Diagnostic Dilemma in a Narrow Complex Tachycardia

atrioventricular nodal reentrant tachycardia, junctional tachycardia, atrial extrastimulus, supraventricular tachycardiaCase A 24-year-old woman presented with episodic palpitations usually associated with exertion.A narrow complex tachycardia was documented during one prolonged episode associated with a febrile illness.Electrocardiogram at rest showed occasional junctional ectopic beats and no preexcitation.During electrophysiology study, dual atrioventricular (AV) nodal physiology in the form of atrial-His (AH) jump was demonstrated and there was no evidence of accessory pathway conduction.No tachycardia could be induced with single and double atrial extrastimuli or atrial burst pacing.During isoprenaline infusion, repeated spontaneous initiation of tachycardia was seen without preceding premature beats or AH prolongation (Fig. 1).This was a regular narrow complex tachycardia at a cycle length of 365 ms with 1:1 ventriculo-atrial (VA) relationship, central VA conduction, and a VA interval of -10 ms.Premature atrial extrastimuli were introduced from the proximal coronary sinus scanning diastole.Shown in Figures 2 and 3 are two extrastimuli.What is the mechanism of the tachycardia based on the response to these extrastimuli? DiscussionNarrow complex tachycardia with a very short VA interval and central atrial activation is most commonly atrioventricular nodal reentrant tachycardia (AVNRT), especially in the presence Disclosures and financial support: None declared.