) have been shown to have some success.
Figure 10-5 Multifocal atrial tachycardia. Note irregular rhythm and P wave with varying morphology and PR interval (arrows).
WIDE-COMPLEX TACHYCARDIAS
· A WCT reflects activation that proceeds through the myocardium without use of the His-Purkinje system or does so in a slow and disorganized manner.
· As a result, the QRS is wide due to the slow propagation of the electrical signal. Only a few rhythms generate a wide QRS tachycardia:
o A ventricular rhythm, that is, ventricular tachycardia (VT)
o A supraventricular rhythm with aberrancy, that is, an intraventricular conduction delay such as left bundle branch block (LBBB) or right bundle branch block (RBBB)
o A supraventricular rhythm with excitation through an accessory tract
o Metabolic derangements (hyperkalemia or drug toxicity) resulting in a wide QRS
Initial Approach
· As with narrow-complex tachycardias, the first priority is evaluation of the patient’s stability and application of ACLS protocols to the unstable patient.
· The immediate question that must be addressed when confronted with a WCT is whether the rhythm is ventricular in origin or supraventricular with aberrancy or preexcitation.
· Attention must also be paid to possible metabolic causes of a wide QRS complex, most importantly drug toxicity and hyperkalemia.
· The distinction between VT and SVT with aberrancy is challenging and is not always readily possible. However, several algorithms have been developed to distinguish these entities.12
Suggestive Features of Ventricular Tachycardia
· There are several suggestive features of VT.
o An extreme rightward axis (−90 to 180 degree) suggests VT.
o An initial R wave in aVR suggests VT.
o Slight irregularity or irregularity at the onset of the rhythm suggests VT.
o A QRS >140 ms in an RBBB-like tachycardia or a QRS >160 ms in an LBBB-like tachycardia suggests VT.
o The presence of precordial concordance, that is, monomorphic QRS complexes, across the precordial leads that are either all entirely positive or all entirely negative suggests VT.
o The presence of fusion beats (combination of a normal QRS and the ectopic beat) and capture beats (intermittent normal QRS complexes within the tachycardia) indicates AV dissociation and thus indicates VT (Fig. 10-6).
· In addition, several stepwise algorithms have been developed to distinguish VT from SVT in a WCT. The most commonly used criteria are those published by Brugada et al. and are summarized in Table 10-2.13 At each step, either the rhythm is identified as VT or one proceeds to the next criterion.
· Although accurate, these criteria are frequently too cumbersome to be applied by those not readily familiar with them. The original Brugada criteria demonstrated a sensitivity of 99% and a specificity of 96.5%; however, further real-world studies demonstrated a sensitivity of 79% to 92% and a specificity of 44% to 56%.14
· A useful rule of thumb is that any WCT is presumed to be VT until proven otherwise. This assumption is justified by the fact that up to 80% of WCT in the setting of heart disease is VT.
· This approach is further reinforced by the fact that many of the pharmacologic treatments for SVT (adenosine and CCBs) have the potential to cause degeneration of VT to VF, whereas the treatments for VT (amiodarone and procainamide) are frequently effective and safe for SVT (Table 10-1). Therefore, use of VT treatments is preferred if the rhythm is unclear.
· In summary, any WCT should be managed as VT. Once the patient is stabilized, expert consultation is warranted to clarify the rhythm and future management.
TABLE 10-2 Brugada Criteria for Wide-Complex Tachycardia
AV, atrioventricular; VT, ventricular tachycardia; LBBB, left bundle-branch block; RBBB, right bundle-branch block.
Modified from Brugada P, Brugada J, Mont L, et al. A new approach to the differential diagnosis of a regular tachycardia with a wide QRS complex. Circulation 1991;83:1649–1659.
Figure 10-6 Ventricular tachycardia. Note fusion beat (arrow).
Ventricular Arrhythmias
· Ventricular arrhythmias encompass a spectrum from single PVCs, couplets and triplets (two to three consecutive PVCs), to VT and VF.
· VT can be described as sustained (definitions vary but are typically defined as >30 seconds in duration or causing hemodynamic collapse requiring immediate cardioversion) or nonsustained (NSVT) (>3 beats but <30 seconds). The abbreviations SVT and NSVT refer to entirely different rhythms despite their similarity. Sustained VT is not abbreviated SVT.
· VT is described as monomorphic (in which all of the QRS complexes exhibit the same morphology) or polymorphic. Polymorphic VT is closer, both in mechanism and treatment, to VF than to monomorphic VT.
· Management of VT depends on the presence or absence of underlying cardiac disease.
· Reversible causes of VT should be evaluated including cocaine and digitalis intoxication, hypokalemia, hypomagnesemia, and acute ischemia.
