Focal Impulse And Rotor Mapping (FIRM): Conceptualizing And Treating Atrial Fibrillation

Abstract

Current approaches for the ablation of atrial fibrillation are often effective, but only partially rooted in mechanistic understanding. Accordingly, they are unable to predict whether a given patient will or will not do well, or which lesions sets should or should not be performed - in any given patient. This goal would require clearer mechanistic definition of what sustains AF after it has been triggered (i.e. electrophysiological substrates). There are two schools of thought. The first proposes disorganized activity that self-sustains with no 'driver', and the second describes drivers that then cause disorganization. Interestingly, these mechanisms can be separated in human studies by mapping approach - proponents of the disorganized hypothesis studying small atrial areas at high resolution, and proponents of the driver model studying wide fields-of-view at varying resolutions. Focal impulse and rotor modulation (FIRM) mapping combines a wide field of view with physiologically based signal filtering and phase analysis, and has revealed that human AF is often sustained by rotors. In the CONFIRM Trial, targeting stable AF rotors/sources for ablation improved the single-procedure efficacy for paroxysmal and persistent AF over conventional ablation alone, as now confirmed by independent laboratories. FIRM mapping gives a mechanistic foundation to predict whether any selected lesions should intersect AF sources in any given patient and which mechanisms may cause recurrence. Rotors of varying characteristics have now been shown by many groups. These insights have reinvigorated interest in AF mapping, and rationalizing these findings will likely translate into improved therapy for our patients.

Figure 1.. Proposed mechanisms in AF. A) spiral wave re-entry with peripheral fibrillatory conduction. B) focal discharges from the pulmonary veins. C) multiple wavelets. Adapted from.[12,52]

Figure 2.. Phase mapping from an isolated sheep heart. A) Optical action potentials recorded using voltage sensitive dyes. B) Phase plots of F(t-2) vs. F(t), where time, t, is the frame number and 2 is the number of lagging frames. The colorbar represents the variation in phase. Two-dimensional phase map of a clockwise rotor during AF. From.[53]

Figure 3.. Stages in FIRM mapping. Right atrium basket is opened vertically on tricuspid valve and left atrium is opened horizontally along mitral valve. A) Rotor in left atrium visualized with isochrones. B) Clockwise rotation and precession of rotor over a small locus. C) Phase plot of same rotor showing convergence of phase at rotor core. D) Snapshot from FIRM movie depicting phase and direction of rotor in red. From.[36]

Figure 4.. Location of focal sources and rotors in patients enrolled in the CONFIRM trial in A) paroxysmal and B) persistent AF. From.[41]

Figure 5.. Cumulative freedom in CONFIRM from atrial fibrillation, in all cases and in those at first ablation for (A) the entire population and (B) the population off anti-arrhythmic medications. From.[43]

Figure 6.. Very long term results from CONFIRM trial. From.[42]

Figure 7.. Rotor precession (white) in right (A) and left (B) atrium does not overlap with CFAE areas on NavX map. From.[8]