Supraventricular tachycardia originating from the posterior atrioventricular node in the univentricular heart with single atrium.

Supraventricular tachycardia (SVT) was observed in a 13-year-old male patient with complex clinical features that included univentricular heart with single atrium, pulmonary atresia, and polysplenia syndrome. During electrophysiologic study, atrial burst stimuli reproducibly induced and terminated the SVT, while the occurrence of ventriculoatrial block did not interrupt the SVT. His bundle electrograms (HBEs) were recognized both in the anterior and posterior regions on the common atrioventricular (AV) valve annulus. The posterior His bundle activation was progressively delayed along with the shortening of atrial pacing cycle length until it finally lagged behind local ventricular activation. Thus, antegrade AV conduction was solely via the anterior AV node. In contrast, during the SVT, the earliest activation was observed in the posterior HBE. These observations suggested that the posterior AV node serves as an origin of the SVT and that two AV nodes were linked together possibly through a sling at the infra-Hisian level. Radiofrequency catheter ablation applied to the posterior HBE eliminated the SVT.