Left-to-right gradient of atrial frequencies during acute atrial fibrillation in the isolated sheep heart

Background-Recent studies demonstrated spatiotemporal organization in atria l fibrillation (AF). We hypothesized that waves emanating from sources in t he left atrium (LA) undergo fragmentation, resulting in left-to-right frequ ency 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 perf using D600 (2 mu mol/L) and by increasing ACh concentration from 0.2 to 0.5 mu mol/L. BB and IPP were subsequently ablated, At baseline, a left-to-rig ht decrease in DFs occurred along BS and IPP, resulting in an LA-right atri um (RA) frequency gradient of 5.7+/-1.4 Hz. Left-to-right impulse propagati on was present in 81+/-5% and 80+/-10% of cases along BB and IPP, respectiv ely, 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 i ncrease 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 fr om 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 chang es in the LA-RA frequency gradient during AF strongly support the hypothesi s that this arrhythmia is the result of high-frequency periodic sources in the LA, with fibrillatory conduction away from such sources.