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(Circulation. 1998;98:866-872.)
© 1998 American Heart Association, Inc.

Clinical Investigation and Reports

Assessment of Small-Diameter Aortic Mechanical Prostheses

Physiological Relevance of the Doppler Gradient, Utility of Flow Augmentation, and Limitations of Orifice Area Estimation

Richard H. Marcus, MBBCh; Russell S. Heinrich, BSE; James Bednarz, BS; Stephen Lupovitch, MD; Joseph Abruzzo, MD; Raphael Borok, MBBCh; Byron Vandenberg, MD; Richard E. Kerber, MD; William Piccione, MD; Ajit P. Yoganathan, PhD; ; Roberto M. Lang, MD

From the Noninvasive Cardiac Imaging Laboratory (R.H.M., J.B., S.L., J.A., R.M.L.), University of Chicago Medical Center, Chicago, Ill; Cardiovascular Fluid Mechanics Laboratory (R.S.H., A.P.Y.), Georgia Institute of Technology, Atlanta, Ga; Departments of Pathology (R.B.) and Cardiovascular Surgery (W.P.), Rush-Presbyterian–St. Lukes' Medical Center, Chicago, Ill; and Echocardiography Laboratory (B.V., R.E.K.), University of Iowa Hospital, Iowa City.

Correspondence to Richard H. Marcus, Cardiovascular Ultrasound Laboratories, Iowa Heart Center, 411 Laurel St, Suite 1250, Des Moines, IA 50314-3046.

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 (P<0.001), and fluid mechanical energy losses were as strongly correlated with orifice as with downstream pressure gradients (r²=0.99 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 P<0.001). 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 (P<0.05).

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.

Key Words: prosthesis • echocardiography • hemodynamics

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