Epicardial foci of atrial arrhythmias apparently originating in the left pulmonary veins

Introduction: Epicardial potential sources of atrial arrhythmias, such as the ligament of Marshall, are in close proximity with, and electrically connected to, the left superior pulmonary vein. Ectopic activity arising from these areas may be difficult to differentiate from ectopy that, according to endocardial only mapping, originates in the left superior pulmonary vein. We hypothesized that in patients with paroxysmal atrial fibrillation (AF) apparently originating in the left pulmonary veins, mapping through the distal coronary sinus might identify possible epicardial locations of the arrhythmogenic focus. Methods and Results: Forty patients (age 48 +/- 12 years) who underwent catheter ablation for paroxysmal AF were studied by, epicardial mapping through the distal, superoposterior coronary sinus. Catheterization of the distal coronary sinus in order to approach the ostium of the left superior pulmonary vein was feasible in 14 of 19 patients with AF originating in the left superior vein (11 patients) or inferior pulmonary vein (3 patients) according to endocardial mapping criteria. In 2 patients, the sole focus of atrial tachycardia/fibrillation was epicardial with earliest activation clearly preceding electrograms recorded at the os of the left superior pulmonary vein or any other endocardial mapping site. Epicardial potentials separated from atrial electrograms were present during sinus rhythm in both patients and during atrial tachycardia in one patient. Catheter ablation through the coronary sinus rendered the arrhythmia noninducible in both patients without abolishing epicardial potentials in one of them. Conclusion: In patients with paroxysmal AF apparently originating from the left superior or inferior pulmonary vein, detailed epicardial mapping through the distal coronary sinus might identify epicardial locations of the arrhythmogenic focus.