David T. Porembka
Echocardiography is a vital diagnostic modality for the intensivist. Numerous investigations using transesophageal echocardiography (TEE), yet not all-inclusive in the intensive care setting (n = 2,738), have shown its merit. The diagnostic capability varies (43%–99%), but most vital and interactive information obtained with beneficial results typically approaches 75%. As a result of TEE, the therapeutic implications for appropriate interventions (medical and surgical) are as high as 69%. Compared to the surface examination (transthoracic echocardiography, or TTE), TEE—because of improved imaging windows—essentially doubles the benefits of the aforementioned data (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22). Furthermore, echocardiography lessens the potential for physician misdiagnosis and misadventures. Because this mode is useful in indicating the most appropriate medical/surgical interventions, outcomes can be potentially improved (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22).
Significant cognitive skills and knowledge are required when using surface or esophageal echocardiography (23,24,25). Echocardiography is an extension of the physical examination and data obtained from the use of invasive monitoring, and encompasses handheld or portable echocardiography (TTE), TEE, three-dimensional reconstruction, stress echocardiography, contrast echocardiography, intravascular ultrasound (IVUS), and intracardiac echocardiography. Several guidelines and recommendations are available in the medical literature (11,23,24,26).
Although controversy on the appropriate level of training between our cardiology experts and intensivists still exists, a selective “training curriculum” is now being provided in selected subspecialties such as Emergency Medicine (27,28,29). In a recent Critical Care Medicine supplement, a suggested limited curriculum for intensivists was presented in detail for consideration (30,31) (Tables 23.1, 23.2, 23.3 and 23.4). Despite the current trend to allow the intensivist to independently interpret basic echocardiography features, the importance of consulting with an expert in TEE for difficult cases cannot be overemphasized. By doing so, a bilateral dynamic exchange in learning, teaching, research, and clinical care can only improve and lead to better outcomes and a probable decrease in overall cost to health care and to the patient. Intensive care physicians should totally embrace echocardiography as an integral complement in the care of the critically ill and injured patient (32,33).
This chapter will review the benefits and the efficacy of echocardiography (TTE, TEE) in the critical care setting.
Indications and Contraindications
Indications
The indications are straightforward but will vary with the type of intensive care setting (cardiac, cardiothoracic, surgery, trauma, or medical), the individual's expertise (fellow, resident, vs. faculty), and the institution's commitment to providing resources on a 24/7 service to assist in the diagnosis of these critically ill and injured patients (Table 23.3). Timely and accurate diagnoses are crucial in numerous situations (e.g., penetrating or blunt trauma-related cardiac structural damage or the presence of cardiac tamponade, aortic dissection/aneurysm or traumatic injury, or shock not responding to conventional treatment). The typical indications for echocardiography include but are not limited to the following:
· Ventricular performance and/or hemodynamic instability (ventricular failure, systolic and/or diastolic failure)
· Hypovolemia
· Pericardial diseases including cardiac tamponade
· Pulmonary embolism
· Complications following myocardial injury
· Complications following cardiothoracic surgery
· Aortic pathology
· Acute valvular dysfunction
· Infective endocarditis (IE) and associated complications
· Unexplained hypoxemia (intracardiac right-to-left shunts)
The benefit of TEE compared to the surface examination includes these prime indications and others because of better imaging quality to assess aortic pathology, cardiac valve endocarditis, and the presence of thrombi in the atrial appendage. TEE is also used as a guide in patients with atrial fibrillation undergoing electrical cardioversion. Another major benefit of imaging characteristics with TEE is that it allows visualization of a good cardiac acoustic window, even in patients with skin tapes, chest tubes, dressings, pneumothoraces, surgical wounds, severe obesity, and emphysema. A classic indication for TEE in the intensive care unit (ICU) is the acute evaluation of ventricular performance in conflicting clinical and pulmonary artery catheter (PAC) presentations. For example, the presence of hypovolemia can be demonstrated by the presence of turbulence in the left ventricular outflow tract (LVOT) via color flow Doppler, or by the appearance of systolic cavitary obliteration and inward movement of the distal anterior mitral valve leaflet that may cause obstruction. A fundamental use of TEE is the assessment of enlarged end-systolic and end-diastolic ventricular volumes in patients with normal or high cardiac output and stroke volume index. In a patient with shock, the clinician echocardiographer can determine with a quick look if there is inadequate ventricular systolic function or hypovolemia. Divergent therapies can be implemented immediately from the echocardiographic hemodynamic findings (31,34,35,36,37,38,39,40,41). Finally, the use of echocardiography, particularly TEE, in cardiac arrest situations and once an artificial airway is secured is a prime indication to assess various abnormalities during and after cardiopulmonary resuscitation (CPR) (34,35,42,43).
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Table 23.1 General Cognitive And Technical Echocardiography Knowledge |
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Table 23.2 Procedural Competency Assessment Based On Successful Interrogation Of Cardiac Pathologic Conditions |
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Contraindications
Contraindications for echocardiography in the surface mode are nil and are limited only by obtaining views sufficiently adequate so an accurate diagnosis can be secured. With any limited acoustic windows or in cases when the diagnosis is in question, one should proceed to TEE. A relative contraindication for TEE is any known or suspected esophageal or gastric pathology, including recent esophageal or gastric surgery, esophageal varices in patients with portal hypertension, and suspected or known cervical spine injury. An uncooperative patient whose airway is not artificially secured is a relative contraindication unless adequate topical anesthesia is provided, or sedation even to the point of total control of the patient's airway and general anesthesia (34,35,36,37,38,39,40 and 41). A penetrating esophageal injury, suspected or known by the mechanism of injury, remains an absolute contraindication to TEE.
Examination
The examination for surface echocardiography and TEE will be briefly presented. Adequate texts and atlases on this topic can be easily accessed. With recent improvements in echocardiographic technologies, and two-dimensional and color flow Doppler echocardiography, excellent views can be obtained. At present with the surface approach, one can obtain three- or four-dimensional imaging; in the near future, TEE will be a standard modality in all the platforms.
For the surface examination, there are four major positions or approaches to the heart on the thorax:
1. Parasternal position with long-axis (left ventricular [LV] in sagittal section, LV inflow, and right ventricular [RV] outflow) and short-axis views (LV apex, papillary muscles [midlevel], mitral valve [basal level], aortic valve/RV outflow, and pulmonary trunk bifurcation)
2. Apical position including the four-chamber view
3. Five-chamber or two-chamber views, suprasternal notch position; involving the long-axis aorta and short-axis pulmonary artery
4. Subcostal position interrogating the RV outflow, the RV and LV inflow, and the inferior vena cava and hepatic vein (31,34,35,36,37,38,39,40,41,43) (Figs. 23.1, 23.2, 23.3, 23.4, 23.5, 23.6, 23.7, 23.8, 23.9, 23.10, 23.11, 23.12, 23.13, 23.14 and 23.15).
In the esophageal approach, the imaging obtained is markedly improved, allowing more extensive pathologies to be diagnosed and interrogated due to the ability of this approach to visualize the structures (cardiac and extracardiac) with better resolution (lower frequency) (Figs. 23.15 and 23.16).
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Table 23.3 Clinical Indication for the Use of Echocardiography in the ICU |
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Ventricular Performance (Systolic and Diastolic Function)
The incidence and prevalence of systolic (SHF) and diastolic heart failure (DHF) is considerable, and is rising, probably due to the increasing aging population. Consequently, much experience with this group has been gained and has led to a better understanding of caring for these marginal patients (44,45,46,47). The reported incidences for SHF in the ICU are 61% to 68% and for DHF 16% to 39%. Overall, when a patient is described with a syndrome of heart failure, echocardiographic investigations reveal the presence of DHF to vary from 40% to 71% (47).
Systolic Function
Determination of systolic function in ICU patients is constantly debated among clinicians, even when echocardiography is not used at the bedside. Echocardiography remains an extension of the clinical examination and the patients' clinical signs and symptoms, but the use of portable handheld echocardiography as part of the physician's armamentarium should be encouraged. The comparison of echocardiography to the pulmonary catheter (PAC) is still significantly controversial; PAC has not been validated in prospective peer-reviewed investigations, and thus should not be considered the gold standard. In concert, when one refers to a patient's ejection fraction (EF) while obtaining an echocardiographic examination, clinical decisions are limited, and intuitive assumptions and interventions are still being entertained (48). This latter LV function parameter (EF) is load dependent (as well as fractional shortening, systolic time tissue velocity of the mitral annulus, and regional wall motional analysis) and often used as an index of myocardial performance, far better in accuracy than PAC-related parameters such as stroke volume, stroke volume index, and cardiac index. Recently, the strain and strain rate via echocardiography has been gaining favor as a useful parameter to evaluate load independently from indices of cardiac performance (49). The physician's capability to construct and interpret pressure/ volume loops for the determination of contractility is a controversial issue, particularly in the clinical setting of septic shock. How to intervene in the ventricular performance or optimization? What is preload? What are the goals of resuscitation and their end points (50,51,52,53,54,55,56,57)? These are all reasonable questions, and why echocardiography is not part of the standard of management of these critically ill patients is yet to be investigated.
