Atrial and Ventricular Electrical and Contractile Remodeling and Reverse Remodeling Owing to Short‐Term Pacing‐Induced Atrial Fibrillation in Horses

Abstract

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 AE 39-171 AE 18 ms at a PCL of 1,000 ms, P o .0001), an attenuation of the AERP rate adaptation, a decrease in AFCL (239 AE 39-194 AE 7 ms, P o .0001), and a decrease in atrial FS (12 AE 3% to 0 AE 2%, P o .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.

Antiarrhythmic and Electrophysiologic Effects of Flecainide on Acutely Induced Atrial Fibrillation in Healthy Horses

“…The present study however did not identify any potentially dangerous ventricular arrhythmias, which is in agreement with other studies 1, 3. However, 3 cases of flecainide‐induced wide QRS‐tachycardia have been reported in horses2, 4 of which 1 episode led to ventricular fibrillation and sudden cardiac death. Combined with the altered ventricular repolarization observed in the present study, it is important to recognize the potential proarrhythmic properties of flecainide.…”

“…When these criteria are fulfilled, treatment with flecainide demonstrates cardioversion rates of 57–92% in human patients with AF of short duration 32. Flecainide terminated all AF episodes in the present study with a termination time comparable to that observed in previous studies,1, 27 and at the evaluated stimulation rates, the presented baseline values of aERP in horses were consistent with those reported by others 4, 33. Our study identified no flecainide‐induced changes in aERP, indicating that flecainide did not have an influence on atrial repolarization at the chosen stimulation rates.…”

“…Another study used flecainide to cardiovert persistent burst pacing‐induced AF of 7 days′ duration. Only 1 of 2 horses regained SR 4. Such observations support the theory of AF duration being an extremely important parameter when estimating the potential efficacy of flecainide, and that treatment with antiarrhythmic drugs always carries a risk of inducing devastating ventricular arrhythmias.…”

Pharmacokinetics and electrophysiological effects of sotalol hydrochloride in horses

“…AF induces electrical remodelling leading to AF stabilisation, both in human subjects and in horses [13,31]. However, if sotalol is to be used to suppress arrhythmias or to prevent AF recurrence, its effects might be different compared with healthy animals.…”

Echocardiographic Assessment of Left Atrial Size and Function in Warmblood Horses: Reference Intervals, Allometric Scaling, and Agreement of Different Echocardiographic Variables

“…Echocardiographic indices of LA mechanical function have previously been described in horses . They are sufficiently reliable for routine clinical use, allow documenting LA mechanical dysfunction after conversion of atrial fibrillation to sinus rhythm and could have prognostic implications in horses recovering from atrial fibrillation . However, the use of these indices in horses with MR and AR has not been described.…”