Structural remodeling in chronic atrial fibrillation (AF) occurs over weeks to months. To study the electrophysiological, structural, and functional changes that occur in chronic AF, the selection of the best animal model is critical. AF was induced by rapid atrial pacing (RAP, 50 Hz stimulation every other second) in pigs (n=4), dogs (n=8), and goats (n=9). Animals underwent MRIs at baseline and 6-month to evaluate LV ejection fraction (EF). Dogs were given metoprolol (50-100 mg, PO, BID) and digoxin (0.0625-0.125 mg, PO, BID) to limit the ventricular response rate to <180 beats per minute and to mitigate the effects of heart failure. The pacing leads in pigs became entirely encapsulated and lost the ability to excite the heart, often before the onset of sustained AF. The LV EF in dogs dropped from 54±11% at baseline to 33±7% at 6 months (p<0.05) while the goats LV EF did not drop significantly (69±8% at baseline vs. 60±9% at 6 months, p=NS). After 6 months of AF, fibrosis levels in the dog atria and ventricles increased, while only atrial fibrosis levels increased in the goats as compared to control animals. In our experience, the pig model is not appropriate for chronic RAP-induced AF studies. Rate controlled chronic AF in the dog model developed HF and LV fibrosis, while the goat model developed only atrial fibrosis without ventricular dysfunction and fibrosis. Both the dog and goat models are representative of segments of the patient population with chronic AF.
- Chronic Atrial Fibrillation
- Heart Failure
- Animal Models
- Rapid Atrial Pacing
- Copyright © 2013, American Journal of Physiology - Heart and Circulatory Physiology