Detection of Microembolic Signals in Patients With Middle Cerebral Artery Stenosis by Means of a Bigate Probe

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Abstract
Background and Purpose Middle cerebral artery (MCA) stenosis is a relatively rare occlusive disease with an annual stroke risk of approximately 7% to 8%. However, the frequent coincidence of cardiac or ipsilateral carotid artery disease may lead to difficulties in identifying the relevant embolizing source in symptomatic patients. We undertook this study to evaluate the prevalence of microembolic signals (MES) as well as the potential and limitations of bigate monitoring in patients with MCA stenosis. Methods Fourteen patients aged 33 to 87 years with angiographically demonstrated symptomatic (acute, n=2; chronic, n=8) or asymptomatic (n=4) MCA stenosis were examined. Six patients (43%) had additional cardiac (n=3) or carotid artery (n=3) disease. By means of a bigate probe, simultaneous insonation of prestenotic and poststenotic vessel segments was attempted. Results In 10 patients (71%), MES detection could be performed sufficiently at target vessel sites. In the remaining patients, either prestenotic (n=3) or poststenotic (n=1) monitoring was not satisfactory due to insufficient transtemporal bone window or the great length or extent of MCA stenosis. Poststenotic MES were detectable in 2 acutely symptomatic and 1 asymptomatic patient (prevalence, 21%). In the latter case, the sequential appearance of MES in both prestenotic and poststenotic channels excluded MCA stenosis but strongly favored coexisting carotid artery stenosis as the active embolic source. Conclusions MES are detectable in patients with MCA stenosis. Bigate monitoring in this setting is feasible and allows identification of the active source among “competing” embolizing conditions.