Atrioventricular reciprocating tachycardia involving twin atrioventricular nodes in patients with complex congenital heart disease

Introduction: Histologic studies of autopsy specimens described the coexistence of two distinct AV nodes (so-called "Monckeberg sling" or "twin AV nodes") in specific congenital heart defects; however, the clinical electrophysiologic (EP) characteristics of twin AV nodes have not been characterized in detail. Methods and Results: Since April 1993, a total of seven patients with complex congenital heart disease presented with AV reciprocating tachycardia suspected to be mediated by twin AV nodes. A common anatomic finding was AV discordance ((S,L,L) or (I,D,D)) with a malaligned complete AV canal defect in 5 of 7 patients. Intracardiac EP study was performed in five cases, and ablation was attempted in three patients with successful elimination of tachycardia inducibility by interruption or modification of 1 of the 2 AV nodes. Important EP characteristics included (1) the existence of two discrete nonpreexcited QRS morphologies, each with an associated His-bundle electrogram; (2) decremental as well as adenosine-sensitive anterograde and retrograde conduction; and (3) inducible AV reciprocating tachycardia with anterograde conduction over one AV nodal pathway and retrograde conduction over the alternate AV nodal pathway. The existence of two AV nodes was further supported in the group treated with radiofrequency ablation by the development of transient accelerated junctional rhythm during energy delivery with an identical QRS morphology to that generated by anterograde conduction over the targeted AV node. Conclusion: Reciprocating tachycardia mediated by twin AV nodes can be a source of recurrent supraventricular tachycardia in patients with specific forms of complex congenital heart disease. Successful treatment with catheter ablation is possible.