Inhomogeneity in the appearance of electrical remodeling during chronic rapid atrial pacing - Evaluation of the dispersion of atrial effective refractoriness

In the present study, the long-term process of progression of electrical re modeling at various atrial sites, which is not well understood, was compare d while monitoring continuously the electrophysiologic parameters at multi- recording sites in canine atria during continuous atrial burst pacing. A ra pid pacing device was implanted in 5 dogs, and continuous atrial burst paci ng (400beats/min) was delivered at the right atrial appendage (RAA). Four p airs of epicardial wire electrodes were sutured on (1) the RAA, (2) Bachman n's bundle (BB), (3) the right atrium close to the inferior vena cava (IVC) , and (4) the left atrium (LA). The distal ends of those wires were exterio rized posteriorly and used fur pacing and recording. The atrial effective r efractory period (AERP), AERP dispersion (AERPd), atrial conduction time (C T) and inducibility of atrial fibrillation (AF) were evaluated during burst pacing for 14 days and during the subsequent 7 days' recovery. The AERP at the LA pacing site was shorter than that at the other sites on day 0. The AERP shortening was greater in the RAA and LA sites than in the BE and IVC sites. The AERPd increased during pacing and reached the maximum level on d ay 3, and then decreased during the recovery phase. Prolongation of CT tend ed to be longer between the RAAand IVC sites than that between the other si tes. The incidence of AF induction became higher in accordance with the tim e course of the rapid pacing phase. There was another peal: of AF induction on days 7-10. In a canine chronic rapid atrial stimulation model, the prog ression of electrical remodeling tie, the shortening of the AERP and the pr olongation of the CT) was not homogeneous in both atria, the AERPd showed a temporal increase between days 3 and 7 and matched the increase in AF indu cibility at the LA pacing site, the increase in the AERPd was mainly caused by more rapid AERP shortening at the RAA or LA sites, and the LA site alwa ys showed a shorter AERP than the other atrial sites in the control state a nd during the rapid pacing phase, whereas AF inducibility was higher at the LA site than the other sites.