Lessons from the post coronary artery bypass graft study in evaluating and controlling technical variability in angiographic trials

Although many investigators have evaluated the technical variability of quantitative angiographic techniques used to study atherosclerosis regression in native coronary arteries, few have studied the variability inherent in repeated studies of atherosclerotic saphenous vein grafts. This study describes 2 studies performed during the course of the Post Coronary Artery Bypass Graft (CABG) Clinical Trial that were designed to assess the reproducibility of: (1) repeated angiographic views within a short time period; and (2) reproducibility of the total process of quantitative analysis of saphenous vein graft angiograms. Statistical methods are described that provide a more meaningful assessment of the impact of measurement variability in the analytic process versus the variability related to changes induced by pharmacologic interventions. One such method, the increase in standard deviation (SD) among patients (ISDP), showed that repeated angiographic views increased the variability of calculation of lesion minimal diameter by 1.5%, whereas the ISDP for repetition of the entire process of quantitative angiographic readings increased variability 6.4%. These data from the Post CABG trial reveal that technical variability is small and has negligible impact on the conclusions of the study.