Ablation of Twin Atrioventricular Node‐Mediated Macroreentrant Tachycardia in a Patient With Complex Heterotaxy Syndrome

Twin atrioventricular (AV) nodes constitute a rare and highly complex electrophysiological substrate for tachycardia in heterotaxy syndrome (complex cardiac heart disease). We present the case of an 18‐year‐old male with right atrial isomerism, asplenia, univentricular physiology, and a Glenn shunt, who presented with a regular wide‐QRS tachycardia associated with severe hemodynamic decompensation. High‐density electroanatomical mapping identified two distinct His bundle recordings separated by 20.3 mm. Together with two non‐preexcited QRS morphologies and different conduction properties, these findings supported suspected twin AV node‐mediated macroreentry, with proposed anterograde conduction via the inferior‐posterior system and retrograde conduction through the superior‐anterior system; complete circuit mapping and entrainment were not possible. Following an initial procedure complicated by pulseless electrical activity clinically attributed to post‐cardioversion myocardial stunning, a second electrophysiological study prioritized functional characterization during sinus rhythm and atrial pacing without preablation reinduction of the clinical tachycardia. Selective ablation of the superior‐anterior His region preserved AV conduction and was followed by noninducibility of the clinical tachycardia. A separate isthmus‐dependent flutter was also ablated. At two months, clinical assessment, ECG, and 24‐hour Holter monitoring showed no documented recurrence or new AV block.