VENTRICULAR ARRHYTHMIAS ASSOCIATED WITH STRUCTURAL HEART DISEASE
GENERAL PRINCIPLES
· VT can be associated with various underlying cardiac diseases, including ischemic cardiomyopathy; nonischemic cardiomyopathy; and infiltrative conditions including amyloidosis and sarcoidosis; either repaired or unrepaired congenital heart disease; and muscular dystrophies.
· Most studies have focused on ischemic and, more recently, nonischemic dilated cardiomyopathies. However, the general approach is applied to cardiomyopathies of other etiologies as well.
TREATMENT
· Premature ventricular contractions
o PVCs in the context of structural heart disease are associated with an increased risk of sudden cardiac death (SCD).
o However, pharmacologic suppression, although effective at reducing the incidence of PVCs, has failed to show a mortality benefit. In fact, use of class I antiarrhythmics (Table 10-1) results in an increased mortality in the setting of ischemic heart disease.15,16
o In light of this, treatment of asymptomatic PVCs themselves is not warranted. Symptomatic PVCs may be treated with β-blockers, antiarrhythmic agents, and, in some circumstances, ablation.
· Nonsustained VT
o NSVT in the context of structural heart disease is similarly associated with SCD. As with PVCs, pharmacologic therapy alone does not reduce the incidence of SCD.
o For patients with at least moderately reduced ejection fraction (EF) (typically defined as ≤35%), an implantable cardiac defibrillator (ICD) is warranted for primary prevention, as discussed below, and the presence or absence of NSVT is largely immaterial.
· Sustained VT
o Sustained VT requires immediate medical attention. In the unstable patient, termination of the rhythm requires immediate cardioversion.
o In the stable patient, consideration can be given to pharmacologic termination with either amiodarone or lidocaine (Table 10-1).
o Unless the rhythm is unequivocally the result of a transient and reversible cause, such as an electrolyte abnormality, ICD therapy is usually indicated.
o Expert consultation is warranted for any sustained VT.
· Polymorphic VT
o In the context of ischemic heart disease, polymorphic VT has a worse prognosis than monomorphic VT. Management focuses on treatment of the underlying ischemic disease whenever possible.
o Other forms of polymorphic VT require different treatment and will be discussed below.
· Long-term treatment options for VT
o After acute termination of the VT, several long-term treatment options are available.
o The first-line treatment is placement of an ICD, which has been shown to reduce mortality when compared with pharmacologic therapy in multiple studies.17–19
o Although successful at reducing VT burden, pharmacologic therapy has not been shown to reduce mortality from SCD. As such, its role in treatment is limited to (a) patients with contraindications to ICD placement or (b) patients with an ICD with the intention of reducing the frequency of ICD shocks. First-line medications include amiodarone and sotalol (Table 10-1).
o In patients with persistent VT, catheter or surgical ablation procedures can be performed. These procedures are most successful in patients with a well-localized scar rather than a diffuse myocardial process.
o In extreme cases of refractory ventricular arrhythmias, cardiac transplantation can be considered.
VT ASSOCIATED WITH ACUTE MYOCARDIAL ISCHEMIA
· The significance of VT in the context of acute myocardial ischemia or infarction depends on the timing of the VT.
· Although VT shortly after acute myocardial infarction (AMI) is a poor prognostic sign with regard to in-hospital mortality, the long-term significance remains unclear. In contrast, late VT portends future malignant arrhythmias.
· One specific form of ischemic arrhythmia, which warrants special mention, is accelerated idioventricular rhythm (AIVR). This ventricular rhythm exhibits a wide QRS, a rate between 50 and 120 bpm, and is frequently associated with reperfusion, either spontaneous or medically accomplished. This is a benign rhythm that requires no treatment; there is no long-term prognostic significance of AIVR.
IDIOPATHIC VT NOT ASSOCIATED WITH STRUCTURAL HEART DISEASE
· A minority of ventricular arrhythmias are not associated with obvious structural heart disease, although as our understanding of these diseases progresses, it is frequently discovered that these patients have more subtle molecular or cellular derangements.
· Idiopathic VT is divided into monomorphic and polymorphic VT.
· Monomorphic VT, as found in conditions including repetitive monomorphic VT (RMVT), right ventricular outflow tract VT (RVOT VT), and idiopathic left ventricular VT, has a fairly benign prognosis. In contrast, polymorphic VT, as found in familial catecholaminergic VT, has a more malignant course. The details of these conditions are beyond the scope of this chapter, and any VT warrants referral to a cardiac electrophysiologist.
TORSADE DE POINTES
GENERAL PRINCIPLES
· Torsade de pointes (TdP) (twisting of the points) is a form of polymorphic VT that occurs in association with a baseline prolonged QT interval.
