Correlation of peak systolic velocity and angiographic measurement of carotid stenosis revisited

Background and Purpose Recent observations from the North American Symptomatic Carotid Endarterectomy Trial (NASCET) questioned the reliability of peak systolic velocity (PSV) criteria for grading carotid stenosis. We compared PSV and angiographic measurements at our center together with known physiological relationships to investigate the accuracy of ultrasound. Methods Consecutive patients who underwent both color-coded duplex ultrasound and intra-arterial digital subtraction angiography were studied. PSV was determined with angle correction at the site of the tightest internal carotid artery narrowing. Carotid stenosis was measured on angiograms with the North American (N) and common carotid (C) methods. Variables for the stepwise multiple linear regression analysis were selected from an axisymmetrical flow model. Results Eighty bifurcations were imaged in 40 patients. PSV did not exceed 140 cm/s in normal vessels. In diseased arteries, PSV increased proportionally with increasing stenosis and decreased to 0 cm/s at occlusion. In stepwise selection of polynomial terms, the linear, quadratic, and cubic correlations of .38, .17, and .22 for N and .45, .24, and .03 for C were found to be significant (P<.02). When only stenosed vessels were evaluated, PSV increase was found with greater scatter for the N measurement: r(2)=.73 for N and r(2)=.85 for C (n=50; P=.03 for the difference between two correlated correlation coefficients). Conclusions At our laboratory PSV consistently correlates well with N and C angiographic measurements, as determined with a simple flow model. The complex nature of these correlations and greater variability of the N measurement should be taken into account when data from different centers are compared.