Transcranial Doppler Detection of Microembolic Signals During Pulmonary Vein Antrum Isolation: Implications for Titration of Radiofrequency Energy

BACKGROUND: Cerebrovascular events are an important complication during pulmonary vein antrum isolation (PVAI). Microembolic signals (MES) have been associated with stroke and neurological impairment. However, the incidence of MES during PVAI, and their relationship to microbubble formation and radiofrequency (RF) parameters are unknown. OBJECTIVES: We sought to assess the relationship between MES, microbubble detection, and neurological outcome and the impact of RF titration strategy on these parameters. METHODS: We studied 202 patients in two groups undergoing PVAI using an intracardiac echocardiography (ICE)-guided technique. MES were detected by transcranial Doppler (TCD) using insonation of the middle cerebral arteries. The number of microbubbles on ICE were qualitatively labeled as FEW, MODERATE, and SHOWER. In group I (n = 107), RF output was titrated to avoid microbubble formation and in group II (n = 95), standard power-limited RF output was used. RESULTS: TCD detected MES in all 202 patients during PVAI with an average of 1,793 +/- 547 per patient; 90% were detected during left atrial ablation. Over 85% of MES occurred after microbubbles. Group I patients had significantly lower numbers of MES (1,015 +/- 438 per patient) compared to group II patients (2,250 +/- 864 per patient) (P < 0.05). Group II also had a 3.1% incidence of acute neurological complications versus 0.9% in group I (P = 0.10). Patients with clinical events had significantly higher numbers of MES. There were no significant correlations between RF power, temperature, or impedence and MES number. CONCLUSIONS: MES directly correlate to the amount of microbubble formation on ICE, and may result in cerebroembolic complications. Titration of RF according to microbubble formation by ICE during PVAI may be important for minimizing the occurrence of MES and possibly acute neurological complications.