Ultrastructural alterations of the myocardium in Coxsackie B-3 virus myocarditis in mice. 18 Month follow-up study by transmission and analytical electron microscopy.

In a series of studies on experimental coxsackie B-3 virus myocarditis, ultrastructural changes of the myocardium in mice were observed for 18 months. On the 5th day a number of necrotic myocardial cells were connected with apparently intact cells at intercalated discs in multiple myocardial lesions. In the necrotic cells, myofibrils underwent lysis, and mitochondria contained very electron-dense spicular or granular inclusions and moderately electron-dense amorphous ones. X-ray analytical electron microscopy proved that the former type of inclusions contained calcium. Macrophages phagocytosed cell debris and many calcified mitochondria which were aggregated into large masses in the cytoplasm. As the macrophages were disorganized, calcified masses remained naked in the interstitial space and were identificable by light microscopy. On the 9th day a crystalloid structure of virus was identified in degenerated myocardial cells. On the 21st day acute inflammatory reaction was rare in the myocardium. In the 3rd month some myocardial cells degenerated near fibrotic or calcified foci. In the 12th and 18th months calcified foci remained, and interstitial fibrosis was extensive in some animals; some myocardial cells showed various degenerative changes including myofibrillar disorientation and lysis, numerous spherical microparticles adjacent to the sarcolemma, amorphous mitochondrial inclusions, and thickening of the basement membrane. Adjacent to fibrotic or calcified foci, some myocardial cells were hypertrophied or atrophied. The hypertrophied cells occasionally possessed multiple intercalated discs and extensive side-to-side junctions. Except for the calcified foci, most myocardial changes in the late chronic phase resembled those seen in myocardial biopsies obtained from patients with various heart diseases including cardiomyopathies and were assumed to be non specific in nature.