Carotid duplex with contralateral disease: the influence of vertebral artery blood flow.

The hemodynamic effect of severe contralateral internal carotid (ICA) disease may result in overestimation of ipsilateral stenosis by duplex ultrasound (DU). This study examines the role of the vertebral artery system (VAS) on duplex results in patients with severe carotid disease. A retrospective study of 110 patients who underwent carotid endarterectomy (CEA) between January 1, 1995 and January 31, 1998 was performed. All patients had a preoperative and postoperative DU within 6.5 months of each other and a preoperative magnetic resonance angiogram or conventional angiogram. Duplex categories of stenosis were mild (0-49%), moderate (50-79%), and severe (80-99%). Pre- and postoperative values for ICA peak systolic velocity (PSV), end diastolic velocity (EDV), and ICA-to-common carotid artery (CCA) ratio were recorded. Paired t-tests were used to assess significant changes within groups and independent t-tests were used to compare changes between groups. Sixty-seven patients had a normal VAS and 43 patients had an abnormal VAS. Patients with an abnormal VAS had significantly greater decreases in EDV after contralateral CEA. In the abnormal VAS group, there was a higher incidence (23.2% vs. 16.4%) of ipsilateral overestimation of stenosis by duplex and a greater incidence (20.9% vs. 10.4%) of postoperative decrease in stenosis following contralateral CEA than in the normal VAS group. Patients who underwent CEA for severe stenosis versus moderate stenosis had significant postoperative decreases in ipsilateral PSV, EDV, and ICA/CCA ratio. Severe contralateral stenosis patients with an abnormal VAS had a significant decrease in EDV compared to patients with a normal VAS. Vertebral artery blood flow contributes significantly to the "hemodynamic effect" of carotid disease identified by duplex.