Epicardial-to-Endocardial Activation Gradients and Conduction Block During Atrial Fibrillation in the Human Left...

Although emerging evidence supports 3-dimensional myocardial activation during atrial fibrillation (AF), human studies remain limited. We thus characterized the endocardial and epicardial left atrial posterior wall (LAPW) in humans to assess the prevalence of asynchronous endocardial-epicardial LAPW conduction during AF.

Patients with symptomatic nonparoxysmal AF who had unsuccessful antiarrhythmic or catheter ablation therapy referred for hybrid epicardial-endocardial AF ablation and left atrial appendage ligation underwent high-density mapping of LAPW with Grid catheters, including simultaneous endocardial-epicardial mapping.

Twenty-seven patients (19 men, median 69 years, 55% long-standing persistent AF) were included. There was significantly greater epicardial compared with endocardial LAPW bipolar voltages during AF. In areas of low endocardial bipolar voltage, normal endocardial unipolar voltage corresponded to normal epicardial bipolar voltage. Asynchronous endocardial-epicardial LAPW AF activation during simultaneous endocardial-epicardial mapping was universal. Furthermore, more rapid epicardial compared with endocardial LAPW AF activity was observed during simultaneous endocardial-epicardial mapping in AF. Conduction block between the endocardial and epicardial LAPW surfaces was also common during organized AF, with instances of isolated or multiple blocked beats, Wenckebach conduction, and sustained endocardial LAPW entrance block with ongoing epicardial AF observed. Epicardial-to-endocardial entrance block was also infrequently observed during sinus rhythm. At 12-month follow-up, freedom from atrial arrhythmias was 68%.

Endocardial-epicardial LAPW asynchrony may be observed during human persistent AF and is characterized by: (1) greater epicardial compared with endocardial bipolar voltages, (2) more frequent epicardial-to-endocardial activation gradients during AF, and (3) conduction block commonly seen between the epicardial and endocardial surfaces during AF. Although the study was predominantly descriptive in nature, the observations suggest a dynamic 3-dimensional arrhythmogenicity of the LAPW and the potential importance of the epicardial layer, with implications for ablation therapies. Future prospective studies are required to determine the significance of these findings to clinical ablation outcomes.