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

By Q. Zhang, A.D. Houghton, J. Derodra, D.H. King, J.F. Reidy and P.R. Taylor

Abstract

Objective:To compare two methods of detecting graft stenoses after infrainguinal bypass.Design:Prospective study.Setting:Vascular Laboratory, University Hospital.Materials:110 infrainguinal graft studies (60 vein, 50 PTFE) in 74 patients were performed prospectively to detect graft-related stenoses.Chief Outcome Measures: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 ≥ 1:4, were confirmed with intraarterial digital substraction 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 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 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

Publisher: Published by Elsevier Ltd.
Year: 1995
DOI identifier: 10.1016/S1078-5884(05)80093-0
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