2007 Abstracts: The Relative Importance of Graft Surveillance and Warfarin Therapy In Infrainguinal Prosthetic Bypass Failure

Background: Poor graft patency rates following infrainguinal prosthetic bypass have not been linked to specific prognostic clinical or hemodynamic factors. We sought to define modes of failure and associated limb loss after polytetrafluoroethylene (PTFE) bypass grafting in patients with lower limb occlusive disease, critical ischemia and lacking autologous venous conduit.
Methods: We identified 121 patients (mean age 67 y, 86 men, 35 women) having determinable outcomes (minimum follow-up 3 mo, mean 17 mo) after 130 prosthetic infrainguinal bypasses between 1997 and 2005. Ischemic presentation was rest pain in 42%, tissue loss in 38%, and disabling claudication in 20% with 26% of patients requiring a 'redo' bypass. Distal targets were the above-knee (n=44) or below-knee (n=21) popliteal or tibial (n=65) arteries. Forty-five (55%) of the infrageniculate bypasses had distal anastomotic vein cuffs or patches. Duplex graft surveillance was performed at 1, 4, and 7 months postoperatively and biannually thereafter with recording of mid-graft velocities (MGV) and imaging encompassing in- and outflow vessels. Arteriography and open/endovascular intervention was done for stenoses identified by duplex scanning (peak systolic velocity > 300cm/s, velocity ratio > 3.5). Attempt was made to salvage occluded grafts using catheter-directed thrombolysis or open techniques. Eighty-seven patients (95% of infrageniculate bypasses) were placed on chronic warfarin therapy with a target INR range between 2 - 3. Stenosis-free primary, assisted primary and secondary patency rates and freedom from limb loss were reported according to SVS guidelines and calculated by Kaplan-Meier methods. Prognostic factors were identified using univariate statistical techniques.
Results: Three-year primary, assisted, and secondary patency rates were 39%, 43%, and 59% for all bypasses with no difference noted between above-knee and infrageniculate grafts (P=.5). At 3-years, freedom from limb loss was 75% and patient survival was only 70% with no adverse effect on survival imparted by amputation. Sixty-seven (51%) bypasses were deemed failed or failing due to thrombotic occlusion (n=49), duplex-detected stenosis (n=12), or graft infection (n=6). Salvage of existing grafts or new bypasses were done in 87% of failed bypasses but 43% of all graft occlusions required eventual amputation. Thirty failed grafts (35% of 87 patients) maintained on chronic warfarin were sub-therapeutic at the time of occlusion. Graft patency was maintained in 87% of patients remaining therapeutic on warfarin compared to only 36% of sub-therapeutic or non-anticoagulated patients (P<.001). Low flow grafts (MGV < 45 cm/s, n=67) occluded more frequently than higher flow grafts (38% v. 80% patency, P<.001). Therapeutic warfarin augmented patency of both low flow (P<.001) and infrageniculate bypasses (P<.001).
Conclusion: Low graft flow appears to be a more common mode of prosthetic bypass failure than development of stenotic lesions detected during duplex surveillance. Duplex scanning may be more important in characterizing mid-graft velocity and related thrombotic potential. Maintenance of therapeutic warfarin is paramount in optimizing prosthetic bypass patency and limb preservation.