NATURAL EVOLUTION OF ANTIMYOSIN SCAN AND CARDIAC-FUNCTION IN PATIENTSWITH ACUTE MYOCARDITIS

Indium-lll monoclonal antimyosin antibody imaging is a convenient meth od to diagnose acute myocarditis. The present study examined the natur al evolution of a positive antimyosin scan in 10 patients with acute m yocarditis, ih relation to left ventricular ejection fraction. All pat ients underwent myosin-specific monoclonal antibody imaging and radion uclide ventriculography; in all patients endomyocardial biopsy was per formed. Repeat assessment of left ventricular function and antimyosin uptake was performed 1, 2 and 6 months later. A heart-to-lung ratio wa s used to quantify antimyosin uptake. Heart-to-lung ratio in patients with myocarditis was 2.12 +/- 0.31, significantly higher than that obs erved in eight controls (1.35 +/- 0.08, P < 0.001). During follow-up 2 .2 repeat scans per patient were performed. Heart-to-lung ratio normal ized(< 1.6) within 1 month in four patients, within 2 months in one pa tient and within 6 months in two patients; three patients continued to have a positive antimyosin uptake at 6 months, suggesting ongoing myo cardial necrosis. At the end of follow-up, ejection fraction improved by > 5% in four patients; normalization or persistence of tracer uptak e could not predict an improvement of ejection fraction. It is conclud ed that antimyosin scintigraphy is useful for diagnosing myocarditis i n its subacute or chronic stage during which unknown or immune mechani sms may be in operation. An improvement in left ventricular function c annot be predicted on the basis of persistence or not of tracer uptake .