The anatomic cause of electrocardiographic changes in virus myocarditis of rabbits

Electrocardiographic studies were made on 25 rabbits which had been inoculated intratesticularly with virus III. During the acute stage of the resulting disease, the majority of these animals developed a histologically demonstrable myocarditis, and, after recovery from the infection, small scars were found in the myocardiums of many. Definite abnormalities in cardiac function, including complete auriculoventricular heart block, were demonstrated in the electrocardiogram during the period in which the acute myocarditis existed. The electrocardiogram failed to show the presence of a noteworthy myocarditis in only 3 animals, and in only one instance was it impossible to demonstrate myocarditis when the tracing was significantly altered. The electrocardiographic diagnosis was thus accurate in 84 per cent of the cases. This association of the abnormal electrocardiogram with the structural lesion in the heart leads to the conclusion that, in this disease of the rabbit, disturbed function is caused by actual lesions, and not by the toxicity of the disease.Twenty-one rabbits which were inoculated intratesticularly with Andrewes' inflammatory strain of the Shope fibroma virus were studied similarly. Although in the hearts of a few of these animals interstitial myocardial fibrosis occurred, the muscle cells escaped for the most part, and in no animal was any abnormality in the electrocardiogram demonstrated.