Mechanical determinants of graft kinking

Vascular grafts can be twisted inadvertently during implantation. If twisted excessively, they may kink and obstruct flow. In this study, in vitro experiments were performed to identify the mechanical factors that determine graft kinking. These included graft material, graft length, graft diameter, graft wall thickness, perfusion pressure, and flow rate. Six-millimeter-diameter saphenous veins were obtained from humans at autopsy. Six-millimeter standard-wall and 6-mm thin-wall polytetrafluoroethylene (PTFE) grafts also were obtained. Both fixed-length and stretchable PTFE grafts were examined. Grafts 15, 30, 50, and 70 cm in length were evaluated. Finally, PTFE grafts 4, 6, 8, 10, 12, and 14 mm in diameter were studied to determine the effect of diameter. The vessels were mounted horizontally in vitro and were perfused with saline at 50, 100, or 150 mmHg pressure at low (49 mL/min), medium (105 mL/min), and high (239 mL/min) flow rates. Each graft was twisted 90 degrees, then subjected to perfusion for 15 sec. Pressure and flow were interrupted, and an additional 90 degrees twist was imposed for another 15 sec. This sequence was repeated until a visible kink developed. We conclude from our results that, when constructing a bypass, particular care should be taken with vein, short grafts, thin-wall grafts, and large-diameter grafts, as these are especially susceptible to kinking.