Clinical applicability of methods to measure carotid stenosis

Abstract

The North American (NASCET) and European (ECST) trials of carotid endarterectomy used discrepant methods to measure carotid stenosis on angiography. The aim of this study was to evaluate clinical applicability of currently available angiographic methods to measure carotid stenosis. Consecutive patients undergoing carotid angiography were evaluated. To estimate the normal internal carotid artery (ICA) bulb diameter on angiography, the common carotid artery (CCA) was used (ICA bulb diameter = 1.2 X CCA diameter measured 3-5 cm below the bifurcation) and the ICA diameter reduction was calculated: 1 - (d/1.2 X CCA) X 100%. We validated this against the planimetry of the intact removed plaque and termed it the Carotid Stenosis Index (CSI). The clinical applicability of NASCET, ECST, and CSI methods was then compared. Four observers evaluated 165 consecutive carotid angiograms performed over a 1-year period; 20% of arteries were normal, and 10% of ICAs were occluded. After these were excluded, the NASCET method was inapplicable in 30% of angiograms because of "negative stenosis" with minor degrees of atherosclerosis, inadequate views of the distal ICA, and two or more segments of distal ICA with parallel walls in which the diameters differed significantly. The ECST method gave an equivocal outline of the bulb in 10% of all angiograms. The CSI method was applicable in 97% of all angiograms, the major limitation being the presence of severe CCA atheroma (3%). The normal ICA bulb has -84% stenosis according to NASCET, whereas NASCET 0% stenosis equals 45-50% diameter reduction of ICA bulb and NASCET-positive stenoses cover only the last 50% of ICA stenoses. Although NASCET and ECST data are singularly irreplacable for surgical decisions, the angiographic methods used are discrepant from each other and of limited clinical applicability. This may affect the generalizibility of the results of these trials. CSI provides a firm scientific basis to make the results of the trials compatible.