Flow-Mediated Dilation in Lower-Extremity Vein Grafts

Abstract

Autogenous vein bypasses manifest a substantial late stenosis and occlusion rate due, at least in part, to the hostile conditions of the arterial milieu. The present study was undertaken to evaluate flow-mediated dilation (FMD)-a putative measure of endothelial health and, potentially, long-term function-in chronically implanted vein grafts performed for critical lower-extremity ischemia. Eleven patients, four men, seven women (mean age: 64 ±14 years; range: 30 to 81 years), with saphenous vein bypasses performed for critical lower-extremity ischemia a mean of 346 ±457 days previously (range: 47 to 1640 days), had their grafts studied in the resting state, following 5 minutes' tourniquet application to produce hyperemia, and following administration of nitroglycerin. Baseline and maximal postischemic brachial artery and vein graft diameters were determined ultrasonographically. An Atherosclerosis Risk Score (ARS) was calculated by assigning one point for each of six established risk factors for atherosclerosis (smoking, diabetes, hypertension, hypercholesterolemia, male gender, and age >60 years). Vein graft flow and diameter increased significantly with hyperemia (20% ±23%; p=0.04, and 3% ±3%; p=0.01 by paired t-test, respectively). Mean ARS was 3.6 ±1.2 (range: 2 to 5). FMD in vein grafts correlated inversely with ARS (r=-0.66, p=0.03). Seven of the 11 vein grafts demonstrated FMD >1% of baseline diameter. No differences were observed between the seven patients with “reacting” grafts and four with “non-reacting” grafts except in the mean ARS (2.9 ±0.9 vs. 4.3 ±0.5, respectively, p=0.05) and in the frequency of diabetes (33% vs. 100%; p=0.05). Chronically implanted saphenous vein grafts performed for limb-threatening ischemia exhibit FMD. FMD in vein grafts appears to be influenced adversely by concurrent atherosclerotic risk factors, and is reduced compared to FMD reported in other vessels.