Evaluation of Hemodynamic Performance of Aortic Valve Bioprostheses in a Model of Oversizing

The risk of patient-prosthesis mismatch drives most surgeons to select the largest bioprosthesis possible during aortic valve replacement, but interactions between the native aortic annulus and valve prosthesis remain poorly defined. We examined the hemodynamic and functional consequences of oversizing contemporary bioprostheses in an in vitro model.

Three sizes each (21, 23, and 25 mm) of 5 aortic bioprostheses (Magna, Edwards Lifesciences, Irvine, CA; Trifecta and Epic, St. Jude, St. Paul, MN; and Mosaic and Hancock II, Medtronic, Minneapolis, MN) were tested on a mock annulus in a pulsatile aortic simulator. After the annulus was sized to match each valve, the annulus was decreased by 3 mm and then by 6 mm to simulate oversizing. We measured the effective orifice area and the mean pressure gradient. Changes in prosthetic leaflet behavior and geometric orifice area were assessed with slow-motion video. Statistical analysis used mixed-effects models for repeated-measures data, allowing comparison within and between groups.

For each valve model and size, oversizing resulted in decreased effective orifice areas and geometric orifice areas and increased pressure gradients. This was more pronounced with smaller valve sizes and higher flow rates but varied between valve types. Slow-motion imaging revealed this change in geometric orifice area was a result of an inward shift of the valve leaflet hinge point.

Bioprosthetic oversizing impairs hemodynamic performance of aortic valve bioprostheses. The magnitude of this effect varies by valve model and size. Clinically, these data suggest that during aortic valve replacement, placing a valve whose internal orifice closely matches the aortic annulus will provide the optimal hemodynamic performance.