T wave and QT interval in the Standardbred horse: A descriptive study

The human T wave and QT interval are well characterized. As long and short QT interval and QT interval dispersion are associated with arrhythmias and sudden death, influential factors, methods of measurement and heart rate (HR) correction are numerous. In horses, significance has been attached to QRS duration, T morphology, and QT interval, but clinical associations are not well supported and measurement not standardized. This study used holter monitoring of clinically normal Standardbred horses at rest and during exercise to develop an automated algorithm for measurement of T characteristics and QT interval. The algorithm was tested on 545 ECG segments of 12 successive RR intervals and successfully identified 97.0% of key waveform points. QT onset and offset were reliably identified 99.8% and 94.5% of the time respectively. While longitudinal studies will be required, this algorithm should aid in establishing normal equine QT intervals and accurate HR correction methods.