Cardiac Arrhythmias in Standardbreds During and After Racing—Possible Association Between Heart Size, Valvular Regurgitations, and Arrhythmias

Abstract

Cardiac arrhythmias during racing and in recovery period are limited in description, as is the relationship between left ventricular size, valvular regurgitations, and arrhythmias. Therefore, the aim of this study was (i) to study development of supraventricular and ventricular premature complexes (SVPCs and VPCs) during and after racing in trotters; (ii) to assess the associations between myocardial hypertrophy, valvular regurgitations, and arrhythmias during and after racing; and (iii) to estimate correlation between cardiac arrhythmias and the myocardial biomarker (cardiac troponin I [cTnI]). Clinically normal trotters (N = 26) were examined using echocardiography and electrocardiography. Left ventricular muscle mass relative to bodyweight (g/kg) was calculated, and valvular regurgitations were registered. ECG recordings were obtained at rest, during racing, and in recovery period. Blood samples were taken on three occasions: at rest, once just after racing (15-60 minutes), and once between 12 and 14 hours after racing. During racing, 50.0% of horses had one or more SVPCs, whereas 3.9% had one or more VPCs. Within the recovery period, 46.2% of horses showed one or more SVPCs, whereas 19.2% had VPCs. There was no significant association between occurrence of arrhythmias and heart size or presence of valvular regurgitations. All horses had plasma cTnI concentrations of <0.022 μg/L. In conclusion, a high number of horses showed SVPCs during racing and in the recovery period. Also, a moderate number of horses developed VPCs after racing. The high number of arrhythmias was not related to heart size or increased cTnI and is probably physiologically normal in origin.