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Table 23.4 Summary of ACC/AHA Recommendations for Physicians in Echocardiography |
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Even though left ventricular ejection fraction (LVEF) is a limited myocardial performance index, it is a strong predictor of clinical outcome in most cardiac abnormalities (58,59,60). Of interest, EF is more reliable as a general predictor of mortality, second only to age, than when used to quantify the extent of coronary artery disease or degree of perfusion defects (61,62). Surface approach echocardiography by the use of the modified Simpson rule is superior to estimating either intracardiac volumes or LVEF (63,64). In fact, TEE in this situation underestimates volume by foreshortening the LV view with less incorporation of apex. Volumetric measurements should be objectively quantified:
LVEF = (LVEDV - LVESV)/LVEDV
where LVEDV refers to left ventricular end-diastolic volume and LVESV to left ventricular end-systolic volume. LVEF may also be calculated from LV dimensions measured with M-mode echocardiography at the midventricular level (65,66) (Figs. 23.17 and 23.18).
Other methods for approximating ventricular volumes are color kinesis and acoustic quantification (67,68) (Fig. 23.19).
Three-dimensional echocardiography is currently the best practice technique for estimating volumes and EF with greater accuracy by minimizing the inherent problems of not being able to always obtain orthogonal foreshortened, short-axis, and four-chamber views. Excellent comparative investigations with magnetic resonance imaging (MRI) and computed tomography (CT) with echocardiography reveal its accuracy as far as quantitative determinations (69,70).
The Doppler measure of systolic function is now a standard methodology in the interrogation of systolic function (71,72); acceleration (dV/dT) is easily measured by using spectral Doppler from the determination of peak outflow velocity and the time to achieve this determination. The first derivative of aortic velocity is the peak acceleration, and the slope from its onset to peak is the mean acceleration (73,74). Stroke volume is directly correlated with this velocity. By using the continuity equation, the determination of velocity of blood leaving a known chamber in relation to the cross-sectional area (CSA) of the orifice that the blood is flowing through, stroke volume can be calculated:
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Figure 23.1. The parasternal long-axis view is shown. Ao, aorta; LA, left atrium; LV, left ventricle; RV, right ventricle. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
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Figure 23.2. This schematic demonstrates the various short-axis planes that can be derived from the parasternal long-axis view. Note that the planes are not exactly parallel but provide views of anatomy from apex to base. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
stroke volume = TVI × CSA
where TVI is the velocity–time integral on spectral Doppler (75). By multiplying by the heart rate, cardiac output is calculated. Diastolic volume and EF are determined using this same principle through the mitral valve:
EF = (stroke volume/diastolic volume) × 100.
There are significant limitations to the methods described that include a rhythm other than sinus, and the accurate determination of the dimension of the orifice through which the blood flows is transverse (76).
Tissue Doppler imaging (TDI spectral analysis), by avoiding the limitations of the above techniques, is gaining acceptance (58,77) (Fig. 23.20).
TDI is also used in the evaluation of diastolic function and preload (78,79). Normal values of Doppler velocities (S) can be determined both in the pediatric and adult population (80,81). Ventricular length and afterload (a minor contributor) will affect this value (82,83); the lower the S-wave velocity, the more depressed the myocardial function will be, even at the point prior to the visualization of thickening of the left ventricle (84). In the context of existing diastolic function, the S-wave velocities will change in relation to worsening LV systolic function (85). A poor prognostic indicator of cardiac events in patients with heart failure is when the S velocities are greater than 5 cm/second (86). For example, TDI is a useful indicator that correlates with biopsies as well as regional segment abnormalities in heart transplant recipients who experience rejection, although difficulties do arise because of tethering (87,88,89).
Strain and strain rate analysis is becoming of greater use in echocardiography but has not reached total acceptance. In addition, TEE may not be readily available in the ICU (49,90). This technique measures the deformity of the LV segment during the cardiac cycle, with strain referring to relative change (%) and strain rate being the absolute of change (s-1) (41,91) (Fig. 23.21).
Both strain and strain rate are being used in heart failure patients (resynchronization) for the early detection of myocardial ischemia and identification of viable myocardium (92,93,94). Technical limitations of this technique include a low signal-to-noise ratio, angle dependence, and a processing power that requires significant data storage and analysis (95). Nevertheless, it is independent of heart rate and afterload, although it is still influenced by preload due to the reliance on the initial diastolic dimension (96,97). Other potential advantages are the use of spectral tracking (which eliminates the angle effect), a feature that has been available only recently (98,99), and the backscatter/tissue characterization, which is similar to magnetic resonance imaging (MRI) in the evaluation of the myocardium (100,101,102).
Peak + dP/dT (typically recorded prior to opening of the aortic valve) is also commonly used, although some investigators believe it to be load independent in the presence of mitral regurgitation. It does have some prognostic importance (when less than 600 mm Hg/second) in congestive heart failure (CHF) and valvular surgery (103,104). Other investigators believe that this index is influenced by preload and that stress-corrected, fiber-shortening velocity (Vcf) is a more viable index of CHF (105,106,107).
Last, the pseudonormalized Doppler total ejection isovolume index (TEI) is a valid, load-independent measure of ventricular performance
Index = (ICT + IRT)/ET
where ICT is isovolumetric time, ET is the ejection time, and IRT is the isovolumetric relaxation time (108,109). As ventricular function worsens (diastolic or systolic), this index increases (110) (Figs. 23.22 and 23.23).
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Figure 23.3. Two short-axis views are provided. A: The short-axis view at the level of the mitral valve (MV) is demonstrated. B: A basal short-axis projection is shown at the level of the aortic valve. LA, left atrium; RA, right atrium; RV, right ventricle. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
Diastolic Function
Diastolic dysfunction is greatly underappreciated in the ICU (111,112). Research and clinical endeavors have emphasized systolic function. Since the addition of pulsed and continuous wave Doppler echocardiography, the importance of diastolic dysfunction came to the forefront, especially when dealing with critically ill patients in whom clinical findings and hemodynamics can often be confusing and misleading. Diastolic dysfunction may be isolated but is usually associated with systolic dysfunction (44,72,111,113,114). Ventricular interactions may be a contributing influence in the presentation of echocardiographic findings.
Even though echocardiography provides a unique insight in left ventricular dysfunction, there are significant difficulties with its use that must be appreciated (112). Diastole is associated with summation of the processes by which the heart loses its ability to generate force and shorten while returning to the precontractile state. Diastolic function is associated with relaxation and early ventricular filling or altered left ventricular pressure/volume and stress–strain relationships. Many confounding factors interplay in early LV filling and compliance that, at times, may be diametrically opposed (111) (Table 23.5). Altered hemodynamics and loading conditions, as well as tachycardia, are confounding issues in accurately determining the extent of LV diastolic dysfunction, particularly in patients who experience shock states—especially distributive events (sepsis, septic shock, systemic inflammatory response syndrome [SIRS], liver insufficiency); inflammatory mediators and cytokines affect all aspects of myocardial performance including atrial dysfunction and volume (115). Tachycardia can be an early deterrent in the accurate measurement of diastolic function (116).
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Figure 23.4. A short-axis plane at the level of the papillary muscles (arrows) is shown. LV, left ventricle. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
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Figure 23.5. The apical four-chamber view is shown. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
Doppler indices can appreciate the complexities of LV relaxation. The rate of LV relaxation is estimated from the maximal rate of pressure decay (-dP/dtmax) and other indices (such as the relaxation half-time [RT]) (117). Tau (isovolumetric relaxation) reflects the aortic valve closure to mitral valve opening and appears to be a better index of relaxation because of the decreased load dependency (118).
Although the pressure/volume relationship of the left ventricle is more often emphasized, the pressure/volume relationship of the atria can also play an important role. Other extrinsic factors and myocardial ischemia may contribute to impairment of diastolic dysfunction. Despite the limitations discussed, echocardiography remains a viable tool for detecting the presence of diastolic dysfunction (111,112). The morphologic and functional differences between diastolic and systolic heart dysfunction are described in Table 23.6.
