Assessment of Small-Diameter Aortic Mechanical Prostheses

Abstract

Background-Noninvasive assessment of functionally stenotic small-diameter aortic mechanical prostheses is complicated by theoretical constraints relating to the hemodynamic relevance of Doppler-derived transprosthetic gradients. To establish the utility of Doppler echocardiography for evaluation of these valves, 20-mm Medtronic Hall and 19-mm St Jude prostheses were studied in vitro and in vivo. Methods and Results-Relations between the orifice transprosthetic gradient (equivalent to Doppler), the downstream gradient in the zone of recovered pressure (equivalent to catheter), and fluid mechanical energy losses were examined in vitro. Pressure-flow relations across the 2 prostheses were evaluated by Doppler echocardiography in vivo. For both types of prosthesis in vitro, the orifice was higher than the downstream gradient (PϽ0.001), and fluid mechanical energy losses were as strongly correlated with orifice as with downstream pressure gradients (r 2 ϭ0.99 for both). Orifice and downstream gradients were higher and fluid mechanical energy losses were larger for the St Jude than the Medtronic Hall valve (all PϽ0.001). Whereas estimated effective orifice areas for the 2 valves in vivo were not significantly different, model-independent dynamic analysis of pressure-flow relations revealed higher gradients for the St Jude than the Medtronic Hall valve at a given flow rate (PϽ0.05). Conclusions-Even in the presence of significant pressure recovery, the Doppler-derived gradient across small-diameter aortic mechanical prostheses does have hemodynamic relevance insofar as it reflects myocardial energy expenditure. Small differences in function between stenotic aortic mechanical prostheses, undetectable by conventional orifice area estimations, can be identified by dynamic Doppler echocardiographic analysis of pressure-flow relations. (Circulation. 1998;98:866-872.)

Interrogation of the aortic valve

“…The problem with this method is that it requires a hemodynamic steady state, as the measurement of the aortic systolic flow and the cardiac output occurs at two different time points, which increases the likelihood of significant error. The classification of AR severity by regurgitant volume is: [3] where R vol is the aortic regurgitant volume (obtained by the methods described above) and R VTI is the time-velocity integral of the aortic regurgitant jet, obtained by CWD echocardiography. The second technique is more technically complicated, and utilizes the proximal isovelocity surface area (PISA) method, which has been validated for calculating the EROA in mitral, tricuspid and AR (10).…”