Interobserver variation in duplex scanning of infrainguinal arterial bypass grafts

Objective: to determine the degree of interobserver variation of color-flow duplex scanning of infrainguinal arterial bypass grafts. Methods: two experienced vascular technologies randomly assessed bypass grafts in 32 consecutive patients, using a color-flow duplex scan. In pre-defined segments the highest peak systolic velocity (PSVmax) and end-diastolic velocity (EDV) were measured and a peak systolic velocity ratio (PSV ratio) was calculated. Results were analyzed as continuous variables (Bland and Altman plots and Intraclass Correlation Coefficient = ICC) and also as categorical data (weighted Kappa coefficient) for the PSV ratio 1-2.5, greater than or equal to2.5-4, greater than or equal to4.0. Results: the ICC for the PSVmax, PSV ratio and EDV indicated "almost perfect" agreement for all three parameters. However, the Bland and Altman plots showed impressive interobserver variation for the higher values of all three parameters. For the PSV ratio categories a weighted kappa of 0.31 was calculated, indicating only fair agreement. Substantial variation was found for the categories with PSV ratios >2.5-4.0 and greater than or equal to4.0. Conclusions: though performing accurately for the lower values of the assessed parameters, duplex scanning shows considerable interobserver variation for the clinically significant higher values. Particularly in the PSV ratio interval greater than or equal to2.5-4.0, most relevant for clinical decision-making, the interobserver variability is unacceptable.