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

Introduction: Histologic studies of autopsy specimens described the coexist ence of two distinct AV nodes (so-called "Monckeberg sling" or "twin AV nod es") in specific congenital heart defects; however, the clinical electrophy siologic (EP) characteristics of twin AV nodes have not been characterized in detail. Methods and Results: Since April 1993, a total of seven patients with compl ex congenital heart disease presented with AV reciprocating tachycardia sus pected to be mediated by twin AV nodes. A common anatomic finding was AV di scordance ((S,L,L) or (I,D,D)) with a malaligned complete AV canal defect i n 5 of 7 patients. Intracardiac EP study was performed in five cases, and a blation was attempted in three patients with successful elimination of tach ycardia inducibility by interruption or modification of 1 of the 2 AV nodes . Important EP characteristics included (1) the existence of two discrete n onpreexcited QRS morphologies, each with an associated His-bundle electrogr am; (2) decremental as well as adenosine-sensitive anterograde and retrogra de conduction; and (3) inducible AV reciprocating tachycardia with anterogr ade conduction over one AV nodal pathway and retrograde conduction over the alternate AV nodal pathway. The existence of two AV nodes was further supp orted in the group treated with radiofrequency ablation by the development of transient accelerated junctional rhythm during energy delivery with an i dentical QRS morphology to that generated by anterograde conduction over th e targeted AV node. Conclusion: Reciprocating tachycardia mediated by twin AV nodes can be a so urce of recurrent supraventricular tachycardia in patients with specific fo rms of complex congenital heart disease. Successful treatment with catheter ablation is possible.