Diseases germane to the critically ill—such as metabolic derangements involving mitochondrial dysfunction as seen in sepsis, SIRS, and liver insufficiency—or simply the postcardiac surgical patient status can affect the passive/active relaxation of the left ventricle (115,119,120,121,122,123,124). Comorbid conditions (hypertensive heart disease) and the presenting hemodynamic picture (the level of the atrial pressure and its rate of development) will also influence this relationship. Diastolic chamber stiffness is dependent on ventricular chamber characteristics (mass, volume) and myocardial stiffness, both load- and chamber size–independent variables of passive chamber and myocardial properties (111,125,126).
The echocardiographic assessment is accomplished through several means: M-mode and two-dimensional echocardiography and Doppler techniques. Left ventricular diastolic pressure, diastolic function, and ventricular and atrial filling patterns are measured by flows through the pulmonary veins (left atrial [LA] filling) and annular velocities through the mitral valve orifice (LV filling) (71,111,127). By measuring these parameters, one can get a sense of prognosis and outcomes in patients with heart failure that can guide treatment (128). In addition, by using these Doppler techniques for measuring pulmonary artery pressures, the clinician can predict the extent of hospitalization and mortality (129). There are several patterns seen via pulsed-wave Doppler through the mitral valve, which reflects the relationship between the LA and LV diastolic pressures. Normally, regarding the early/late filling pattern and ratio, E/A is greater than one. The deceleration time of E velocity (DT) and isovolumic relaxation time (IVRT) are other parameters obtained in the interrogation of this flow. Other patterns easily detected are restriction (E/A less than 2), pseudonormalization (E/A 1–1.5), and abnormal relaxation (E/A less than 1) (111) (Table 23.7). To clarify the second pattern, tissue Doppler index (TDI Ea [early annular] velocity) is measured through the mitral annulus. This technique measures high amplitude and low velocity of the myocardium (130). It appears that early diastolic annular velocity Ea is relatively load independent and should be completed in every patient (131). Ea will decrease in the presence of elevated filling pressures associated with increases in early diastolic transmitral velocity. Of interest, the transmitral early diastolic velocity/tissue Doppler early diastolic annular velocity E/Ea correlates with pulmonary artery occlusion pressure and mean diastolic LV pressure over an extended range of ejection fraction (EF) (132,133,134,135).
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Figure 23.6. Starting from the four-chamber, the transducer can be tilted to a shallower angle to produce a plane that includes the left ventricle outflow tract and proximal aorta (Ao). LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
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Figure 23.7. An apical two-chamber view is demonstrated. LA, left atrium; LV, left ventricle. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
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Figure 23.8. The special long-axis view is similar to the parasternal long-axis view but is recorded from lower interspace. Ao, aorta; LA, left atrium; LV, left ventricle; RV, right ventricle. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
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Figure 23.9. From the apical four-chamber view, pulsed Doppler imaging can often be used to record pulmonary venous flow by positioning the sample volume at the junction of the pulmonary vein and left atrium. In this example, pulmonary venous flow has three phases: a systolic phase (PVs), a diastolic phase (PVd) and a small wave of flow reversal during atrial systole (PVa). (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
Interrogation of the pulmonary venous patterns (PVF) is helpful in depicting diastolic dysfunction. Both modes of echocardiography (TTE and TEE) are useful, but invariably, TEE can more easily assess the flow characteristics usually in the left upper superior vein. The pattern seen is related to the suction effects of the LV and the LA. The systolic component represents LA filling during atrial relaxation (S1) and ventricular contraction (S2). The diastolic forward phase reflects opening of the mitral valve. Atrial reversal flow represents retrograde flow during atrial contraction (less than 20 cm/second). The extent of reversal of atrial flow may also reflect elevated LA pressure with or without LV compliance changes (111).
Color M-mode Doppler is another method for identifying diastolic function abnormalities and is believed to be load independent (136). Thus, the propagation velocity (Vp) is inversely related to the time constant of LV relaxation (137). This method can be used with the E velocities and the IVRT to estimate pulmonary occlusion pressure (138). It is of interest that Vp may distinguish between restrictive and constrictive pericardial cardiomyopathies (136).
M-mode and two-dimensional echocardiography are underappreciated in diastolic function assessment. The timing and extent of LV thinning rate and wall motion as well as the duration of atrial contraction and early relaxation can provide useful data. Filling dynamics can be obtained by measuring, frame by frame, the LV volume with either apical four-chamber or short-axis views (139,140). Assessing ventricular volume and mass with M-mode echocardiography provides information of the ventricular pressure/volume relationship relating to operative chamber compliance (72). Also, a marker for duration and severity of diastolic dysfunction is LA volume (141).
Tissue Doppler imaging is an echocardiographic technique that directly measures myocardial velocities. Diastolic tissue Doppler velocities reflect myocardial relaxation and, in combination with conventional Doppler measurements, ratios (transmitral early diastolic velocity/mitral annular early diastolic velocity [E/Ea]). Ea is a relatively preload-independent measure of myocardial relaxation in patients with cardiac disease as compared to early transmitral velocity, and has been developed to noninvasively estimate left ventricular (LV) filling pressure. Consequently, mitral E/Ea can help to establish the presence of clinical congestive heart failure in patients with dyspnea. However, E/Ea has a significant gray zone and is not well validated in nonsinus rhythm and mitral valve disease. B-type natriuretic peptide (BNP) is a protein released by the ventricles in the presence of myocytic stretch and has been correlated to LV filling pressure and, independently, to other cardiac morphologic abnormalities. In addition, BNP is significantly affected by age, sex, renal function, and obesity. Given its correlation with multiple cardiac variables, BNP has high sensitivity, but low specificity, for the detection of elevated LV filling pressures. Taking into account the respective strengths and limitations of BNP and mitral E/Ea, algorithms combining them can be used to more accurately estimate LV filling pressures in patients presenting with dyspnea (142).
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Figure 23.10. The suprasternal notch also permits the aortic arch (AA) to be recorded in cross section. The plane allows visualization of the superior vena cava and demonstrates the right pulmonary artery (RPA) coursing below the arch and above the left atrium (LA). (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
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Figure 23.11. The apical four-chamber view is sometimes recorded with this orientation that places just the right heart on the right. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
In summary, systolic and diastolic dysfunction are two definitive entities or syndromes of heart failure. Even though the clinical symptoms and hemodynamic presentations may appear similar, the primary function and myocardial structural derangements are quite distinctive. There are marked advancements for treatment of systolic heart failure, but treatment for diastolic failure is still empiric. Echocardiography can serially follow and evaluate the treatment management of these patients (112), and in so doing, prognostic indicators can be detected (129,143). Therefore, the use of echocardiography in the syndromes of heart failure is crucial for enhancement of patient care and outcome. Even in sepsis, bedside evaluation of the ventricular function with echocardiography is a proven imaging tool (144).
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Figure 23.12. M-mode recording at the level of the mitral valve is shown. A B bump is indicated by the arrows. IVS, interventricular septum; MV, mitral valve; PW, posterior wall. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
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Figure 23.13. M-mode echocardiograms recorded in two patients with significant systolic dysfunction. Top: An E-point septal separation (EPSS) of 1.2 cm (normal M6 mm). Bottom: Recording in a patient with more significant left ventricular systolic dysfunction in which the EPSS is 3.0 cm. Also note the interrupted closure of the mitral valve with a B bump (top), indicating an increase in the left ventricular end-diastolic pressure. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
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Figure 23.14. M-mode echocardiogram recorded through the aortic valve in a patient with reduced cardiac function and decreased forward stroke volume. Note the rounded closure of the aortic valve, indicating decreasing forward flow at the end of systole. Normal and abnormal aortic valve opening patterns are noted in a schematic superimposed on the figure. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
Left ventricular morphologic and functional characteristics in primary systolic and diastolic heart failure compared with controls and their follow-up changes are represented in Tables 23.8 and 23.9.
Pericardial Disease and Pericardial Tamponade
Echocardiography is an ideal technique to detect pericardial maladies such as pericardial effusions leading toward tamponade (acute vs. chronic), restrictive versus constrictive pericardial disease processes, and infiltrative processes, infective or not (congenital, neoplastic, metabolic, radiation induced, iatrogenic, and traumatic) (35,41,43).
Pericardial effusions can readily be identified by either the surface or esophageal approach. When the effusion is posterior and/or loculated (regional), the surface image may bypass its presence. Regional tamponade is not securely identified but may be juxtaposed to either ventricle and/or may involve the right atrium, vena cava, or pulmonary veins. The detection of a pericardial effusion ensures the diagnosis of a pericarditis. However, a patient with fibrinous acute pericarditis may often present with a normal echocardiogram. When fluid is detected, the clinician may proceed to drain it and determine if it is of an infectious cause (exudative), a complication of congestive heart failure (transudative), or traumatic in nature (hemorrhagic) (145).
