a

Prosthetic Cardiac Valves

Echocardiography is a critically important tool in the evaluation and serial follow-up of mechanical and bioprosthetic valves. Unfortunately, the increased echo reflectivity of prosthetic valves (especially the mechanical models) causes extensive distal shadowing and reverberations that markedly limit the utility of transthoracic 2D echocardiography (Figs. 15–91 and 15–92). TTE imaging may detect partial ring dehiscence manifest as abnormal "rocking" motion of a prosthetic valve. TTE may also identify reduced movement of the valve disks or leaflets and may occasionally visualize adherent thrombi, tissue ingrowth, and vegetations.190 Leaflet thickening, detachment, and flail motion also may be visualized for bioprosthetic valves.   Figure 15–91. Apical two-chamber view of a mechanical prosthetic valve (mitral position) during systole. The left atrium is completely obscured by ultrasonic shadowing (arrows). LV = left ventricle.   Figure 15–92. Apical view of a bioprosthetic valve (arrow) in the mitral position (two of the three prosthetic valve struts are apparent). Spontaneous echo contrast (SEC) is also present, secondary to systolic dysfunction and enlargement of the left ventricle (LV); LA = left atrium. Doppler interrogation is the cornerstone of the echocardiographic assessment of prosthetic valvular stenosis and regurgitation.191 Color-flow imaging can document the presence, direction, and size of the forward flow stream. CFD can also detect regurgitant flow jets, but—like 2D imaging—it is limited by acoustic shadowing distal to the prosthesis. Doppler color jets due to prosthetic AR can be readily visualized from the transthoracic apical view, but jets produced by prosthetic mitral and tricuspid regurgitation are often obscured. Therefore, although detection of prosthetic regurgitation by transthoracic Doppler is usually feasible, quantitation is often difficult. A small flow signal shortly after valve closure may be observed frequently with prosthetic valves and is likely related to the blood caught behind the occluder as it closes.192 Doppler flow velocities and gradients (calculated by the Bernoulli equation) through normal prosthetic valves vary depending upon the type, position, and diameter of the prosthesis.191 The velocities and gradients across prosthetic valves are flow-dependent as well and therefore related to LV function. Given these variables, it is not surprising that a wide range of transvalvular gradients exists for normally functioning prosthetic valves. Nevertheless, "normal" ranges have been reported for various valve types and can be used as a guide to recognize malfunction.192 High prosthetic valvular gradients due to increased flow volume rather than stenosis can be recognized by high flow velocity across the remaining native valves, a short pressure half-time for mitral prostheses, and a short ejection time for aortic prostheses. With aortic valve prostheses, peak systolic Doppler velocities may indicate higher systolic pressure gradients than those actually found during cardiac catheterization.193 This problem may be more prevalent with Starr-Edwards (ball-in-cage) and St. Jude (bileaflet tilting disk) valves than with Medtronic-Hall (single tilting disk) and bioprosthetic valves. The inaccuracies with Starr-Edwards and St. Jude valves are probably due to the presence of multiple flow channels (with various orifice areas) and the phenomenon of pressure recovery.194 Because of these variabilities, an echocardiographic examination is warranted following prosthetic valve implantation to establish its baseline Doppler characteristics. As opposed to peak gradients, mean transvalvular gradients calculated by Doppler correlate reasonably well with direct catheter measurements. TEE has dramatically changed the diagnostic approach to prosthetic valve dysfunction and is especially useful for assessing mitral prostheses, as it overcomes the problem of left atrial shadowing and reverberation (Fig. 15–93). TEE is extremely accurate in the detection of prosthetic regurgitation and impaired movement of the valve occluder, and it is the diagnostic procedure of choice in most cases of suspected prosthetic valve endocarditis.195 Small thrombi, tissue ingrowth, infected or sterile vegetations, and even sutures in the sewing ring can usually be readily visualized. The enhanced sensitivity of TEE requires operator experience and judgment, as nearly all mechanical prostheses normally exhibit a small amount of regurgitation, which should not be misinterpreted as pathologic.192 TEE may also visualize thin, fibrinous strands sometimes attached to prosthetic valves; these structures appear to be a potential source of cardiogenic embolization.196 The technique is quite accurate in the diagnosis of prosthetic valve thrombosis, a potentially fatal medical emergency, and can assist clinical decision making in this disorder.197   Figure 15–93. TEE images from a patient with a St. Jude prosthetic valve in the mitral position. A. Diastolic image. The two struts of the open valve are seen (large arrows) as well as their ultrasonic shadows (small arrows). LA = left atrium; LV = left ventricle. B. Systolic image. The two prosthetic leaflets are closed (arrows) and cast a dense ultrasonic shadow, obscuring the left ventricle.

