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14-12-2018 | Rhythm Puzzle – Answer | Uitgave 2/2019 Open Access

Netherlands Heart Journal 2/2019

An irregular narrow complex tachycardia: atrial fibrillation or something else?

Netherlands Heart Journal > Uitgave 2/2019
M. J. Mulder, C. P. Allaart, H. A. Hauer, M. J. B. Kemme


The intracardiac recording during tachycardia (Fig. 1) shows a regular atrial rhythm, excluding atrial fibrillation. His bundle activation precedes ventricular activation and there is atrioventricular dissociation. The main differential diagnosis comprises atrioventricular node reentrant tachycardia (AVNRT), which may occur without atrial activation, and focal junctional tachycardia (FJT). Distinction is possible by analysing the response to a sinus beat which occurs before junctional depolarisation when the His bundle is non-refractory. Normal conduction of the sinus beat excludes AVNRT with bidirectional AH block. The sinus beat is conducted down the fast AV nodal pathway, leading to advancement of His bundle and ventricular activation without terminating or resetting the tachycardia. In common type (slow-fast) AVNRT, the subsequent refractoriness of the fast pathway would terminate the tachycardia. In contrast, termination is not expected during FJT, because of its focal nature [1]. Therefore, this tachycardia was diagnosed as FJT.
FJT is a rare arrhythmia in adults and is characterised by a rapid heart rate, narrow QRS complexes and atrioventricular dissociation. Frequently, an irregular rhythm is present which could lead to misdiagnosis of atrial fibrillation. The response to antiarrhythmic drugs is usually poor. Ablation is considered an effective alternative [2]. In this patient, after diagnosis of FJT, radiofrequency energy was delivered in the lower two-thirds of the Koch’s triangle, during which the tachycardia converted to sinus rhythm. Atrioventricular conduction was preserved. She remained free of symptoms during 3 months of follow-up.

Conflict of interest

M.J. Mulder, C.P. Allaart, H.A. Hauer and M.J.B. Kemme declare that they have no competing interests.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://​creativecommons.​org/​licenses/​by/​4.​0/​), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Netherlands Heart Journal

Het Netherlands Heart Journal wordt uitgegeven in samenwerking met de Nederlandse Vereniging voor Cardiologie en de Nederlandse Hartstichting. Het tijdschrift is Engelstalig en wordt gratis beschikbaa ...

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