Assessment of wall shear stress changes in arteries and veins of arteriovenous polytetrafluoroethylene grafts using magnetic resonance imaging.

The purpose of the study was to determine simultaneously the temporal changes in luminal vessel area, blood flow, and wall shear stress (WSS) in both the anastomosed artery (AA) and vein (AV) of arteriovenous polytetrafluoroethylene (PTFE) grafts. PTFE grafts were placed from the iliac artery to the ipsilateral iliac vein in 12 castrated juvenile male pigs. Contrast-enhanced magnetic resonance angiography with cine phase-contrast magnetic resonance imaging was performed. Luminal vessel area, blood flow, and WSS in the aorta, AA, AV, and inferior vena cava were determined at 3 days (D3), 7 days (D7), and 14 days (D14) after graft placement. Elastin von Gieson staining of the AV was performed. The average WSS of the AA was highest at D3 and then decreased by D7 and D14. In contrast, the average WSS and intima-to-media ratio of the AV increased from D3 to D7 and peaked by D14. Similarly, the average area of the AA was highest by D7 and began to approximate the control artery by D14. The average area of the AV had decreased to its lowest by D7. High blood flows through the AA causes a decrease in average WSS and increase in the average luminal vessel area, whereas at the AV, the average WSS and intima-to-media ratio both increase while the average luminal vessel area decreases.