Transcranial Doppler test for evaluation of cerebral artery embolism: Microemboli detection

Abstract

About one third of ischaemic cerebrovascular diseases have embolic properties. Because of that, transcranial Doppler (TCD) test for detection of microembolic signals (MES), as the only one method for detection of microemboli, is a very important test for the evaluation of cerebral artery embolism. Cerebral emboli are particles of thrombus or atheromatous plaque, platelet aggregates, lipid or air particles in cerebral circulation, which can occlude arterioles and cause ischaemic transient attack (TIA) or stroke. Most frequently, they derive from exulcerated plaques of the carotid bifurcation or the aortic arch, from the atrial thrombus, prosthetic heart valves, as well as during carotid endarterectomy, arterial stent, aortocoronary by-pass. For MES detection, bilateral monitoring of a. cerebri mediae (ACM) is performed with each probe held in place over a temporal bone. MES are represented as brightly coloured embolic tracks as they pass through the insonated arteries. A computer hard disk provides continuous recording that is replayed for counting embolic signals. Colour intensity or acoustic range indicate the size and structure of MES. MES in the range of one ACM indicate the source of embolism on the ipsilateral carotid artery, while the bilateral detection of MES suggests a cardiogenic source. Indications for TCD detection of MES are the evaluation of pathogenesis and risk for embolic stroke or TIA and assessing the source of embolism. We started applying this method at the Institute of Neurology in Belgrade 2 years ago. We have investigated 78 patients till today and detected MES in 23 patients (28.7%). The Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology, 2004, considers that TCD is probably useful for detection of cerebral MES in various cardiovascular and cerebrovascular disorders and procedures.