The effect of unilateral internal carotid arterial occlusion upon contralateral duplex study: Criteria for accurate interpretation

To determine the influence of unilateral internal carotid arterial occlusion (ICO) on Doppler frequency spectral analysis (DFSA) of the patent contralateral carotid artery, a retrospective review of 154 patients between July 1987 and December 1991 with angiographically confirmed ICO was performed, correlating duplex and arteriographic findings in a blinded fashion. Biplane arteriograms and bilateral carotid artery duplex studies that used a 5.0 MHz Doppler probe with a 1.5 mm³ sample volume at a 60 degree angle of insonation were performed on all patients. Each carotid artery was categorized by the severity of stenosis as quantified by arteriography: 1% to 15% (n = 41); 16% to 49% (n = 48), 50% to 79% (n = 21), 80% to 99% (n = 34), and bilateral occlusion (n = 10). DFSA peak systolic frequencies were commonly exaggerated in the presence of contralateral ICO and use of standard criteria for DFSA interpretation overestimated bifurcation stenoses in 43 of 89 lesions (48.3%) when determining nonhemodynamically significant lesions (<50% diameter reduction) with a sensitivity of only 57.3% and specificity of 96.9%. Conversely, prediction of hemodynamically significant lesions (> 50% diameter reduction) with standard criteria had 96.9% sensitivity but only 57.3% specificity. Modification of these criteria to account for the velocity increase or "jet effect" in the ipsilateral carotid artery system increased the sensitivity and specificity to 97.8% in predicting nonhemodynamically and hemodynamically significant stenoses respectively. A Doppler frequency spectrum with a peak systolic frequency (PSF) >4.0 kHz and end-diastolic frequency (EDF) <5 kHz with an "open window" distinguished lesions with <50% diameter reduction. A PSF >4.5 kHz with associated spectral broadening differentiated stenosis >50%, whereas an increase in EDF >5 kHz further categorized those stenoses with 80% to 99% diameter reduction. Kappa statistics were significantly different (p < 0.001) when validating these findings using the standard criteria (K = 0.577 ± 0.113) versus the modified criteria (K = 0.872 ± 0.060). We conclude that the presence of unilateral ICO influences the resultant flow velocity in the patent companion cerebral vessels, including the contralateral carotid artery and may lead to an overestimation of the actual degree of stenosis by standard DFSA criteria. A simple modification of the DFSA interpretation criteria permits more accurate differentiation between hemodynamically significant and nonhemodynamically significant lesions and is therefore important in the management of progressive extracranial cerebrovascular disease opposite an already occluded carotid artery system.