· Congenital forms of TdP occur in the context of genetic long QT syndromes (discussed below).
· Most cases occur as the result of acquired QT prolongation due to medications, electrolyte abnormalities (hypokalemia, hypomagnesemia, and hypocalcemia), hypothyroidism, cerebrovascular events, ischemia, or severe HF.20
· In addition, bradycardia (which results in a relatively lengthened QT interval) can exacerbate TdP, although usually this occurs in the context of another precipitating factor.
· A substantial number of medications (summarized in Table 10-3 or available at www.qtdrugs.org) have been associated with QT prolongation, although not invariably with TdP.
TABLE 10-3 Selected Medication Associated with QT Prolongation
DIAGNOSIS
· The ECG appearance of TdP consists of a WCT with a continuously changing axis, giving rise to an undulating appearance (Fig. 10-7).
· Further laboratory evaluation is focused on electrolyte levels, thyroid function, and myocardial ischemia.
Figure 10-7 Torsade de pointes.
TREATMENT
· Immediate DCCV is the treatment of choice for an unstable patient with TdP.
· Intravenous magnesium is frequently helpful in terminating stable TdP.
· Avoidance of QT-prolonging medications is crucial in these patients.
Ventricular Fibrillation
VF is a pulseless and rapidly fatal rhythm without prompt defibrillation and ACLS management.
WOLFF-PARKINSON-WHITE SYNDROME AND PREEXCITATION
GENERAL PRINCIPLES
· A wide variety of abnormal connections have been described that bypass the normal atria → AV node → bundle of His → Purkinje fiber pattern of excitation.
· The most common and clinically significant of such pathways are Kent bundles, which directly connect atrial and ventricular tissue and are responsible for the Wolff-Parkinson-White syndrome.
· Although other connections exist, their role in arrhythmias is more complex and the Kent bundles serve to illustrate this class of arrhythmias.1
· The clinical importance of these pathways is twofold. First, it provides the substrate for reentrant AVRT rhythms (see above). Second, by bypassing the slowed conduction of the AV node, it provides the potential for an atrial arrhythmia such as AF to be conducted to the ventricle at dangerously rapid rates.
· In general, preexcitation is not associated with other underlying cardiac diseases. In the absence of symptoms or a family history of SCD, the occurrence of malignant arrhythmias is rare.
DIAGNOSIS
· The Wolff-Parkinson-White pattern on ECG
o A short PR interval of <120 ms
o A wide QRS interval of >110 to 120 ms, frequently with a slurred upstroke (delta wave) in some leads
o ST-T segment deviation opposite the QRS vector
· The Wolff-Parkinson-White syndrome consists of the above criteria on the baseline ECG in addition to an SVT (e.g., AVRT) with symptoms.
TREATMENT
· Acute management is typically required when the patient has developed a reentrant tachycardia or AF with a rapid ventricular response.
· Immediate DCCV is the treatment of choice in the unstable patient.
· Use of AV nodal blocking agents (adenosine, CCBs, and β-blockers) should be avoided in the case of preexcited AF since this can result in acceleration of the tachycardia via the accessory pathway (Table 10-1).
· IV procainamide or amiodarone (Table 10-1) can be used safely.
· In patients without symptoms and at low risk for SCD, treatment may not be necessary.
· Medical treatment options include amiodarone, sotalol, flecainide, or propafenone (Table 10-1).
· Radio-frequency ablation is 85% to 95% effective at eliminating the bypass tract.
Primary Prevention of Sudden Cardiac Death
· With the increased use of ICDs for the termination of potentially fatal ventricular arrhythmias, much attention has been devoted to identifying patients at the greatest risk for SCD.21
· The placement of an ICD in patients at high risk for SCD is termed primary prevention, in contrast to secondary prevention in patients who have already experienced either SCD or sustained VT/VF.
· The current ability to identify patients at highest risk for SCD remains limited, as only 30% of patients currently regarded as high risk (i.e., those who receive ICDs) ever experience an aborted arrest, and conversely, 50% of SCD occurs in patients not identified as high risk.22
· At this point in time, no screening of the general population is recommended for SCD risk factors beyond standard screening for cardiovascular health.
· Criteria for the placement of an ICD are summarized in Table 10-4. Briefly, placement of an ICD for primary prevention is warranted in patients with
· Ischemic or nonischemic cardiomyopathy and EF ≤35% with clinical NYHA class II to III symptoms.
· Ischemic cardiomyopathy and EF ≤40% with NSVT and inducible VT on EP study.
TABLE 10-4 Selected Indications for Automatic Implantable Cardiac Defibrillator Placement
CABG, coronary artery bypass graft; CAD, coronary artery disease; HF, congestive heart failure; EP, electrophysiology; LV, left ventricular; LVEF, left ventricular ejection fraction; MI, myocardial infarction; NYHA, New York Heart Association; VF, ventricular fibrillation; VT, ventricular tachycardia.
