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 va lve leaflet and, hence, closely related to the anticipated slow pathway con sidered to play a role in atrioventricular nodal reentrant tachycardia (AVN RT). This report documents a patient, 65 years of age, with dilated cardiom yopathy and AVNRT. The tachycardia was successfully terminated using select ive radiofrequency (RF) ablation, delivered at a site where a slow potentia l was recorded and validated by atrial pacing, located between the tricuspi d valve and the os of the coronary sinus (CS), close to its superior rim. I n subsequent years the patient developed progressive heart failure and even tually died. Histopathologic examination revealed extensive scar tissue at the site of the burn, extending onto the crest of the underlying ventricula r septum. Serial sections revealed the compact AV node superiorly and an in ferior extension surfacing from the scar which could be traced inferiorly b eyond the os of the CS. This is the first documentation of RF ablation inte rrupting an inferior extension of the compact AV node in a patient successf ully ablated for AVNRT. The observation suggests that the slow pathway in t his patient found its anatomic substrate in the inferior extension of the c ompact AV node.