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 (ICA^psv/CCA^psv) 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. CCA^psvand ICA^psv/CCA^psvwere 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). ICA^psv/CCA^psv 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. CCA^psv-proximal values, 75 ± 20 cm/sec, were significantly higher than CCA^psv-distal, 68 ± 16 cm/sec (p < 0.001). ICA^psv/ CCA^psv-distal ratios, 2.36 ± 2.77, were significantly higher than ICA^psv/CCA^psv-proximal, 2.11 ± 2.46, (p < 0.001). The average absolute difference between CCA^psv-proximal and CCA^psv-distal was 15% ± 13% (range, 0%–93%). For an ICA^psv/CCA^psv ≥ 50%, proximal and distal ratios would both be < 2 in 66%, ≥ 2 in 29%, and 5% were contradictory. For an ICA^psv/CCA^psv ≥ 60%, proximal and distal ratios would both be < 3 in 78%, ≥ 3 in 18%, and 4% contradictory. For an ICA^psv/CCA^psv ≥ 70%, proximal and distal ratios would both be < 4 in 85%, ≥ 4 in 12%, and in 3% contradictory.

Conclusions

Significant differences in ICA^psv/CCA^psv calculation as a function of location of the CCA^psv measurement were confirmed. Proximal and distal sampling sites, however, did not affect ICA^psv/CCA^psv classifications for 95% of the vessels analyzed. For contradictory classifications, ICA^psv/CCA^psv-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.