Class I: Evidence or general agreement that the treatment is useful and effective.
Class IIa: Conflicting evidence or divergence of opinion, with a weight of evidence favoring a benefit.
Class IIb: Conflicting evidence or divergence of opinion, with benefit less well established.
Class III: Evidence or general agreement that the treatment is not effective or is harmful.
Data from Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities. Circulation 2008;117:e350–408.
BRADYARRHYTHMIAS
· A heart rate <60 bpm (or according to some, 50 bpm) constitutes bradycardia.
· A considerable variation in normal heart rate has been recorded among healthy patients. Of particular note, trained athletes frequently exhibit heart rates as low as 40 while at rest and can even include sinus pauses and AV nodal blocks. Similarly, heart rates decrease by approximately 24 bpm during sleep.23
· As a result of these considerations, it is difficult to define a heart rate alone that warrants treatment. Associated symptoms and the underlying mechanism of the bradycardia must be considered.
· Bradyarrhythmias may result in syncope, light-headedness, weakness, fatigue, dizziness, or HF symptoms.
· Broadly, pathologic bradyarrhythmias result from either a failure of impulse generation by the SA node or by a failure of impulse propagation (i.e., a conduction block).
Sinus Node Dysfunction
GENERAL PRINCIPLES
· Sick sinus syndrome is a broad term that encompasses various sinus node dysfunctions.
· One specific form of sick sinus syndrome is known as tachycardia-bradycardia (or tachy-brady) syndrome. This can take the form of almost any combination of tachyarrhythmia and bradyarrhythmia but frequently includes a prolonged sinus pause accompanying the termination of a tachyarrhythmia.
· Sick sinus syndrome can result from either intrinsic fibrosis of the sinus node or extrinsic causes including medications, hypothyroidism, hypothermia, increased intracranial pressure, electrolyte abnormalities, increased vagal tone, ischemia, and surgical trauma.
DIAGNOSIS
· Sick sinus syndrome can have a variety of ECG appearances, including inappropriate sinus bradycardia, sinus pauses, atrial tachyarrhythmias, and inappropriate heart rate responses to exercise.
· Laboratory testing should include thyroid function and electrolyte levels.
TREATMENT
· Reversible causes and offending medications should be addressed before considering pacemaker implantation. However, if a responsible medication (such as a β-blocker in a patient with CAD) is required, one can consider pacemaker implantation to permit continuation of the medication.
· Selected indications for pacemaker placement are summarized below in Table 10-5. They generally include bradycardias that are either of the following:
· Likely to persist/recur and cause symptoms
· Likely to progress to profound bradycardia or asystole
TABLE 10-5 Selected Indications for Permanent Pacemaker Placement
AVB, atrioventricular block; bpm, beats per minute; EP, electrophysiologic.
Class I: Evidence or general agreement that the treatment is useful and effective.
Class II: Conflicting evidence or divergence of opinion.
Class III: Evidence or general agreement that the treatment is not effective or is harmful.
Data from Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for device-based therapy of cardiac rhythm abnormalities. Circulation 2008;117:e350–e408.
Conduction Abnormalities
GENERAL PRINCIPLES
· Normal cardiac conduction is initiated at the sinus node and spreads through the atrium to the AV node where it experiences a brief pause before continuing through the His-Purkinje system to activate the ventricular myocardium.
· Defects in electrical conduction are described as atrioventricular block (AVB) and are categorized based on the behavior of conduction, which typically corresponds to the site/mechanism of the block.
· Causes of AV conduction block are similar to sinus node dysfunction and include fibrosis of the conduction system with age, medications, thyroid disease, infiltrative disease, increased vagal tone, ischemia, and surgical trauma.
DIAGNOSIS
· As with tachyarrhythmias, correlation of symptoms with bradycardia is important and may require the use of ambulatory monitoring. However, the bradyarrhythmia is frequently persistent and readily identified on the 12-lead ECG even at a time that the patient is asymptomatic or minimally symptomatic.
· Laboratory evaluation should include tests of thyroid function and electrolyte levels.
· The ECG features of AV blocks are summarized in Table 10-6.
· In addition, there are two special cases of AVB.
o 2:1 AVB: Because of the absence of sequential conducted P waves, it is impossible to categorize 2:1 AV block as type 1 or type 2. The anatomic level (within the AV node or below the AV node) of the block must be inferred (e.g., if atropine or exercise results in enhanced AV nodal conduction and improvement in block, it is likely an intranodal block).
o High-grade block: This term describes an AVB with multiple sequential nonconducted P waves. If the block is not associated with intense vagal activity, the anatomic level of the block is usually infranodal.
