Discordant temporal changes in electrophysiological properties during electrical remodeling and its recovery in the canine atrium

Prolonged rapid atrial excitation gives rise to atrial electrical remodeling, which perpetuates atrial fibrillation (AF). However, there has been controversy regarding the nature of temporal changes in conduction characteristics during the development and recovery of electrical remodeling. This study was designed to clarify the nature of the development and recovery of electrical remodeling in relation to AF inducibility in dogs subjected to rapid atrial pacing. Eleven dogs underwent rapid atrial pacing (400/min) for 28 days. The electrophysiological study was performed on the day just prior to the commencement of pacing, on days 2, 7, 14, and 28 of rapid pacing, as well as 1 and 7 days after the cessation of pacing. In response to rapid atrial pacing, atrial effective refractory period (ERP), conduction velocity and wavelength decreased significantly (p<0.05). ERP had shortened significantly and rapidly within 2 days of pacing, while conduction velocity decreased more gradually. During the recovery, ERP returned to almost baseline levels within a day, whereas conduction velocity returned to baseline by day 7. Sustained AF became inducible in 37% of the dogs from 7 days of pacing until 1 day after the cessation, when wavelength fell below 8.7 cm. In conclusion, rapid atrial excitation causes a progressive but discordant temporal pattern of a decrease in ERP and conduction velocity. The resultant shortening of the wavelength determines the inducibility and maintenance of AF. The electrophysiological changes produced by one month of rapid atrial pacing can be fully reversed within a week, although in a discordant temporal pattern.