Pilot Study: Heart Rate and Heart Rate Variability Indices in Mules Evaluated by 24-Hour Electrocardiogram

Area of Science:

• Veterinary Cardiology
• Equine Physiology

Background:

• Mules represent a significant equine population in the U.S.
• Limited data exists on mule heart rate and arrhythmia prevalence.
• Heart rate variability (HRV) analysis offers insights into autonomic function differences.

Purpose of the Study:

• To pilot the evaluation of heart rate and variability in healthy mules.
• To establish baseline electrocardiographic data for mules.
• To compare mule cardiac parameters with horses and donkeys.

Main Methods:

• Collected 24-hour ambulatory electrocardiogram (aECG) recordings from seven athletic mules.
• Utilized Vision 5 Holter Analysis Software for ECG review.
• Analyzed heart rate, heart rate variability, and arrhythmia prevalence.

Main Results:

• Mean heart rate was 36 ± 3 bpm over approximately 24 hours.
• Observed minimum heart rate of 16-24 bpm and maximum of 70-156 bpm.
• Detected supraventricular complexes, sinoatrial heart block, and second-degree atrioventricular block.

Conclusions:

• Mule heart rate is similar to horses and lower than donkeys.
• Arrhythmia prevalence in mules aligns with horses and exceeds donkeys.
• Further research with larger sample sizes is needed to establish reference values and assess clinical relevance of arrhythmias.