TABLE 10-6 Features of Conduction Abnormalities
AV, atrioventricular; AVB atrioventricular block.
TREATMENT
· Reversible causes and offending medications should be addressed before considering pacemaker implantation. However, if a responsible medication (such as a β-blocker in a patient with CAD) is required, one can consider pacemaker implantation to permit continuation of the medication.
· Indications for pacemaker placement are summarized in Table 10-5.24
CONGENITAL ARRHYTHMIAS
Management of congenital arrhythmias is a complex and rapidly evolving field. Any patient suspected of having a congenital arrhythmia syndrome requires evaluation by an experienced specialist.
Brugada Syndrome
· Brugada syndrome is due to mutations in the sodium channel, although the genetics of the disease are complex and incompletely understood.25
· Diagnostic criteria continue to evolve but include a typical ECG appearance of ST elevation in leads V1 to V3, an association with spontaneous VT/VF, and a familial pattern.
· Incidence is higher in men than in women and particularly prevalent among Asian males.
· Although pharmacologic therapy (usually amiodarone or quinidine, Table 10-1) can be considered, affected individuals usually require placement of an ICD for the prevention of SCD.
Long QT Syndrome
· To date, mutations in at least 13 genes that generate a congenital QT prolongation have been identified. Subtle differences in clinical features and ECG findings exist among some of these mutations.
· Patients can present with palpitations, syncope, SCD, and TdP.
· Management is complex and depends in part on the genotype of the affected individual. Referral to a cardiac electrophysiologist is warranted.26
Short QT Syndrome
· Short QT syndrome is a recently described genetic syndrome. To date, mutations in at least six different potassium and calcium channel genes have been associated with short QT syndrome.27
· Clinical features include a short QT interval (typically <330 ms when corrected for heart rate), a propensity for AF, and a risk of SCD.
· Patients with short QT syndrome have a high risk for sudden death, and ICD implantation is recommended as first-line therapy. Optimal medical management for this condition remains undefined.
Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy
· Arrhythmogenic right ventricular dysplasia (ARVD) is characterized by a fibrofatty infiltrate of the right ventricle (RV), although the LV is sometimes involved, with a resultant thinning of the ventricular wall.28
· A subset of patients exhibit a familial pattern with mutations in genes involved in cell adhesion; however, mutations of other genes and at loci for which the gene is yet to be identified have also been associated with ARVD.
· Naxos disease is an autosomal recessive form of ARVD associated with palmoplantar keratosis and woolly hair.
· Clinical features of ARVD include arrhythmias (most commonly an RVOT VT), syncope, palpitations, and SCD. Despite the involvement of the RV, evidence of RV failure is relatively uncommon.
· Although sotalol and amiodarone may have role in suppressing the ventricular arrhythmias, only ICD placement is likely to reduce the risk of SCD (Table 10-1).
Familial Polymorphic Ventricular Tachycardia
· In contrast to TdP, familial polymorphic VT (also called catecholaminergic polymorphic VT) occurs in the absence of QT prolongation. Unlike the other forms of idiopathic VT, this condition is associated with a substantial risk of SCD.
· This syndrome occurs in the absence of apparent cardiac disease and typically manifests as syncope and sudden death; polymorphic VT and VF are most prominent during stress and physical exertion.
· Two genes have been implicated in this condition: the ryanodine receptor (with autosomal dominant transmission) and the calsequestrin 2 gene (with autosomal recessive transmission). Both proteins are involved in calcium handling by the sarcoplasmic reticulum.29
· Treatment includes β-blockers, given the catecholamine-induced nature of the arrhythmias. Even with medical treatment, the incidence of SCD is considerable and ICD placement is warranted when high-risk features (such as syncope) are present.
SYNCOPE
GENERAL PRINCIPLES
· Syncope and presyncope can result from a wide variety of mechanisms, including cardiac, neurologic, and metabolic. This section will focus only on the cardiac and, particularly, arrhythmic causes of syncope.
· Studies have estimated that approximately 15% of syncope cases result from arrhythmias. Further, it should be kept in mind that 30% to 50% of cases of syncope have no identifiable cause. Therefore, the diagnostic approach should focus on the identification of high-risk predictors of future events rather than definitive diagnosis of the episode in question.
· Cardiovascular causes of syncope include neurocardiogenic (also known as vasovagal syncope), valvular heart disease, hypertrophic cardiomyopathy, bradyarrhythmias, and tachyarrhythmias.
· Neurocardiogenic syncope is believed to result from a paradoxical bradycardic and/or hypotensive response to a catecholamine surge with resultant syncope.
· Although no findings in the history or physical exam are particularly sensitive or specific, syncope resulting from cardiac arrhythmias tends to occur abruptly and with minimum prodromal symptoms, whereas neurocardiogenic syncope is frequently preceded by a feeling of flushing and light-headedness.
