Electrocardiograms (ECGs) are infrequently performed on Asian elephants (Elephas maximus), and few studies have been reported in the literature. The aim of this study was to determine reference ranges of ECG parameters in Asian elephants and to ascertain if age, body weight, and position of the elephant significantly affected the ECG. Electrocardiograms were obtained from 27 captive, nonsedated apparently healthy Asian elephants while they were standing (ST), in right lateral recumbency (RL), and/or in left lateral recumbency (LL). Six-lead ECGs were obtained using novel clamps and long ECG cables (71 cm). From lead I, standard waveforms and intervals were analyzed, including PR interval, QT interval, ST segment, P, QRS, T, and U waves if they were present. One animal was determined to have a previously undiagnosed conduction abnormality and was not included in the study. Most elephants had a sinus arrhythmia in at least one position. With increasing age, there was a trend toward a slower heart rate and significantly longer P waves. Increasing body weight was significantly correlated with longer QT intervals and T waves with lower amplitude. Compared with measurements in ST, LL resulted in P waves and QRS complexes with shorter amplitude, U waves with greater amplitude, PR intervals with shorter duration, and an increased heart rate. Compared with measurements in LL, RL resulted in larger QRS complexes. U waves were most commonly detected in RL and LL. Mean electrical axis calculated in the frontal plane were as follows: standing range −125 to 141°, mean −5°; left lateral range −15 to 104°, mean 27°; right lateral range −16 to 78°, mean 9°. Position-specific reference ranges should be used when interpreting ECGs, and clinicians must be aware of how age and body weight may affect the ECG.
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Vol. 40 • No. 3