Indium 111-monoclonal antimyosin antibody imaging in the diagnosis of acute myocarditis

Localization of In-111 antimyosin Fab and 99mTc-pyrophosphate in reperfusion myocardial infarction model

The myocardial uptake of In-111 antimyosin Fab and Tc-99m pyrophosphate was studied in dogs undergoing coronary artery occlusion for 90 minutes followed by reperfusion. The regional myocardial blood flow was determined by injecting Sc-46 labeled microsphere and was related to the relative concentrations of In-111 antimyosin and Tc-99m pyrophosphate. There was an inverse linear correlation between In-111 antimyosin Fab localization and the regional blood flow in both the subendocardial (r = 0.81) and subepicardial myocardium (r = -0.80). The greatest uptake of antimyosin was observed in areas of severe blood flow reduction (0-10% of normal). On the other hand, there was no correlation between the Tc-99m pyrophosphate uptake and the degree of blood flow reduction. Maximal subendocardial localization of Tc-99m degree of blood flow reduction. Maximal subendocardial localization of Tc-99m pyrophosphate was observed in areas where the blood flow was reduced to 31-50% of the normal. In the case of the subepicardium, the greatest uptake was localized to areas of 0 to 10% of the normal flow. In addition, there was significant myocardial uptake in regions where the blood flow was minimally reduced (greater than 81%). This study suggests that In-111 antimyosin Fab is a specific and quantitative tool in the evaluation of myocardial necrosis.

Infarct sizing by scintigraphic techniques and nuclear magnetic resonance imaging

Assessment of myocardial infarct size is the cornerstone in the evaluation of interventions designed to salvage myocardium, such as thrombolytic therapy and urgent coronary angioplasty. Enzymatic methods have probably the highest accuracy but can only be used in the very early phase of infarction. The electrocardiogram allows a reasonable estimate of infarct size, but its confidence limits are wide, and in inferior wall infarction the estimates are unreliable. In recent years, radionuclide techniques have been successfully used to identify, localize and determine infarct size in the course of acute myocardial infarction. These scintigraphic measurements have provided important diagnostic, therapeutic and prognostic information based on the extent of myocardial damage. Nuclear magnetic resonance imaging, particularly with contrast enhancement, is one of the methods that have the greatest potential in accurately delineating myocardial infarct size. Nuclear medicine procedures, on the other hand, employ more biologically oriented tracers and offer promise in view of their ability to monitor biochemical alterations as an effect of therapy in the course of myocardial infarction.

High prevalence of myocardial monoclonal antimyosin antibody uptake in patients with chronic idiopathic dilated cardiomyopathy

Monoclonal antimyosin antibody studies were undertaken to assess the presence of myocardial uptake in patients with chronic idiopathic dilated cardiomyopathy. Three groups were studied: 17 patients with chronic (greater than 12 months) idiopathic dilated cardiomyopathy, 12 patients with a large, poorly contracting left ventricle not due to dilated cardiomyopathy (control patients) and 8 normal individuals. The patients in the cardiomyopathy and control groups showed a similar degree of clinical and functional impairment. Imaging was undertaken 48 h after antimyosin injection. The heart/lung ratio of antimyosin uptake was used to assess the results. The mean ratio in the cardiomyopathy group was 1.83 +/- 0.36 (range 1.40 to 2.80), a value significantly higher than that obtained in the control patients without cardiomyopathy (mean 1.46 +/- 0.04, range 1.38 to 1.50) or normal subjects (mean 1.46 +/- 0.13, range 1.31 to 1.6) (p less than 0.01). No difference in the ratio was noted between the normal subjects and control patients. Abnormal antimyosin uptake was seen in 12 (70%) of the 17 patients with cardiomyopathy and in only 1 (8%) of the 12 control patients. Positive monoclonal antimyosin antibody studies are highly prevalent in chronic idiopathic dilated cardiomyopathy.

Clinical and experimental aspects of viral myocarditis

Picornaviruses are frequently implicated as the etiological agents of acute myocarditis. This association is based historically on serological evidence of rising antibody titers to specific pathogens and more recently on identification of viral genomic material in endocardial biopsy specimens through in situ hybridization. Only rarely is infectious virus isolated from either the patient or the heart during periods of maximum myocardial inflammation and injury. Thus, despite a probable viral etiology, much interest centers on the role of the immune system in cardiac damage and the likelihood that the infection triggers an autoimmune response to heart-specific antigens. Heart-reactive antibodies and T cells are found in most myocarditis patients, and immunosuppressive therapy has proven beneficial in many, though not all, cases. Furthermore, murine models of coxsackievirus group B type 3-induced myocarditis also demonstrate that virus infection initiates autoimmunity and that these autoimmune effectors are predominately responsible for tissue injury. How virus-host interactions overcome presumed self-tolerance to heart antigens is discussed, and evidence supporting various theories of virus-initiated autoimmunity and disease pathogenesis are delineated.

