Arrhythmogenic Difference Between the Left and Right Atria During Rapid Atrial Activation in a Canine Model of Atrial Fibrillation

Abstract

t has been documented that atrial electrical remodeling characterized by shortening of the atrial effective refractory period (ERP) and a decrease in the conduction velocity plays a role in promoting atrial fibrillation (AF) by shortening the electrophysiological wavelength of the atrial muscle. [1][2][3][4][5][6][7] However, the progression of atrial remodeling does not seems to be homogeneous 8-11 and we have previously reported that both dispersion of the ERP and AF inducibility were increased during several weeks of rapid atrial pacing in a canine model of AF. 9,12 Interestingly, the ERP shortening was always more prominent in the left atrium (LA) than in the sites in the right atrium (RA), and the AF inducibility was always higher in the LA than in the RA. 9,13 Because it has been revealed that premature atrial activation that originates from the pulmonary veins cause AF in many clinical cases, the LA is considered to play a key role, even in clinical cases, 13,14 which might be explained not only by higher arrhythmogenicity of the LA, but also by the origin of the premature atrial contractions (APC). [15][16][17] In the present study, the arrhythmogenicity of both atria was evaluated by comparing a left and right atrial pacing model to reveal the importance of the location of rapid atrial firing in promoting AF in a canine rapid atrial Methods Subjects and Surgical ProcedureIn 14 adult beagle dogs weighing 12.7±1.3 kg, the cardiac surface was exposed via a right thoracotomy under pentobarbital anesthesia (30 mg/kg, iv) and mechanical ventilation (Model SN-480-5, Shinano Manufacturing, Circ J 2007; 71: 1629 -1635 (Received April 4, 2007 revised manuscript received June 6, 2007; accepted June 14, 2007 Background Continuous rapid atrial stimulation causes atrial remodeling, but little is known about the difference in the arrhythmogenicity of the left (LA) and right atria (RA). Methods and ResultsIn 14 beagle dogs, continuous rapid pacing (400 beats/min) was delivered from the right (n=7) or left (n=7) atrial appendage (RAA or LAA) for 2 weeks. The atrial effective refractory period (ERP), ERP dispersion, and inducibility of atrial fibrillation (AF) were evaluated along the time course from 4 atrial sites: (1) RAA, (2) area close to the inferior vena cava (IVC), (3) Bachmann's bundle (BB) and (4) LA. The ERP exhibited progressive shortening at all sites, but the degree of shortening differed among them. In the RA stimulation group, ERP shortening was more prominent in the RAA and LA than in the IVC or BB. In contrast, in the LA stimulation group, ERP shortening was more prominent in the LA than in the other sites. As a result, ERP dispersion was larger in the LA stimulation group than in the RA stimulation group and the AF inducibility was higher in the LA stimulation group than in the RA stimulation group, especially at the LA site (p<0.05). Conclusion LAA stimulation was more arrhythmogenic than RAA stimulation in this model. This result may partly explain the importance of premature contractions occur...

Inhomogenic Effect of Bepridil on Atrial Electrical Remodeling in a Canine Rapid Atrial Stimulation Model

“…Mechanical ventilation was maintained via an endotracheal tube using a mechanical ventilator (Model SN-480-5, Shinano Manufacturing, Tokyo, Japan) with 100% oxygen. [11][12][13][14][15] Two pairs of stainless steel wire electrodes were sutured against the epicardial surface of the RA free wall within the pectinate muscle area and left atrial appendage. The other ends of the wire electrodes were tunneled subcutaneously and exposed at the back of the neck.…”

“…Atrioventricular block was not produced in this study in order to mimic the hemodynamic situation of clinical cases of AF. [11][12][13][14][15] All studies were performed in accordance with the guidelines specified by the Animal Experimentation and Ethics Committee of the Kitasato University School of Medicine.…”

“…Analog signals were converted to digital signals, stored on a computer hard-disk (Power Lab, ADInstrument, CO, USA) and subsequently subjected to analysis. 11,12,14,15 During these studies, rapid pacing was stopped temporarily, and all measurements were performed after pharmacological block of the autonomic nervous system had been produced by infusing atropine 0.04 mg/kg and propranolol 0.2 mg/kg. 11,14 AERP At each evaluation time point, the AERP was measured at the 2 atrial sites where the electrodes were sutured, with basic drive cycle lengths (BCL) of 300, 200, and 150 ms.…”

“…The longest coupling interval of the premature beat that failed to capture the atrium was determined as the local AERP. 11,12 %CV The conduction time between the RA and LA was measured during the pacing at cycle lengths of 300, 200, and 150 ms. The CV was calculated as the reciprocal of this conduction time, and the values were expressed in percentages as the %CV by dividing each piece of data by the data for day 0 to exclude the influence of the difference in the actual distance of the electrodes in each dog.…”

“…Most recently,(LCC), but they did not document any difference between the right and left atrium (RA and LA). 10 Because we have demonstrated an inhomogeneity of electrical remodeling in the RA and LA, at least in our canine rapid atrial stimulation model without atrioventricular block, 11,12 in the present study we focused on the effect of bepridil on atrial electrical remodeling and the difference between the RA and LA in using a new protocol in which we started administering the drug in the later phase of the pacing protocol.…”