Dual ventricular response to a single supraventricular impulse through dual atrioventricular (AV) nodal pathways is an interesting and uncommon phenomenon. Rarely, some patients can exhibit sustained one-to-two conduction producing a non-reentrant AV nodal tachycardia during sinus rhythm [1–6]. We report the case of a patient whose arrhythmia was caused by this mechanism. A 44-years-old male patient who had frequent irregular palpitations was admitted to hospital. He was misdiagnosed with atrial fibrillation and referred to our institute for consideration of pulmonary vein isolation. He did not have any significant disease in his medical history. Echocardiography was normal. The electrocardiogram showed an irregular narrow QRS complex tachycardia. Careful evaluation of the electrocardiograms revealed the presence of two ventricular activations for each atrial beat (Fig. 1). On some occasions, the wide QRS complexes with right bundle branch block (RBBB) morphology not preceded by P waves simulating premature ventricular complexes (PVCs) were observed. Electrophysiological study revealed regular 1:2 AV relationship. Each ventricular signal was preceded by a His deflection with a constant HV interval (46 ms) (Fig. 2a). The AH1 interval between the atrial wave and the first His deflection was 159 ms. The AH2 interval between the atrial wave and the second His deflection was 528 ms. Both AH1 and AH2 intervals were slightly variable. When AH2 interval was shorter than 520 ms, second ventricular responses were conducted by RBBB morphology (Fig. 2a). Because of sustained double responses, we could not perform programmed atrial extra stimulation to identify a jump in AH interval. After detailed electrophysiological examination, radiofrequency (RF) energy was delivered (40 W, 55 C, 66 s) in the posterior aspect of Koch’s triangle, where the typical ‘‘slow pathway potentials’’ were observed. After first RF application, 1:2 response disappeared (Fig. 2b). During post-ablation tests, we did not observe dual AV nodal conduction properties, and we could not induce any arrhythmia. On the 6 month follow-up, the patient was asymptomatic. Non-reentrant AV nodal tachycardia (1:2 tachycardia) is a rare manifestation of dual AV nodal physiology. Persistent simultaneous conduction of P waves over a fast and a slow nodal pathways may lead irregular supraventricular tachycardia. The two major electrophysiological properties of simultaneous anterograde fast and slow conduction during sinus rhythm are: (1) Absence of retrograde ventriculoatrial conduction via fast and slow pathways and (2) Critical conduction delay in slow pathway to allow sequential conduction of impulse from both pathways [1, 2]. Delay has to be longer than the effective refractory period of infranodal conduction system. A recently published review reported just 49 cases between dates of 1950 and 2011 [3]. Nevertheless, the prevalence of AV nodal non-reentrant tachycardia is likely to be underestimated because of difficulties in differential diagnosis. Sustained cycle length alternans is the characteristic for this arrhythmia [4]. However, changes in autonomic tone affecting conduction properties may lead irregular cycle length alternans and rate-dependent aberrancy. For these reasons, it can be erroneously diagnosed as atrial fibrillation, atrial flutter or atrial tachycardia with Wenckebach periodicity [3, 5, 7, 8]. These arrhythmias, E. E. Ozcan G. Szeplaki B. Merkely L. Geller (&) Heart Center, Semmelweis University, Gaal Jozsef street 9, Budapest 1122, Hungary e-mail: laszlo.geller@gmail.com
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Dec 22, 2023
A Hellemans + 6
