An experimental model of acute and subacute viral myocarditis in the pig

Twenty-six young pigs were infected with encephalomyocarditis virus, observed clinically, studied at intervals by noninvasive and invasive methods to assess cardiac function and eventually examined pathologically. All infected animals appeared ill, usually manifesting diminished appetite, lethargy and fever. Spontaneous mortality occurred either 1 to 4 or 20 to 21 days after infection. Electrocardiographic abnormalities, seen in the majority of animals, comprised ST-T wave changes, conduction disturbances or ventricular ectopic rhythm. The majority of animals manifested echocardiographic evidence of left ventricular dilation and decreased systolic function, which improved with time in some animals. Hemodynamic studies revealed elevation of biventricular filling pressures in 3 of 10 animals; as a group, infected animals manifested significantly elevated right ventricular filling pressures. In selected animals, the feasibility of gallium scans as well as left ventriculography and coronary angiography was demonstrated. At autopsy, heart weight/body weight ratio was significantly elevated in infected animals. The heart of all but two animals showed active myocarditis associated with fibrosis and focal calcification in the later stages. In general, the cardiovascular manifestations were parallel with those seen in acute and subacute myocarditis in humans. It is concluded that encephalomyocarditis infection in the pig is a large animal model of viral myocarditis suitable for assessing alterations in the structure and function of the cardiovascular system and the effects of interventions.