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 ele ments within the aortic valve may be responsible. We propose that aortic ro ot dilation does not require any active mechanism within the leaflets or ao rtic wall, and provide an explanation based entirely on the passive hemodyn amics of the aortic valve and root. Methods and Results: Previous studies using cine fluoroscopy and sonomicrom etry have reported a 5-7% expansion of the aortic root during ventricular c ontraction, prior to aortic valve opening. Simplified force calculations in dicate that the mechanical interactions between the aortic valve and root p roduce an inward pull on the commissures, constraining the aorta from fully dilating. During systole, as the pressure in the ventricle increases and t he aortic valve becomes unloaded, the inward pull on the commissures is red uced and the aorta is able to dilate fully. Aortic dilation therefore occur s before the aortic valve opens. Conclusion: We conclude that this mechanism of aortic root dilation prior t o valve opening is purely passive, and does not require any active process by the aortic valve or the aortic root.