Effect of twist on flow and patency of vein grafts

This article examines the effect of twist on flow through reversed vein segments in vitro and its effect on graft patency in vivo. Excised canine superficial femoral veins were perfused in vitro with normal saline solution or canine blood. Perfusion was carried out at five pressures and against three outflow resistances. Increasing increments of twist were applied to the outflow end of the vein. Flow was measured at each level of twist. With both saline solution and blood, flow was unaltered until twist reached 140 to 180 degrees. Flow then decreased sharply, stopping completely at 175 to 200 degrees of twist. In vivo experiments were then performed in 13 dogs. Reversed superficial femoral veins were used as end-to-end grafts to bypass the iliac arteries. Each graft was deliberately twisted 0, 45, 90, 135, or 200 degrees. All grafts were harvested 6 months after surgery. Eighteen of 20 grafts twisted 135 degrees or less remained patent. However, all five grafts twisted 200 degrees were thrombosed within 4 hours of surgery (p less than 0.05). These data suggest that in patients a slight amount of graft twist probably does not reduce flow; however, more than 135 degrees of twist will greatly reduce flow, leading to early graft thrombosis.