A preliminary experience with use of magnetic resonance angiography in assessment of failing lower extremity bypass grafts.

Abstract

This study evaluates the ability of magnetic resonance angiography (MRA) to detect hemodynamic failure of lower extremity bypass grafts and questions whether conventional angiography is necessary for this purpose. A prospective surveillance protocol with segmental plethysmography and color flow Doppler scanning has been used to detect hemodynamic graft failure in 110 patients with 120 lower extremity bypass grafts (90 vein, 30 polytetrafluoroethylene). Twenty (17%) bypass grafts fit the criteria for impending failure (drop in ankle/brachial index determination greater than or equal to 0.15; velocity less than 45 cm/sec; focal velocity two to three times mean graft flow). Intraarterial digital subtraction angiography and MRA studies were performed on all 20 grafts. Intraarterial digital subtraction angiograms showed graft occlusion in two grafts, severe native artery progression in three grafts, graft wall defects in six grafts, and anastomotic strictures in nine grafts. MRA results showed an exact correlation in 15 (75%) of 20 cases. False-positive tests occurred in four cases (20%), and false-negative tests occurred in one case (5%). Common reasons for interpretation error were metallic clips and field-of-view limitations. These problems are preventable. When MRA results were compared with color flow scan data, overall accuracy improved to 95%. Our studies suggest that MRA can be useful in graft surveillance and that the need for conventional angiography may be reduced in the future.