Infrainguinal Prosthetic Failure Due to Low Flow

By Sharon Worcester 

RIO GRANDE, P.R. -- Low graft flow, not Duplex-ultrasound detected stenosis, was the primary mode of graft failure in patients with lower limb occlusive disease after undergoing infrainguinal prosthetic bypass, Dr. Robert S. Brumberg reported at the annual meeting of the Southern Association for Vascular Surgery.

The 121-patient study also showed that therapeutic warfarin maintenance is key for limb preservation and optimization of bypass patency, according to Dr. Brumberg, a research fellow, Dr. Dennis Bandyk, professor of surgery, and colleagues at the University of South Florida, Tampa.

Patients included 86 men and 35 women (mean age of 67 years) who presented with critical limb ischemia and were lacking autologous venous conduit. They underwent 130 prosthetic infrainguinal bypasses between 1997 and 2005. Mean follow-up was 17 months. Of the 130 bypasses, 67 were shown to have failed or to be failing, because of thrombotic occlusion (49 bypasses), duplex-detected stenosis (12 bypasses), or graft infection (6 bypasses). Existing grafts were salvaged or new bypasses were performed in 87% of these, but 43% of occluded grafts required amputation.

Of the failed grafts, 35% were maintained on subtherapeutic doses of warfarin at the time of occlusion; graft patency in these patients--and in those not on warfarin--was only 36%, compared with 87% in patients on therapeutic doses, Dr. Brumberg noted.

In 67 low-flow grafts (defined as those with midgraft velocity of less than 45 cm/sec), occlusion was more common than in high-flow grafts (38% vs. 80% patency). Therapeutic warfarin significantly improved patency in low-flow and infrageniculate bypasses.

Three-year primary, assisted, and secondary patency rates in this study were 39%, 43%, and 59% respectively; freedom from limb loss was 75%; and survival was only 70%. Amputation did not affect survival.

Ischemic presentation included rest pain in 42% of patients, tissue loss in 38%, and disabling claudication in 20%. Distal targets were above-knee arteries in 44 procedures, below-knee arteries in 21, and popliteal or tibial arteries in 65. All patients underwent Duplex surveillance at 1, 4, and 7 months postoperatively, then biannually thereafter, to measure midgraft velocity and in- and outflow velocities. Arteriography and open or endovascular interventions were performed when stenoses were identified.

Although low graft flow appears to be a more common mode of prosthetic bypass failure than stenotic lesions detected by Duplex surveillance, Duplex scanning does appear to be important for characterizing midgraft velocity and estimating related thrombotic potential, he concluded. He also noted that maintaining patients on a therapeutic dose of warfarin is a challenge but appears to be associated with improved graft patency