Effects of age on the prevalence of cardiac dysrhythmias in ponies

This study describes the prevalence of cardiac dysrhythmias occurring over a single 24 h period in ponies and compares the heart rate and frequency of dysrhythmias in two groups of ponies of different ages. Electrocardiograms were recorded using a Holter monitoring system from twenty four ponies aged less than 15-year-old (n = 14) and greater than 15-year-old (n = 10). Subsequent analyses of cardiac rhythm revealed that only 3/24 ponies maintained a regular rhythm throughout the recording period. In the remaining 21 ponies, 6 different types of dysrhythmias were detected, the majority of which were vagally mediated; sinus arrhythmia (n = 12), sinoatrial block (n = 6) and second degree atrioventricular block (n = 10). Premature beats of both atrial (n = 3) and ventricular (n = 1) origin were observed only in the older group. There were no significant differences between the 2 groups with respect to mean 24-h heart rates or the prevalence of cardiac dysrhythmias.