Mapping and ablation of atypical AVNRT from the morphologic left atrium in a patient with dextrocardia and situs inversus.

A 75-year-old woman with dextrocardia, situs inversus, and subpulmonic outflow obstruction presented with recurrent supraventricular tachycardia (SVT). This SVT was easily inducible during electrophysiology study, and pacing maneuvers during SVT were consistent with atypical, slow-slow atrioventricular nodal reentrant tachycardia (AVNRT). The His bundle was identified in the low postero-septal morphologic right atrium, at the typical anatomic site for slow pathway ablation of AVNRT. Mapping of the retrograde earliest atrial electrogram during AVNRT localized this site to the mid-septal morphologic left atrium, and cryoablation at this site terminated the AVNRT and rendered it noninducible.