Objective—To determine the effect of endurance
training on QRS duration, QRS-wave amplitude, and
Animals—100 sled dogs in Alaska.
Procedure—Dogs were examined in early
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
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 ECG, 23%; signal-averaged ECG, 27%).
Signal-averaged QRS 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 leads
II and rV2, 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—Electrocardiographic
changes reflected physiologic cardiac
hypertrophy in these canine athletes in response to
repetitive endurance exercise. The QRS duration
increases in response to endurance exercise training
and, therefore, may be of use in predicting performance
in endurance activities. (Am J Vet Res 2000;61:582–588)