Purpose: To evaluate duplex ultrasonographic thresholds for the determination of 70-99% stenosis of the ipsilateral and contralateral internal carotid artery in patients with symptoms of amaurosis fugax, transient ischemic attack (TIA), or minor stroke based on two criteria: maximizing accuracy and optimizing cost-effectiveness and to compare these with current recommendations.

Methods: From January 1997 to January 2000, a prospective multicenter study was conducted including 350 consecutive patients with symptoms of amaurosis fugax, TIA, or minor stroke, who underwent bilateral duplex ultrasonography and digital subtraction angiography. A linear regression analysis was performed to estimate the degree of angiographic stenosis as a function of the peak systolic velocity (PSV). PSV thresholds were calculated for both the ipsilateral and contralateral carotid arteries based on maximizing accuracy and optimizing cost-effectiveness.

Results: The PSV measurements significantly overestimated the angiographic stenosis in the contralateral artery (9.5%; 95% CI 6.3-12.7%) compared with the ipsilateral carotid artery. The recommended PSV threshold for the diagnosis of 70-99% stenosis is 230 cm/s. Maximizing accuracy the optimal PSV threshold for the ipsilateral artery was 280 cm/s and for the contralateral artery 370 cm/s for diagnosing a 70-99% stenosis. Optimizing cost-effectiveness, the optimal PSV threshold was 220 cm/sec for ipsilateral and 290 cm/sec for contralateral carotid arteries.

Conclusions: PSV measurements overestimate the degree of angiographic stenosis in the contralateral carotid artery in patients with symptoms of amaurosis fugax, TIA, or minor stroke. Separate PSV thresholds should be used for the ipsi- and contralateral carotid artery. PSV thresholds that optimize cost-effectiveness differ from the recommended thresholds and from thresholds that maximize accuracy.