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Figure 6 The hypothesized fibrillatory process during vagal excitation and the effect of pulmonary vein (PV) isolation on this process. (A) During vagal excitation, PVs act as driving sources. Acceleration of cycle length in the PVs causes acceleration of cycle length in the coronary sinus (CSCL), thus favoring maintenance of atrial fibrillation. (B) After PV isolation, acceleration of atrial cycle length may be attenuated by elimination of driving sources.