Orthodromic Atrioventricular Reentrant Tachycardia Masquerading as Atrial Fibrillation

Abstract

A 17-year-old boy with a heart rate of 210 beats per minute was referred to our department for catheter ablation to treat his paroxysmal supraventricular tachycardia. The 12-lead electrocardiogram (ECG) was normal at baseline. Cardiac electrophysiologic study was performed after the informed consent was obtained. There was retrograde conduction via the atrioventricular (AV) node and the bypass tract. Irregular narrow QRS tachycardia was induced by programmed electrical stimulation (Fig. 1). During the tachycardia, there was a stable 1:1 ventriculoatrial (VA) relation and the same retrograde atrial activation sequence was seen with a fixed VA interval of 100 ms at the distal coronary sinus. Variations in the AH interval preceded the respective changes in the subsequent ventricular cycle length [the relative risk (RR) interval]. Catheter ablation of the concealed left free wall bypass tract was successfully done. Because there were AH jump and two AV nodal echo beats with the patient under isoproterenol infusion, ablation of the slow pathway was also performed. He remained free of palpitations during a 6-months follow-up period after the procedure. The differential diagnosis of irregular narrow QRS tachycardia includes atrial fibrillation, atrial tachycardia or flutter with variable AV block and a sinus rhythm with a double ventricular response. The dual AV node physiology and changes in the AV node refractoriness in this patient were attributed to the cycle length alternation during the atrioventricular reentrant tachycardia. Orthodromic AV reentrant tachycardia with marked cycle length alternations can mimic atrial fibrillation and it should be included in the differential diagnosis of irregular narrow QRS tachycardia.