To determine if a significant contralateral stenosis affects interpretation tables of the ipsilateral internal carotid artery's degree of stenosis in duplex Doppler ultrasound, the records of 307 patients with carotid duplex ultrasound studies with an angiogram performed within 3 months without intervening intervention were retrospectively reviewed for peak systolic velocity, end-diastolic velocity, internal carotid artery-common carotid artery ratio, and angiographic degree of stenosis. Data were grouped into categories of degree of contralateral stenosis, and Pearson r correlation was used to determine significance of ipsilateral Doppler parameters to angiographic data.
As the degree of contralateral stenosis increases, the correlation of ultrasound parameters becomes less significant. At a contralateral stenosis of less than 40%, the P value for peak systolic velocity was 0.0006; at a contralateral stenosis between 40% and 59%, the P value was 0.133; at a contralateral stenosis between 60% and 79%, the P value was 0.241; and at a contralateral stenosis between 80% and 99%, the P value was 0.439. Therefore, correlations are no longer significant at levels above 40% contralateral stenosis. The Doppler parameters were scattered in patients with greater than 40%contralateral stenosis, and "corrected" correlation tables could not be derived. As stenosis increases in the contralateral internal carotid artery, Doppler values become inaccurate in determining the degree of stenosis in the ipsilateral internal carotid artery, with the occurrence of both the overestimation and underestimation of the degree of stenosis.