In the syndrome of congestive heart failure (14%), myocardial infarction (15%), and valvular heart disease (21%), pericardial effusion is relatively common and may proceed to a tamponade syndrome (146,147). In cardiac surgical patients, the vast majority will have an effusion that presents usually on the second postoperative day and maximizes toward the tenth day (148). Fortunately, cardiac tamponade is unusual in these surgical patients, typically averaging 1% of the cases, with the exception of the cardiac transplanted patient in whom a higher frequency can result from repeated mediastinal procedures or rejection (149,150). Of interest, female gender, valvular intervention, and/or anticoagulants are predisposing factors (151).
An asymptomatic patient with chronic effusive pericarditis can present with a large effusion (152). Etiologic factors of this chronic process include uremia, neoplasm, tuberculosis (knobbed calcified pericardium), and connective tissue disorders (127,153). Typically, extensive effusion without any inflammatory disorders can be associated with a malignancy (127,152,154).
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Figure 23.15. Diagram of cardiac structures from standard tomographic planes: parasternal long-axis view (left), parasternal short-axis view (upper right), and apical four-chamber view (lower right). |
Echocardiography easily characterizes the relative contributions of cardiac enlargement or encroachment on the atrial/ ventricular chambers and their ventricular and atrial performance, identifying underlying physiologic hemodynamic aberrations (35,41,43). Via M-mode echocardiography, one will see an echo-free space between the visceral and parietal pericardium dynamically throughout the cardiac cycle (Fig. 23.24).
If during systole there is a prominent separation, the fluid extent is deemed important. This modality is quite sensitive, as is two-dimensional echocardiography, which can detect either small (less than 5 mm), moderate (5–10 mm), or large (greater than 10 mm) fluid amounts, as well as its global or regional involvement. As stated earlier, as the fluid volume increases, it will extend from the posterobasilar LV apically and then anteriorly, subsequently lateral and posterior to the LA (Fig. 23.25).
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Figure 23.16. From the esophagus, the probe can be flexed to yield a basal short-axis projection. LA, left atrium; RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
Drainage is performed for diagnostic purposes (e.g., infectious pathogens, cancer) or therapeutic reasons (hemodynamic compromise or pericardial tamponade) (35,41,43,151,155,156).
In regard to the end of this dynamic progression of fluid involvement, cardiac tamponade becomes a life-threatening event that must be correctly identified, diagnosed, and relieved in an expeditious fashion (157,158). Dynamic tamponade presentation depends on several physiologic considerations: the underlying ventricular performance; the rate of its development (increasing pericardial pressures in contrast to the intracardiac pressures with elevating venous pressures and decreasing to negative transmural pressures); the inherent intracardiac pressures, particularly of the ventricles; and the presenting intravascular volume or preload, especially in a hemorrhagic condition. If the patient has pre-existing right ventricular afterload and/or pulmonary artery hypertension, the echocardiographic findings will be delayed because of the abnormal RV loading conditions. Normally, the diastolic collapse of the RV—depicted as abnormal posterior motion of the anterior RV wall during diastole—indicates that the pericardial pressure is exceeding the early diastolic RV pressure. In other words, the RV diastolic transmural pressure is negative (159). In contrast, if the patient's underlying left ventricular systolic dysfunction is impaired, the echocardiographic characteristics of tamponade will present earlier in the hemodynamic “fluid” progression with smaller volumes (160).
The echocardiographic indicators of pericardial tamponade include the following:
· Decrease in end-systolic and end-diastolic dimensions
· Relative increase in RV dimensions during spontaneous ventilation (inspiration) as compared to an increase in LV dimension
· Right atrial diastolic collapse
· Left ventricular diastolic inversion
· Greater than 50% decrease in transmitral inflow
· Decrease in aortic flow velocities during inspiration.
A large pericardial effusion (greater than 10 mm) may reveal a “swinging” heart throughout the cardiac cycle. In contrast, flow across the tricuspid valve and pulmonary flow velocities (PVF) increase dramatically during inspiration, primarily in the systolic component of the PVF (161). Even though RV diastolic collapse is a sensitive indicator of tamponade, different loading conditions with varied ventricular performance will lower its specificity. Right atrial (RA) diastolic volume is an even more sensitive (100%) marker for tamponade but, again, its specificity is not the best (162).
Of note, if the duration of RA diastolic collapse exceeds one third of the cardiac cycle, the specificity increases (162). LA collapse is not usually detected (25%), but when it does exist, the specificity is markedly higher. LV diastolic collapse is much less common, probably due to the ventricular chamber properties (163, 164 and 165). As in any dynamic hemodynamic setting, clinical conditions may vary, and pericardiocentesis is not necessary in every case of pericardial effusion. The absence of any chamber inversion has a high negative predictive value (92%), with the positive predictive value reaching 58%. Abnormal right-sided venous flows carry 82% and 88% positive and negative predictive values, respectively, for pericardial effusion (166).
If the pericardial fluid increases rapidly, the patient may initially have no prominent symptoms or may have only shortness of breath, with or without chest pain. Shortly thereafter, the patient will deteriorate to systolic hypotension, venous hypertension (distended jugular veins), and pulsus paradoxus. In the volume-depleted patient, these findings might not be initially present until rapid repletion of preload unmasks these characteristics (35,41,43,167).
Diastolic filling is also limited in constrictive pericarditis. Normal thickness of the pericardium does not preclude this diagnosis, which can be surgically confirmed in 28% of the cases of a negative series (168). The observed venous patterns of constrictive pericarditis from tamponade are characteristic. Because the ventricular chambers are fixed in volume by the pericardium, venous return is unimpeded during ejection, thereby ablating the normal venous surge during systole. Cardiac compression at end systole does not occur, so when the tricuspid valve opens the return of flow into the ventricle, it is of higher velocity, resulting in a biphasic venous return with a diastolic component faster than the systolic component (145). In contrast with tamponade, during inspiration in constrictive pericarditis, the decrease in intrathoracic pressure is not transmitted to the heart, and venous return does not fall (125,145,169). TEE measurement of the LV wall is markedly better than the surface approach (170,171).
The echocardiographic findings of this type of pericarditis include the flattening of the LV posterior wall, abnormal posterior septal motion in early diastole, rapid atrial filling, and the occasional premature opening of the pulmonic valve due to elevation of the RV pressure above the pulmonary artery pressure. Via the M-mode modality, there may be notching of the ventricular septum during early diastole or atrial systole secondary to a transient reversal of ventricular septal transmural pressure gradient (172). The above findings are not highly sensitive, yet a normal examination essentially excludes the diagnostic presence of constrictive pericarditis (173). Via two-dimensional echocardiography, the sonographer will detect dilation or lack of collapse of the hepatic veins and inferior vena cava, biatrial distention, and an abnormal contour between the LA and LV posterior walls. LV performance may be preserved unless there is a mixed pattern of restrictive–constrictive physiology (174,175). By applying Doppler techniques, the E velocities and E/A ratios on LV and RV inflow increase (due to the abnormal rapid early diastolic filling-restrictive pattern). In constrictive pericarditis, there is a prominent early diastolic velocity Ea when interrogated by tissue Doppler. The linear response to LA pressure increases, and the ratio of E/Ea is inverted (176).
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Figure 23.17. Schematic representation of two-dimensionally derived measurements of left ventricular systolic function. Top: The methodology for determining fractional area change, which is defined by the formula in the figure. Middle and bottom: Using the geometric assumption that the left ventricular cavity represents a cylinder and cone configuration, the volume of each separate component can be calculated as noted. The overall left ventricular volume equals the sum of the two volumes. See text for further details. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
When evaluating propagation velocity with color M-mode Doppler, the early diastolic transmitral flow is greater than 45 cm/second (176). These findings are counterintuitive to restrictive pathology and filling with reduced Ea (less than 8 cm/second) (177,178). A classic characteristic of constrictive pericarditis is when the mitral inflow velocity decreases up to 40% while flow through the tricuspid valve is greatly enhanced in the first cardiac cycle after inspiration. In concert, the respiratory variation in PVF is markedly influenced (179,180). When there is coexisting elevated LA pressure, this exaggerated transmitral inflow velocity may not be apparent (179,181). Even though there is an increased velocity in the PVF, especially during expiration, the ratio of S/D is reduced even further by affecting the diastolic component (182). Figure 23.26 describes in detail the comparisons and dissimilarities in the restrictive and constrictive pathologies (145).
