Equine cardiac arrhythmias during the immediate post-transvenous electrical cardioversion period

Introduction: R wave synchronisation of transvenous electrical cardioversion (TVEC) is important to avoid fatal arrhythmia. However, arrhythmias immediately after the shock have yet to be described. Methods: Records of 50 horses with a first episode of atrial fibrillation (AF) treated with TVEC procedure were reviewed. First 10 minutes of the ECG after successful cardioversion were analysed. Results: Mean age was 9.5 years, there were 34 geldings, 4 stallions and 12 mares including various breeds (Warmblood, Standardbred, Thoroughbred). Median estimated AF duration (n=30) was 60 days (range 6-730). Mild or moderate mitral (n=22), aortic (n=7), tricuspid (n=21) or pulmonary (n=4) valve regurgitation were present. Arrhythmias between the shock and return of sinus rhythm (SR) were observed in 29 horses (58%) and included atrial premature depolarisations (APDs) (n=3), ventricular premature depolarisations (VPDs) (n=19), narrow complex supraventricular (junctional) depolarisations (n=9) (Fig.1), atrial tachycardia (n=1) and impaired atrioventricular (AV) conduction (n=17) requiring ventricular pacing in 3 horses. Arrhythmias after return of SR were observed in 42 horses (84%) and included APDs (n=12), VPDs (n=13), AF (n=1), 1st and 2nd degree AV block (n=32) and sinus block (n=2). Progressive changes in P wave morphology were observed in 2 horses. No significant correlation was found between the presence of arrhythmias or specifically APDs and recurrence of AF within one year. The number of shocks or energy levels used had no influence on the occurrence of arrhythmias post cardioversion. Discussion: Different arrhythmias occurred in the immediate post-TVEC period. Ventricular premature beats were seen but not malignant or fatal. No relation could be established between the presence of arrhythmias in the immediate post-TVEC period and recurrence of AF. Placement of a pacing catheter in the right ventricular apex seems justified as a precaution in cases of temporary asystole