FRAME-MOUNTED PORCINE VALVE BIOPROSTHESES - PREPARATION DURING AORTIC-ROOT DILATION - BIOMECHANICS AND DESIGN CONSIDERATION

The leaflet geometry and function of frame-mounted porcine bioprosthes es prepared with dilation of the aortic root during frame mounting was investigated. The diameter of the porcine aortic root increased by 47 % when dilated with a pressure of 120 mm Hg. In the absence of pressu re dilation, the ratio of circumferential leaflet length to the radius of the aortic root (S/R(A)) was 2.7 +/- 0.1, and the angle of inclina tion of the leaflet to the base of the valve was 17 +/- 4.3 degrees. I n this condition, the leaflet geometry was similar to that of some sec ond-generation porcine bioprostheses, which demonstrated high open-lea flet bending strains at the commissures. Dilation of the porcine root with 120 mm Hg reduced the value of S/R(A) to 1.84 and produced a tria ngular open-leaflet configuration with minimum open-leaflet bending st rains. Open-leaflet bending strains were also reduced in two prototype frame-mounted valves prepared with partial dilation of the aortic roo t, which had an S/R(A) ratio of less than 2.3 and a leaflet angle grea ter than 27 degrees. The study indicates that the next generation of p orcine bioprostheses should be prepared with at least 17 % dilation of the aortic root during frame mounting and with zero pressure differen ce across the leaflets during fixation. This can be achieved by applyi ng an equal hydrostatic pressure to both sides of the valve leaflets d uring fixation and frame mounting.