Impedance analysis compared with Quickscan in the detection of graft-related stenoses.

Abstract

To compare two methods of detecting graft stenoses after infrainguinal bypass. Prospective study. Vascular Laboratory, University Hospital. 110 infrainguinal graft studies (60 vein, 50 PTFE) in 74 patients were performed prospectively to detect graft-related stenoses. The diagnostic accuracy of computer assisted impedance analysis was assessed using Quickscan (QS) as the gold standard in the detection of graft-related stenoses. CHIEF RESULTS: QS showed occlusion in 4 grafts (two vein and two PTFE), no stenosis in 86 graft studies and stenoses in 20 studies. All 12 stenoses with a frequency ratio > or = 1.4, were confirmed with intraarterial digital subtraction angiography (IADSA). Eight stenoses with a frequency ratio of 1:3 continued graft surveillance. The median thigh impedance score of vein grafts with QS confirmed stenoses was 0.51 (0.36-0.70) compared with 0.44 (0.30-0.60) for non-stenosed vein grafts (p = 0.015, Mann-Whitney U test). The median thigh impedance score in PTFE graft with QS confirmed stenosis was 0.58 (0.53-0.76) compared with 0.42 (0.28-0.73 for non-stenosed grafts (p = 0.0001). An impedance score > 0.45 has been suggested for detection of "at risk" grafts. Using QS as the gold standard, impedance assessment gave 90% sensitivity, 63% specificity in the thigh; 80%, 52% in the calf and 90%, 46% taking the higher score on calf for thigh data. Taking a QS frequency ratio of 1:4 as indicating a significant stenosis (50% diameter reduction), 11% (12/106) of surveillance studies went on to intervention, that is 12/74 (16%) grafts. If the higher impedance score derived from either the calf or thigh was used to detect stenoses, 60% (64/106) of graft studies would have been referred for intervention. We believe this high level of intervention is unrealistic and cannot therefore recommend impedance analysis for graft surveillance.