TABLE 13.1 Prosthetic Heart Valves and Clinical Indications for TEE
TABLE 13.2 Prosthetic Valve Types
Confirm leaflet motion: 2D and 3D imaging confirms the opening and closure of the two mechanical leaflets (Video 13.1). In the short-axis imaging plane, the two leaflets in the open position produce two linear shadows within a circular annulus (Fig. 13.4). For valves implanted in the mitral position, leaflet motion is best examined using the mid-esophageal long-axis views (Fig. 13.5). Multiplane rotation through the valve to generate a cross-sectional imaging plane that is perpendicular to the two leaflets permits the motion of both leaflets to be observed simultaneously (Fig. 13.5). The two leaflets tilt open symmetrically to an angle of 85 to 90° and close at an angle of 30° in relation to the plane of the annulus for a travel arc of approximately 60°. Leaflet motion of a valve implanted in the aortic position is more difficult to evaluate (Figs. 13.1 and 13.4). Acoustic shadowing from the sewing ring and leaflets typically obscure leaflet motion in the mid-esophageal aortic valve long-axis view. Individual leaflet motion is better visualized in the transgastric long-axis and deep transgastric long-axis views that provide unobstructed views of the aortic valve in the far field through the left ventricle and left ventricular outflow tract (LVOT) (Figs. 13.2 and 13.6, Video 13.2).
Confirm proper valve seating: Incomplete fixation of the prosthetic sewing ring to the native annulus or dehiscence of the sewing ring will cause paravalvular regurgitation. Paravalvular regurgitation is defined as regurgitation originating outside of the prosthetic valve annulus or sewing ring (Fig. 13.7, Video 13.3). The most common cause for incomplete fixation immediately after prosthetic implantation is a severely calcified native valve annulus or an avulsed annular suture. Prosthetic endocarditis is the most common cause for late valve dehiscence and can produce a “rocking” motion of the entire valve apparatus on 2D imaging. Proper seating of the prosthetic valve, paravalvular regurgitation, and dehiscence are best identified from the multiplane long-axis images of the valve.
Confirm normal blood flow patterns and the absence of pathologic transvalvular and paravalvular regurgitation: Color flow Doppler imaging will demonstrate central antegrade flow through the valve annulus when the leaflets open and small characteristic regurgitant jets during leaflet closure. A small amount of regurgitation is normal for bileaflet prosthetic valves and is caused by closure backflow and leakage backflow. Closure backflow is the reversal of flow required for closure of the leaflets. Leakage
backflow occurs after closure of mechanical valves, originates from the four hinge points of the leaflets and at other locations between the edges of the occluder and the prosthetic valve stent. The leakage backflow jets originating from the hinge points produces four centrally directed regurgitant jets that are best visualized in the long-axis image through the prosthetic valve at a multiplane angle aligned parallel to the leaflets (Figs. 13.1, 13.5, 13.6; Videos 13.2, 13.4, and 13.5). These washing jets originate laterally near the inner border of the prosthetic annulus and are directed medially into the left atrium. The bileaflet valves are designed to permit a small amount of regurgitation at the hinge points to prevent the formation of thrombus within the hinge mechanism. Sometimes, small leakage regurgitant jets originating along the edge of the leaflet where it meets the annulus during closure can also be imaged by color Doppler imaging (Fig. 13.5). Normal physiologic regurgitant jets are small and short in duration and can be distinguished from pathologic transvalvular regurgitation based on their size, location, direction, and duration.
Pathologic regurgitation with a jet originating within the sewing ring is called transvalvular regurgitation. Pathologic transvalvular regurgitation immediately after valve implantation indicates malfunctioning of the valve leaflets. Intraoperative causes of leaflet malfunction causing transvalvular regurgitation include retained tissue preventing valve closure, a misplaced suture interfering with leaflet motion, or debris
within the hinges causing trapping of the leaflet in a fixed position (Fig. 13.8). Significant regurgitant jets originating outside of the sewing ring are always pathologic and called paravalvular regurgitation.
