Evaluation of carotid stenosis by angiography: potential bias toward overestimated measurements introduced by prior interpretation of Doppler sonograms

Abstract

Background and purpose: Doppler sonography of the carotid arteries is routinely performed before catheter angiography, and its results may bias the subsequent interpretation of angiograms. We attempt to establish that Doppler sonography may show an exaggerated degree of carotid stenosis, introducing bias to the evaluation of carotid stenosis by subsequent catheter angiography.

Methods: Angiograms of the carotid arteries obtained to evaluate potential carotid stenosis in patients who had undergone Doppler sonography of the carotid arteries were retrospectively reviewed (from 1993 to 1998). Readers who were blinded to the previous interpretations of the angiography and Doppler sonography results measured carotid stenosis. The results of Doppler sonography of the carotid arteries were not re-evaluated. Based on the original Doppler sonograms, stenoses were categorized as normal/mild (<30%), moderate (30-59%), severe (60-79%), and critical (80-99%). Within these categories, the differences between the original percent stenosis, as determined by angiography, and the blinded measurements were determined.

Results: A total of 106 patients with angiographically measurable stenoses in 128 vessels were identified. The difference between the blinded readers was 3% (+/-8%), with no category statistically different from the other. The difference between original and remeasured stenoses in carotid arteries in the Doppler categories were as follows: mild stenosis, 2% (+/-9%); moderate stenosis, 6% (+/-15%); severe stenosis, 8% (+/-15%); and critical stenosis, 22% (+/-12%). A significant overestimation occurred in the severe (P < .05) and critical (P < .0001) stenosis categories. One third of patients with stenoses in the severe or critical Doppler category had significant stenoses on the original angiograms that were less than 60%, according to blinded remeasurement.

Conclusion: Doppler sonography of the carotid arteries has the potential to bias the subsequent interpretation of catheter angiography. Care must be taken to measure stenosis accurately, using strict criteria to determine the potential benefit of carotid endarterectomy for the individual patient and to ensure that the criteria for Doppler sonography of the carotid arteries are based on accurate catheter angiography measurements.

fig 1.

Results of Doppler sonography of the carotid arteries were interpreted as mild stenosis with a peak systolic velocity of 104 cm/s. Percent stenosis was measured as 25% according to the original interpretation and as 23% by the blinded readers. Arrow indicates point of maximum stenosis, and arrowhead indicates normal distal internal carotid artery.fig 2. Results of sonography of the carotid arteries were interpreted as moderate stenosis with a peak systolic velocity of 132 cm/s. Percent stenosis was measured as 33% according to the original interpretation and as 28% by the blinded readers. Arrow indicates point of maximum stenosis, and arrowhead indicates normal distal internal carotid artery.fig 3. Results of Doppler sonography of the carotid arteries were interpreted as severe stenosis with a peak systolic velocity of 170 cm/s. Percent stenosis was measured as 70% according to the original interpretation and as 52% by the blinded readers. Arrow indicates point of maximum stenosis, and arrowhead indicates normal distal internal carotid artery.fig 4. Results of Doppler sonography of the carotid arteries were interpreted as critical stenosis with a peak systolic velocity of 450 cm/s. Percent stenosis was measured as 83% according to the original interpretation and as 61% by the blinded readers. Arrow indicates point of maximum stenosis, and arrowhead indicates normal distal internal carotid artery