PVD: Graft Surveillance

The longterm success of peripheral vascular bypass grafts is dependent, in large part, upon a program of repeated and careful reassessment of the graft by ultrasound to identify new lesions and permit their timely correction before graft thrombosis or failure occurs. Although either recurrent claudication symptoms or a drop in ABI’s may signal graft disease, these are late and unreliable signs of impending graft failure. Less than one half of patients who develop a graft threatening stenosis admit to claudication symptoms. The development of graft stenosis is frequently clinically silent and requires direct diagnostic evaluation for detection.

The pathology of graft failure differs depending upon when it occurs. Perioperative failures (less than 30 days) result from technical errors, poor conduit quality, or inadequate runoff. From 30 days to 2 years, myointimal hyperplasia within the graft or at anastamotic sites account for 75% of all graft revisions. Beyond 2 years, progression of atherosclerotic disease accounts for most graft failures.

Routine surveillance can improve long term patency by at least 20%. Surveillance programs based on duplex scanning have resulted in a patency rate at 5 years of 87% compared with a 65% patency rate if followed clinically or only 40% after secondary procedures to salvage thrombosed grafts. Studies have shown a 25% incidence of graft thrombosis in stenotic bypasses when a policy of no intervention is followed

Duplex ultrasound scan surveillance can have a significant effect on the longterm outcome of peripheral vascular reconstructions. Duplex scanning provides conclusive evidence of changes in graft anatomy and flow characteristics which signal failure of the bypass graft.

A re-evaluation protocol should include measurement of ABI’s, Duplex color imaging of the entire bypass graft plus inflow and outflow vessels, measurement of graft diameter and measurement of peak systolic and diastolic flow velocities in the graft as well as the inflow and outflow vessels. The duplex scan is more sensitive (81%) than ABI or clinical assessment (24%) in predicting graft failure.

Evaluations should be performed at regularly scheduled intervals. The first should be near the time of hospital discharge as a baseline. If normal, then repeat evaluation should be performed at six weeks postoperatively, every three months for the first year, every six months for the second year, then on a yearly basis.  Graft surveillance should be continued indefinitely on an annual basis given the chronic and progressive nature of peripheral vascular disease pathology.

Duplex findings which warrant further attention include a Peak Systolic Velocity of 150cm/sec, a Velocity Ratio (V=PSV at lesion / PSV proximal) of 2.5 or greater, end diastolic velocity at a stenosis of >20cm/sec, and failure of waveforms to convert to a triphasic configuration over time. Doubling of the velocity at any point in the graft-arterial system compared with the velocity immediately above or below correlates with a >50% reduction in diameter.

Identification of graft abnormalities will prompt additional evaluations which may include more frequent additional duplex scans to monitor disease progression or angiography to define anatomy as indicated by the patient’s status. The combined use of both physiologic (Duplex) measurements and anatomic (angiogram) finding gives the most accurate assessment of graft flows and abnormalities.

Revision of patent but hemodynamically failing grafts results in significant improvements in graft patency rates when compared with either thrombolysis or surgical thrombectomy. Vein graft patency and limb salvage rates are improved by a program of postoperative graft surveillance.

We strongly encourage the regular reassessment of peripheral vascular patients using Duplex scan techniques to maximize their long-term graft and limb survival.