IMPEDANCE ANALYSIS COMPARED WITH QUICKSCAN IN THE DETECTION OF GRAFT-RELATED STENOSES

Objective: To compare two methods of detecting graft stenoses after in frainguinal bypass. Design: Prospective study. Setting: Vascular Labor atory, University Hospital. Materials: 110 infrainguinal graft studies (60 vein, 50 PTFE) in 74 patients were performed prospectively to det ect graft-related stenoses. Chief Outcome Measures: The diagnostic acc uracy of computer assisted impedance analysis was assessed using Quick scan (QS) as the gold standard in the detection of graft-related steno ses. 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 greater than or equal to 1:4, were confirmed with intraarterial digital substraction angiography (IADSA) . Eight stenoses with a frequency ratio of 1:3 continued graft surveil lance. The median thigh impedance score of vein grafts with QS confirm ed stenoses was 0.51 (0.36-0.70) compared with 0.44 (0.30-0.60) for no n-stenosed vein grafts (p=0.015, Mann-Whitney U test). The median thig h 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 c alf and 90%, 46% taking the higher score on calf or 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. Conclusions: If the higher im pedance score derived from either the calf or thigh was used to detect stenoses, 60% (64/106) of graft studies would have been referred far intervention. We believe this high level of intervention is unrealisti c and cannot therefore recommend impedance analysis for graft surveill ance.