Myocardial cell damage during experimental infective endocarditis.

Infective endocarditis was induced in 15 catheterized rabbits by a single intravenous injection of Streptococcus viridans and the papillary muscles from the left ventricle were examined for histologic and ultrastructural changes at 3 and 6 days of infection. Papillary muscles from 10 normal and 12 catheterized uninfected animals were used for comparison. Catheterized animals, infected and uninfected, had cardiac hypertrophy and papillary muscles which showed an increase in myofiber size and some interstitial edema. The muscle from infected hearts had areas of focal necrosis, diffuse monocytic infiltration, and loss of normal myocardial architecture. The papillary muscles from catheterized uninfected animals showed some degree of mitochondrial and sarcotubular swelling as well as contracture of myofibrils; the infected myocardium exhibited dramatic changes in ultrastructure such as mitochondrial swelling and destruction, sarcotubular swelling, separation of the intercalated disc, and myofibrillar contracture and disruption. These histopathologic and ultrastructural changes in papillary muscles from rabbits with bacterial endocarditis are indicative of the presence of myocardial cell damage.