Mapping and ablating stable sources for atrial fibrillation: summary of the literature on Focal Impulse and Rotor Modulation (FIRM)
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Atrial fibrillation (AF) is the most common sustained arrhythmia and the most common indication for catheter ablation. However, despite substantial technical advances in mapping and energy delivery, ablation outcomes remain suboptimal. A major limitation to AF ablation is that the areas targeted for ablation are rarely of proven mechanistic importance, in sharp contrast to other arrhythmias in which ablation targets demonstrated mechanisms in each patient. Focal impulse and rotor modulation (FIRM) is a new approach to demonstrate the mechanisms that sustain AF (“substrates”) in each patient that can be used to guide ablation then confirm elimination of each mechanism. FIRM mapping reveals that AF is sustained by 2–3 rotors and focal sources, with a greater number in patients with persistent than paroxysmal AF, lying within spatially reproducible 2.2 ± 1.4-cm2 areas in diverse locations. This temporospatial reproducibility, now confirmed by several groups using various methods, changes the concepts regarding AF-sustaining mechanisms, enabling localized rather than widespread ablation. Mechanistically, the role of rotors and focal sources in sustaining AF has been demonstrated by the acute and chronic success of source (FIRM) ablation alone. Clinically, adding FIRM to conventional ablation substantially improves arrhythmia freedom compared with conventional ablation alone, and ongoing randomized trials are comparing FIRM—ablation with and without conventional ablation to conventional ablation alone. In conclusion, ablation of patient-specific AF-sustaining mechanisms (substrates), as exemplified by FIRM, may be central to substantially improving AF ablation outcomes.
KeywordsAtrial fibrillation Rotors Ablation Focal sources Substrates Phase mapping
This work was supported by grants to S.M. Narayan from the NIH (HL83359 and HL103800).
Conflict of interest
Dr. Narayan is a coauthor of intellectual property owned by the University of California Regents and licensed to Topera Inc. Topera does not sponsor any research, including that presented here. Dr. Narayan holds equity in Topera and reports having received honoraria from Medtronic, St. Jude Medical, and Biotronik. The other authors report no conflicts.
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