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Infective Endocarditis Infective endocarditis remains an all too common illness, with a significant risk of morbidity and mortality (Chap. 86). Traditionally, the diagnosis has been based on either the cumulative results of blood cultures, physical examination, and laboratory findings or on pathologic proof of infected valvular vegetations at surgery or autopsy. Echocardiography may play an important role in infective endocarditis in regard to diagnosis, detection of associated cardiac abnormalities and hemodynamic dysfunction, prognosis, and the need for surgery. Vegetations can now be visualized noninvasively in many (but not all) cases of endocarditis and have become the echocardiographic hallmark of this disorder.198,199 Thus even though TTE cannot exclude endocarditis, abnormal findings may strongly suggest the disorder, even in the presence of negative blood cultures. Since no single abnormality has 100 percent diagnostic accuracy for infective endocarditis, strategies for diagnosis have been devised based upon a number of criteria,200 and definite echocardiographic vegetations are designated as a major criterion. Both TTE and TEE are valuable in the detection of perivalvular abscesses and prosthetic-valve endocarditis.102 Although there is considerable debate concerning the most accurate diagnostic criteria for endocarditis, echocardiography has become one of the most commonly used techniques for the evaluation of potentially affected patients.201 Echocardiography (both TTE and TEE) is also useful for evaluation of patients with systemic lupus erythematosus complicated by Libman-Sacks endocarditis.202 Even though M-mode recordings produced the first echocardiographic description of vegetations, this modality has been largely replaced by 2D imaging. With 2D echocardiography, valvular vegetations typically appear as irregular, usually localized masses of varying echocardiographic density attached to valvular or perivalvular structures (Figs. 15–94 and 15–95) without significantly altering their mobility. The vegetations may be small or quite large and may attach directly to the valve leaflets or the supporting chordal apparatus.198,199,203 Occasionally, vegetations may be attached to unusual structures, such as the atrial wall or the eustachian valve.204,205 Both small, nonmobile vegetations on a normal valve and large vegetations on a markedly abnormal valve may be difficult or impossible to identify with certainty. Aggressive infections often cause perforation or distortion of the affected leaflet, leading to varying degrees of valvular regurgitation. This is distinctly different from most cases of nonbacterial thrombotic (marantic) endocarditis, where the valvular vegetations are usually nondestructive. In cases of infective endocarditis, the presence of vegetations by TTE increases the risk of heart failure, embolic events, and the ultimate necessity of valve replacement.206 Unfortunately, TTE is not 100 percent sensitive in detecting vegetations, and up to 20 percent of patients with proved native-valve endocarditis may have unremarkable examinations. The sensitivity of TTE in prosthetic valve endocarditis has been found to be even lower (approximately 60 percent) due to technical limitations in imaging.   Figure 15–94. A. Apical four-chamber view demonstrating a large tricuspid valve vegetation (arrow). RA = right atrium; LA = left atrium; LV = left ventricle; RV = right ventricle. B. Parasternal long axis view demonstrating a vegetation (arrow) on the anterior valve leaflet; AO = aorta.   Figure 15–95. Longitudinal TEE view of a large mitral valve vegetation (arrow). a = left atrium; v = left ventricle. (Courtesy of William D. Keen, Jr., MD.) TEE has proved significantly more sensitive than TTE for detection of infective vegetations and is extremely helpful for the diagnosis of perivalvular abscesses, mycotic diverticula, and prosthetic valve involvement.102,207 The technique is also useful for assessing valvular regurgitation, fistulas (Fig. 15–96), other hemodynamic complications of endocarditis, and risk of embolization.208 Although a negative TEE examination cannot completely exclude infective endocarditis, it confers a relatively good prognosis in those cases where the diagnosis is eventually confirmed. The optimal use of TEE in suspected endocarditis remains controversial: some authorities recommend routine TEE in all cases, but many do not. A reasonable approach may be to perform TTE as the first screening test in patients with suspected endocarditis. If the study is technically difficult or equivocal or detects vegetations in patients at high risk for perivalvular complications or hemodynamic compromise, TEE should be performed. If TTE is unremarkable or detects vegetations in patients at low risk for complications, TEE may not be necessary.103 Exceptions to this last recommendation might include patients with prior antibiotic treatment or those with persistent bacteremia or fever of unknown etiology. In high-risk patients (i.e., with possible prosthetic valve involvement, congenital heart disease, or infection with especially virulent organisms), TEE is recommended even if TTE is normal.103   Figure 15–96. Longitudinal TEE image demonstrating a fistula between the aorta (A) and left atrium (LA) in a patient with endocarditis. AV = aortic valve; P = pulmonary artery; LV = left ventricle; M = mitral valve. (From Sobel J, Maisel AS, Tarazi R, Blanchard DG. Gonococcal endocarditis: Assessment by transesophageal echocardiography. J Am Soc Echocardiogr 1997;10:367–370. With permission.) Echocardiographic evaluation of suspected endocarditis is not without pitfalls. It may be quite difficult to detect active vegetations in patients with preexisting valvular abnormalities such as calcification, myxomatous change, rheumatic involvement, and healed vegetations. Despite recent technologic advances, the diagnosis of infective endocarditis remains a clinical one, and overreliance on echocardiography may cause mistakes. Therefore, echocardiographic results should be integrated with other clinical information to diagnose this disorder accurately.209