Surveillance of lower extremity bypass grafts

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Duplex ultrasound graft surveillance can prevent graft failure by accurate detection and then repair of lesions prior to graft thrombosis occurring. Lower limb bypass grafts are prone to develop intrinsic lesions after implantation into the arterial circulation, despite careful operative technique. Duplex surveillance after infrainguinal vein bypass grafting should begin in the operating room because 15% of grafts will have lesions identified—conduit stenosis/fibrosis, inadequate valve lysis, anastomotic stenosis, and formation of platelet thrombus. The correction of graft lesions reduces the incidence of early thrombosis and the need for secondary interventions for residual stenosis. Vein bypasses with normal intraoperative duplex studies demonstrate <1% incidence of graft thrombosis within the first 3 months of implantation; by comparison, residual duplex abnormalities result in thrombosis or revision in 15–25% of grafts. Duplex testing should be repeated prior to discharge, as the identification of a low-flow (<40 cm/s) graft may indicated need for anticoagulation. Testing at 4–6 weeks is recommended if pre-discharge scanning was not complete or a residual stenosis (PSV < 300 cm/sec, Vr < 3.5) identified. Repair of all stenoses with a PSV > 300 cm/s and Vr > 3.5 is recommended, especially if the lesion has progressed (increasing PSV) on serial scans, or a low (PSV < 40 cm/s) graft flow velocity is detected. The combination of high- and low-velocity criteria identifies bypasses at the highest risk for thrombosis. These threshold criteria identified all grafts at risk for thrombosis, and <5% of lesions with high-velocity criteria regressed. Most graft stenoses are asymptomatic, and thus appropriate criteria of the “severe” stenosis should be applied when recommending intervention by either balloon angioplasty or open surgical repair. The incidence of vein graft stenosis decreases (annual incidence of 2–4%) with time, but because of atherosclerotic disease progression in native arteries (5–10% incidence) and aneurysm formation in the vein conduit, life-long surveillance is recommended. Duplex surveillance is cost effective and improves long-term graft patency and limb salvage rates by approximately 15–20%.