The great saphenous vein (GSV) is commonly used as a conduit during infrainguinal bypass (IIB) and is usually well seen on computed tomography angiography (CTA) which is frequently performed for preoperative planning. In this study, we asked whether CTA could replace ultrasonography (US) as the primary mode of conduit assessment, by comparing GSV measurements for patients who underwent both CTA and US vein mapping prior to IIB.
All IIB that were completed in the six-and-a-half-year period from January 1, 2012, to July 31, 2018, at the authors’ institution were examined. Great saphenous vein measurements were analyzed for patients who had undergone both CTA and US vein mapping. Correlation between the measurements was calculated with the Pearson correlation coefficient. Data were then examined using Bland-Altman plots. Then categorical analysis was used to determine the adequacy of GSV for use as a bypass conduit.
There were 302 patients who underwent IIB, with 73 legs, in 47 patients, examined with CTA and US. Computed tomography angiography and US measurements were moderately correlated ( r = 0.531) across all measurement locations. Correlation progressively reduced distally (proximal thigh r = 0.534, midthigh r = 0.536, knee r = 0.35, midcalf r = 0.185, P = .074, ankle r = 0.078, P = .485). Bland-Altman plots of the pooled location data demonstrated no systematic bias. However, the upper and lower limits of agreement were wide, between −2.02 and +2.37 mm, demonstrating a lack of agreement between CTA and US. Analysis of each location revealed similar findings. A receiver operator characteristic curve was constructed based on a minimum US GSV diameter for adequate bypass conduit of 3 mm. The CTA value that maximized the Youden index was 3.8 mm.
The level of error between CTA and US measurements, demonstrated by the large limits of agreement on Bland-Altman plots, would not be clinically acceptable. However, if a larger threshold is accepted, CTA has the potential to replace preoperative US vein mapping of GSV.