Specific regional and directional contractile responses of aortic cusp tissue

The control of valve size and function is a dynamic process that may be modulated by vasoactive factors. The exact response of different regions of the cusp tissue with regard to extent and direction could influence valve shape, function and response to stress.

Porcine aortic valve cusps were cut into either circumferential (basal, belly and coapting edge) or radial (left, center and right) strips. Together with an intact cusp orientated circumferentially, specimens were set up in isolated organ baths.

In response to 90 mM KCI, the belly of the cusp (0.66 +/- 0.05 mN; p <0.05) was significantly more responsive than either the basal region (0.41 +/- 0.06 mN) or the coapting edge (0.31 +/- 0.03 mN) and all three regions of radially orientated strips (left: 0.13 +/- 0.02 mN; center: 0.23 +/- 0.04 mN; right: 0.11 +/- 0.03 mN). All strips showed contraction to endothelin-1 (10(-9) to 10(-7) M). When corrected for weight, the responses of the basal (15.2 +/- 1.8 mN/g) and belly (11.3 +/- 1.5 mN/g) regions were significantly greater than that of the coapting edge (8.4 +/- 1.0 mN/g; p <0.05) and the intact cusp (7.1 +/- 1.9 mN/g, n = 7, p <0.05). In the radially orientated tissue, responses to endothelin-1 were similar in all three regions (left: 3.4 +/- 1.0 mN/g; center: 3.2 +/- 0.5 mN/g; right: 2.3 +/- 0.9 mN/g).

The contractile ability of valve cusps occurs preferentially in the circumferential direction. The enhanced contraction of the basal region may have important implications for the management of stresses experienced by the hinge of the valve. In addition, these findings may be relevant in designing tissue for valve repair by cusp extension or for the tissue engineering of a whole valve.