Radiation-induced cardiomyopathy. I. An electron microscopic study of cardiac muscle cells.

This investigation demonstrates sequential ultrastructural lesions of cardiac myocytes in rabbits exposed locally to a single dose (1008 and 1300 rads) of x-irradiation. A wide spectrum of lesions were observed as early as 24 hours postirradiation and were followed for as long as 4 months after x-irradiation. Myofibrillar degeneration and dissociation of intercalated discs seen at 24 and 48 hours postirradiation were followed by gradual progression of myofibrillolysis and myofiber degeneration to myofiber atrophy, myofiber collapse and eventual progressive pericellular interstitial myocardial fibrosis. The possible role of dissociation of intercalated disca in the pathogenesis of well-known postirradiation electrocardiographic changes is suggested. Myofibrillar degeneration appears to be the characteristic (although non-specific) lesion of radiation having a multifactorial etiology: direct radiation effect, vascular compromise and endogenous (cardiac) catecholamine liberation.