Assessment of mechanical aortic valve prosthesis by means of Doppler echocardiography: what to measure and why?

See related articles on pages 313 and 337. C omprehensive 2-dimensional Doppler echocardiography is the modality of choice for anatomic and hemodynamic evaluation of prosthetic heart valves. However, Doppler hemodynamic assessment of mechanical aortic valve prostheses, especially bileaflet valves, requires consideration of the physical principles governing transvalvular flows. In this issue De Carlo and colleagues have evaluated the hemodynamic performance of the small-sized, bileaflet, Sorin Bicarbon aortic valve prosthesis (SBP) using Doppler peak and mean gradients and calculated effective orifice area (EoA) and effective orifice area index (EoAi). They have shown that these parameters are comparable with those of other small bileaflet mechanical valves in the aortic position and that there is significant regression in left ventricular hypertrophy (LVH). Because these data provide references for small SBP valves in the aortic position, it is relevant to ask the question of how best to evaluate aortic mechanical valves by means of Doppler echocardiography. To answer this question, it is important to understand the many physical principles that govern transvalvular flow dynamics and the problems and pitfalls associated with any single parameter. Routine echocardiographic evaluations of transvalvular gradients are done by using a simplification of the modified Bernoulli equation as follows: PG 1/2 V, where PG is the pressure gradient, is the density of blood, and V is the Doppler transvalvular velocity. Because 1/2 is approximately 4 for blood, the formula is simplified as follows: PG 4V.