Spontaneous left-sided atypical flutter: revising the mechanisms in patients not submitted to prior linear ablation

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. INTRODUCTION: The decrease in the use of linear ablation for atrial fibrillation treatment has reduced the frequency of iatrogenic feft-sided atypical flutters (AFl). However, AFl are becoming increasingly frequent, associated with population age and risk factors for atrial scar. Revising the mechanisms of non-iatrogenic AFl may lead to a better procedure workflow. PURPOSE: To describe the mechanisms of non-iatrogenic AFl. METHODS: Retrospective single-center study of AFl patients (pts) submitted high-density mapping from 2018 to 2022. Patients submitted to any prior left atrial linear ablation were excluded. Map collection was performed just visualizing the voltage map and a comprehensive workflow was applied for activation map interpretation, starting by facing the mitral annulus and following the sequence of colors to systematically identify all potential circuits, their common-isthmuses, and eventual slow-conduction sites. Entrainment maneuvers were performed to confirm the circuit interpretation if sinus rhythm was not restored with the completion of the planned ablation set. RESULTS: A total of 59 pts were included (male: 56% male; 67 ± 13 years), 28 previously submitted to atrial fibrillation ablation, restricted to pulmonary vein (PV) isolation. About 88% presented a macro-reentrant mechanism, either restricted to the left atrium (N=50) or biatrial (N=2) and involving 2 or 3 loops in 61% - Figure 1. Perimitral loop was the most frequent reentrant circuit, representing 60% of macro-reentrant arrhythmias (N=30) and exhibiting an evident out-of-proportion predominance of counterclockwise rotations (73% versus 27%). Among perimitral flutters with at least one additional loop, a balanced distribution was recognized of rotations around the left and right PVs (10 versus 10). As a result of the existence of additional loops producing common-isthmuses locations in various atrial regions, the classical inferior mitral isthmus line (from the mitral annulus to the left inferior PV) would only terminate as much as 53% of the perimitral AFl. The mechanism-tailored ablation strategy, particularly targeting the AFl common-isthmuses, resulted in restoration of sinus rhythm in 96.6% of pts (N=57). CONCLUSIONS: In pts not previously submitted to linear ablations, AFl are predominantly caused by macro-reentrant circuits involving a perimitral rotation but not necessarily possible to treat with a conventional mitral isthmus line. With current high-density mapping tools, a comprehensive analysis of the substrate and activation maps and a mechanism-tailored ablation strategy results in an unprecedently high acute success rate. [Figure: see text] [Figure: see text]