Immunosuppressive treatment in myocarditis

Twenty patients (13 males and seven females) with a biopsy-proven diagnosis of myocarditis underwent a period of treatment with prednisone and azathioprine. The primary objective of the study was the observation of histologic changes which occur during treatment and after treatment withdrawal. The secondary objective was the detection, if any, of changes in left ventricular ejection fraction. Multiple endomyocardial biopsies were obtained and the treatment was adjusted in order to achieve complete disappearance of the myocardial inflammation. The histologic status was improved in all patients, although complete disappearance of the signs of active disease was seen in 15 patients only. Two patients died during the observation period. A clear relationship between histologic status and immunosuppression was established in some patients (50% of all cases showed a worsening after withdrawal from the treatment). An overall improvement of the ejection fraction was observed (from 0.37 +/- 0.14 to 0.46 +/- 0.17), but a direct effect of the treatment on the recovery of ventricular function cannot be stated. In some patients, however, a direct relationship between the histological changes and the changes in ejection fraction was seen. These data suggest that treatment with prednisone and azathioprine may be beneficial in some patients with biopsy-proven myocarditis and depressed ventricular function.

Clinical applications of SPECT

The clinical use of single photon emission computed tomography (SPECT) has grown steadily over the last decade. SPECT is now an essential technique for certain studies such as cerebral blood flow imaging. Many other common nuclear medicine studies give better results when they are performed with SPECT. These include myocardial perfusion imaging with thallium-201 or the new technetium-99m perfusion agents, myocardial infarct imaging with infarct-avid agents, imaging of tumors or infections with agents such as gallium-67 or indium-111 WBC's, and certain cases of bone imaging. Still other studies such as liver/spleen imaging, most brain studies, and perhaps renal imaging may benefit from SPECT even though planar imaging gives satisfactory results. Future developments in 3D display techniques and faster computers may extend the clinical usefulness of SPECT to other areas such as pulmonary perfusion imaging and gated cardiac blood pool imaging.

Detection of experimental myocarditis by monoclonal antimyosin antibody, Fab fragment

The purpose of this study was to determine whether monoclonal antimyosin Fab (antigen binding fragment) was capable of labeling hearts with experimental coxsackievirus myocarditis, and to determine whether Fab could be used for detecting myocardial damage in either early or chronic phases of the disease. Sixty-five, 3-week-old cesarean-derived 1 (CD 1) mice were divided into two groups: group I (noninfected animals) and group II (infected with coxsackievirus B3). Mice from each group were killed on days 7, 17, 30, or 90 of infection. Forty-eight hours before killing, mice were injected with monoclonal I125 antimyosin, Fab (25 microCi/injection) and radioactivity was counted in the heart. Selected heart sections were also examined by autoradiography. Heart radioactivity, count/m/mg (m +/- SEM) on days 7, 17, 30, and 90 of infection was 10.8 +/- 1.7, 21.3 +/- 1.1, 11.2 +/- 3.4, and 12.4 +/- 1.5 for group I, versus 36.7 +/- 8.0 (p less than 0.01), 50.0 +/- 4.5 (p less than 0.001), 33.4 +/- 16.1 (p = NS), and 40.6 +/- 8.5 (p less than 0.01) for group II, respectively. Autoradiography revealed focal uptake within areas of necrotic myocardium. We conclude that I125 Fab may be useful in detecting myocardial damage in the experimental model of murine myocarditis up to day 90 of infection.

Patterns of evolution of myocyte damage after human heart transplantation detected by indium-111 monoclonal antimyosin

The indium-111 labeled Fab fragment of antimyosin monoclonal antibody was used to study cardiac rejection and the time course of myocyte damage after transplantation. Fifty-three studies were performed in 21 patients, 17 men and 4 women, aged 19 to 54 years (mean 37 +/- 8), from 7 to 40 months after transplantation. Repeat studies were available in 8, and 10 were studied after the first year of transplantation. A heart-to-lung ratio was used for quantitation of uptake (normal 1.46 +/- 0.04). Differences between absent (1.69 +/- 0.29) and moderate (1.90 +/- 0.36) rejection were significant (p less than 0.03). Antimyosin ratio at 1 to 3 months (1.89 +/- 0.35) differed from that at greater than 12 months (1.65 +/- 0.2) (p less than 0.01). Repeat studies revealed a decrease in antimyosin ratio in 5 patients with uneventful clinical course; 2 had persistent activity after transplantation and suffered heart failure from rejection. After 1 year of transplantation uptake was within normal limits in 7 of 10 patients, and high uptake was associated with vascular rejection in 1. Because they can define evolving patterns of myocardial lesion activity, antimyosin studies could be useful both in patient management and in concentrating resources for those patients who most require them. The heart-to-lung ratio is suggested to monitor sequentially the degree of myocyte damage after transplantation.