Active myocarditis with fibrosis. Poor correlation of ejection fraction with histology of follow-up biopsy

Patients with myocarditis are followed clinically, with determination of left ventricular ejection fraction (LVEF), and histologically, with right ventricular endomyocardial biopsy. We have compared the LVEF with follow-up biopsy histology in 29 patients with active myocarditis with fibrosis. These patients had chronic disease (average duration 40.6 months) and at the time of initial biopsy had reduced LVEF (average 0.25) and diagnostic biopsy histology. The patients were evaluated at one month after diagnosis and then at 6-month intervals. An increase of more than 0.05 in LVEF was considered as improved ventricular function. Follow-up biopsies were classified as ongoing, resolving or resolved myocarditis. A total of 66 biopsies were performed in the 29 patients. All patients were treated supportively with digitalis and diuretics; immunosuppressive therapy (prednisone alone or with azathioprine) was used in 16 patients. The biopsy histology was a poor predictor of clinical status with or without immunosuppression. Of 21 instances of ongoing myocarditis histology, six were accompanied by improved LVEF. Of 45 instances of resolved or resolving histology, only 17 were accompanied by improved LVEF. The mechanism of cardiac dysfunction in this group of patients with a chronic form of active myocarditis with fibrosis may be independent of light microscopic evidence of active inflammation or myocyte degeneration.