ANATOMY
Coronary circulation begins at the sinus of Valsalva, where the right and left coronary arteries (RCA, LCA) arise. The left main artery branches into the left anterior descending and the left circumflex arteries. The left anterior descending artery supplies the anterior of the left ventricle, the apex of the heart, the intraventricular septum, and the portion of the right ventricle that borders the intraventricular septum (Fig. 17-1). The left circumflex artery travels in the groove separating the left atrium and ventricle and gives off marginal branches to the left ventricle. The RCA travels between the right atrium and ventricle to supply the lateral portion of the right ventricle (Fig. 17-2). The posterior descending artery (PDA) comes from the RCA in 90% of patients and supplies the arteriovenous node. Patients whose PDA arises from the RCA are termed right dominant. If the PDA arises from the left circumflex, the system is left dominant.
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Figure 17-1 • Schematic showing the origin of the coronary circulation. LMA, left main artery; LAD, left anterior descending; RCA, right coronary artery; RPD, right posterior descending; LCX, left circumflex; AV, aortic valve; L, left; R, right. LifeART image copyright (c) 2009 Lippincott Williams & Wilkins. All rights reserved. |
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Figure 17-2 • Schematic showing the path of the coronary circulation. The left main artery gives rise to the left anterior descending and left circumflex arteries. |
The aortic valve is located between the left ventricle and the aorta. It usually has three leaflets, which form three sinuses. One sinus gives rise to the RCA, another to the LCA, and the third forms the noncoronary sinus. The mitral valve is located between the left atrium and ventricle. It normally has two leaflets, with the anterior protruding farther across the valve. Chordae tendineae attach the leaflets to the papillary muscles, which in turn serve to tether the leaflets to the ventricular wall.
CONGENITAL HEART DISEASE
Approximately 0.6% of live births will be complicated by congenital heart defects. This risk more than doubles in subsequent siblings. Most cases are sporadic, although there are well-known associations of genetic syndromes and congenital heart defects. These include atrioventricular canal defects in children with Down syndrome, coarctation of the aorta in children with Turner's syndrome, and supravalvular aortic stenosis in children with William's syndrome.
Congenital heart defects are best understood by the pathophysiology they cause, either congestive heart failure or cyanosis. Most anomalies fit into one of these categories.
Congestive heart failure can be caused either by a left-to-right shunt or an obstructive lesion. Left-to-right shunts result in a certain fraction of blood leaving the left side of the heart to the right side, increasing pulmonary pressure and necessitating large volume of left ventricular output to satisfy peripheral demands. Among these lesions are patent ductus arteriosus, in which the normal fetal connection between the pulmonary artery and aorta is not obliterated at birth. Depending on the size of the communication, it can cause severe failure. Premature infants with pulmonary compromise and/or children with an audible murmur should undergo closure, which can be achieved via catheter-based therapies.
Atrial and ventricular septal defects also result in left-to-right shunting. Patients with atrial septal defects classically have a second heart sound in which the split is of fixed duration. Over time such patients can develop pulmonary hypertension, right and left ventricular failure, and atrial arrhythmias. Most atrial septal defects can be closed using percutaneous methods. Ventricular septal defects may present in a similar fashion with pulmonary hypertension and congestive heart failure, culminating in Eisenmenger syndrome when the shunt reverses to a right-to-left shunt, causing cyanosis. These lesions should be fixed.
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Atrioventricular canal defects are complicated lesions involving the atrial and ventricular septae and the atrioventricular valves. When diagnosed, these lesions should be fixed. In its extreme form, a single arterial trunk arises from a joined ventricular chamber; this is termed a truncus arteriosus.
Obstructive lesions can also cause congestive heart failure. Aortic stenosis most commonly occurs as a result of a bicuspid aortic valve, but can also occur at the supravalvular or subvalvular location, or as a result of subvalvular ventricular hypertrophy, termed hypertrophic muscular subaortic stenosis. Although many procedures may be used to treat this condition, of particular interest is the Ross operation, which involves transposing the pulmonary valve to the aortic position and using a prosthetic graft for a new pulmonary valve.
Mitral stenosis commonly occurs in association with other congenital heart defects. Pulmonic stenosis is often mildly symptomatic and is generally treated with percutaneous methods.
