Relationships between heart score, heart weight and body weight in Greyhound dogs.

The aim of this study was to determine the relationships between heart score (mean QRS interval), heart weight and body weight in Greyhound dogs. Highly significant correlations between these measurements have been observed and distinct sex differences have been demonstrated. The results of multiple regression analysis indicated that 66% of the variation in heart weight was due to variation in heart score and body weight. From the regression analysis, a formula for heart weight prediction with a standard deviation of 27.1 g was derived. The implications of these findings have been discussed briefly and emphasis has been placed on the need for good electrocardiographic technique, if the procedures outlined are to be used successfully. The positive correlation between heart score and heart size demonstrated here in Greyhounds is in accord with similar correlations reported previously in racehorses and human athletes.

Cardiac monitoring during exercise tests in the horse. 3. Changes in the electrocardiogram during and after exercise.

Changes that occur in the equine ECG during and after exercise have been described and compared with resting ECG's obtained from the same horses. When the speed of work equals or is greater than "three-quarter pace" (i.e. "even time" or 200 metres in 15 seconds) the high heart rates developed cause the loss of ECG waveforms that are readily discernible at rest. Although differences in the waveforms between horses with normal and abnormal resting ECG's have been observed, the more definitive useful information is the fact that abnormal horses showed significantly higher heart rates than normal horses at a particular speed of work. When this occurs in combination with a resting ECG classified as borderline or abnormal and the exercise ECG shows positive, low amplitude, broad rounded T waves or transient bursts of sine-waves suggestive of ventricular flutter, racing performance is likely to be impaired. Although more work needs to be done and improvements in technology are necessary, the exercise ECG has potential for improving understanding of physical fitness and the significance of resting cardiac abnormalities.

Cardiac monitoring during exercise tests in the horse. 2. Heart rate responses to exercise.

Data on resting heart rates, pre-exercise heart rates, the anticipatory rises before exercise, the influence of speed of work and recovery heart rates have been presented. Some observations on differences in the heart rate response on slow and fast working days are also recorded. In conformity with other workers, a linear relationship between heart rate and working speed within the range of 400-800 metre/min was observed. When the speed of work was between 400-800 metre/min, horses with resting ECG's classed as abnormal had significantly higher heart rates than those regarded as normal. It was also observed that the abnormal animals showed lower heart rates than a small number classed as borderline. The significance of these findings is discussed and the need for further work indicated.

Cardiac monitoring during exercise tests in the horse. 1. Magnetic tape recording in preference to radio-telemetry.

Different techniques for monitoring cardiac responses to exercise in the horse have been described and evaluated. For experimental work of this type in a normal training and racing environment, the electrode system described when used with a portable magnetic tape recording system provided the best means of obtaining useful and reproducible data.