TEMPORAL VARIABILITY OF ASYMPTOMATIC EMBOLIZATION IN CAROTID-ARTERY STENOSIS AND OPTIMAL RECORDING PROTOCOLS

Background and Purpose-Although asymptomatic embolization can be detec ted in patients with carotid artery stenosis, its temporal variability is unclear. An understanding of this is important in designing optima l recording protocols for future prospective studies of the predictive value of embolic signals (ES), We determined the effect of repeating and extending recording times in patients with symptomatic and asympto matic carotid stenosis. Methods-In 20 asymptomatic and 20 symptomatic subjects with >60% carotid stenosis, we used transcranial Doppler ultr asound to record for ES in the ipsilateral middle cerebral artery. Thr ee 1-hour recordings were performed on three separate days, and on one occasion (not necessarily the first) the recording was extended to 2 hours. The recordings were saved onto digital tape for subsequent blin ded analysis, Results-Marked temporal variability was seen in symptoma tic patients in whom the cumulative proportion of subjects with ES inc reased from 10 (50%) after a single hour of recording to 12 (60%) and 15 (75%) after two and three recordings, respectively. Extending the r ecording to 2 hours increased the yield of ES-positive patients from 6 (30%) to 8 (40%), In symptomatic patients there was excellent agreeme nt between whether patients were positive for ES during each of two co nsecutive 1-hour recordings (kappa=0.78, P=0.0003) but poor agreement between the results of two single-hour recordings performed on differe nt days (kappa=0.22, P=0.27). In asymptomatic patients, 4 (20%) were E S positive during the first hour; this increased to 5 (25%) after the recording was repeated once, with no further increase after the third recording. Extending the recording to 2 hours increased the yield from 3 (15%) to 7 (35%), In contrast to symptomatic stenoses, in patients with asymptomatic stenoses there was fair agreement between whether pa tients were ES positive on two consecutive 1-hour recordings (kappa=0. 49, P=0.01) or two single-hour recordings performed on different days (kappa=0.48, P=0.02). Symptomatic subjects were more likely to have ES (when all 1-hour recordings were considered, 24/60 versus 10/60; P=0. 0046), ES in symptomatic subjects had a higher relative intensity incr ease than in asymptomatic subjects (P=0.01), Conclusions-The temporal variability of ES needs to be taken into account in the design of opti mal recording protocols and comparisons of results from different stud ies. Extending the duration of recording beyond an hour in symptomatic stenoses is of less value, but repeating the recording on a different day will often identify additional subjects with ES. in intervention studies in symptomatic patients, the time since last symptoms must be considered. In asymptomatic stenosis, extending the duration of record ing beyond an hour will increase the proportion of patients positive f or ES.