Hemodynamics of high-performance bileaflet valves: comparison to simulated clinical Doppler measurements

The newly designed, so-called 'high performance' bileaflet heart valve prostheses are suggested to be especially beneficial in small sizes. Herein, valvular energy loss and transvalvular gradients were evaluated using an in-vitro pulsatile flow model for aortic prostheses (St. Jude Medical Regent and On-X, sizes 19-23 mm). Gradients were compared with simulated clinically derived Doppler gradients to determine the extent of pressure recovery.

Valves were analyzed using a pulsatile circulatory mock loop simulator at heart rates of 70 and 110 bpm, and at cardiac outputs of 2, 4, 5, and 7 l/min, respectively (FDA requirements). Measurements consisted of computed calculation of energy loss and determination of mean pressure gradient by pressure transducers. A Doppler probe was mounted into the device for simultaneous measurement of Doppler gradient according to the Bernoulli equation.

The systolic energy loss of the SJM Regent valve averaged 5.0 +/- 4.6% (range: 0.2 to 14.9%) of the effective forward energy, while that for the On-X valve was 6.5% (range: 0.7-22.8%). Total energy loss was 9.9% (range: 4.8-22.1%) for the SJM Regent valve, and 12.7% (range: 6.5-27.7%) for the On-X valve. The average extent of pressure recovery was 64% for both valve types.

All tested valves were characterized by excellent hemodynamic performance, with overall low systolic and total energy losses, but results were slightly favorable for the SJM Regent valve. Valve performance was concluded to be much better than expected by clinical routine Doppler measurements, which significantly overestimates transvalvular gradients; this effect was explained by pressure recovery. Nevertheless, Doppler gradient remains a valuable follow up technique for patients with heart valve prostheses.