A cavotricuspid isthmus-dependent flutter with an unexpected left atrial activation sequence: A case report

Objective:The isthmus-dependent right atrial flutter is a known arrhythmia, but few studies described the sequence activation of the left atrium.It is well established that the interatrial connection occurs through different pathways: the coronary sinus (CS), the Bachmann's bundle and the fossa ovalis.We describe a case of a cavotricuspid isthmusdependent right atrial flutter with an unexpected left atrial activation sequence.Case presentation: A 47-year-old female with scleroderma and a history of isolated right ventricular cardiomyopathy had recurrent atrial flutter episodes despite medical therapy.The patient was still symptomatic despite full medical therapy.She presented to the electrophysiology laboratory for mapping and ablation of atrial flutter with 2:1 and 3:1 conduction.A decapolar deflectable CS catheter placed in the coronary sinus showed a distal to proximal CS activation with a flutter cycle length of 240 msec.Then, the cavotricuspid isthmus (CTI) demonstrated a concealed entrainment with a post-pacing interval almost equal to the total cycle length confirming the diagnosis of an isthmus-dependent flutter.The CS activation in sinus rhythm also showed a distal to proximal activation.This confirmed that the CS and the left atrium are being activated most probably through the Bachman bundle anteriorly and superiorly.CTI line was performed under intracardiac echo guidance.Clinical improvement was noticed.A distal to proximal CS activation does not exclude a right atrial arrhythmia.Conclusion: A systemic entrainment mapping of both the right and left atrium is crucial to prevent unneeded transseptal puncture.