Interruption of the inferior extension of the compact atrioventricular node underlies successful radio frequency ablation of atrioventricular nodal reentrant tachycardia.

A recent anatomic study has revived interest in the inferior extensions of the compact atrioventricular node in humans. The rightward extension is on the right atrial aspect, close to the septal attachment of the tricuspid valve leaflet and, hence, closely related to the anticipated slow pathway considered to play a role in atrioventricular nodal reentrant tachycardia (AVNRT). This report documents a patient, 65 years of age, with dilated cardiomyopathy and AVNRT. The tachycardia was successfully terminated using selective radiofrequency (RF) ablation, delivered at a site where a slow potential was recorded and validated by atrial pacing, located between the tricuspid valve and the os of the coronary sinus (CS), close to its superior rim. In subsequent years the patient developed progressive heart failure and eventually died. Histopathologic examination revealed extensive scar tissue at the site of the burn, extending onto the crest of the underlying ventricular septum. Serial sections revealed the compact AV node superiorly and an inferior extension surfacing from the scar which could be traced inferiorly beyond the os of the CS. This is the first documentation of RF ablation interrupting an inferior extension of the compact AV node in a patient successfully ablated for AVNRT. The observation suggests that the slow pathway in this patient found its anatomic substrate in the inferior extension of the compact AV node.