Imaging of myocardial infarction in dogs and humans using monoclonal antibodies specific for human myosin heavy chains

Cardiac myofibrillar proteins: biochemical markers to estimate myocardial injury

Ischaemic heart disease represents the most common of the serious health problems in the contemporary society and acute myocardial infarction (AMI) is the major cause of cardiovascular morbidity and death. The accurate localization and determination of the infarct size and the volume of myocardium at risk at the time of insult is crucial and vital for the choice of treatment. Initially the ischaemic cells are reversibly injured. However, if these changes are not reverted at the earliest, it results in the death of the myocyte. This irreversible myocyte necrosis travels transmurally towards epicardium in the form of a wavefront. A timely intervention during evolving infarct could reduce and delimit the infarct and preserve the left ventricular function. Enzyme analysis and electrocardiography (ECG) along with the clinical history of the patient is still considered to constitute a reliable triad in the diagnosis of myocardial infarction (MI). Efforts have been made to relate infarct size with the serum enzyme level changes without much success. In addition, a number of specialist techniques such as planar radioisotope imaging, single photon emission computed tomography (SPECT), positron emission tomography (PET), Echocardiography, Ventriculography and nuclear magnetic resonance (NMR) imaging have been devised to support diagnosis in the patients who show ambiguous symptoms and ECG findings. However most of these procedures are unavailable to the patients due to economic reasons while others have suffered due to non-availability of ideal radiopharmaceuticals. Major advances have been made in the methods based on immunological techniques to improve the detection and estimation of infarct. These methods are exclusively based upon the production and availability of specific antibodies against intracellular, cardiac specific components.

Myocardial indium-111 antimyosin uptake after uncomplicated coronary artery bypass surgery

The prevalence of myocardial damage after coronary artery bypass grafting is related to the criteria of its evaluation. Indium-111 monoclonal antimyosin antibody scintigraphy has been shown to be highly sensitive and specific for even small areas of myocardial necrosis or injury like those of myocarditis or transplant rejection. Our purpose was to evaluate, by using this method, myocardial damage after uncomplicated coronary artery bypass grafting. Uptake of this radio tracer was evaluated after coronary artery bypass grafting in 14 informed and consenting consecutive patients without previous myocardial infarction, with no post-surgical complications and a favorable postoperative course, following coronary artery bypass grafting for stable angina pectoris. Monoclonal antimyosin antibody indium-111 74 MBq (Myoscint Centocor) was injected on the third postoperative day; planar images in the anterior, left anterior oblique 45 degrees and 70 degrees projections were obtained 24 and 48 h later and analyzed for myocardial uptake. Indium-111 antimyosin uptake was present in 10 out of 14 patients (71.4%); it was diffuse in 6 and localized in 4. The ratio of the maximal counts in the myocardium to the counts in the adjacent lung background was measured and found elevated: 1.94 +/- 0.23, higher than the normal values reported in the literature. Indium-111 antimyosin uptake was clear in a group of patients after uncomplicated coronary artery bypass grafting. No correlation was observed between indium-111 antimyosin uptake or heart to lung ratio and creatine kinase, creatine kinase isoenzyme MB, glutamic oxalacetic transferase levels, duration of cardiopulmonary bypass or aortic cross-clamp time, while elevated serum beta myosin heavy chain fragments (IRMA Pasteur) were observed (1378 +/- 238 microU/l). This study suggests that some degree of myocardial damage, though silent, is common after coronary artery bypass grafting.

The earliest diagnosis of acute myocardial infarction

Acute myocardial infarction results from the cessation of myocardial blood flow caused by thrombotic occlusion of a coronary artery. Rapid restoration of blood flow to the ischemic myocardium minimizes cardiac damage and improves early and long-term morbidity and mortality. Chest pain is the first symptom of myocardial infarction, but in some patients with silent ischemia, the disease can be diagnosed only in retrospect. In symptomatic patients, myocardial infarction should be accurately and promptly diagnosed so that reperfusion therapy can begin immediately. Electrocardiography is the simplest diagnostic modality. Although regional ST-segment elevation is specific, it is not sensitive. In contrast, new computerized algorithms for electrocardiographic analysis and serial monitoring increase sensitivity without decreasing specificity. In the emergency room, echocardiography is used to diagnose patients with no prior history of coronary artery disease whose electrocardiograms proved nondiagnostic. Time-consuming perfusion nuclear studies are inferior to echocardiography but may nevertheless enable physicians to diagnose myocardial infarction in the emergency room. Although the presence of excess creatine kinase is a sign of myocardial necrosis, its increase is delayed for a few hours after coronary occlusion. Doctors can diagnose myocardial infarction as early as two hours after coronary occlusion with the help of simpler automatic assays of MB-creatine kinase mass that use monoclonal antibodies. Other investigational markers of myocardial necrosis include myoglobin and troponin. Elevation of a circulating protein marker also signifies established necrosis, but physicians hope to achieve reperfusion through therapy before irreversible damage occurs.