Australia & New Zealand Society of Vascular Surgeons

Purpose Haemodynamically significant internal carotid artery (ICA) stenosis leads to increased flow in the contralateral carotid system. This has been recognized as a potential source of error in duplex grading of the contralateral ICA. An audit was therefore performed and its clinical impact considered. Methods All patients who underwent carotid duplex before & after carotid endarterectomy at a tertiary vascular laboratory, from 1994 to 2002, were included. We analysed the pre-endarterectomy velocity indices measured from the ICA contralateral to the side of surgery. Post-endarterectomy velocity indices were used as reference values for comparison. The data was explored further in an attempt to adjust for the error in grading. Results 96 patients were identified, with a median of 4 months between duplex studies. When compared to post-endarterectomy readings, Peak Systolic Velocity in the pre-endarterectomy contralateral ICA was significantly elevated by an average of 12.4cm/s (95%CI: 3.0-21.9) and End Diastolic Velocity was significantly elevated by an average of 10.4cm/s (95% CI: 4.6-16.2). The internal carotid/ common carotid Peak Systolic Velocity Ratio was not significantly affected (increased by 0.08, 95%CI: -0.14-0.30). Translated into clinical terms, pre-endarterectomy doppler ultrasound over-estimated the stenotic grading of contralateral ICA in 18.8% of the subjects and under-estimated the same in 9.4%. Discussion We found that ICA stenosis significantly increases contralateral ICA velocity indices, with potentially important impact on duplex grading of the contralateral ICA. Decisions for carotid intervention or other treatment should be based on post first-side carotid endarterectomy duplex examination, and not on pre-endarterectomy studies.