Cerebral microembolism during AF ablation: an innocent bystander or an accessory to brain injury?

摘要

Stroke remains an important risk despite the recent advances made in the field of catheter ablation of atrial fibrillation (AF). Thrombus formation at sites of radiofrequency (RF) application can be unpredictable, and the monitoring of temperature and impedance to titrate radiofrequency power is not reliable in preventing its formation. Intracardiac echocardiography (ICE) has been used as a tool to evaluate ablation lesions,2 and microbubble formation at the site of RF application has been forwarded as a better method to titrate the RF power during AF ablation.An embolus reaching the cerebral circulation can vary greatly in size. Microscopic emboli or microemboli, when about 100 um in diameter, can lodge in small cerebral end-arterioles. Here, lysis by endogenous agents may reestablish the circulation, or these emboli may cause microinfarctions. Cardiovascular surgeons have used transcranial Doppler (TCD) to detect cerebral microemboli for over two decades. Microemboli reflect a higher amount of ultrasound compared with the surrounding whole blood, resulting in an increase in Doppler power that is usually measured in decibels.7 The reflected signals can be recorded for prolonged periods of time and counted off-line to obtain an accurate mi-croembolic signal (MES) count for a given procedure. The MES also depends on the insonated ultrasound frequency? solid microemboli reflect more ultrasound at a higEeFfre-quency than at a lower frequency, whereas the opposite is true for gaseous microemboli. Thus, discrimination between solid and gaseous microemboli is possible using multifre-quency TCD.