Microembolic Signals and Early Recurrent Cerebral Ischemia in Carotid Artery Disease
To the Editor:
Valton et al1 in the October 1998 issue of Stroke report on finding early recurrence of cerebral ischemia in patients showing presence of microembolic signals (MES) as detected by Doppler sonography. Of considerable interest to us is their finding the association significant in cases of stroke or transient ischemic attack of presumed arterial origin. Our research supports similar conclusions, though our study was more restricted. Where Valton et al examined a more heterogeneous group of patients, we have been investigating the relationship between MES and early recurrence of cerebral ischemia in a particular group of patients, those with varying degrees of carotid stenosis and carotid occlusion.
We examined 87 patients with unilateral or bilateral carotid stenosis (a total of 107 stenoses) and 13 patients with carotid occlusion. The degree of narrowing (30% to 99%) was determined by duplex Doppler sonography and digital subtraction angiography. We classified 69 of the stenoses as moderate (30% to 69% reduction in diameter) and 38 as high grade (70% to 99%). In the group with moderate-grade stenosis 56 were asymptomatic and 13 symptomatic, whereas in the high-grade group 15 were symptomatic and 23 asymptomatic. Five of the 13 ICA occlusions were symptomatic; the remaining 8 patients with occluded ICA had no symptoms. Presence of MES was assessed using a Multi-Dop X4 TCD-8 DWL with a 2-MHz transducer (14 mm diameter), at an insonation depth ranging between 45 and 55 mm, with a sample volume of 8 mm. Signal intensity was measured relative to total screen background. A 64-point fast Fourier transform with a length of 2 ms was used. Two independent observers analyzed the recording offline. Intensity threshold (9 dB) was determined on analysis of 100 high-intensity Doppler speckles of the normal Doppler signal.
But what we would like to draw particular attention to is our results on patients with symptomatic carotid stenosis (moderate and high grade). All patients with symptomatic carotid stenosis and occlusion were admitted to the hospital with acute carotid territory ischemia. They were monitored for MES within 10 days of the onset of cerebrovascular symptoms. In an attempt to determine whether early recurrence of cerebral ischemia is related to the detected presence of MES, we collected background information on previous ischemic attacks or monocular blindness (30 days prior to hospital admission), later following up the patient’s course. Recurrent cerebrovascular events in the 15 to 30 days following admission were recorded. Six of 9 MES-positive patients with symptomatic carotid stenosis and occlusion had TIA either before or after the main ischemic event that precipitated admission, whereas only 4 of 24 MES-negative symptomatic patients had such events (P<0.05).
Detection of MES by TCD is contributing to better understanding the physiology of recurrent ischemic events in patients with carotid stenosis, focusing attention, as it does, on the part recurrent embolization plays. What Valton et al reported on, which our study corroborates, is the association between recurrent ischemic events and registration of MES by transcranial Doppler monitoring in particular groups of patients with cerebrovascular disease (in our case, carotid artery disease), both studies serving to underscore the instability of embolic plaque.
- Copyright © 1999 by American Heart Association