Aortic root dilation prior to valve opening explained by passive hemodynamics.

BACKGROUND AND
AIM OF STUDY: During the June 1999 World Symposium on Heart Valve Disease, the mechanism by which the aortic valve opens was discussed. It was suggested, indirectly, that the recently discovered contractile elements within the aortic valve may be responsible. We propose that aortic root dilation does not require any active mechanism within the leaflets or aortic wall, and provide an explanation based entirely on the passive hemodynamics of the aortic valve and root. METHODS AND
RESULTS: Previous studies using cine fluoroscopy and sonomicrometry have reported a 5-7% expansion of the aortic root during ventricular contraction, prior to aortic valve opening. Simplified force calculations indicate that the mechanical interactions between the aortic valve and root produce an inward pull on the commissures, constraining the aorta from fully dilating. During systole, as the pressure in the ventricle increases and the aortic valve becomes unloaded, the inward pull on the commissures is reduced and the aorta is able to dilate fully. Aortic dilation therefore occurs before the aortic valve opens.
CONCLUSION: We conclude that this mechanism of aortic root dilation prior to valve opening is purely passive, and does not require any active process by the aortic valve or the aortic root.