Detection of middle cerebral emboli during coronary artery bypass surgery using transcranial Doppler sonography.

Detection of Middle Cerebral Emboli During Coronary Artery Bypass Surgery Using Transcranial Doppler Sonography To the Editor: Spencer et al recently described the use of transcranial Doppler sonography to record the passage of emboli through the middle cerebral artery (MCA) during carotid endarterectomy. They recorded transient signals at the time of releasing common carotid cross clamps and inferred that these were due to microbubbles. Similar signals at other times were assumed also to be indicative of emboli, although of unproven constitution. They suggested that the usefulness of this technique might be extended to cardiac sources of embolism. We have recently concluded such a study. Transcranial Doppler (TC2-64 EME) was used to record middle cerebral artery flow velocity before, during, and immediately after bypass during coronary artery surgery. Continuously recorded velocities from the right MCA were averaged over 30 seconds and stored on an Apple 2e microcomputer. The software also detected high-amplitude transients (more than twice the amplitude under steady-flow conditions) and recorded their number over each 30-second period. High-amplitude signals were common at the time of aortic cannulation and at the inception of bypass, but were also recorded during stable bypass. In vitro studies by ourselves and others using model extracorporeal circulations show that the signal characteristic recorded during surgery can be attributed to microemboli. This interpretation is strengthened by the results of a randomized study of the effect of an additional arterial line filter on the incidence of "emboli" and on the neuropsychological sequelae of coronary artery bypass surgery.