ELECTROCARDIOGRAPHIC CHARACTERISTICS OF ENDURANCE-TRAINED ALASKAN SLED DOGS

Objective-To determine electrocardiographic characteristics of enduran ce-trained Alaskan sled dogs. Design-Case series. Animals-319 Alaskan sled dogs entered to compete in the 1994 Iditarod Trail Sled Dog Race. Procedure-ECG were recorded while dogs were standing and were analyze d digitally. Results-Amplitudes of P waves (median, 0.40 mV; fifth to 95th percentile range, 0.11 to 0.61 mV) and R waves in lead II (median , 3.02 mV; fifth to 95th percentile range. 1.49 to 4.40 mV) were high; durations of P waves in lead II (median, 61 milliseconds; fifth to 95 th percentile range, 36 to 96 milliseconds), QRS complexes (median. 64 milliseconds; fifth to 95th percentile range, 52 to 80 milliseconds), and QT intervals (median. 236 milliseconds; fifth to 95th percentile range, 208 to 277 milliseconds) were prolonged. Median value for mean axis of ventricular depolarization was 57 degrees (fifth to 95th perce ntile range. 19 to 90 degrees). Atrial and ventricular premature depol arizations were observed in 3 (0.9%) and 4 (1.3%) of 319 dogs, respect ively, and paroxysmal ventricular tachycardia was detected in 1 (0.3%) . Clinical Implications-Results suggest that electrocardiographic char acteristics of endurance-trained Alaskan sled dogs differ from those r eported for nonsled dogs, probably as a result of effects of endurance training on heart size. Some of these characteristics could be mistak en as evidence of pathologic cardiac hypertrophy.