Microemboli detection in acute ischemic stroke

Abstract

Microembolic signals (MES) are detectable by transcranial Doppler monitoring and represent small, clinically silent particles in the cerebral circulation. MES are related to increased risk of first or recurrent ischemic stroke, and MES detection may be used to clarify stroke etiology and evaluate the effect of antithrombotic treatment.

Most studies have assessed the occurrence of MES with a single monitoring session of up to one hour. However, microembolization may be infrequent with distinct temporal variability. We aimed to explore the time course of microembolization in acute ischemic stroke and assess the utility of prolonged and repeated MES detection.

During three observational ultrasound studies, we explored the time course of microembolization in acute stroke patients, in patients with carotid artery plaques, and in healthy volunteers after infusion of a microbubble-based contrast agent.

In NOR-MASS (The Norwegian Microemboli in Acute Stroke Study), MES detection was performed within 24 hours after onset in 47 patients with suspected ischemic stroke and repeated on the following two days and after three months. MES occurred in 63% of acute stroke patients and decreased during follow-up. The examinations led to treatment changes in 25% of MES positive patients. Patients who were MES negative during the initial one-hour session tended to remain negative during follow-up. MES occurrence or persistence did not predict recurrent stroke.

In NOR-PLAQ (The Norwegian Carotid Plaque Study), 15 patients with carotid artery plaques underwent duplex ultrasound, contrast-enhanced ultrasound, and MES detection at baseline and after three and six months. MES decreased during follow-up while the degree of intraplaque neovascularization did not change significantly.

In a NOR-MASS sub-study, ten healthy volunteers received an infusion of the ultrasound contrast agent sulfur hexafluoride followed by MES detection for 3.5 hours. After completed infusion, MES persisted for up to 77 minutes. To avoid confounding from contrast microbubbles, MES detection with the intention to detect stroke-related microemboli should wait for at least this long after contrast infusion.