Spontaneous transition of double tachycardia with atrial fusion between atrioventricular reciprocating tachycardia and atrial tachycardia: a case report.

UNLABELLED: Direct transition between double tachycardias is rarely observed. We report successful ablation of the spontaneous transition of double tachycardia between atrioventricular reciprocating tachycardia (AVRT) and atrial tachycardia (AT). A 53-year-old female patient who complained of palpitations, and was diagnosed with drug-refractory supraventricular tachycardia (SVT), was referred for catheter ablation. Two types of SVT (AT and AVRT) were induced. The AT was sometimes sustained with a Wenckebach AV block. When the AH interval was prolonged beyond 200 ms without the jump-up phenomenon, the HA interval of the next beat stabilized at 135 ms, and there was a transition of AVRT. At an AH interval of 280 ms, spontaneous bidirectional transitions of both tachycardia types, not only AT to AVRT but also AVRT to AT, were observed with a fusion beat reproducibly. The patient underwent radiofrequency catheter ablation for double tachycardia successfully. We focused on the AH intervals and successive HA intervals during tachycardias and examined the spontaneous transition and its mechanism of AT and AVRT.

LEARNING OBJECTIVE: Most spontaneous transition of double tachycardias has been reported with atrioventricular nodal reentrant tachycardia. It can occur after premature atrial or ventricular activity if the cycle lengths of the two tachycardias are similar. In the present case, there was a transition between atrioventricular reciprocating tachycardia and atrial tachycardia as well as fusion of double tachycardias, and the preceding AH interval defined the next beat atrial activation.