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Introduction

In recent years, flutter circuits utilising epicardial structures have been a focus of interest, as their occurrence has become more frequent after endocardial catheter ablation and understanding the mechanisms of complex macroreentrant tachycardias has become deeper through high resolution mapping. As already known from several anatomical and invasive studies, the coronary sinus (CS) musculature connects to the right atrium (RA) as well as the left atrium (LA) forming electrical interatrial connections. The connections to the LA can vary from 1 or 2 up to a wide continuum.
The coronary sinus often is a critical part of various forms of left atrial macroreentrant tachycardias, mostly of common perimitral flutter, and biatrial tachycardias, such as large circuits around both mitral and tricuspid valves or biatrial flutter with perimitral circuit using only the right atrial septum.
The CS musculature with its connections to RA and LA and the adjacent myocardium of LA can serve substrate for a macroreentrant circuit without utilizing other atrial areas. However, this kind of tachycardia has only been reported once.
We herein report a rare case of a peri-CS atrial flutter in a female patient after pulmonary vein isolation (PVI) four years ago and roof line ablation due to roof-dependent atypical flutter during the same procedure.

Case presentation

A 77-year-old female patient presented with shortness of breath and tachycardia of 125bpm. The electrocardiogram showed \soutan atypical flutter with atrial cycle length (CL) of 240msec. The flutter waves were monophasic positive in II, III, aVF and V1-V2, negative in aVL and isoelectric in I. A PVI-only procedure was performed four years ago. We performed a new electrophysiological study upon admission. Written informed consent was obtained. The procedure was performed under conscious sedation. A steerable decapolar catheter (Inquiry, Abbott, spacing 2-5-2) was introduced into the coronary sinus and showed a “chevron” pattern. An activation map of the left atrium (NavX Ensite Precision, Abbott, St. Paul, MN) was created using a high-density mapping catheter (HD Grid catheter SE, Abbott) with support from a steerable long sheath (Agilis, Abbott). LAT mapping and post pacing interval (PPI) mapping revealed a roof dependant atrial flutter with a “figure of 8” propagation around both pulmonary vein pairs. The pulmonary veins were persistently isolated. Low voltage was documented in the roof of LA. A roof line led to abrupt cycle length prolongation to 270msec with CS propagation distal to proximal. The P-Wave was biphasic negative in II, III, aVF, positive in V1-V2 and isoelectric in I. The decapolar catheter had one large sharp signal per cycle on each bipole Figure 1. An ultrahigh density activation mapping from both LA and RA was performed. In the LA it seemed that the tachycardia was centrifugal propagating from a focal exit in the inferolateral mitral annulus with highly fractionated signals. The entrance of the tachycardia to the RA was at the CS ostium. A focal mechanism of the tachycardia was primarily assumed.