Background: The North American (NASCET) and European (ECST) carotid surgery trials have shown a surgical benefit for symptomatic stenosis greater than 70%. The Asymptomatic Carotid Artery Surgery (ACAS) trial have shown some benefit for the stenosis greater than 60%. Although the NASCET/ACAS angiographic methods were similar, these are discrepant from ECST and have technical limitations inherent to measurement of the distal internal carotid artery (ICA) or guessing the ICA bulb diameter.
Methods: Consecutive carotid angiograms were analyzed to verify the relationships between proximal and distal aspects of the common carotid artery (CCA) and ICA bulb. We then compared the NASCET and ECST methods and, two new techniques, the Common Carotid (CC) and Carotid Stenosis Index (CSI). The CC method is based on a direct comparison of the residual lumen to the distal CCA diameter adjacent to the bulb. The CSI is based on the known relationship between the proximal CCA and ICA (1.2 x CCA diameter = proximal CCA diameter). The normal ICA bulb diameter can therefore be calculated from direct measurement of the CCA.
Results: 125 consecutive carotid angiograms were evaluated (250 arteries). Technical applicability of NASCET was 89%, ECST 95%, CC/CSI 99%. The CCA/ICA diameter ratios were established: 1.23 +/- 0.23 (ICA bulb/distal CCA), and 1.27 +/- 0.2 (ICA bulb/proximal CCA). The CCA is enlarged at its distal end that such the distal CCA/proximal CCA ratio is 1.04 +/- 0.12. The CC and CSI methods were statistically different in 8 of 10 groups when these methods were compared per decile stenosis (p < 0.04). However, CC and CSI methods disagreed in classifying patients into mild (0-29%), moderate (30-69%), and severe (70-99%) only in 3%, 5%, and 8% of cases. Linear regression analysis shows excellent correlation between the methods (CC = 15.7 + 0.82 x CSI, r2 = 0.92). Lumen asymmetry is most common with mild-to-moderate stenoses which may affect accuracy and reproducibility of measurements.
Conclusions: We have confirmed previous data on the relationships between the components of the carotid artery. Of the different angiographic techniques, CSI is the most reliable validated method of measuring carotid stenosis, and is proposed as a bridge between results of carotid surgery trials, and to validate noninvasive modalities against angiography.