DIAGNOSIS
· The cardiac evaluation of syncope should include echocardiography and a baseline ECG. Depending on the frequency of events, a Holter or event monitor can be considered to identify a causative arrhythmia.
· The role of tilt table testing is controversial. This diagnostic test is designed to elicit bradycardia and hypotension in response to persistent upright position after lying supine (on a tilting table with footstand) and thereby diagnose neurocardiogenic syncope. Sensitivity has been reported as high at 70%; however, 45% to 65% of normal individuals also exhibit a positive response to tilt table testing, markedly reducing the specificity of this test.30In addition, there is a small but distinct risk of cardiac arrest and death.
· The diagnosis of neurocardiogenic syncope can usually be made based on the history and exclusion of other causes without recourse to tilt table testing.
TREATMENT
· The management of symptomatic tachyarrhythmias and bradyarrhythmias is covered in the appropriate sections of this chapter.
· Management of neurocardiogenic syncope can be difficult. Although placement of a pacemaker is tempting, the hypotensive response is frequently due to a vasodilatory effect and not a result of the bradycardia. Therefore, patients often continue to have syncope despite control of the bradycardia. Only a subset of patients with a primarily bradycardic cause of their syncope are likely to benefit from a pacemaker.
· Behavioral modification plays an essential role in the control of neurocardiogenic syncope; patients are educated to avoid environmental triggers and volume depletion. Medications should be reviewed and vasodilatory medications eliminated.
· In selected patients, increased intake of salt and fluids can reduce both orthostatic and neurocardiogenic syncope.
· In general, pharmacologic therapy has been found to be ineffective for neurocardiogenic syncope.31
o β-Blockers (some, such as acebutolol, with intrinsic sympathomimetic activity) have been used, though clinical trial data are conflicting.
o Midodrine, an α-sympathomimetic drug, may inhibit vasodilation, but there is a risk of hypertension.
o Some data support a role for selective serotonin reuptake inhibitors (SSRIs), such as paroxetine, and serotonin/norepinephrine reuptake inhibitors (SNRIs), such as venlafaxine.
IMPLANTABLE DEVICES FOR RHYTHM MANAGEMENT
With the increasing prevalence of both pacemakers and implanted defibrillators, it is important for the internist to be familiar with these devices.32
PACEMAKERS
· A pacemaker system consists of one or more electrical leads and a generator containing the battery and processor.
· Pacemaker systems may be either endocardial or epicardial. The more common endocardial system is placed by a percutaneous approach with the electrode leads in a subclavian vein and the generator placed in the subcutaneous pocket near the clavicle. The epicardial system is placed by a surgical approach with the electrodes on the epicardial surface and the generator located either in the upper abdomen or near the clavicle.
· The general principle of all pacemakers is to deliver stimuli that trigger a heartbeat in a pattern that most closely reproduces the normal cardiac activity.
· The full array of algorithms used by modern pacemakers is beyond the scope of this review. However, some general principles of pacemaker function (for pacemakers programmed in the dual/dual/dual [DDD] mode, the most common for patients not in AF) include the following:
o If atrial activity is intact, the pacemaker will sense the atrial activity and deliver a ventricular stimulus (if necessary) in response to an atrial P wave.
o If atrial activity is absent but the intrinsic conduction system is intact, the pacemaker will stimulate the atrium to generate a P wave, which is followed by conduction to the ventricle, generating a QRS complex. If the QRS does not occur within a programmed period of time, the pacemaker delivers a ventricular stimulus.
o If atrial activity is absent and the conduction system is not intact, the pacemaker will deliver stimuli to both the atrium and ventricle with a time delay that simulates the typical P wave and QRS timing.
· Pacemakers can be categorized by the number of leads.
o Dual chamber: the most common configuration. Leads are placed in both the right atrium and the RV. This provides the greatest flexibility of pacemaker modes.
o Single chamber: one lead in the RV. This design is used for patients in whom atrial pacing is not possible, such as permanent AF. Placement of a single atrial lead is an option in patients with an intact conduction system; the frequent progression of disease and subsequent requirement for a ventricular lead may make this an unappealing option.
o Biventricular: In addition to the right atrial and right ventricular leads, a third lead is placed in a coronary vein (via the coronary sinus) to permit early activation of the left ventricle. This design is used in patients with severe HF and mechanical dyssynchrony. The selection of patients who will benefit from this device remains under investigation and is beyond the scope of this chapter. Current indications, however, are shown in Table 10-7.
· In addition to the lead configuration, pacemakers and defibrillators are described based on their mode. A five-letter code (although frequently only the first three or four letters are used) describes the sensing and pacing behavior of the device, as summarized in Table 10-8.
