Background: In patients undergoing atrial fibrillation (AF) ablation, wide antral circumferential ablation of the left pulmonary veins (PV) may not result in pulmonary vein isolation (PVI) despite a confluent circular lesion set. Empiric ablation of the left PV carina can increase the success rate of PVI. The mechanism of this is unknown but it could be due to the ligament of Marshall (LOM), an epicardial fiber that can connect the left PV to the left atrium and courses adjacent to the anterior carina.
Objective: Establish criteria for identifying LOM connections that are responsible for initial left PVI failure or recurrence, assess their incidence, and determine if successful PVI can be achieved by targeting LOM connections with endocardial ablation at the anterior carina of the left superior pulmonary vein (LSPV).
Methods: All patients undergoing radiofrequency ablation for AF by a single operator were included. If first pass isolation was not achieved after an initial wide antral contiguous circumferential ablation of the left PV, bidirectional mapping was performed. A LOM connection was diagnosed if the earliest entrance into the left PV was mapped to the anterior LSPV, while the earliest exit out of the left PV was mapped inferior to the left inferior pulmonary vein. Focal ablation at the LSPV anterior carina was then performed, even if not at the site of earliest entrance activation. The primary endpoint was successful left PVI immediately after LOM ablation.
Results: Of the 473 consecutive patients who underwent 593 radiofrequency AF ablations, 363 were first-time procedures. A LOM connection was identified in 50 procedures (8.4%) and in 39 patients undergoing first-time procedures (10.7%). All (100%) of the identified LOM connections were successfully ablated at the anterior carina of the LSPV, resulting in persistent left PV entrance and exit block. No patient required epicardial ablation from the coronary sinus or vein of Marshall.
Conclusion: LOM connections are a previously unrecognized cause of initial PVI failure and recurrent left PV conduction in those with AF recurrence. They can be easily identified and reliably ablated from the endocardium with focal ablation at the anterior carina, avoiding extensive empiric ablation of the entire carina.