The most common obstructive lesion in children is coarctation of the aorta. This occurs when the aorta becomes narrowed, usually just after the takeoff of the left subclavian artery (Fig. 17-3). Often, blood flow to the lower extremities will depend on a patent ductus arteriosus, closure of which can cause severe heart failure. Because of the risk of endocarditis, severe hypertension, congestive heart failure, and stroke, these lesions are repaired.
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Figure 17-3 • Coarctation of the aorta. The aorta is narrowed distal to the takeoff of the left subclavian artery. The increased pressure caused by this lesion frequently causes the ductus arteriosus to remain open. From Pillitteri A. Maternal and Child Nursing. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2003. |
Right-to-left shunts occur when deoxygenated blood makes its way into the peripheral circulation; this is also referred to as cyanotic heart disease. The most common cause is Tetralogy of Fallot (Fig. 17-4). This abnormality has four components: ventricular septal defect, pulmonic stenosis, right ventricular hypertrophy, and an overriding aorta.
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Figure 17-4 • Tetralogy of Fallot. Coronal view of heart in tetralogy of Fallot. Characteristics include pulmonary trunk stenosis, right ventricular hypertrophy, dextroposition of the aorta, and ventricular septal defect. LifeART image copyright (c) 2009 Lippincott Williams & Wilkins. All rights reserved. |
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Tricuspid atresia prevents flow from the right atrium to the right ventricle, and instead, deoxygenated blood traverses an atrial septal defect into the left atrium. Other lesions that can cause a right-to-left shunt include pulmonic atresia, transposition of the great arteries, and total anomalous pulmonary venous connection.
CORONARY ARTERY DISEASE
EPIDEMIOLOGY
Atherosclerosis of the coronary arteries is the most common cause of mortality in the United States, responsible for one third of all deaths. Approximately 5 million Americans have coronary artery disease, which is five times more prevalent in men than in women. Risk factors include hypertension, family history, hypercholesterolemia, smoking, obesity, diabetes, and physical inactivity.
PATHOPHYSIOLOGY
Coronary artery stenosis is a gradual process that begins in the second decade. When the lumen decreases to 75% of the native area, the lesion becomes hemodynamically significant.
HISTORY
Patients with ischemic heart disease usually complain of substernal chest pain or pressure that may radiate down the arms or into the jaw, teeth, or back. Typically, the pain occurs during periods of physical exertion or emotional stress. Episodes that are reproducible and resolve with rest are termed stable angina. If the pain occurs at rest or does not improve with rest, is new and severe, or is progressive, it is termed unstable angina and suggests impending infarction. Presentation can be variable, with patients complaining of indigestion, nausea, vomiting, diaphoresis, cough, new onset arrhythmia, syncope, and, in older adult patients, confusion or delirium. Ischemic heart disease can also be asymptomatic, classically in patients with diabetes.
PHYSICAL EXAMINATION
The patient may have evidence of peripheral vascular disease, including diminished pulses. Signs of ventricular failure, including cardiomegaly, congestive heart failure, an S3 or S4, or murmur of mitral regurgitation (MR), may occur.
DIAGNOSTIC EVALUATION
Electrocardiogram (ECG) may show signs of ischemia or an old infarct. A chest radiograph may show an enlarged heart or pulmonary congestion. An exercise stress test is sensitive in identifying myocardium at risk. These areas can be localized using nuclear medicine scans, including thallium imaging. Echocardiography is extremely useful in evaluating myocardial function and valvular competence. Angiography is the gold standard for identifying lesions in the coronary arteries, assessing their severity, and planning operative intervention.
TREATMENT
Patients with severe disease of the left main artery or with severe disease in the three major coronary arteries have decreased mortality after coronary artery bypass surgery. Pain is reliably relieved in >85% of patients. Surgical options include bypass using the internal mammary arteries or saphenous veins. Internal mammary bypass is preferred because of higher patency rates.
Percutaneous coronary interventions include balloon angioplasty and stent placement. Despite the tremendous volume of procedures performed in the United States, the exact indications for interventions
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are not well known. A large study in 2005 in the New England Journal of Medicine by Hannon et al. demonstrated that in patients with two or more diseased vessels, stents were associated with an increased need for further procedures and increased mortality compared with bypass grafting. Because early mortality was higher with bypass grafting, care must be individualized to the patient.
One common problem with coronary stents is in-stent restenosis. Benefits of drug-eluting stents, which elaborate various substances including sirolimus and paclitaxel, remain unclear.
It is important to note that nearly all risk factors for coronary artery disease are modifiable before and after an event. Preventive medicine used to aggressively lower blood pressure and cholesterol, combined with diet and exercise regimens, is critical.
