Coupled Beats After AV Node Ablation: What is the Mechanism?

An 83 year old lady was highly symptomatic from paroxysmal Atrial Fibrillation (AF) despite numerous antiarrhythmic and rate-limiting medications. Given her preserved left ventricular function, a pace and ablate strategy was pursued. Ablation of the AV node proved challenging requiring 2 procedures with apparently stable AV block and regular escape at 40bpm after the first sitting. Persistent Right Bundle Branch Block (RBBB) was created prior to AV node block at the first sitting. Two irrigated-tip ablation catheters (Coolflex, medium curve, St Jude’s Medical, MN, USA) were placed on either side of the interventricular septum but with the intention to ablate the AV node from the left. Identification of the His bundle from the left proved difficult as the patient was now in AF. Instead the left bundle was targeted and complete AV block achieved by combined Right Bundle Branch (RBB) and Left Bundle Branch (LBB) ablation.