Background: Wave propagation during early atrial fibrillation (AF) is poorly understood partially due to inadequate mapping techniques. We developed a new optical approach enabling endocardial panoramic mapping of the intact right and left atria (RA, LA).
Objective: To test the hypothesis that AF onset involves formation of short-lived rotors in rapid succession underlying the acceleration in activation frequencies.
Methods: Four sheep hearts were Langendorff-perfused in the presence of 0.25 μM carbachol. Wide-view optical mapping covered the entire endocardial surfaces of both atria. AF was induced with an S1-S2 protocol (300 ms cycle length, CL). Movies were obtained at onset and 30 s later during early stabilization. Phase singularity points (SPs; >1 rot; <10х10 pix meandering) were used to analyze stable rotor dynamics.
Results: AF was induced 14 times (mean 3.5 inductions/sheep). In 11/14, the first wave patterns were breakthroughs (LA: 8/11, RA: 3/11). In the remaining 3/14, first patterns were extremely fast unstable rotors (CL: 70±21 ms) in the RA (2/3) or the pulmonary veins (1/3). In all cases, appearance of series of brief (~1 cycle) rotors followed AF onset in both the RA and LA-pulmonary vein region. Rotors became more stationary as AF stabilized within 1-10 cycles and AF maximal dominant frequency (DFmax) increased from 11.5±1.6 Hz at onset to 16.0±1.2 Hz at early stabilization (p<0.01). Concomitantly, local CL at all rotor appearance sites abbreviated from 85±8 ms at AF onset to 74±6 ms following the first 3 cycles (p=0.02), and then returned to pre-rotor values (p<0.01) after 339±179 ms, while other rotors formed. Increased AF stabilization in time was apparent by the change in number of SPs from 3.14±1.8 SPs/s at onset to 0.16±0.42 SP/s (p<0.05) at early stabilization. The average number of SPs at the shortest CL area (ranged 10-15 % of all SPs) increased from null at induction to 1.9 / heart / 100 ms at t = 3 s and then to 2.5 during early stabilization.
Conclusion: Panoramic optical mapping of cholinergic AF in the sheep heart reveals that AF onset involves a cascade of short-lived rotors forming in rapid succession across the entire RA and LA, with increased rotor life span and transient acceleration as AF stabilizes.