Comparison of preoperative and postoperative duplex ultrasound evaluation of the contralateral carotid artery

Duplex ultrasound has become the dominant imaging modality used in the eval uation and preoperative planning for carotid artery stenosis. Numerous stud ies have addressed the impact of contralateral stenoses on the accurate ass essment of ipsilateral disease. Several of these investigators have employe d arteriography as a standard of comparison, but this technique is less com monly 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 measureme nts. They retrospectively reviewed the noninvasive laboratory records of al l patients who underwent CEA from January 1996 to August 1998. Inclusion cr iteria required a preoperative and postoperative scan within 6 months of su rgery and patency of both internal carotid arteries. Velocities were expres sed in centimeters per second (cm/sec). Results were categorized into group s according to severity of the stenosis (0-49%, 50-79%, 80-99%). Peak systo lic and end-diastolic velocities were recorded, and the difference between contralateral velocities before and after surgery was determined. Ipsilater al systolic and diastolic velocities were compared with the contralateral d ifferences. Paired Student's t test and correlation coefficients were emplo yed in the statisticalanalysis with significance assumed for a p value <0.0 5. Seventy-nine patients met the study criteria. The preoperative contralat eral carotid systolic velocity ranged from 53 to 516 cm/sec and the diastol ic velocity from 0 to 182 cm/sec. The contralateral systolic velocity and d iastolic velocities did not change after ipsilateral CEA (p=0.59 and p=0.63 , respectively). No significant correlation between changes in either contr alateral systolic or diastolic velocities and ipsilateral systolic: or dias tolic velocities were observed (r less than or equal to 0.13 for all compar isons). After CEA, the contralateral carotid changed categories in 10 patie nts: six decreased from 50-79% to <50% and four increased from <50% to 50-7 9%. No changes in patient management resulted from these shifts. There is d ebate over the accuracy of contralateral duplex evaluation of a carotid art ery when ipsilateral disease exists. Even after taking into account the sev erity of the ipsilateral stenosis, we identified no statistical difference in measured contralateral velocities after CEA. Duplex ultrasound appears t o provide an accurate assessment of carotid artery stenosis even in bilater al disease.