Figure 1.

Amplitude modulation (AM)/frequency modulation (FM) concept and study design. A, AM and FM in radio broadcasting. B, Left, during cardiac fibrillation, scroll wave/rotor drifting gives rise to AM and FM. When a drifting scroll wave filament/rotor core approaches the square, the amplitude of the action potential decreases increasing instantaneous AM (iAM; in red). Simultaneously, as the wave-emitting source (scroll wave filament/rotor core) approaches, the perceived instantaneous FM (iFM; (Continued )Figure 1 Continued. in blue) at the spot increases (Doppler Effect). Therefore, simultaneous iAM/iFM increase indicates drifting scroll waves/rotors in the surroundings. Additionally, the areas with the highest average iFM are those potentially driving fibrillation. Right, average iFM is estimated from its median and mean values (8 Hz both) and with the conventional dominant frequency (DF) spectral approach (5.6 Hz). Interestingly, the time intervals with the highest iFM usually show the lowest amplitudes and vice versa, which conditions the height of their corresponding power spectral peaks and limits the value of DF-based hierarchical approaches. C, Translational approach for the study. D, Porcine experimental model of persistent atrial fibrillation (PersAF). AF indicates atrial fibrillation; HRAP, high-rate atrial pacing; and PVI, pulmonary vein isolation.