Flow patterns and preferred sites of intimal thickening in end-to-end anastomosed vessels

Fluid mechanical factors are suspected to be involved in the pathogenesis and localization of intimal hyperplasia in anastomosed vessels. However, no direct correlation has been established between the flow and the exact sites of intimal hyperplasia. Hence we have studied the relationship between the flow and preferred sites of wall thickening in 90-degree- and 45-degree-cut and end-to-end anastomosed vessels.

Twenty-five 90-degree and twenty-five 45-degree end-to-end anastomoses were performed on the femoral arteries of 17 adult mongrel dogs. The vessels were harvested at 3 months after operation, fixed at 100 mm Hg, dehydrated with ethanol, and rendered transparent by immersing them in methyl salicylate. Exact locations and sizes of intimal thickening and characteristics of the flow prevailing at sites of anastomoses were studied in detail by means of flow visualization and cinemicrographic techniques.

It was found that a perfect correlation exists between the preferred sites of intimal thickening and the regions of slow recirculation flows with low wall shear stresses. In both 90-degree and 45-degree anastomosed vessels, intimal thickening developed only in those vessels in which formation of slow recirculation flows was observed. It was also found that although a pronounced and localized intimal thickening developed in 45-degree anastomosed vessels, the degree of circumferential constriction caused by both surgical procedures and development of intimal thickening was much milder in 45-degree than 90-degree anastomosed vessels.

The results suggest that key hemodynamic factors involved in the localization of intimal thickening in end-to-end anastomosed vessels are low velocity of flowing blood and the resultant low shear stresses acting on the vessel wall.