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


OBJECTIVE
Induced AF produces rapid atrial electrical and contractile remodeling in horses.


METHODS
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
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.
De Clercq
D
D
Department of Large Animal Internal Medicine, Ghent University, Belgium. Dominique.DeClercq@Ugent.be
van Loon
G
G
Tavernier
R
R
Duchateau
L
L
Deprez
Piet
P
D000818:Animals; D001281:Atrial Fibrillation / Q000473:pathology / Q000662:veterinary*; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects / Q000662:veterinary*; D006734:Horse Diseases; D006736:Horses; D009200:Myocardial Contraction / Q000502:physiology*; D013997:Time Factors; D020257:Ventricular Remodeling / Q000502:physiology*