Effects of endurance training on standard and signal-averaged electrocardiograms of sled dogs

Objective-To determine the effect of endurance training on QRS duration, QRS-wave amplitude, and QT interval. Animals-100 sled dogs in Alaska. Procedure-Dogs were examined in September (before training) and late March (after training). During the interim, dogs trained by pulling a sled with a musher (mean, 20 km/d). Standard and signal-averaged ECG were obtained before and after training. Results-Endurance training significantly increased mean QRS duration by 4.4 milliseconds for standard ECG (mean +/- SEM; 62.3 +/- 0.7 to 66.7 +/- 0.6 milliseconds) and 4.3 milliseconds for signal-averaged ECG (51.5 +/- 0.7 to 55.8 +/- 0.6 milliseconds) without changing body weight. increase in QRS duration corresponded to a calculated increase in heart weight (standard EGG, 23%; signal-averaged EGG, 27%). Signal-averaged ORS duration was correlated with echocardiographically determined left ventricular diastolic diameter for the X orthogonal lead (r = +0.41), Y orthogonal lead (r = +0.33), and vector (r = +0.35). Training also increased QT interval (234 +/- 2 to 249 +/- 2 milliseconds) and R-wave amplitude in reads it and rV(2), increased peak-to-peak voltage and S-wave amplitude in the Y orthogonal lead, and decreased Q-wave amplitude in the Y orthogonal lead. Conclusions and Clinical Relevance-Electro-cardiographic changes reflected physiologic cardiac hypertrophy in these canine athletes in response to repetitive endurance exercise. The ORS duration increases in response to endurance exercise training and, therefore, may be of use in predicting performance in endurance activities.