Comparison of Preoperative and Postoperative Duplex Ultrasound Evaluation of the Contralateral Carotid Artery

Abstract

Duplex ultrasound has become the dominant imaging modality used in the evaluation and preoperative planning for carotid artery stenosis. Numerous studies have addressed the impact of contralateral stenoses on the accurate assessment of ipsilateral disease. Several of these investigators have employed arteriography as a standard of comparison, but this technique is less commonly used and often underestimates the degree of plaque bulk and stenosis. The authors therefore used duplex ultrasound to examine the postprocedural effect of carotid endarterectomy (CEA) on contralateral velocity measurements. They retrospectively reviewed the noninvasive laboratory records of all patients who underwent CEA from January 1996 to August 1998. Inclusion criteria required a preoperative and postoperative scan within 6 months of surgery and patency of both internal carotid arteries. Velocities were expressed in centimeters per second (cm/sec). Results were categorized into groups according to severity of the stenosis (0-49%, 50-79%, 80-99%). Peak systolic and end-diastolic velocities were recorded, and the difference between contralateral velocities before and after surgery was determined. Ipsilateral systolic and diastolic velocities were compared with the contralateral differences. Paired Student's t test and correlation coefficients were employed in the statistical analysis with significance assumed for a p value <0.05. Seventy-nine patients met the study criteria. The preoperative contralateral carotid systolic velocity ranged from 53 to 516 cm/sec and the diastolic velocity from 0 to 182 cm/sec. The contralateral systolic velocity and diastolic velocities did not change after ipsilateral CEA (p=0.59 and p=0.63, respectively). No significant correlation between changes in either contralateral systolic or diastolic velocities and ipsilateral systolic or diastolic velocities were observed (r <0.13 for all comparisons). After CEA, the contralateral carotid changed categories in 10 patients: six decreased from 50-79% to <50% and four increased from <50% to 50-79%. No changes in patient management resulted from these shifts. There is debate over the accuracy of contralateral duplex evaluation of a carotid artery when ipsilateral disease exists. Even after taking into account the severity of the ipsilateral stenosis, we identified no statistical difference in measured contralateral velocities after CEA. Duplex ultrasound appears to provide an accurate assessment of carotid artery stenosis even in bilateral disease.