Background The mechanism(s) of persistent and long-standing persistent (LSP) atrial fibrillation (AF) is/are poorly understood. We performed high density, simultaneous, bi-atrial, epicardial mapping of persistent and LSP AF in patients undergoing open heart surgery (OHS) 1) to test the hypothesis that persistent and LSP AF are due to one or more drivers, either focal or reentrant, and 2) to characterize associated atrial activation. Methods and Results Twelve patients with persistent and LSP AF (1 month - 9 years duration) were studied at OHS. During AF, electrograms (AEGs) were recorded from both atria simultaneously for 1-5 minutes from 510-512 epicardial electrodes with ECG lead II. Thirty-two consecutive seconds of activation sequence maps were produced per patient. During AF, multiple foci (QS unipolar AEGs) of different cycle lengths (mean 175±18 ms) were present in both atria in 11/12 patients. Foci (2-4 per patient, duration 5-32 secs) were either sustained or intermittent, were predominantly found in the lateral left atrial free wall, and likely acted as drivers. Random and nonrandom breakthrough activation sites (initial r or R in unipolar AEGs) were also found. In 1/12 patients, only breakthrough sites were found. All wave fronts emanated from foci and/or breakthrough sites, and largely either collided or merged with each other at variable sites. Repetitive focal QS activation occasionally generated repetitive wannabe reentrant activation in 5/12 patients. No actual reentry was found. Conclusions During persistent and LSP AF in 12 patients, wave fronts emanating from foci and/or breakthrough sites maintained AF. No reentry was demonstrated.

Patients with LVA had an equally favorable long-term ablation outcome compared to those without. As an adjunct to PVI, voltage-guided substrate modification may be an important ablation strategy in patients with LA structural remodeling.