PACING-INDUCED CHRONIC ATRIAL-FIBRILLATION IMPAIRS SINUS NODE FUNCTION IN DOGS - ELECTROPHYSIOLOGICAL REMODELING

Background We assessed the effects of pacing-induced chronic atrial fi brillation (AF) on sinus node function, intra-atrial conduction, and a trial refractoriness. Methods and Results In 15 mongrel dogs (20 to 30 kg), AV nodal block was produced by radiofrequency catheter ablation, and a ventricular-inhibited (VVI) pacemaker (Minix 8330, Medtronic) w as implanted and programmed to pace at 80 pulses per minute. In 11 of these dogs, right atrial endocardial pacing leads were connected to a pulse generator (Itrel 7432, Medtronic) and set at a rate of 20 Hz to induce AF. Corrected sinus node recovery time, P-wave duration, 24-hou r Holter ECG to assess AF duration, maximal heart rate in response to isoproterenol (10 mu g/min), intrinsic heart rate after administration of atropine (0.04 mg/kg) and propranolol (0.1 mg/kg), and atrial effe ctive refractory periods (ERPs) were obtained at baseline (EPS-1) and after 2 to 6 weeks (EPS-2) of VVI pacing alone (n=4) or VVI pacing and rapid atrial pacing (n=11). At EPS-2, corrected sinus node recovery t ime and P-wave duration were prolonged, maximal heart rate and intrins ic heart rate were decreased, atrial ERPSs were shortened, and the dur ation of AF was increased significantly compared with EPS-1. These cha nges partially reversed toward baseline 1 week after conversion to sin us rhythm. Sinus node function and AF inducibility observed in the con trol dogs that underwent ventricular pacing alone (n=4) did not change . Conclusions Pacing-induced chronic AF induces sinus node dysfunction , prolongs intra-atrial conduction time, shortens atrial refractorines s, and perpetuates AF, changes that reverse gradually after terminatio n of AF.