Penetrating cardiac injury should be briefly presented here considering that it is a unique pathology with life-threatening lesions that are not always obvious by routine clinical examination (183). If the patient arrives at a definitive tertiary care setting alive, immediate control of the hemorrhage should be attempted, at times with an immediate thoracotomy in the emergency department or in the operating room (184,185). A bloody effusion may be contained in the pericardial space (if there is a contiguous pathway to the thorax) or extend externally, followed by profound shock and rapid death by exsanguination. The lesions have multiple configurations, ranging from a ventricular mural wound to small, irregular, and multiple lesions. In obvious cases, surface echocardiography may identify pericardial tamponade and/or large lesions (ventricular septal defect [VSD]). Following resuscitation, the clinician should further investigate the clinical picture via TEE, since small lesions—yet significant and potentially fatal—may be missed, including VSD, defects through valve leaflets, intracardiac thrombi, or regional tamponade (186,187). One of the largest studies to date on this topic is by Degiannis et al. (188). In a 32-month period, 117 patients with penetrating injuries of the mediastinum were evaluated retrospectively. A 17% mortality by stabbing was observed, whereas victims with gunshot wounds (GSW) revealed an expected higher mortality of 81% (158). Another series revealed a 7% occult injury, with a similar mortality rate contrast between GSW and stab wounds (185). The clinician should always keep in mind that these patients are a complex challenge and that hemodynamic stability does not preclude an unexpected malady. Complacency should not occur (186,187).
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Figure 23.18. Schematic representation of a simplified method for determining the left ventricular ejection fraction from three separate minor-axis dimensions at the base, mid, and distal portion of the left ventricle in an apical view. The contribution of the apex is expressed as a constant (Kapex) ranging from -5% to +15%. (From Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum's Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005, with permission.) |
Assessment of Myocardial Performance
In extrapolating the information reviewed in the sections of LV performance and pericardial disease, echocardiography is found to be an extremely useful diagnostic tool that can be used in a timely manner to delineate the cause of the shock state, whether hypovolemia, hyperdynamic derangements—type B metabolic lactic acidosis (sepsis, septic shock, liver failure, heavy metal poisoning)—and myocardial injury. An echocardiographic examination is easily performed, and the information obtained can avoid the placement of a PAC. The initial echocardiographic observation evaluates LV function and volume. In a hypovolemic condition, the ventricle exhibits systolic cavitary obliteration, with turbulence in the left ventricular outflow tract (LVOT) seen via color flow Doppler. In extreme hypovolemia, the distal anterior leaflet of the anterior mitral valve in systole will cause obstruction to flow (39,40,189). This condition is amplified if relative hypovolemic states and tachycardia are observed in patients with hypertrophic obstructive cardiomyopathy (HOCM) (40). Some of these echocardiographic indicators of a decreased preload state may be observed in patients who appear clinically normovolemic, regardless of baseline ventricular function (39,189).
Ventricular performance and ventricular interactions and loading conditions are quite complex in sepsis, SIRS (systemic inflammatory response syndrome), and septic shock (115,119,120,121,122,123,124). Echocardiography may clarify the effects of medical and/or pharmacologic interventions in these profoundly critically ill patients. However, often their physiologic effects are affected by the inherent (premorbid) chamber physical properties (pressure/volume characteristics) or fluid dynamics. A paradoxical response between survivors and nonsurvivors can be observed when a Frank-Starling curve is plotted against volume load in an animal model. The greater the end-systolic and end-diastolic volumes, the better the chance for survival (190). Furthermore, a paradoxical decrease in the slope of isovolumetric/pressure line (an index of contractility that is load independent) is associated with a decrease in cardiac compliance but increase in survival (191).
The effect of sepsis cardiomyopathy may result in a lower ejection fraction (which is load dependent) with high cardiac output, tachycardia, higher stroke volume, and elevated mixed venous saturation. As the patient deteriorates, hypotension occurs, impairment of cellular function follows, and the global ventricular volume response to resuscitation and fluid becomes ineffective (192,193,194,195). If there is no normalization of the above parameters within 48 to 72 hours, the chance for survival greatly diminishes. Persistent tachycardia is a marker of death (49). An apparent sympathovagal imbalance increases heart rate variability in the adult and pediatric patient populations. Atrial dysrhythmia and dysfunction is common in the clinical presentation and the progression of sepsis. TEE is obviously a valuable diagnostic tool for evaluating atrial function and volume by reviewing the left atrial appendage flow characteristics in concert with analysis of ventricular function and volume, ventricular interaction of dependency, transmitral inflow velocities, and pulmonary venous flow patterns (195,196).
In sepsis or SIRS, the right ventricle responds to fluid loading, but at some unknown end point, when the volume and pressure are exceedingly high, the compensatory response is no longer beneficial and mortality dramatically rises. A transitory increase of pulmonary artery pressure appears to be associated with increased mortality, but no serial investigations have been completed (197,198). In a clinical investigation by Poelaert et al. (22) based on transmitral inflow velocities and pulmonary venous flow patterns, patients with a decreased transmitral inflow velocity, abnormal pulmonary venous flow, and decrease in fractional area contraction are more likely to die as compared to two other subgroups. This pattern is particularly seen in older patients.
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Figure 23.19. The left ventricular volume cast (lower right) was created from 3D echocardiography imaging. Regional left ventricular volume changes are shown in the plot at the bottom. The color of each line corresponds to the segment of the same color in the left ventricular cast. (From Oh JK, Seward JB, Tajik AJ. The Echo Manual. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006. Used with permission of Mayo Foundation for Medical Education and Research.) |
The hyperdynamic circulatory response of sepsis was earlier associated with a myocardial depressant factor (199) and presently is related to various mediators, cytokines, and humoral factors that are all related and intertwined (200). Interestingly, it is now known that there is a protective effect of early exposure to some of these mediators/cytokines that can induce the reversal of myocardial depression (192,194,201,202).
In summary, appreciating cardiac function in septic shock patients will assist in the determination of the pharmacologic interventions, fluid augmentation, and other modalities (203,204,205). It is intuitive reasoning that if the baseline cardiac junction is poor, the volume should be instilled judiciously and adjunct pharmacologic measures should be administered earlier and more aggressively. Echocardiography is a useful tool to initially identify and follow all hemodynamic variables. This diagnostic tool alone might suffice, but until further data are available, using it in conjunction with invasive monitoring is crucial (192,194,201,206).
Pulmonary Embolism
One of the most catastrophic cardiovascular events that can occur that is either underdiagnosed or overdiagnosed is pulmonary embolism (PE) (207,208,209,210,211,212). A low cardiac output and RV failure post PE presages mortality. Early identification of these derangements may assist in managing these critically ill patients by providing prognostic indicators, stratification for more intensive surveillance, and any necessary interventions (213). Even appropriate anticoagulation may not eliminate a PE. Several diagnostic tests are available, including a 64-cut chest computed tomography, magnetic resonance imaging, pulmonary angiography, and echocardiography (207) (Table 23.10).
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Figure 23.20. Normal spectral tissue Doppler. (From Dittoe N, Stulz D, Schwartz BP, et al. Quantitative left ventricular systolic function: from chamber to myocardium. Crit Care Med. 2007;35(8):S330, with permission.) |
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Figure 23.21. Recording of strain rate, which represents the rate of deformation; the peak negative strain rate (arrow) was -1.3/s. (From Oh JK, Seward JB, Tajik AJ. The Echo Manual. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006. Used with permission of Mayo Foundation for Medical Education and Research.) |
The classic echocardiographic signs for a PE are the following:
· Dilation of the chamber and thinning of the right ventricle wall with global hypokinesis
· Pulmonic insufficiency
· Tricuspid insufficiency
· Right atrial dilatation with decreased atrial function
· Septal flattening or paradoxical motion of the ventricular septum
· Increased RV/LV dimensions
· Pulmonary artery hypertension
· Dilation of the pulmonary artery
· Identification of thrombi.
If the patient's RV function is normal until the event, these echocardiographic events would occur acutely, and catastrophic events would result when 75% of the pulmonary vasculatures are obstructed. Earlier signs may manifest with as little as a 25% obstruction of the pulmonary vasculature (214). According to the International Cooperative Pulmonary Embolism registry, the presence of RV hypokinesis is associated with increased mortality at 30 days even with a systolic systemic pressure greater than 90 mm Hg (215).
