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J Thorac Cardiovasc Surg 2003;126:317-320
© 2003 The American Association for Thoracic Surgery
Editorial |
a the Drexel University College of Medicine, Hahnemann University Hospital, Philadelphia, Pa. USA
Received for publication September 30, 2002; accepted for publication October 17, 2002.
* Address for reprints: Mani A. Vannan, MBBS, Drexel University College of Medicine, Hahnemann University Hospital, 215 N 15th St, Philadelphia, PA 19102, USA
mav25@drexel.edu
| The first 20% of the full text of this article appears below. |
Comprehensive 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 colleagues1 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 
V2 , 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 = 4V2.
This simplified equation neglects convective acceleration, flow acceleration, and viscous forces. Neglecting flow acceleration will overestimate transvalvular pressure decrease when the proximal (left ventricular outflow tract [LVOT]) velocities exceed 1 m/sec; normal velocity is between 0.7 and 1 m/sec. Patients who
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