Atrial and ventricular electrical and contractile remodelling and reverse remodelling due to chronic pacing-induced atrial fibrillation in horses: preliminary results

Abstract

In humans, electrical and contractile reverse remodelling following restoration of sinus rhythm (SR) after a prolonged period of spontaneous atrial fibrillation (AF), requires several weeks. There is little known about this phenomenon in horses. In the present study, six healthy horses were instrumented with a neurostimulator and a pacemaker to maintain AF for four months by intermittent burst pacing and to study atrial and ventricular electrophysiology. AF became persistent in all horses after two to six weeks of burst pacing. Before, during and after the AF period, parameters, such as the atrial fibrillation cycle length, the right atrial and ventricular refractory period and vulnerability, such as inducing atrial arrythmias, atrial tachyarrythmias or maintaining AF, were determined. Two-dimensional echocardiography was used to measure atrial and ventricular contractility expressed as fractional shortening and size expressed as diameter and area. In two of the six horses, the procedure was discontinued due to an increased threshold (1 horse) and due to infection at the level of the pacemaker pocket (1 horse). In the four remaining horses, significant electrical and contractile remodelling compared to baseline values was observed from 48 hours onwards after AF induction. Upon restoration of SR with quindine sulfate, all electrical and contractile values returned to normal within one to two months. No ventricular remodelling was observed. Four months of pacing-induced AF resulted in electrical and contractile remodelling and reverse remodelling. The results suggest that pacing-induced chronic AF does not cause permanent damage and suggest that a resting period of six to eight weeks before returning to training might be beneficial.