Relationship of heart rate and electrocardiographic time intervals to body mass in horses and ponies.

The research investigates how heart rate and electrocardiogram (ECG) time intervals in horses and ponies relate to their body weight, revealing that smaller breeds typically exhibit quicker heart rates and shorter ECG intervals compared to their larger counterparts.

Methodology

• The study examined 250 healthy horses of over 30 different breeds, ranging in age from 1 to 30 years and weighing between 46 and 1018 kg.
• The research employed a prospective method, with ECGs recorded when the horses were calmly standing in a box stall.
• The researchers calculated the mean heart rate over a 15-second period, and from the ECG recordings measured the RR interval, PQ interval, QRS duration, and QT interval.
• Fridericia’s formula was used to correct the QT for differences in heart rate.
• The relationship between ECG variables and body weight, age, sex, and RR interval was assessed using multivariate backward stepwise regression analyses.
• The research found that using the logarithm of body weight (log(BWT)) provided a better fit for the model compared to unadjusted body weight.
• Given its strength as a predictor, log(BWT) was included in the model as an independent variable.

Findings

• Heart rate showed a significant negative relationship with log(BWT), meaning as the weight of the horse increases, the heart rate decreases.
• PQ interval, QRS duration, QT interval, and corrected QT (QTcf) all showed significant positive relationships with log(BWT), meaning as the weight of the horse increases, these ECG time intervals increase.
• Hence, it can be deduced that smaller equine breeds tend to have slightly faster heart rates and shorter ECG time intervals compared to larger equine breeds.

Conclusions

• Even though the absolute differences may be small, body weight needs to be considered along with other factors when comparing heart rate and ECG time intervals to normal ranges in horses.
• This research emphasizes the importance of taking into account the body weight of the horse when interpreting ECG results, helping in better diagnosis and monitoring of equine cardiac health.