Left-to-Right Gradient of Atrial Frequencies During Acute Atrial Fibrillation in the Isolated Sheep Heart

Abstract

Background —Recent studies demonstrated spatiotemporal organization in atrial fibrillation (AF). We hypothesized that waves emanating from sources in the left atrium (LA) undergo fragmentation, resulting in left-to-right frequency gradient. Our objective was to characterize impulse propagation across Bachmann’s bundle (BB) and the inferoposterior pathway (IPP) during AF. Methods and Results —In 13 Langendorff-perfused sheep hearts, AF was induced in the presence of acetylcholine (ACh). Fast Fourier transform of optical and bipolar electrode recordings was performed. Frequency-dependent changes in the left-to-right dominant frequency (DF) gradient were studied by perfusing D600 (2 μmol/L) and by increasing ACh concentration from 0.2 to 0.5 μmol/L. BB and IPP were subsequently ablated. At baseline, a left-to-right decrease in DFs occurred along BB and IPP, resulting in an LA–right atrium (RA) frequency gradient of 5.7±1.4 Hz. Left-to-right impulse propagation was present in 81±5% and 80±10% of cases along BB and IPP, respectively. D600 decreased the highest LA frequency from 19.7±4.4 to 16.2±3.9 Hz ( P <0.01) and raised RA DF from 8.6±2.0 to 10.7±1.8 Hz ( P <0.05). An increase in ACh concentration increased the LA-RA frequency gradient from 4.9±1.8 to 8.9±1.8 Hz ( P <0.05). Ablation of BB and IPP decreased RA DF from 10.9±1.2 to 9.0±1.5 Hz ( P <0.01) without affecting LA DF (16.8±1.5 versus 16.9±1.8 Hz, P =NS). Conclusions —Left-to-right impulse propagation and frequency-dependent changes in the LA-RA frequency gradient during AF strongly support the hypothesis that this arrhythmia is the result of high-frequency periodic sources in the LA, with fibrillatory conduction away from such sources.