Emboli detection during continuous-wave doppler sonography of internal carotid artery stenosis

Continuous-wave (cw)-Doppler sonography is a wellestablished noninvasive method for examining the extracranial vessels. It is extremely rare for an acute ischemic event to occur during cw-Doppler sonography of carotid stenosis. However, no data are available concerning the influence of mechanical stress connected with this procedure on the emboli rate distal to the stenosis.

The study involved 46 patients (28 men, 18 women) aged 66+/-10 years with an unilateral moderate (n=10) or severe (n=36) stenosis of the internal carotid artery (ICA). Twenty patients had a symptomatic stenosis and the remaining 26 were asymptomatic. Patients with other embolic sources, such as atrial fibrillation or mechanical heart valves, were excluded. All patients underwent bilateral emboli detection of the middle cerebral artery for a period of 29+/-8 minutes. In a second step, emboli detection (5+/-1 minutes) was performed simultaneously with cw-Doppler sonography of the carotid stenosis.

Seven of 46 patients (15%) had a median emboli rate of 5 emboli per hour distal to the carotid stenosis before the procedure. During cw-Doppler sonography of the carotid stenosis, 6 patients (13%) had a median emboli rate of 14 emboli per hour without clinical symptoms of cerebral ischemia. One patient had no change of the emboli rate and 2 patients showed a nonsignificant increase in emboli rate during cw-Doppler sonography. Three patients had no emboli before cw-Doppler sonography, but between 12 and 15 emboli per hour during the extracranial examination (P<.001).

It must be presumed that patients with severe stenoses of the ICA represent a subgroup with fragile atheromatous plaques, which are more vulnerable to mechanical stress. The observations support the hypothesis that mechanical stress associated with routine ultrasound examinations of carotid stenosis may, in rare cases, evoke asymptomatic artery-to-artery embolism.