97 urn:lsid:arphahub.com:pub:B5033382-9D21-53CE-B630-B4E3A1146D51 Bulgarian Cardiology Bulgarian Cardiology 1310-7488 2683-1015 Bulgarian Society of Cardiology 10.3897/bgcardio.29.e106912 106912 Case Report Arrhythmias (аритмии) Narrow QRS tachycardia with alternating R-R intervals - what is the mechanism? Shalganov T. t_shalganov@yahoo.com https://orcid.org/0000-0003-2268-0759 1 Stoyanov M. https://orcid.org/0000-0002-1226-6119 1 National Heart Hospital, Sofia, Bulgaria National Heart Hospital Sofia Bulgaria

Corresponding author: T. Shalganov (t_shalganov@yahoo.com).

Academic editor: Vassil Traykov

 2023 31 12 2023 29 4 73 81 97CFA142-EEF1-57D1-8BE1-37852D0F8A8E 24 05 2023 17 06 2023 T. Shalganov, M. Stoyanov This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

A case is presented of a patient with a rare narrow QRS tachycardia with alternating R-R intervals in the presence of dual AV nodal physiology. The tachycardia was successfully treated by catheter ablation. The mechanism of the arrhythmia and the intracardiac and ECG recordings are discussed.