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Figure 23.22. Ventricular remodeling in systolic and diastolic heart failure. Left: Autopsy examples. Right: Cross-sectional 2-dimensional echocardiographic views of systolic and diastolic heart failures compared with normals are illustrated. In systolic heart failure, the left ventricular cavity is markedly dilated and wall thickness is not increased. In diastolic heart failure, the cavity size is normal or decreased and wall thickness is markedly increased. (Reprinted from Konstam MA. Systolic and diastolic dysfunction in heart failure? Time for a new paradigm. J Card Fail. 2003;9:1–3, with permission.) |
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Figure 23.23. Schematic diagram of pressure–volume relations in normals, systolic and diastolic heart failure. In systolic heart failure, a downward and rightward shift of the end-systolic pressure–volume line indicates decreased contractile function, which is the principal cause of reduced ejection fraction and forward stroke volume (SV). In primary diastolic heart failure, diastolic pressure–volume relation (dashed line) shifts upward and to the left, indicating a disproportionate and a greater increase in diastolic pressures for any increase in diastolic volumes. If there is also a decrease in end-diastolic volume, then a decrease in stroke volume also occurs. (Reprinted from Aurigemma GP, Gassach WH. Diastolic heart failure. N Engl J Med. 2004;35:1097–1105, with permission.) |
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Table 23.5 Factors Influencing The Left Ventricular End-Diastolic Pressure–Volume Relation (Chamber Stiffness) |
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If the patient exhibits pre-existing chronic pulmonary artery hypertension with RV hypertrophy, thrombosis of the right-sided circulation may be initially better tolerated. Eventually, RV failure will ensue and dominate the cardiovascular presentation (211,216). Morris-Thurgood and Frenneaux (217) describe RV and RA pressures with reversal of the transseptal diastolic pressure gradient when intravascular volume replacement is attempted to enhance diastolic ventricular interaction. In the situations where other diagnostic tests may fail, echocardiography is a useful diagnostic tool to determine right ventricular afterload and associated hemodynamic findings significant for PE (207,208,209,210,211,215).
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Table 23.6 Morphologic and Functional Changes in Diastolic vs. Systolic Heart Failure |
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Aortic Pathology: Atherosclerotic Debris, Trauma, Aneurysm and Dissection, Sinus of Valsalva Aneurysm
Atherosclerotic Debris
Prior to the advent of enhanced diagnostic imaging techniques, clinicians routinely underappreciated the prevalence and importance of diseases affecting the aorta, particularly in patients following cardiac surgery and the general population in the critical care setting (218,219,220,221,222,223,224,225,226,227,228,229). Adverse events, such as a cryptogenic stroke, could previously not be explained until advancements were made for better resolution in head CT, MRI, carotid ultrasound with color flow and Doppler capabilities, and TEE (228). Cardiac-originating embolism accounts for 15% to 30% of ischemic strokes in the general population. In the SPARC (Stroke Prevention Assessment of Risk in a Community) study, the incidence of detecting a plaque greater than 4 mm in the aorta of 588 randomly chosen patients (average age 66.9 years) was 43.7% (230). Of these, 29.9% presented lesions either in the arch or ascending portions of the thoracic aorta. The presence of a protruding debris or plaque greater than 4 mm approached 7.6% in the ascending aorta and 2.4% both in the arch and ascending portion (220,221,231). In an earlier investigation, an atheromatous plaque greater than 4 mm was regarded as an independent risk factor for a central event (232). Because of the excellent acoustic window to the heart and thoracic aorta, TEE is considered to be one of the first diagnostic tools to evaluate the potential source for the embolic phenomenon (233,234,235,236,237,238,239). Although it remains insensitive to detecting smaller and irregular cardiac emboli and intraaortic debris (240), it is a far superior diagnostic tool than TTE (241,242). TEE can easily identify the cause for a cerebral infarction, especially in the ascending aorta and its arch (243). Even if patients' underlying rhythm is sinus, patients with atherosclerotic plaques are at risk for stroke (244,245,246).
Unfortunately, in the presence of pre-existing atrial fibrillation, the chance for such an embolic event greatly increases (196). If there is associated atherosclerotic debris, particularly protruding, pedunculated, and free-flowing debris, the issue of anticoagulation does not reduce the problem (247,248). In addition to atrial fibrillation, if there is concurrent presence of a patent foramen ovale (PFO), the risks continue to rise (249). The existence of an atrial septal aneurysm increases the incidence for paradoxical embolism and stroke to 8.8% (250,251,252).
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Table 23.7 Classification Of Left Ventricular Filling Patterns |
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Aortic Trauma
The identification and pathogenesis of aortic trauma is better understood since TEE was added to the arsenal of the acute care physician. A vast number of these patients will succumb in the field due to extensive comorbid conditions, exsanguination, or tamponade. As expected, a significant number of patients (13% to 20%) will have been identified with this fatal injury (253), usually at postmortem; these deaths are second in frequency only to traumatic brain injury (TBI). A vast majority (75%) of blunt aortic injuries are due to motor vehicular crashes (253). If the patient arrives to the hospital trauma bay with vital signs, the presence of an aortic injury may be hidden or occult, considering that the physician is concentrating on the other life-threatening conditions (e.g., TBI, intraabdominal hemorrhage, pelvic injury, chest trauma, or pneumothoraces) (254). Of the patients who arrive to the hospital alive (33%), about a third of them will rapidly become hemodynamically unstable (255,256,257,258,259). Unless the clinician interrogates the aorta at the time of admission, this injury may be missed (220,222). Autopsy series reveal that the site of injury (acceleration-deceleration) is usually located near the aortic isthmus (54% to 65%), and multiple sites may be involved in extreme physical forces. In vertical acceleration-deceleration, the injury may occur at the root of the aortic valve (253,255,256,260). Aortography is not the gold standard, and the addition of TEE complements helical CT. If the patient is hemodynamically stable, high-definition (356-cut) computed tomography may be the gold standard followed by TEE (220,222,224) (Tables 23.11 and 23.12). At present, if the patient is hemodynamically stable, CT angiography or a 64-cut chest CT should be performed initially, with TEE used to complement the diagnostic imaging modality (261). In these imaging schemes, most of the aorta is visualized. The benefit of TEE is its capability to visualize the aortic valve, the presence of aortic insufficiency, and the LV function and preload in real time, as well as identify pericardial effusions, especially when they are smaller, posterior, and loculated. These latter findings are typically not seen in the emergent FAST (focused assessment with sonography for trauma) examination commonly used in the trauma bay. Another benefit of TEE is color flow Doppler identification of differential flow and/or turbulence as a sign of a potential injury (transection, subadventitial tear, intimal flap, intraluminal defect, or thrombus formation) (35,36,220,262,263,264,265,266,267). The detection of a periaortic hematoma or mediastinal hematoma may lead the physician to suspect an aortic injury (Table 23.13). The major disadvantages for echocardiography are reverberation artifacts, limited access to the superior ascending thoracic aorta, and the inability to adequately define the great vessels. However, in reviewing TEE investigations in aortic trauma, it is clear that the operator experience, training, and its availability are crucial to uniformly identifying or excluding aortic injury (268).
