Characteristics of compressive strains in porcine aortic valves cusps.

BACKGROUND AND AIM OF STUDY: Previous studies in our laboratory have revealed the presence of compressive strains at the base of the non-coronary (NC) cusp of porcine aortic valves. Since these strains have been shown to damage bioprosthetic valve tissue, the mechanism by which they are induced in valve tissues should be investigated.

METHODS

Whole porcine aortic valves were pressurized and the induced strain patterns measured on aortic valve cusps and roots. Measurements were made before and after trimming of excess ventricular muscle and mitral valve tissue.

RESULTS

Negative (compressive) radial strains were found only in the NC cusp. Trimming of surrounding muscle increased the magnitude of both the tensile circumferential strains and compressive radial strains in the NC cusp. The left and right coronary cusps (LC, RC respectively) had similar positive radial and circumferential strains, and trimming had inconsistent effects on the strain patterns. Trimming of the aortic root increased root strains adjacent to the NC cusp, thus increasing positive circumferential strains and negative radial strains in the NC cusp. Analysis of images obtained during loading indicated that a wrinkle formed at the base of the NC cusp in 66% of cases in which negative strains were observed.

CONCLUSION

Negative radial strains were induced in the NC cusp as it stretched circumferentially during static pressurization. In many valves, negative strains resulted from radial folding or wrinkling of the valve cusp. Since the RC and LC cusps had circumferential and radial strains that were not similar to those of the NC cusp, it is likely that the NC cusp has a different internal fibrous organization.