THE AORTIC-VALVE MICROSTRUCTURE - EFFECTS OF TRANSVALVULAR PRESSURE

We undertook this study to establish a more quantitative understanding of the microstructural response of the aortic valve cusp to pressure loading. Fresh porcine aortic valves were fixed at transvalvular press ures ranging from 0 mmHg to 90 mmHg, and small-angle Light scattering (SALS) was used to quantify the gross fiber structure of the valve cus ps. At all pressures the fiber-preferred directions coursed along the circumferential direction. Increasing transvalvular pressure induced t he greatest changes in fiber alignment between 0 and 1 mmHg, with no d etectable change past 4 mmHg. When the fibrosa and ventricularis layer s of the cusps were re-scanned separately, the fibrosa layer revealed a higher degree of orientation while the ventricularis was more random ly oriented. The degree of fiber orientation for both layers became mo re similar once the transvalvular pressure exceeded 4 mmHg, and the la yers were almost indistinguishable by 60 mmHg. It is possible that, in addition to retracting the aortic cusp during systole, the ventricula ris mechanically may contribute to the diastolic cuspal stiffness at h igh transvalvular pressures, which may help to prevent over distention of the cusp. Our results suggest a complex, highly heterogeneous stru ctural response to transvalvular pressure on a fiber level that will h ave to be duplicated in future bioprosthetic heart valve designs. (C) 1998 John Wiley & Sons, Inc.