Key result
Pacing-induced chronic atrial fibrillation in dogs induces sinus node dysfunction, prolongs intra-atrial conduction time, shortens atrial refractoriness, and perpetuates AF.
Why the study?
Does pacing-induced chronic AF impair sinus node function, intra-atrial conduction, and atrial refractoriness in dogs?
Does pacing-induced chronic AF impair sinus node function, intra-atrial conduction, and atrial refractoriness in dogs?
Pacing-induced chronic AF in dogs causes reversible sinus node dysfunction and electrical remodeling that perpetuates AF.
Should not change clinical AF practice; hypothesis-generating for reversible remodeling, requiring human validation.
BACKGROUND: We assessed the effects of pacing-induced chronic atrial fibrillation (AF) on sinus node function, intra-atrial conduction, and atrial 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) was 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-hour Holter ECG to assess AF duration, maximal heart rate in response to isoproterenol (10 micrograms/min), intrinsic heart rate after administration of atropine (0.04 mg/kg) and propranolol (0.1 mg/kg), and atrial effective 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 time and P-wave duration were prolonged, maximal heart rate and intrinsic heart rate were decreased, atrial ERPs were shortened, and the duration of AF was increased significantly compared with EPS-1. These changes partially reversed toward baseline 1 week after conversion to sinus rhythm. Sinus node function and AF inducibility observed in the control 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 refractoriness, and perpetuates AF, changes that reverse gradually after termination of AF.
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Elvan et al. (1996) studied Atrial fibrillation (n=15). Rapid atrial pacing to induce AF + VVI pacing vs. VVI pacing alone was evaluated on Sinus node function, intra-atrial conduction, and atrial refractoriness. Pacing-induced chronic atrial fibrillation in dogs induces sinus node dysfunction, prolongs intra-atrial conduction time, shortens atrial refractoriness, and perpetuates AF.
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