MORPHOLOGY OF PORCINE AORTIC-VALVE CUSP ELASTIN

Background and aim of study: While the structure and function of heart valve cusp collagen have been relatively well defined, the role and m orphology of elastin remains poorly understood, despite the fact that it comprises up to 13% of the cusp dry weight. Material and methods: T he elastin structure of 24 hotalkali-digested porcine aortic valve cus ps was investigated with scanning electron microscopy. Elastin structu res were categorized according to their morphology and a model of the distribution of these structures within the cusp was developed. Result s: The two main types of elastin observed, amorphous and fibrillar, we re further categorized based on their morphology. Amorphous structures included continuous sheet sheet with integrated fibers on the surface and sheet with fenestrations. Fibrillar structures identified were lo ose fibers, loose mesh/woven fibers and compact mesh. By imaging sampl es of digested fibrosa and ventricularis that had been microdissected apart, we were able to produce maps of the elastin structure in the tw o layers. The ventricularis contains a large continuous sheet of amorp hous or compact mesh elastin that covers the entire layer, Elastin in the fibrosa is much more complex, consisting of large tubes that emerg e from the aortic attachment and extend circumferentially across the c usp. The tubes, constructed of amorphous fenestrated sheet and loose m esh elastin, likely surround the large circumferential collagen bundle s observed in the fibrosa. Conclusions: The elastin structures that we have identified help explain the measured mechanics of this tissue an d suggest that collagen and elastin are highly integrated. As a result , we believe that elastin plays an important functional role in the cu sp and that a full explanation of heart valve cusp mechanics must inco rporate the contributions of both collagen and elastin.