· Common modes of pacemakers
o AAI or VVI: simple modes in which the pacemaker will sense and pace the atrium or ventricle at a given rate unless inhibited by intrinsic activity.
o DDDR: a complex mode in which the pacemaker will sense and pace both the atrium and the ventricle in a pattern that attempts to recapitulate normal electrical activity. In addition, a sensor will increase the heart rate if physical activity is detected.
o VOO: The pacemaker will deliver ventricular pacing a set rate without regard for endogenous activity. This mode has a theoretical risk of R-on-T-induced arrhythmia but is necessary during surgery or other procedures in which electrical interference could cause the pacemaker to fail to pace appropriately.
TABLE 10-7 Selected Indications for Cardiac Resynchronization Therapy
Pacemaker Management
· Patients with a pacemaker require regular follow-up with an electrophysiologist or cardiologist skilled in pacemaker management. However, the increased use of transtelephonic monitoring has reduced the need for office visits. More sophisticated home monitoring systems are also being introduced, most utilizing the Internet. Pacemaker batteries require replacement after approximately 3 to 7 years of use, depending on device details and the degree of pacemaker activity.
· Application of a strong magnet will convert any pacemaker to an asynchronous (VOO) mode as long as the magnet is in place over the device. In this mode, the pacemaker will deliver stimuli at a preset rate regardless of sensed cardiac (or extraneous) signals.
Pacemaker Complications and Malfunction
· Device infection
o Device infection is a serious complication and may occur either shortly after implantation or because of seeding of the device at a later time.
o The possibility of endocarditis and device infection must be considered in any patient with bacteremia or signs of local infection at the device site. Explantation of the device is frequently required for definitive treatment.
o In the case of local infection, incision and drainage should be avoided because of the possibility of introducing infection to the device pocket. In general, patients with a possible device infection should be admitted to a facility with experience in this area.
· Pacemaker syndrome
o In the setting of ventricular pacing, some patients experience a syndrome of neck/abdominal pulsations, palpitations, fatigue, dyspnea, and presyncope because of the lack of optimal AV synchrony and resulting decreased cardiac output and increased AV valvular regurgitation.
o Avoiding ventricular-only pacing is the best approach to ameliorating symptoms.
· Pacemaker-mediated tachycardia (PMT)
o Various reentrant arrhythmias may occur, which include the pacemaker as part of the circuit despite the use of programming features that minimize this complication. In this situation, application of a magnet to the pacemaker (see above) will interrupt the circuit and terminate the tachycardia.
o Reprogramming may be necessary to prevent recurrences.
· Failure to capture
o Obviously, failure of the pacemaker to stimulate cardiac contraction is a serious malfunction, especially in the pacemaker-dependent patient. In this situation, the first priority is to stabilize the patient with transcutaneous or temporary transvenous pacing if necessary.
o Further evaluation includes consideration of electrolyte disturbances or AMI, both of which can increase the threshold for pacemaker capture. Interrogation of the device will then provide further information regarding device and lead function.
· Failure to sense and oversensing
o Failure to sense intrinsic cardiac activity results in pacemaker-stimulated beats despite an adequate endogenous rhythm. This rarely presents an acute problem and can be evaluated with device interrogation and expert consultation.
o More seriously, oversensing results when noncardiac signals (diaphragmatic or muscle potentials or environmental signals) are misinterpreted by the device as cardiac activity with a resulting suppression of pacemaker activity. In this case, application of a magnet to the device will result in asynchronous pacing until the problem can be further evaluated.
AUTOMATIC IMPLANTABLE CARDIAC DEFIBRILLATOR
· The role of the ICD (also sometimes referred to as automatic ICD) is to continuously monitor the cardiac rhythm and to terminate potentially lethal ventricular arrhythmias.21
· Two groups of patients are considered candidates for ICD placement. Patients who have experienced VT/VF and survived warrant ICD placement for secondary prevention of future events. In addition, prophylactic placement of ICDs for prevention of SCD in high-risk patients (primary prevention) has become the standard of care. However, accurate identification of high-risk patients continues to evolve.24The current guidelines are summarized in Table 10-3.
· As with pacemakers, both the more common endocardial and surgical epicardial systems can be placed.
· All ICDs have a basic backup pacing ability. For patients with indications for both a pacemaker and an ICD, a more comprehensive combination device that combines a full array of pacemaker and ICD functions is used.
· To terminate ventricular arrhythmias, ICDs use two techniques:
o Antitachycardia pacing: a burst of pacing stimuli is delivered at a rate slightly faster than the tachycardia. Frequently, this will interrupt and terminate a reentrant rhythm.
o Shock delivery: the device is capable of delivering a defibrillatory shock identical in function to external unsynchronized cardioversion.
