The preoperative angiogram as a predictor of peripheral vascular runoff

The preoperative angiogram is widely used as a means of assessing peripheral vascular runoff before bypass grafting, but the correlation between preoperative angiographic findings and actual measurements of peripheral vascular resistance has not been adequately examined. To test this correlation, we first devised a simple technique for measuring peripheral resistance and validated it in five dogs. Increases in peripheral resistance were artificially produced by temporarily occluding either the deep or superficial femoral artery or by intravenous administration of phenylephrine hydrochloride, a vasoconstrictor. In each instance, significant increases in resistance could be measured. We then used a similar technique to measure resistance in 23 patients undergoing peripheral bypass surgery. In addition, preoperative angiograms for these 23 patients were independently scored by four readers as 0, 1, 2, or 3 based on the number of patent vessels seen below the knee. Variations in scoring from reader to reader suggested that the present criteria for grading angiograms on this basis are unclear. Moreover, the correlation between angiographic score and measured resistance was poor for three of the four scorers (-0.21 to -0.29, p greater than 0.05). The angiographic scores of one reader, however, correlated reasonably well with the peripheral resistance measured at surgery (-0.59, p = 0.01). These findings demonstrate that current criteria for grading the preoperative angiogram are not sufficiently standardized to reliably predict runoff from a preoperative angiogram. However, these findings also suggest that it may be possible to identify angiographic findings that correlate well with changes in measured resistance.