Simultaneous Biatrial High-Density (510–512 Electrodes) Epicardial Mapping of Persistent and Long-Standing Persistent Atrial Fibrillation in Patients: New Insights Into the Mechanism of Its Maintenance

BACKGROUND—The mechanism(s) of persistent and long-standing persistent (LSP) atrial fibrillation (AF) is/are poorly understood. We performed high-density, simultaneous, biatrial, epicardial mapping of persistent and LSP AF in patients undergoing open heart surgery (1) to test the hypothesis that persistent and LSP AF are due to ≥1 drivers, either focal or reentrant, and (2) to characterize associated atrial activation. METHODS AND RESULTS—Twelve patients with persistent and LSP AF (1 month to 9 years duration) were studied at open heart surgery. During AF, electrograms were recorded from both atria simultaneously for 1 to 5 minutes from 510 to 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 atrial electrograms) of different cycle lengths (mean, 175±18 ms) were present in both atria in 11 of 12 patients. Foci (2–4 per patient, duration 5–32 s) 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 atrial electrograms) were also found. In 1 of 12 patients, only breakthrough sites were found. All wave fronts emanated from foci and 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 of 12 patients. No actual reentry was found. CONCLUSIONS—During persistent and LSP AF in 12 patients, wave fronts emanating from foci and breakthrough sites maintained AF. No reentry was demonstrated.