Atrial and ventricular electrical and contractile remodeling and reverse remodeling owing to short-term pacing-induced atrial fibrillation in horses

• Published in: Journal of veterinary internal medicine 2008-11, Vol.22 (6), p.1353-1359
• Main Authors: Clercq, D. de, Loon, G. van, Travernier, R, Duchateau, L, Deprez, Piet
• Format: Article
• Language: English
• Subjects: Animals; arrhythmia; Atrial Fibrillation - pathology; Atrial Fibrillation - veterinary; Burst-pacing; Cardiac Pacing, Artificial - adverse effects; Cardiac Pacing, Artificial - veterinary; Echocardiography; heart rate; Horse Diseases; Horses; Myocardial Contraction - physiology; normal values; Pacemaker; Time Factors; Ventricular Remodeling - physiology
• ISSN: 0891-6640; 1939-1676
• DOI: 10.1111/j.1939-1676.2008.0202.x

Background: In humans, atrial fibrillation (AF) induces electrical, contractile, and structural remodeling leading to AF stabilization. Little is known about AF‐induced atrial remodeling in horses. Hypothesis: Induced AF produces rapid atrial electrical and contractile remodeling in horses. Animals: Six horses, 5 animals completed the study. Methods: Each horse was instrumented with a pulse generator and pacemaker to maintain AF by burst pacing and to study atrial and ventricular electrophysiology (AF cycle length [AFCL], AF duration, and atrial/ventricular effective refractory period [AERP/VERP] at different pacing cycle lengths [PCL]). Left atrial and ventricular contractile remodeling were assessed echocardiographically by calculation of fractional changes in atrial and ventricular dimensions, respectively, during the cardiac cycle. Measurements were performed at baseline, a 7‐day AF period and a 2‐day recovery period. Results: Atrial electrical and contractile remodeling could be demonstrated after 4 and 12 hours of AF, respectively. A progressive shortening of the AERP (261 ± 39–171 ± 18 ms at a PCL of 1,000 ms, P < .0001), an attenuation of the AERP rate adaptation, a decrease in AFCL (239 ± 39–194 ± 7 ms, P < .0001), and a decrease in atrial FS (12 ± 3% to 0 ± 2%, P < .05) occurred. AF duration increased progressively and became persistent in 2 animals. VERP did not change significantly. Upon restoration of sinus rhythm, values returned to baseline within 48 hours. Conclusions and Clinical Importance: Atrial electrical and contractile remodeling appears rapidly. After 7 days of AF, reverse remodeling occurred within 2 days. These observations suggest that early conversion of AF might be beneficial for success rate and early return to training.