Electrophysiological characteristics of the human atria after cardioversion of persistent atrial fibrillation

Background-In animal models, induced atrial fibrillation shortens the atria l effective refractory period (ERP) and reverses its physiological adaptati on to rate. It is not clear whether this process, known as "electrical remo deling," occurs in humans. Methods and Results-We determined the ERPs, at 5 pacing cycle lengths (300 to 700 ms) and in 5 right atrial sites, after internal cardioversion of chr onic atrial fibrillation in 25 patients (14 in pharmacological washout and 11 on amiodarone). The ERPs were 195.5+/-18.8 ms in the washout and 206.3+/ -17.9 ms in the amiodarone patients (P<0.0001). ERPs were closely correlate d with the stimulation rates (r=0.95 in the washout and r=0.94 in the amiod arone group), and slope values indicating a normal (greater than or equal t o 0.07) or nearly normal (0.05 to 0.06) adaptation of ERP to rate were foun d in 77% of the 84 paced sites. The mean ERP was shorter in the lateral wal l (198.1+/-17.9 ms) than in the atrial roof (203.3+/-21.5 ms) and in the se ptum (210.5+/-20.0 ms) (P<0.03). After 4 weeks of sinus rhythm, the mean ER P, determined again in 8 patients (4 in wash-out and 4 on amiodarone), was significantly increased compared with the basal study (221.4+/-21.4 versus 197.8+/-18.3 ms, P<0.0001), Conclusions-After cardioversion of chronic atrial fibrillation, (1) atrial ERP adaptation to rate was normal or nearly normal in the majority of the c ases, (2) a significant dispersion of refractoriness between different righ t atrial sites was present, and (3) ERPs were significantly increased after 4 weeks of sinus rhythm in both washout and amiodarone patients.