Intramural stress as a causative factor in atherosclerotic lesions of the aortic valve.

Topographic distribution of atherosclerotic lesions of the aortic valve was investigated in rabbits on a 2%-cholesterol-enriched diet and related to distribution of intramural stress in the valve. Initially the lesions appeared at the base of the leaflet on the aortic face and with time spread further out into the leaflet and up the wall of the aortic sinus. In the leaflet, the lesion occurred only in the pressure-bearing part and was primarily composed of a mass of foam cells. By 10 weeks primary fatty plaques were still confined to the aortic face but fibroblasts within the leaflet had also taken up fat. Even after 33 weeks, the atheromatous plaque had not spread beyond the pressure-bearing part of the leaflet. From silicone rubber casts of the valve it was observed that only part of the leaflet was under pressure and the remaining leaflet sustained no pressure gradient. The maximum intramural stress occurred during diastole on the pressure-bearing part. In systole, the blood flow produced shear stress on the entire leaflet. Hence, occurrence of atherosclerotic lesions only in the area of maximum intramural stress suggests that intramural stress and not shear stress plays an important role in accelerating the process of atherosclerosis.