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172/Perimitral flutter: mapping the slow isthmus critical for tachycardia to guide ablation

European Journal of Arrhythmia & Electrophysiology. 2019;5(Suppl. 1):abstr172

Introduction: Peri-mitral flutter (PMF) is common after ablation of atrial fibrillation (AF). Ablation therapy is conventionally aimed at creating a linear lesion, often between the mitral annulus and isolated left lower pulmonary vein, that transects the macroreentrant circuit. Conduction block across linear lesions is hard to achieve, often requiring epicardial ablation. Reconnection and subsequent recurrence is therefore common, and reported at about 30%. Ripple mapping (RM) is known to improve tachycardia diagnosis and termination by identification of the critical isthmus supporting tachycardia. We performed a retrospective comparison of peri-mitral flutter ablation performed by ripple mapping or conventional methods.

Methods: Retrospective identification and analysis of catheter ablation procedures for PMF from seven centres. Mapping was performed on the CARTO3v6 system with the CONFIDENSE module. Cases were analysed for mapping diagnosis, ablation strategy and outcome.

Results:
Demographics: A total of 16 patients were identified. Mean age 64.5 years, 12 male. The mean LVEF was 54.9% and mean LA diameter 4.5 cm. All patients had a history of AF, 14/16 had undergone at least one previous left atrial ablation, 7/16 had undergone > one ablation and 5/16 had a previous mitral line performed. Mapping of the PMF was performed by RM in eight and LAT in eight. No significant differences observed in the demographic details between groups.

Mapping procedure: Stable tachycardia was the starting rhythm in 13/16, in the remainder tachycardia developed after AF ablation. In the RM group 8/8 tachycardias were identified as PMF without use of entrainment, based on the first map acquired. In the LAT group, 4/8 of patients had a diagnosis of PMF based on the first map acquired, whilst the remaining four required entrainment to clarify the diagnosis, of which two required a complete remap. A critical isthmus, defined as a narrow area bordered by non-conducting tissue demonstrating a slowing of conduction, was identified in 8/8 RM patients.

Ablation procedure: The first ablation set terminated tachycardia in 8/8 in the RM group and 2/8 in the LAT group. A linear lesion at the mitral isthmus was performed in 3/8 in the RM group, and in 8/8 in the LAT group. Two out of 8 in the LAT group were still in PMF despite ablation and required cardioversion. The mean RF energy delivered (kWs) in the RM group was 1,474.14 and 2,423.78 in the LAT group.

Critical isthmus sites: An isthmus was identified and targeted for ablation in 8/8 in the RM group. All sites displayed complex electrograms and were bounded, at least on one end, by atrial scar (defined by bipolar voltage). The average isthmus width was 6.76 mm and conduction velocity 33.94 cm/s; normal LA tissue velocity was 67.91 cm/s (p 0.007). Three isthmus sites were on the anterior LA wall, between scar and the mitral annulus. Two were gaps in previous mitral lines and the remainder from inferior margin of PVI lesions to the mitral annulus.

Discussion and Conclusion: Our data confirms that RM improves the diagnostic accuracy, without a requirement for entrainment, of the mapping procedure during PMF compared to LAT. Furthermore, we demonstrate that RM can identify isthmus sites that support PMF. These sites display slow conduction, are narrow and led to tachycardia termination in all cases. As a result, a smaller proportion of RM patients required linear ablation of the mitral isthmus and less energy was delivered during the RM procedures.

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