Prevalence and Time Course of Microembolic Signals in Patients With Acute Stroke
Authors: Sliwka Ulrich , Lingnau Ariane , Stohlmann Wolf-Dirk , Schmidt Peter , Mull Michael , Diehl Rolf R. , Noth Johannes 
Published: June 2011

Background and Purpose
Cerebral emboli can be identified by the presence of typical microembolic signals (MES) in transcranial Doppler (TCD) spectral curves. The usefulness of this technique was studied by evaluating the prevalence and time course of MES in patients with acute stroke. In addition, we examined the influence of anticoagulation therapy on the occurrence of MES. Another study objective was to identify the value of MES in elucidation of the underlying pathology of cerebral ischemia in patients with acute stroke.

Methods
We used bilateral TCD monitoring of the middle cerebral artery to search for microemboli in 100 patients with acute nonhemorrhagic stroke in the anterior circulation. Monitoring time was for 30 minutes at admission (examination I), after 24 hours (examination II), and again after 48 hours (examination III).

Results
Twenty-two of the 100 patients had to be excluded from the study after examination I because retrospectively they did not fulfill the inclusion criterion or because they had an insufficient bone window. Forty of the patients (51%) showed MES during at least one of the three TCD examinations. In 9 of the 47 patients without MES during examination I (19%), MES could be recorded subsequently during examinations II and III. A statistically significant decrease in the prevalence of MES occurred between examinations I and III (
P
=.01). The frequency of MES in a single patient decreased between examinations I and II but increased again in examination III, although it did not reach the initial level. Prevalence of MES was the highest during the period up to 6 hours after the onset of symptoms. However, even at >72 hours after the onset of symptoms, a substantial number of MES could be recorded. In 18 of the 21 patients with carotid artery stenosis or occlusion who showed MES (86%), these signals occurred ipsilateral to the affected carotid artery. In 5 of the 13 patients with MES and a potential cardiac source of embolism (38%), MES were observed bilaterally. Forty-one patients were without anticoagulation treatment at the time of examination; 19 of these patients (46%) presented with MES. In contrast, of the 37 patients receiving anticoagulation treatment at the time of the first examination, MES could be recorded in only 12 (32%).

Conclusions
Microemboli are a frequent phenomenon in patients with acute stroke arising from a variety of causes, both in the very early stages and several days after the onset of symptoms. The prevalence of MES decreases significantly over time. MES occur more frequently in patients with carotid artery disease than in patients with a potential cardiac source of embolism. Ipsilateral MES are frequent in patients with carotid artery disease, whereas bilateral MES are suggestive of a cardioembolic origin. Anticoagulation treatment appears to decrease the prevalence of MES, but microemboli still occur in patients receiving intravenous therapy with heparin. Because MES occur intermittently, TCD examinations should be repeated several times, even in patients without MES in the first examination, and long-term monitoring equipment is necessary.