Variability of Doppler Velocity Ratios as a Function of Location in the Common Carotid Artery: Potential Problems When Quantifying Significant Internal Carotid Artery Stenoses

Abstract

Introduction The use of the internal carotid artery (ICA) to common carotid artery (CCA) peak systolic velocity ratio (ICApsv/CCApsv) to quantitate ICA stenosis has been challenged based on the variability of Doppler-derived velocities at various locations within the CCA. We investigated these alleged differences to determine whether they affect actual classification of significant ICA stenoses. Methods Data from consecutive patients for an 18-month period were prospectively entered into a database. Only initial studies were included in this investigation. Follow-up examinations, postendarterectomy vessels, ICA occlusions, and CCA vessels with a PSV of >150 cm/sec were excluded from analysis. CCApsvand ICApsv/CCApsvwere obtained and based on Doppler analysis at both the proximal most visualized CCA segment (proximal), and 1.5 cm proximal to the ICA flow divider (distal). ICApsv/CCApsv values of ≥ 2, ≥ 3, and ≥ 4 were used as threshold values for ≥ 50%, ≥ 60%, and ≥ 70% diameter stenoses. Results A total of 383 patients and 588 vessels were analyzed. CCApsv -proximal values, 75 ± 20 cm/sec, were significantly higher than CCApsv -distal, 68 ± 16 cm/sec (p < 0.001). ICApsv/ CCApsv -distal ratios, 2.36 ± 2.77, were significantly higher than ICApsv/ CCApsv -proximal, 2.11 ± 2.46, (p < 0.001). The average absolute difference between CCApsv -proximal and CCApsv -distal was 15% ± 13% (range, 0%–93%). For an ICApsv/CCApsv ≥ 50%, proximal and distal ratios would both be < 2 in 66%, ≥ 2 in 29%, and 5% were contradictory. For an ICApsv/CCApsv ≥ 60%, proximal and distal ratios would both be < 3 in 78%, ≥ 3 in 18%, and 4% contradictory. For an ICApsv/CCApsv ≥ 70%, proximal and distal ratios would both be < 4 in 85%, ≥ 4 in 12%, and in 3% contradictory. Conclusions Significant differences in ICApsv/CCApsv calculation as a function of location of the CCApsv measurement were confirmed. Proximal and distal sampling sites, however, did not affect ICApsv/CCApsv classifications for 95% of the vessels analyzed. For contradictory classifications, ICApsv/CCApsv -distal had more potential for a positive result. To improve accuracy and address sensitivity or specificity interpretation parameters, the influence of the CCA sampling site should be considered and standardized when using carotid ratio criteria.