Mural thrombi in mice with acute viral myocarditis

In an investigation of the relationship between mural thrombosis and congestive heart failure (CHF) in acute viral myocarditis, inbred BALB/c mice were inoculated intraperitoneally with the M variant of encephalomyocarditis (EMC) virus and sacrificed on days 7 (n = 33), 10 (n = 35) and 14 (n = 39). Myocarditis was found in 105 of 107 sacrificed mice (98.1%). Myocardial necrosis with cellular infiltration was evident after day 7 and was extensive in the ventricles and atria. In the 105 mice with myocarditis, 17 mice (16.2%) developed CHF after day 10, and 15 mice (14.3%) had thrombi as early as day 7. All thrombi were in the left and/or right atrium. The incidence of thrombi in mice with CHF was higher, but not significantly so, than that in mice without CHF (23.5% vs 12.5%). All 50 control mice had no myocardial lesions or thrombi. This study demonstrates that thrombus formation was not rare in the absence of CHF in the acute stage of viral myocarditis and suggests that clinically acute viral myocarditis has a risk of systemic and/or pulmonary embolism even when resting cardiac function is normal.