Effect of contralateral disease on duplex measurements of internal carotidartery stenosis

Background: Duplex ultrasonography is increasingly used as the sole method of imaging before carotid endarterectomy. This study investigated the measu red degree of stenosis in the contralateral carotid artery before and after operation. Methods: Duplex-derived peak systolic velocity (PSV), end-diastolic velocit y (EDV) and internal carotid artery/common carotid artery (ICA/CCA) velocit y ratios were measured in the contralateral unoperated ICA before 131 conse cutive unilateral endarterectomies and compared with preoperative angiograp hic findings. Three months later duplex scans were repeated to assess wheth er there had been any alteration in the severity of the stenosis in the con tralateral unoperated artery. Results: Bilateral ICA disease (greater than 50 per cent stenosis) was pres ent in 50 patients (38 per cent). Three months after operation, ultrasonogr aphy of the 105 unoperated, patent, contralateral arteries showed a decreas e in mean(s.d.) PSV (1.21(0.83) versus 1.07(0.69) m/s; P < 0.01) and EDV (0 .41(0.29) versus 0.35(0.24) m/s; P < 0.01). This resulted in 14 (42 per cen t) of 33 patients with contralateral disease being downgraded to a less sev ere category of stenosis. Use of the ICA/CCA velocity ratio prevented overe stimation in eight of the 14 patients, while preoperative angiography corre ctly classified 13 of the 14 patients. Conclusion: Bilateral carotid artery disease can cause overestimation of th e severity of stenosis by duplex ultrasonography if absolute velocity is us ed as the main criterion.