AORTIC STENOSIS
ETIOLOGY
Aortic stenosis (AS) can present early in life–-for example, when the valve is unicuspid–-but more commonly occurs in the older population. A congenitally bicuspid valve usually causes AS by the time the patient reaches 70 years of age. Other causes include rheumatic fever, which results in commissural fusion and subsequent calcification, and degenerative stenosis, in which calcification occurs in the native valve (see Color Plate 13).
PATHOPHYSIOLOGY
The initial physiologic response to AS is left ventricular hypertrophy to preserve stroke volume and cardiac output. Left ventricular hypertrophy and increasing resistance at the level of the valve result in decreased cardiac output, pulmonary hypertension, and myocardial ischemia.
HISTORY
Patients often complain of angina, syncope, and dyspnea, with dyspnea being the worst prognostic indicator.
PHYSICAL EXAMINATION
A midsystolic ejection murmur, as well as cardiomegaly and other signs of congestive heart failure, may be present. Pulsus tardus et parvus, a delayed, diminished impulse at the carotid, may be apparent.
DIAGNOSTIC EVALUATION
Echocardiography or cardiac catheterization reliably studies the valve. A decrease in the aortic valve area from the normal 3 or 4 cm to <1 cm signifies severe disease.
TREATMENT
Patients who are symptomatic should undergo aortic valve replacement unless other medical conditions make it unlikely that the patient could survive the operation. In asymptomatic individuals< progressive cardiomegaly is an indication for operation, because surgical therapy is superior to medical therapy.
AORTIC INSUFFICIENCY
ETIOLOGY
Aortic insufficiency can be caused by rheumatic fever, connective tissue disorders including Marfan and Ehlers-Danlos syndromes, endocarditis, aortic dissection, and trauma.
PATHOPHYSIOLOGY
The incompetent valve causes a decrease in cardiac output, and left ventricular dilatation occurs. The larger ventricle is subject to higher wall stress, which increases myocardial oxygen demand.
HISTORY
Patients complain of angina or symptoms of systolic dysfunction.
PHYSICAL EXAMINATION
Typically, there is a crescendo-decrescendo diastolic murmur and a wide pulse pressure with a water hammer quality. The point of maximal impulse may be displaced or diffuse.
DIAGNOSTIC EVALUATION
Echocardiography is a sensitive and specific means of making the diagnosis.
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TREATMENT
Symptomatic patients should undergo replacement surgery if their medical condition allows them to tolerate a major procedure.
MITRAL STENOSIS
ETIOLOGY
Mitral stenosis (MS) develops in 40% of patients with rheumatic heart disease. Rheumatic heart disease occurs after pharyngitis caused by group A streptococcus. A likely autoimmune phenomenon causes pancarditis, resulting in fibrosis of valve leaflets. Histologic findings include Aschoff nodules. MS may also be caused by malignant carcinoid and systemic lupus erythematosus.
PATHOPHYSIOLOGY
Fibrosis progresses over a period of two or three decades, causing fusion of the leaflets, which take on a characteristic "fish mouth" appearance, significantly impeding blood flow through the valve. Increased left atrial pressures lead to left atrial hypertrophy, which in turn may cause atrial fibrillation or pulmonary hypertension. Pulmonary hypertension can further progress to right ventricular hypertrophy and right-sided heart failure.
EPIDEMIOLOGY
MS has a female predominance of 2:1.
HISTORY
Characteristic complaints include dyspnea and fatigability. Occasionally, pulmonary hypertension leads to hemoptysis.
PHYSICAL EXAMINATION
Cachexia or symptoms of congestive heart failure may be present, with pulmonary rales and tachypnea. Jugular venous distention, peripheral edema, ascites, and a sternal heave of right ventricular hypertrophy may be appreciable. Heart sounds are usually characteristic, consisting of an opening snap followed by a low rumbling murmur. The splitting of the second heart sound is decreased, and the pulmonary component is louder. The heart rate may demonstrate the irregular pattern of atrial fibrillation.
DIAGNOSTIC EVALUATION
Chest x-ray may show cardiomegaly, including signs of left atrial hypertrophy. Pulmonary edema may be present. ECG may show atrial fibrillation. Broad, notched P waves are an indication of left atrial hypertrophy. Right axis deviation is evidence of right ventricular hypertrophy. Echocardiography with Doppler flow measurement is extremely useful for demonstrating MS, estimating flow, and assessing the presence of thrombi. Cardiac catheterization gives a direct mea-surement of transvalvular pressure gradient, from which the area of the mitral annulus can be calculated.