Calculate valve gradient and EOA: The hemodynamic performance of the prosthetic valve can be assessed using Doppler echocardiography (Fig. 13.9). The interpretation of Doppler-derived prosthetic valve hemodynamic parameters is complicated because even normally functioning prosthetic valves are
inherently obstructive to blood flow, and blood flow velocity profiles across prosthetic valves are not uniform depending upon prosthetic valve type, model, and annular diameter. Since the blood flow velocity through the central rectangular orifice is greater than the blood flow velocity through the two semicircular orifices of the bileaflet valves, some studies suggest that Doppler-derived gradients based on the Bernoulli equation may overestimate the true transvalvular gradient (11). Yet the same and other studies suggest also that differences observed between Doppler- and catheter-derived gradients across prosthetic valves can be explained by localized gradients and pressure recovery downstream from the valve orifice (11,12). Based on this interpretation, differences between Doppler- and catheter-derived pressure gradients may not represent an overestimation of catheter-derived gradients, but represent instead inherent differences in measurement technique, line of interrogation, and precise location of pressure gradients relative to the prosthetic valve orifices. Furthermore, the equation used to estimate mitral valve area based on pressure half-time (MVA = 220/PT1/2) may not apply to prosthetic valves that differ in structure and flow characteristics to the native valve. For clinical purposes of quantifying prosthetic valve function, several approaches can be applied for interpretation of Doppler-derived measurements. One approach is to report only actual values of Doppler transvalvular peak and mean flow velocities across the prosthetic valve and compare the values to established normal values for the specific type, model, and size of the prosthetic valve based on clinical reports, specifications published by the manufacturers that can be obtained from their respective websites or the package insert accompanying the prosthetic valve (9), or in the appendix of the American Society of Echocardiography guidelines for the evaluation of prosthetic valves (Appendix D) (1,10). Similarly, Doppler-derived EOAs calculated using the continuity equation for a prosthetic valve can be compared to those observed for that specific prosthetic valve type, model, and size (Table 13.3 and Appendix D) (1,10). Another variable adding to the complication of interpreting Doppler-derived hemodynamic information in patients with prosthetic valves is that Doppler-derived pressure gradients are dependent on blood flow and even blood viscosity. Decreased blood viscosity from hemodilution or increased cardiac output from inotropic support immediately after prosthetic valve implantation
may lead to overestimation of prosthetic valve gradients using the simplified Bernoulli equation. One approach to address this problem of assessing aortic valve prosthetics is to index transvalvular Doppler blood flow velocity through the prosthetic valve to the blood flow velocity through the LVOT using the Doppler velocity index (DVI = VLVOT/VAoV) (Table 13.4) (1,13,14). For example, using the DVI or the “double envelope” technique for assessing the function of a prosthetic valve in the aortic position, a peak blood flow velocity in the LVOT (VLVOT) to peak transvalvular blood flow velocity (VAoV) ratio less than 0.25 (VLVOT/VAoV < 0.25) suggests significant prosthetic valve stenosis (Table 13.5) (1,13). Another approach is to estimate prosthetic valve gradients using the nonsimplified Bernoulli equation that accounts for the velocity of blood flow on the upstream side of the valve ([P1 – P2] = 4[V22 – V12]). Similarly, for assessing the function of a prosthetic valve in the mitral position, a transvalvular velocity-time integral (VTIMV) to LVOT velocity-time integral (VTILVOT) ratio greater than 2.5 (VTIMV/VTILVOT > 2.5) suggests significant prosthetic valve stenosis (Tables 13.4 and 13.6) (14).
TABLE 13.3 Determining the Effective Orifice Area (EOA) Using the Continuity Method
TABLE 13.4 Determining the Doppler Velocity Index (DVI)
TABLE 13.5 Doppler Parameters for Diagnosis of Prosthetic Aortic Stenosisa
Confirm proper tilting action of the occluder in the long-axis imaging plane.
In the short-axis imaging plane, one edge of the disc occluder should move in and out of the imaging plane as the valve tilts open.
Doppler color flow imaging showing a centrally directed leakage regurgitant jet originating from the hinge point of the disc occluder or small leakage regurgitant jets originating at the site of contact between the disc and the annular stent are normal findings for the BjÖrk-Shiley valve (Figs. 13.11 and 13.12). Two regurgitant jets originating from the inner edges of the annular stent that are directed laterally are a normal characteristic of the BjÖrk-Shiley valve (Fig. 13.11).
Calculate the transvalvular gradient with continuous wave Doppler. The Doppler beam alignment should travel through the major orifice of the valve in order to obtain the best estimate of the transvalvular blood flow velocity and gradient.
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