Transcranial Doppler monitoring for microemboli: a marker of a high-risk carotid plaque

In the United States, 90% of carotid intervention is being performed for asymptomatic carotid stenosis, even though 90% of patients would be better treated with intensive medical therapy. This is being justified by comparing risks of stroke or death with medical therapy during clinical trials completed decades ago (approximately 2% per year) with risks of intervention with carotid artery stenting (CAS) versus carotid endarterectomy in recent trials that did not have a medical arm. Such extrapolations are, simply put, invalid. Even though the two most recent papers comparing carotid endarterectomy with CAS reported that the long-term risk (after first deducting periprocedural risks) is similar to that with medical therapy (approximately 0.5% per year), when the periprocedural risks are considered (approximately 3% with stenting v 1.5% with CAS), most patients would be better treated with intensive medical therapy. Furthermore, it must be recognized that the low risks observed in clinical trials with highly selected surgeons and interventionalists are much lower than in real-world practice. It is therefore necessary to have ways to identify, among patients with asymptomatic carotid stenosis, the few (approximately 10% to 15%) who could benefit from intervention. Indicators of vulnerable plaque, such as ulceration, juxtaluminal lucent plaque, intraplaque hemorrhage on magnetic resonance imaging, and plaque inflammation on positron emission tomography/computed tomography are in development for that purpose. The best-validated approach is detection of microemboli on transcranial Doppler. A prospective single-center study of 468 patients showed that microemboli identified high-risk asymptomatic stenosis; this was validated by a prospective multicenter international study in 467 patients. Increased risk with microemboli persisted in the era of lower risks with intensive medical therapy. Patients with asymptomatic carotid stenosis should not be offered CAS or carotid endarterectomy without first being identified as high risk; percent stenosis does not do so. Currently, the best way to improve the risk to benefit ratio for intervention is transcranial Doppler embolus detection.