Clinical application of antimyosin monoclonal antibody imaging in cardiology

Abstract

Indium-111 (In-111) labeled antimyosin monoclonal antibody is specific for myocardial necrosis since it binds to cardiac myosin which becomes exposed during the process of myocardial cell membrane disruption and death. Myocardial uptake of anti myosin is directly related to the amount of necrosis and does not depend on regional myocardial blood flow which is often severely reduced during acute myocardial infarction and its positive uptake is observed even when it is injected very early after the onset of myocardial infarction. In a multicenter clinical trial (16 sites in the United States and 9 in Europe), the clinical safety of antimyosin was documented and its utility was evaluated in 497 patients with chest pain. The overall sensitivity and specificity of anti myosin were 87.5 % and 95 %. Using the Bayesian approach to the diagnostic utility of anti myosin it becomes apparent that patients who have an intermediate (25 % to 75 % ) likelihood of myocardial infarction will benefit most from this test. These include 1) patients with conflicting clinical and laboratory findings for presence of infarction, 2) patients with equivocal or nondiagnostic electrocardiograms and/or cardiac enzymes such as a) patients who have conduction disturbances on their electrocardiograms, b) those who might have suffered infarction during bypass surgery or coronary angioplasty, and c) those following thrombolysis therapy or with non-Q wave infarction in whom the size of necrosis cannot be accurately determined by the conventional methods, and 3) patients who present late after developing symptoms suspicious of myocardial infarction. An important application of antimyosin is risk stratification early following myocardial infarction. In the multicenter trial, there was a linear relationship between the minimum number of segments of antimyosin uptake and the incidence of cardiac death, nonfatal myocardial infarction, or both. An antimyosin study demonstrating less than 10 segments of uptake or no uptake identified patients with a low risk of developing events (5 %) compared to those with 10 or more segments of antimyosin uptake who represented a high risk category with 25 % cardiac event rate. The presence of extensive antimyosin uptake had superior prognostic value and was independent of other variables such as Killip class, Q wave myocardial infarction, recurrent ischemia and total creatine kinase. The intensity of regional myocardial uptake of antimyosin may be quantified which represents the degree of transmurality of infarction and correlates with the development of ischemic events following myocardial infarction. Furthermore, dual isotope imaging with In-111 antimyosin and thallium-201 (TI-201) may identify the amount of necrotic and viable but jeopardized myocardium as markers of prognosis after myocardial infarction. Antimyosin imaging has been helpful in identifying patients with a low risk for cardiac transplant rejection and decreases the total number of biopsies that are obtained in the post operative course. Similarly, in patients with dilated cardiomyopathy who are being evaluated for the presence of myocarditis, a negative antimyosin study effectively rules out this possibility and obviates the need for endomyocardial biopsy.