What is the origin of this arrhythmia?

The existence of inter-atrial epicardial connections bridging the two atria at different levels has well been described and their implication in some forms of supraventricular arrhythmias is a known fact. However, up to date, little data exists in the literature showing their role in the mechanisms of focal atrial tachycardias, providing at the same time clear electroanatomical and activation maps using a three-dimensional, non-fluoroscopic mapping system.

We present the case of a 29-year-old woman with a focal atrial tachycardia with the origin in a pulmonary vein, manifested as a right atrial origin due to the conduction of the electrical impulse form the right inferior pulmonary vein (RIPV) to the postero-inferior right atrium (RA) via inter-atrial epicardial connections. Using a three-dimensional, non-fluoroscopic mapping system (CARTO, Biosense Webster), an RA activation map was created during tachycardia.

Radiofrequency (RF) application at the earliest endocardial breakthrough site situated in the postero-inferior RA changed the right atrial depolarization sequence without terminating the arrhythmia. Subsequently, a left atrium activation map was created showing the earliest endocardial breakthrough site at the level of the RIPV ostium and RF application at this level abolished the atrial tachycardia.

Inter-atrial epicardial connections can be part of the substrate of some forms of supraventricular arrhythmias. Awareness of their existence is important to the electrophysiologist, since a better understanding of transseptal activation can avoid, in some cases, unnecessary RF applications at the level of the postero-septal right atrium, with a subsequent increase in procedural risk.