1Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran
2Department of Clinical Sciences, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian UK, EH25 9RG, England
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.