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Table 23.8 Echocardiographic Left Ventricular Morphologic and Functional Characteristics in Primary Systolic and Diastolic Heart Failure Compared With Controls |
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Table 23.9 Changes in Left Ventricular End-Diastolic Volumes (LVEDV) and Pressures (LVEDP), Ejection Fraction (LVEF), and Left Ventricular Stiffness Modulus (Stiff-Mod) During 64 + 9 Months in Patients with diastolic heart failure |
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Figure 23.24. Left: End-diastolic pressure–volume in two ventricles with differing passive diastolic properties. Chamber stiffness is dP/dV at any point on the end-diastolic pressure–volume relation. The stiffer chamber on the left has a steeper overall slope. Right: Same data plotted as pressure vs. chamber stiffness. Because of the exponential nature of the end-diastolic pressure–volume relation, the relation between chamber stiffness and pressure is a straight line whose slope is the chamber stiffness constant (kc) that characterizes the overall slope of the end-diastolic pressure–volume relation. A similar relationship holds for stress and strain. (Reproduced from LeWinter MM, Osol G. Normal physiology of the cardiovascular system. In: Hurst's The Heart. 11th ed. New York, NY: McGraw-Hill; 2004:S342, with permission.) |
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Figure 23.25. The four phases of diastole are schematically shown and include the isovolumic relaxation time (IVRT), which begins with aortic valve closure and extends to mitral valve opening, rapid early filling (RFP), diastasis, and atrial systole. Doppler E and A waves are superimposed. Note the points of left atrial-left ventricular (LA-LV) crossover and their relation to the mitral filling waves (MVF). |
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Figure 23.26. Approach to diagnostic use of echocardiography. TTE, transthoracic echocardiography; TEE, transesophageal echocardiography; IE, infective endocarditis. (Reproduced from Bayer AS, Bolger AF, Taubert KA, et al. Diagnosis and management of infective endocarditis and its complications. Circulation. 1998;98:2936–2948, with permission.) |
Thoracic Aortic Dissection
Thoracic aortic dissection is another potentially life-threatening event that can be detected by TEE. Besides TEE, other imaging techniques following the historical use of angiography, which continue to gain acceptance, are 64-slice chest CT and MRI (particularly for chronic evaluation), or a combination of the above (41,220,269,270,271). The incidence for aortic dissection approaches 4.5/1,000 and is ranked 13th in cause of death in Western societies (41,220,253,254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275). Common predisposing conditions are well known and have been documented in the IRAD (International Registry of Aortic Dissection) (e.g., hypertension 72%, atherosclerosis 31%, previous cardiac surgery 18%). In the population subgroup younger than 40 years of age, the predominant etiologic factors are Marfan syndrome, bicuspid aortic valve, or prior aortic surgery. Symptoms can range from chest pain and/or abdominal sharp constant tearing pain, back pain, syncope to the presence of tachycardia, hypotension, or hypertension (269). Diagnostic imaging needs to be urgently performed to assess the potential for immediate surgery, as well as to determine the preferred surgical approach. There are several classifications of dissections: type A or B, De Bakey, or Stanford. In patients with acute proximal aortic involvement, surgery is considered, as the mortality with this group is 20% by 24 hours and 30% by 48 hours (269). Most type B dissections (73%) have been managed medically with pharmacotherapy to lessen the shear forces and flow and distention of the aorta (269,276). The classic echocardiographic depiction for a dissection is a smaller true lumen, larger false lumen, and an intimal flap with an site. The presence of a thrombus in the false lumen reveals the propensity for a lower morbidity and mortality. These lesser untoward events are seen in patients when the flow is minimal or unidirectional versus bidirectional from the true to false lumens. At times, there may be several entry sites, and flow may not be limited to one area of the thoracic aorta. TEE visualizes the integrity or involvement of the aortic valve leaflets in type A dissections, and allows the evaluation of LV performance and regional wall motion analysis (RWMA) and the detection of a pericardial effusion or tamponade.
A recent meta-analysis compared the accuracy of TEE, helical CT, and MRI for suspected thoracic aortic dissection results. In 1,139 patients (16 investigations), the pooled sensitivity varied between 98% and 100%, whereas the specificity ranged from 95% to 98%. There was a higher positive likelihood ratio comparison for MRI: mean 25.3 (11.1–57.1); for TEE, 14.1 (6.0–33.2); and helical CT, 13.9 (4.2–46.0). If patients' pretest probability was 5% (low risk), their likelihood of having a dissection approached 0.1% to 0.3%. In contrast, in high-risk patients with a 50% pretest probability, the presence of an aortic dissection ranged from 93% to 96% (277).
Aortic Aneurysms and Rupture
Thoracic aorta aneurysms may occur alone or in concert with an aortic dissection and typically are found in the elderly patient. This disease process is related to the presence of hypertension and atherosclerosis. Other population subsets for its occurrence are Marfan syndrome, bicuspid aortic valve (accelerated degeneration of the media), familial aortic aneurysmal disease, or annuloaortic ectasia. The ascending portion of the thoracic aorta can be noted via either echocardiographic modality, although TEE is the preferred choice. The aortic size is well characterized by gender and age. Once the dilatation reaches greater than 5 cm, there is an increased risk of rupture, and replacement is generally considered. After the size of the aorta expands past 6.0 cm, the risk for rupture and dissection reaches greater than 6.9% per year, with a mortality rate of 11.8% annually (278). TEE can assist in the decision process for root replacement or placement of a prosthetic device and reimplantation of the coronary arteries. In patients with bicuspid aortic pathology, greater than 50% of the patients will have root dilatation and aortic insufficiency (41,220,272,278,279,280,281).
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Table 23.10 Imaging and Biomarker Findings Suggestive of Higher Risk in PE Patients |
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Table 23.11 Transesophageal echocardiography (TEE) and angiography (aortography or contrast-enhanced spiral computed tomography for traumatic aortic imaging (TAI) |
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The localized absence of the media in the aortic wall will result in possible rupture of the sinus of Valsalva. Usually, it will rupture into adjacent structures such as the cardiac chambers (RV or RA) or through the ventricular septum. TEE invariably will visualize the aneurysm (ventricular side of the aortic valve), particularly of the ventricular septum. The apical long and parasternal views may discriminate between this pathology and a membranous septum. In a nonruptured sinus of Valsalva aneurysm, echocardiography will visualize thinning of the wall that is larger than the other sinuses. The intensivist needs to be aware that this situation can be associated with endocarditis, syphilis, a potentially fatal rupture, a source of emboli, and fistulae communicating with ventricular chambers. In the latter case, a significant left-to-right shunting can be demonstrated by using color flow Doppler echocardiography, with a continuous turbulent jet within the ruptured aneurysm into the receiving chamber (41,220,282,283,284,285,286,287,288). If the aneurysm communicates with the right atrium, the flow is continuous during systole and diastole. An increase in size of either the RA or RV will eventually occur (225,287,289,290,291,292).
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Table 23.12 TEE And Helical Chest CT For The Identification Of Traumatic Arterial Injuries In Severe Blunt Trauma |
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Table 23.13 Aortic Pathology: Computed Tomography For Trauma |
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Intramural Hematoma
A subpopulation of trauma patients will present with intramural hematoma (IMH), which arises from rupture of the vasa vasorum in the aortic medial wall layers, and is characterized by blood in the aortic wall in the absence of an intimal tear. IMH may be a precursor for the progression to a dissection. The associated prevalence is 10% to 30% of patients with a pre-existing dissection (274). Surgery is usually contemplated for type A dissection whereas intervention is warranted for a type B. The comparative mortality rates (medical vs. surgical), respectively, for types A and B are 36% versus 14% and 20% versus 14% (269,293).
Infective Endocarditis
Infective endocarditis (IE) is a challenge to all disciplines, particularly for intensive care physicians who have to analyze how IE factors into the differential diagnosis of a fever of unknown origin. Recurrent positive blood cultures while the patient is on antibiotics may provide a clue to its existence, especially if the pathogens are Staphylococcus aureus, streptococci, and enterococci. However, there is an increasing incidence of culture-negative IE that includes such fastidious agents as Coxiella burnetii, Tropheryma whipplei, Legionella pneumophila, Bartonella spp., the HACEK group (Haemophilus spp., Actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella spp.), and fungi (including Candida, Histoplasma, and Aspergillus spp.) (294,295). The classic patient presentation with Janeway lesions, Osler nodes, Roth spots, and petechiae and history of rheumatic heart disease is not seen in the developed world (296). However, in the industrial world, the risks are related to age, degenerated valvular disease, prosthetic valves, and the increasing incidence of nosocomial infections. Besides in HIV infection patients where it can be present in up to 90% of the cases, IE can be found increasingly in the younger population, with social trends such as body piercing and self intravenous injection of recreational drugs, including HIV infection (40%–90%) (294,295) (Tables 23.14 and 23.15).
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Table 23.14 Definition Of Infective Endocarditis (IE) According To The Modified Duke Criteria |
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Identification of Vegetations
Perhaps more important than clinical findings, echocardiography is very useful for the identification of vegetations. Two fundamental predisposing factors are associated with the development of IE: cardiac endothelial injury and a microbiologic source. In endothelial injury, there is aberrant flow with a high-velocity jet directed onto the endothelial surface or increased shear stress through a narrow orifice. In the latter, there is a propensity for bacterial deposits downstream of the constriction via a Venturi effect. The detection of vibratory oscillations of vegetation or associated disruptive cardiac structures (torn leaflet, rupture of chordae tendineae) may indicate the presence of IE, as well as noting diastolic vibrations of the aortic valve or systolic vibrations of the mitral valve (M-mode echocardiography). Other characteristic findings involve structures that are in the path of a high-velocity jet as seen in valve regurgitation; these include motion of the valve that is chaotic and independent; texture that is gray scale in relation to the myocardium; an amorphous shape; the presence of a fistula or abscess; and new onset of regurgitation for either native or prosthetic valves. There may be associated obstructions, perivalvular leaks, or dehiscence. With these findings, there are stringlike mobile strands of vegetations or degenerative areas adjacent to the prosthetic device. In the mitral valve position, if there is a prosthetic device, TEE will easily identify these maladies. However, TTE is a better tool for visualizing the mechanical valve in the aortic position. Overall, TEE is a better diagnostic modality to visualize vegetations and associated complications. The sensitivities for TTE and TEE are 60% to 90% and 85% to 95%, respectively, while the specificities for both techniques (TTE and TEE) are far better: 90% to 98% (295,297,298,299,300,301,302,303,304,305). In the context of a negative TEE, the negative predictive value is only 90%; thus, maintaining good clinical judgment with clinical correlation is always a necessity (306,307,308). An algorithm proposed by Bayer et al. (309) can be used by the echocardiographer intensivist for this diagnostic dilemma (295,309).
