13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

RT-49

Predictors of atrial fibrillation during rapid atrial pacing in dogs

Andreas Goette, J. Christoph Geller, Joerg Mittag, Wolfgang M. Hartung, Jonathan J. Langberg*, Helmut U. Klein.
University Hospital Magdeburg, Department of Internal Medicine, Division of Cardiology, Magdeburg, Germany, *Emory University Hospital, Division of Cardiology, Atlanta, USA

Abstract

Rapid atrial pacing is used to induce atrial fibrillation in animal models. An important phenomenon in the genesis of chronic atrial fibrillation is a decrease of the atrial effective refractory period (ERP) during rapid pacing. The decrease of the ERP may shorten the wavelength of the wavelets during atrial fibrillation so that the arrhythmia is more likely to persist. The induced electrophysiological changes have been called "electrical remodeling" of the atria. Electrical remodeling can be observed even after short runs of atrial fibrillation. The influence of short term electrical remodeling on induced atrial fibrillation has not been characterized so far.

Methods. Nine closed-chest dogs (25 ± 1 kg) were studied during continuous autonomic blockade with IV atropine (bolus: 0.04 mg/kg followed by 0.007 mg/kg/hr) and propranolol (bolus: 0.2 mg/kg followed by 0.04 mg/kg/hr). The right atrial appendage was paced for 7 hours at a rate of 800 bpm (4 mA, 2 ms). The atrial ERP was determined in the right atrial appendage every hour at a basic cycle length of 350 ms. Bipolar intracardiac electrograms were also continuously recorded throughout the experiment at the lateral wall of the right atrium.

Results. Electrical remodeling was observed in all animals during the pacing period despite complete autonomic blockade. The ERP decreased from 158 ± 20 ms at baseline to 138 ± 31 ms after 7 hours of rapid pacing (p < 0.05). 7/9 animals developed 21 episodes of atrial fibrillation during the experiment. The mean duration of atrial fibrillation was 29 ± 19 sec. The mean cycle length of induced atrial fibrillation decreased from 136 ± 25 ms to 120 ± 6 ms (p = ns). The decrement of the ERP showed a significant correlation to the cycle length of atrial fibrillation (r = 0.8; p < 0.05). There was a significant correlation between ERP and duration of induced atrial fibrillation (r = 0.77; p < 0.05). The mean atrial rate during rapid pacing did not correlate with the duration and cycle length of induced atrial fibrillation, respectively.

Conclusions. Brief episodes of induced atrial fibrillation cause a decrease of the atrial ERP which seems to correspond to changes of the local fibrillatory cycle length. The relation of the observed changes is less pronounced compared to chronic models of atrial fibrillation.

Key Words

Atrial fibrillation
atrial pacing, effective refractory period, electrical remodelling, prediction of arrhythmias, OA