Computed Tomography Angiogram Area Stenosis Calculations Overestimate the Degree of Carotid Stenosis

Abstract

Degree of carotid artery stenosis, as calculated by catheter-based angiography using North American Symptomatic Carotid Endarterectomy Trial (NASCET) methodology, has been shown to predict stroke risk in several large randomized controlled trials. In the current era, patients are increasingly being evaluated with computed tomography angiography (CTA) before carotid artery revascularization, especially as transcarotid artery revascularization (TCAR) adoption grows. Interpretation of CTA for degree of carotid stenosis has not been standardized, with both NASCET methodology and area stenosis being used. We performed a single-institution, blinded, retrospective analysis of CTA using both NASCET methodology and area stenosis to assess concordance/discordance between the two methods when evaluating ≥70% and ≥80% stenosis. The University of Massachusetts vascular laboratory database was queried for all carotid duplex ultrasounds performed from 2008 to 2017. The dataset was winnowed to patients with peak systolic velocity of ≥125 cm/s, internal carotid-to-common carotid ratio of ≥4, and a correlative CTA performed <1 year from duplex. A blinded review of all correlative CTA, using centerline measurements on a three-dimensional workstation (Terarecon, Redmond, Calif) was performed to characterize the degree of carotid stenosis by NASCET methodology and by area stenosis (Fig). Patients were excluded if revascularization was performed between the two imaging studies. Of 37,204 carotid duplex ultrasound examinations reviewed (2008-2017), 3480 arteries met criteria for peak systolic velocity of ≥125 cm/s and internal carotid-to-common carotid ratio of ≥4. A correlative CTA within 1 year of the duplex examination was identified in 460 arteries, of which 320 were adequate quality for blinded review. The median number of days between ultrasound examination and CTA was 9.5. Using NASCET methodology, 44 patients were calculated to have ≥80% stenosis and 128 patients were calculated to have ≥70% stenosis. Using area stenosis, 167 patients were calculated to have ≥80% stenosis (3.8-fold increase compared to NASCET methodology) and 247 patients were calculated to have ≥70% stenosis (1.9-fold increase compared to NASCET methodology). Area stenosis CTA calculations of carotid artery stenosis dramatically overestimate the degree of carotid stenosis compared to that calculated by NASCET methodology. Given that stroke risk estimates are based on trials that used NASCET methodology, area stenosis likely overestimates the risk of stroke. Therefore, area stenosis calculations may lead to unnecessary carotid revascularization procedures. This model highlights the need for standardized use of NASCET methodology when using CTA as the imaging modality to determine threshold for carotid revascularization.