Carotid duplex overestimation of stenosis due to severe contralateral disease

BACKGROUND: In the quest to use carotid duplex to assess carotid occlusive disease, it has been repeated that the current velocity criteria to calculate stenosis tends to overestimate the severity when there is a contralateral highly stenotic or occluded carotid artery. METHODS: patient records were reviewed for 592 consecutive carotid endarterectomies performed from 1987 to 1994. Preoperative and postoperative duplex scan results were compared in a subset of patients in whom duplex overestimated the degree of stenosis, as compared to preoperative angiography. RESULTS: A fetal of 146 patients were identified in whom duplex overestimated the degree of stenosis contralateral to a high grade stenosis or an occlusion. Of 76 arteries, 18 (23.7%) contralateral to an occluded artery were overestimated by duplex, and 128 (27.0%) of 474 arteries contralateral to a high grade stenosis were overestimated, Following endarterectomy 44 (51.8%) of 128 nonoperated contralateral stenoses decreased by at least one duplex category. The average peak systolic frequency (PSF) decreased by 1175 Hz (P = 0.0018), and the average end diastolic frequency (EDF) decreased by 475 Hz (P = 0.011). CONCLUSIONS: Patients with high grade stenosis have a significant decrease in PSF and EDF in the unoperated carotid after endarterectomy, supporting a compensatory flow phenomenon, This often results in a decrease in the postoperative duplex defined stenosis by at least one category, The clinical significance of these findings is of increasing importance as carotid surgery is being performed more frequently without angiography.