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Automaticity has been described in Mahaim pathways, both spontaneously and during radiofrequency ablation. We describe an unusual case of automatic rhythm from a Mahaim pathway presenting as parasystole. The parasystolic beats were also found to initiate tachycardia, resulting in initial presentation with incessant tachycardia and tachycardia induced cardiomyopathy.

An elderly woman presented with recurrent syncope. Sinus bradycardia and sinoatrial block were seen on the electrocardiogram; however, PR interval prolongation after sinus pauses suggested atrioventricular conduction system disease. The occurrence of complete atrioventricular block after a pause during the electrophysiological study confirmed a diagnosis of paroxysmal atrioventricular block precipitated by sinus pauses secondary to sinus nodal disease.

We present an interesting image showing sequential loss of anterograde, and subsequently, retrograde conduction during radiofrequency ablation of an accessory pathway. We discuss the possible mechanisms and prior literature concerning this interesting finding.