· Complex and currently imperfect algorithms are used by the device to differentiate VT and VF from atrial arrhythmias. Heart rate remains the most important criterion for detection of ventricular arrhythmias. Inappropriate shocks due to atrial tachyarrhythmias are a risk of ICD therapy.
ICD Management
· Patients should be followed on a regular basis by the electrophysiologist who implanted or who monitors the device.
· As with pacemakers, remote follow-up is becoming more common, reducing the frequency of routine office visits.
· Discharge of the ICD is an uncomfortable and alarming experience for the patient. However, it should be remembered that this is the role of the device.
· A single shock does not necessarily require immediate evaluation; however, the patient should contact his or her cardiologist or electrophysiologist at the first opportunity. Multiple shocks or shocks associated with symptoms such as syncope, chest pain, or shortness of breath warrant an immediate emergency department evaluation.
· Magnet application
o Application of a strong magnet to the ICD activates a switch that disables the antitachycardia functions of the device; it has no effect on the backup pacing function (in contrast to the effect of a magnet on the pacemaker as discussed above).
o This is used when the device is delivering shocks inappropriately. With the increased prevalence of devices and, consequently, device malfunction, any facility with ACLS equipment should have a magnet available for management of this situation.
o Appropriate magnets can be obtained from the manufacturers of ICDs.
ICD Complications and Malfunction
· Device Infection: As with pacemakers, ICD infection is a serious problem and should be managed as discussed above.
· Inappropriate defibrillator firing/shock
o The current algorithms used by the ICD to distinguish SVT from VT/VF are imperfect, sometimes resulting in inappropriate shocks for supraventricular rhythms. Inappropriate shocks may also result from extrinsic signals or noise, such as electrocautery or other electromagnetic interference (including that generated by arc welding).
o Acute management of this situation includes ECG monitoring to determine the rhythm and application of a magnet if the shocks are inappropriate. Immediate availability of resuscitation personnel and equipment is necessary while the device is inactivated.
o Expert consultation is required to address the reason for the inappropriate therapy.
· Failure to treat VF/VT: Episodes of VF/VT that are not treated by the device require expert consultation for possible reprogramming of the ICD. In the interim, the patient requires monitoring in a facility able to manage these rhythms.
Other Device Concerns
· Perioperative management
o Several concerns arise with pacemaker or ICD function during an operation. Vibrations, pressure, and electrical signals from electrocautery can interfere with normal pacemaker function.
o In general, reprogramming the pacemaker to a DOO/VOO mode and inactivation of the rate-responsive element will prevent these complications. After the procedure, the device should be interrogated to ensure that no damage occurred.
o For thoracic operations, a chest radiograph should be performed to confirm that the lead position was not affected.
· Magnetic resonance imaging (MRI) imaging
o MRI imaging is contraindicated in patients with a pacemaker or ICD because of the possibility of heating and torque forces on the device itself from the magnetic field as well as potential reprogramming of the device.
o There is currently one MR conditional pacemaker system (leads and pulse generator) available. There are currently no approved MR conditional or MR safe ICDs. However, more MR conditional pacemakers and ICDs are likely to be approved within the next several years.
· Radiation therapy
o Radiation therapy has minimal immediate effect on the device if the beam is not directed directly at or near the pulse generator; however, cumulative radiation doses can result in device damage and warrant regular device interrogation.
o In addition, the shielding effect of the device may reduce the efficacy of the radiation treatment. Consultation with the patient’s cardiologist and/or device manufacturer is desirable.
· Cardioversion/defibrillation
o Application of external defibrillation or cardioversion may damage the device. The pads should be applied at a distance from the implanted device and proper device function confirmed once the patient is stabilized.
o This concern should not prevent the application of appropriate ACLS treatments to the unstable patient.
· Exposure to environmental electromagnetic radiation
o Electromagnetic interference (EMI) is ubiquitous in the modern world. Common sources include cell phones, antitheft devices, metal detectors, microwave ovens, and high-voltage power lines. However, few cases of significant interference have been reported.
o Patients can limit the potential for interference by not carrying the cell phone in a pocket over the device and using the more distant ear during conversations and by not lingering in the field of antitheft or metal detectors.
o Modern microwave ovens are no longer considered a significant concern (in contrast to early generation ovens).
o Patients exposed to significant electrical signals from industrial equipment should consult their cardiologist.
· Driving and physical activity
o Few clear guidelines have been published on the issue of physical activity; however, avoidance of contact sports that risk device damage and competitive exertion in patients at risk for arrhythmias is reasonable.
o With regard to driving, physicians should be familiar with local statutes.
o However, it is recommended that patients avoid driving until they are free of VT/VF and ICD shocks for a period of 6 months.
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