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Table 23.15 Definition Of Terms Used In The Modified Duke Criteria For The Diagnosis Of Infective Endocarditis (IE) |
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Indications for Surgery
The most prominent indications for surgery are hemodynamic compromise or collapse from valve destruction, a persistent fever despite antibiotic treatment, and development of a fistula or abscess due to perivalvular spread of infection. Other indications are the presence of highly resistant organisms or aggressive pathogens, perioperative prosthetic valvular endocarditis, and large vegetations (greater than 10 mm). This latter indication is of particular concern given that the increasing size of the vegetation is associated with embolic events (294,295). A task force that includes input from the American Heart Association and the American College of Cardiology recently corroborated this last indication (310).
Myocardial Injury
In patients with acute myocardial infarction, echocardiography is a crucial tool in the diagnosis and exclusion of myocardial injury, especially in patients with chest pain and nondiagnostic electrocardiographic (ECG) findings. Other roles for echocardiography are evaluating the extent of myocardium at risk and involvement after reperfusion; evaluating viable myocardium; assessing patients with hemodynamic instability and related complications following infarction; and risk stratification (102).
Echocardiography is also commonly used for evaluating acute coronary syndromes (ACS) by measuring intraventricular dyssynchrony by tissue velocity and strain imaging (41) (Fig. 23.27).
Resting and stress echocardiography are modalities for detecting ACS and complications of myocardial injury by prognostication using analysis of regional wall motion abnormalities (RWMA) scoring, as well as assessing diastolic dysfunction and stress-induced alterations (311). All LV wall segments can be seen from the apical, parasternal, and occasionally subcostal views. The American Society of Echocardiography proposes a standard for this RWMA scoring by using either a 16- or 17-segment model (43,312). The benefit of observing RWMA is that the patient may be asymptomatic and hemodynamically may not exhibit any aberrations. However, not all RWMAs are related to myocardial ischemia, such as loading conditions applied to the heart, paced rhythms, and conduction delays. Typically, after reperfusion, there may be persistent RWMA representing a delayed return of normal function, which is described as a stunned myocardium. This physiology, as well as the existence of global transitory dysfunction such as hibernating myocardium, must be put into the clinical context of the patient's condition.
In patients with acute ST-elevation myocardial infarction (STEMI), the affected myocardium becomes an akinetic or dyskinetic segment. Following interventions (reperfusion), there is usually improvement in the afflicted segments within 24 to 48 hours, and echocardiography can be used serially to assess these patients for improvements or extension of the injury. Contrast echocardiography, low-dose dobutamine infusion, or strain imaging can also assess viability (49,313).
Complications
Numerous complications follow an acute myocardial infarction. Echocardiography is a mainstay in assessing these problems, which range from rupture of papillary muscle and ventricular septal defects (VSD) to cardiopulmonary resuscitation (41,314).
Rupture
Acute free wall rupture also occurs less frequently in the postinterventional period (1.0%). About half of the ruptures will result in out-of-hospital sudden deaths. Following myocardial injury, the mortality of free wall rupture varies between 8% and 17%, with a significant number (40%) occurring within the first 24 hours and 85% after 1 week (266,315,316). Besides hemodynamic collapse or cardiac arrest, there may be severe bradycardia. Some patients may experience syncope, chest pain, or emesis. In these dire situations, echocardiography (TEE) is the diagnostic tool of choice. Pericardial effusions and/or cardiac tamponade may be found, keeping in mind that 25% of myocardial infarctions will have a pericardial effusion. Thrombus may exist, as well as the identification of flow via color flow Doppler (317). Also, a pseudoaneurysm may form following a free rupture that is contained in a limited portion of the pericardial space, most frequently the posterior wall. A pseudoaneurysm is traditionally characterized by a small neck communication between the LV and the aneurysmal cavity (ratio less than 0.5). Color flow Doppler may reveal flow, especially bidirectional (318).
Another cause for a new murmur is a ruptured papillary muscle (partial or complete) and mitral regurgitation (the extent of the murmur does not correlate with pathology). Extenuating circumstances for a new murmur may be LV regional or global remodeling, papillary muscle dysfunction with annular dilatation, or acute systolic anterior motion of the mitral valve. The latter cause is managed in a totally different way than with volume replacement, with primary intervention accomplished with beta-blockade and avoidance of vasodilators (319).
The most serious cause of new mitral regurgitation that must be acted on quickly is rupture of the posteromedial papillary segment. This acute problem may be even related to a small infarct corresponding to the circumflex or right coronary artery. The rupture may be complete or partial and is identified by color flow Doppler imaging. After papillary muscle rupture and its discovery by TEE, surgery is imminent for mitral valve replacement, with or without coronary revascularization. In a series by Moursi et al. (320), in 65% of the patients with TEE, the head of the papillary muscle was observed in the LA.
Another characteristic finding seen in these patients (90%) was some erratic motion in the body of the LV (315,320,321,322).
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Figure 23.27. Measurement of intraventricular dyssynchrony by tissue velocity and strain imaging. A: Recording of strain from the basal segment of the ventricular septum from the apical four-chamber view. Time to peak systolic strain is measured from onset of QRS to the peak negative value including the postsystolic shortening. The timing of the peak negative strain is when shortening of the myocardium is maximum. B: Recording of tissue velocity from the basal segment of the ventricular septum. Peak systolic velocity is the positive wave during the ejection period. Time to peak tissue velocity is from onset of QRS to the positive peak velocity. The time interval is determined from 2 to 12 segments to measure intraventricular dyssynchrony. (From Oh JK, Seward JB, Tajik AJ. The Echo Manual. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006. Used with permission of Mayo Foundation for Medical Education and Research.) |
Right Ventricular Infarction and Failure
Right ventricular infarction and/or failure is one of the most difficult clinical entities to support. Diagnosis of isolated failure or biventricular failure alters the management of these complex patients. Inferior myocardial infarction is associated with RV infarction (35%) (315,323). The subcostal view may visualize the RV easily. In suboptimal acoustic windows, TEE is considered. The classic findings are tricuspid regurgitation, a dilated thinned RV, severe global hypokinesis, reduced descent of the base of the RV free wall (apical four-chamber view), and plethora of the inferior vena cava without any respiratory variations in its diameter. In diastole, there is flattening of the ventricular septum and occasional paradoxical motion and, at times, bulging of the septum into the LV, indicative of a right-sided pressure/volume overload situation. The RA may reveal right atrial hypertension with displacement of the interatrial septum (315,323,324). If there is coexisting PFO in the presence of RV and/or RA afterload, a right-to-left shunt is possible through the atrial septum, resulting in hypoxemia and thus complicating the clinical presentation. The identification of a PFO is greatly enhanced by choosing TEE over the surface approach (325).
Hemodynamics and Valve Area Calculations
The intraoperative or perioperative physician expert in echocardiography must not only deal with the evaluation of ventricular function (global and regional), identification of aortic pathology, detection of masses, and visualization of normal abnormal pathology of native and prosthetic valves but must also be competent in the hemodynamic assessment of these patients. An appreciation of the basics of the hemodynamic calculations sets the stage for the building blocks of accurate detection of flow hemodynamics and physiology that may affect the patient's clinical care (medical or surgical). The calculation of pressure gradient determination uses the Bernoulli equation. Additional valve area calculations use the continuity equation, pressure half-time and deceleration time, proximal isovelocity surface area (PISA), and effective regurgitant orifice. Similarly, the determination of valvular area is complex and based on several echocardiographic and Doppler principles evaluating the continuity equation pressure half-time method, deceleration time method, and planimetry. An extensive review of these topics is beyond the scope of this chapter but is available in all major textbooks on echocardiography (31,41).
Summary
The critical care physician should have at the bedside the availability and expertise to correctly use echocardiography as a first-line diagnostic and monitoring tool. Eventually, this field of critical care echocardiography should be encompassed in the training of the fellows in intensive care medicine. The implementation of training—basic skills versus full certification—is still being debated. Nevertheless, this imaging modality is crucial for timely medical and surgical interventions. Having a remote echocardiographic team may be helpful in this short term period, and the impact of echocardiography in critically ill and injured patients must not be minimized. A subset of the total field of echocardiography should include intensive care medicine. In the meantime, collaborating with our cardiology colleagues is the key for better understanding of echocardiographic findings in the setting of a critical illness.
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