Echocardiographic and electrocardiographic study of the normal kangaroo heart

Healthy kangaroos are prone to sudden death. To investigate possible causes of this phenomenon, echocardiographic and electrocardiographic studies were conducted in seven healthy sedated (intramuscular ketamine 20 mg/kg, xylazine 2 mg/kg) kangaroos aged 1.5-5 years weighing 5.5-48 kg. As in human hypertrophic cardiomyopathy, kangaroos showed relative left ventricular hypertrophy measured as a ratio of (internal left ventricular end-diastolic diameter)/(septal + posterior wall thickness): 1.7 (SD 0.2) in kangaroos and 1.3 (SD 0.4) in hypertrophic cardiomyopathy cf 2.6 (SD 0.6) in normal man (p less than 0.001 respectively). Peak left ventricular diastolic filling velocity was smaller in kangaroos (2.6 (SD 0.3)/sec) and hypertrophic cardiomyopathy (3.3 (SD 0.7)/sec) than in normal man (4.1 (SD 1.0)/sec) (p less than 0.01, p less than 0.05). The end of T wave occurred earlier than the closing of aortic valve. Corrected QT interval (0.20 (SD 0.02) sec) was shorter than the normal value for man (0.34-0.40 sec). In conclusion, kangaroos have cardiac hypertrophy of unknown aetiology, with impaired diastolic function, as in non-obstructive hypertrophic cardiomyopathy patients. Corrected QT interval was short. These echocardiographic and electrocardiographic findings may explain the mechanism of sudden death in kangaroos, a species which may be used as an experimental model of non-obstructive hypertrophic cardiomyopathy in man.