THERAPY
Surgical options include valvulotomy or replacement. Therapy is indicated for symptomatic patients.
MITRAL REGURGITATION
ETIOLOGY
Approximately 40% of cases are caused by rheumatic fever; other causes include idiopathic calcification associated with hypertension, diabetes, AS, and renal failure. Mitral valve prolapse progresses to MR in 5% of affected individuals. Less common causes include myocardial ischemia, trauma, endocarditis, and hypertrophic cardiomyopathy.
PATHOPHYSIOLOGY
As regurgitation becomes hemodynamically significant, the left ventricle dilates to preserve cardiac output. A significant volume is ejected retrograde, increasing cardiac work, left atrial volumes, and pulmonary venous pressure. This, in turn, may lead to left atrial enlargement and fibrillation or cause pulmonary hypertension, which could result in right ventricular failure.
EPIDEMIOLOGY
MR is more common than MS and has a male predominance.
HISTORY
Patients commonly complain of dyspnea, orthopnea, and fatigue.
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PHYSICAL EXAMINATION
Patients may appear cachectic. Frequently, there is an irregular pulse, pulmonary rales, and a sternal heave. The pulse characteristically has a rapid upstroke, and vwaves may be present. A holosystolic murmur that radiates to the axilla or back is common. The point of maximal impulse is often displaced.
DIAGNOSTIC EVALUATION
Chest x-ray may show cardiomegaly and pulmonary edema. ECG commonly demonstrates left ventricular or biventricular hypertrophy, left atrial enlargement, and P mitrale. Echocardiography is extremely useful in establishing the diagnosis and the underlying lesion. Cardiac catheterization is useful in establishing pulmonary pressures and cardiac output.
TREATMENT
Medical therapy consists of afterload reducing agents, such as angiotensin-converting enzyme inhibitors, nitroglycerin, and diuretics. Surgical intervention is indicated if congestive failure interferes with daily life, if pulmonary hypertension or left ventricular dilation worsens, or if atrial fibrillation develops. If life-threatening MR develops from endocarditis, ischemia, or trauma, aggressive treatment with afterload reduction, a balloon pump if necessary, and antibiotics if indicated should be used to convert an emergency operation to an elective one. Because of the severe hemodynamic instability that can occur, operative intervention involving repair or replacement may be necessary in the acute setting. These emergency operations carry >15% mortality rate.
AORTIC BALLOON PUMPS AND VENTRICULAR ASSIST DEVICES
In patients with markedly decreased cardiac output insufficient to sustain end organ perfusion, an intra-aortic balloon pump may be useful to decrease afterload, increase coronary perfusion, decrease myocardial oxygen demand, and increase cardiac output (Figs. 17-5 and 17-6). These are temporary devices, generally placed via a femoral approach. Correct placement is critical. Occlusion of the left subclavian artery during inflation must be avoided, and proximal location above the renal arteries is also critical. Vascular complications, including arterial thrombosis and embolism, must be
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constantly checked for and may necessitate balloon removal.
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Figure 17-5 • How the intra-aortic balloon pump works: Balloon inflation. The balloon inflates as the aortic valve closes and diastole begins. Diastole increases perfusion to the coronary arteries. From Nursing Procedures. 4th ed. Ambler, PA: Lippincott Williams & Wilkins, 2004. |
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Figure 17-6 • How the intra-aortic balloon pump works: Balloon deflation. The balloon deflates before ventricular ejection, when the aortic valve opens. This permits ejection of blood from the left ventricle against a lowered resistance. As a result, aortic end-diastolic pressure and afterload decrease and cardiac output increases. From Nursing Procedures. 4th ed. Ambler, PA: Lippincott Williams & Wilkins, 2004. |
When medical therapy and intra-aortic balloon pumps are insufficient to provide adequate cardiac output, left ventricular assist devices may be used. These are divided into pulsatile flow pumps and nonpulsatile flow pumps, which use axial or centrifugal flow. These pumps can be used in the short term, generally in patients with temporary heart failure. These patients are expected to improve, and a common indication is postcardiotomy syndrome. Left ventricular assist devices can also be useful longer term as a bridge to transplantation. Thromboembolism, bleeding, and infection are common complications.
KEY POINTS