Localization of cardiac myosin-specific antibody in myocardial infarction

Myocardial uptake of antimyosin antibody compared with serum myosin light chain I levels in patients with myocardial infarction

Myocardial accumulation of In-111-antimyosin (InAM) was evaluated in comparison with circulating serum myosin light chain I (LCI) level at the time of InAM injection. Seventeen consecutive patients were studied at various stages ranging from 6 days to 34 days after myocardial infarction (MI). The infarct area was positive for InAM uptake in all patients (100%), and significant myocardial uptake was observed in 14 patients (82.4%). The intensity of InAM uptake correlated with the infarct location shown by ECG and CAG. In contrast, 12 patients (70.6%) had normal or undetectable serum myosin LCI levels, with 5 being normal (0.42-2.5 ng/ml) and 7 undetectable (0.42 ng/ml or less). Only 5 patients (29.4%) had elevated serum myosin LCI levels at the time of InAM injection, and this elevation was slight, ranging from 3.4 to 4.5 ng/ml (mean: 3.75 ng/ml). Among patients with undetectable, normal, and elevated serum myosin LCI levels, there was no significant correlation between InAM uptake and the serum myosin LCI level. Thus, even after the serum myosin LCI level has decreased to normal, InAM can still bind to cardiac myosin in patients with MI, presumably until there is complete recovery from the hibernating myocardium due to ischemic damage.

Radiopharmaceucticals for cardiovascular imaging

Radionuclide cardiac imaging is a noninvasive technique routinely used to detect coronary artery disease (CAD). This imaging modality includes techniques such as planar, single photon emission computed tomography (SPECT), positron emission tomography (PET) and radionuclide ventriculography--each technique having unique features of its own. Each technique employs various radiopharmaceuticals suitable for assessing different physiological and functional parameters that may become abnormal in the presence of CAD. Various cardiac imaging techniques include myocardial perfusion or blood flow, myocardial metabolism and cardiac function and wall motion. While radionuclide ventriculography gives the global functional status of the heart, SPECT and PET techniques provide information as to the regional blood flow and metabolic status of the myocardium. The following is a review of radiopharmaceuticals that are utilized clinically and in research in different types of nuclear cardiac imaging. Radiopharmaceuticals have been grouped according to the technique employed in which they are used. Various characteristics, merits and disadvantages of each radiopharmaceutical are discussed in detail.

Evaluation of the protective effect of verapamil on reperfusion injury by 111In anticardiac myosin antibody in canine myocardial infarction

We quantitated the protective effect of verapamil on reperfusion injury in canine myocardial infarct using 111In-anticardiac myosin antibody and correlated to the electronmicroscopic findings. Experimental myocardial infarction was performed by one hour occlusion of the anterior descending coronary artery and followed by reperfusion. Saline or verapamil (0.6 mg/kg/hr) was started at 40 minutes after coronary artery occlusion and continued throughout the experiment. There was an inverse exponential relationship between anticardiac myosin uptake and regional coronary blood flow in both the control (r = -0.86) and the verapamil treated (r = -0.71) groups. Less uptake of 111In-anticardiac myosin antibody was observed in the verapamil treated group than in the control group of the regions where blood flow was lower than 30% of normal. In the control group, the myocardium showed signs of the typical contraction band necrosis. In the verapamil treated group, however, the myocardium contained fewer electron dense granules and mild degree of contraction bands.

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

The use of three different monoclonal antibodies specific for human ventricular myosin heavy chains in the visualization of the location and extent of necrosis in dogs with experimental acute myocardial infarction and in humans is described. Using a classic immunohistochemical method or ex vivo analysis of heart slices in dogs with acute myocardial infarction subjected to intravenous injection of unlabeled antimyosin antibodies or antimyosin antibodies labeled with indium-111, it was observed that all antibody fragments specifically reached the targeted necrotic zone less than 2 h after antibody injection and remained bound for up to 24 h. In a limited but significant number of cases (5 of the 12 humans and 11 of 43 dogs), it was possible to image the necrotic zone in vivo as early as 2 to 4 h after antibody injection. In other cases, individual blood clearance variations retarded or even prevented in vivo necrosis detection. Higher antimyosin fixation values were obtained in the necrotic zones in dogs with a rapid blood clearance relative to that of the other dogs. It is concluded that antimyosin antibodies always reached necrotic areas within 2 h. If blood clearance was rapid, in vivo imaging of the necrotic area was possible 2 to 6 h after necrosis, even in humans. In some cases, however, uncontrolled individual variations in the timing required for sufficient blood clearance hampered this rapid in vivo detection of myocardial necrosis.

Indium-111 myosin-specific antibodies and technetium-99m pyrophosphate in the detection of acute cardiac rejection of transplanted hearts: studies in a heterotopic rat heart model

111In-labelled myosin-specific antibodies were evaluated as an indicator of early changes in acute rejection in a rat heart heterotopic transplant model. Uptake of antibodies was measured in allograft and isograft hearts of animals undergoing different regimens of cyclosporine treatment and compared with the uptake of technetium-99m pyrophosphate. The data were correlated with histological estimation of the severity of myocyte necrosis and signs of early rejection (venous cuffing and endocardial inflammation, indicators of perivascular infiltrate and intermyocyte extension, respectively). Myocyte necrosis in transplanted hearts was reflected by increases in technetium-99m pyrophosphate accumulation (r = 0.88) but was poorly correlated with labelled antibody uptake (r = 0.58). There was no positive correlation between the degree of early cardiac rejection and uptake of either of the radiopharmaceuticals: accumulation of the labelled antibodies paradoxically declined with increased histological severity scores, whereas that of technetium-99m pyrophosphate remained unchanged. Cyclosporine treatment augmented the uptake of labelled antibodies in transplanted hearts. This may be due to alterations in plasma membrane permeability brought about by the drug, resulting in a rise in antibody binding to intracellular myosin.

Natural evolution of cardiac function, cardiac pathology and antimyosin scan in a murine myocarditis model

Serial technetium-99m radionuclide ventriculograms, indium-111 antimyosin antibody scans and tissue biodistribution studies were performed in C3H/He mice with experimentally induced viral encephalomyocarditis and the results were compared with pathologic assessments of myocardial necrosis. Postinfection ejection fraction decreased on days 10 (20.7 +/- 5.5%, n = 6), 20 (18.6 +/- 15.2%, n = 5), 30 (18.5 +/- 7.7%, n = 5) and 150 (30.0 +/- 18.7, n = 6) (p less than 0.001) in comparison with that in uninfected control mice (63.3 +/- 3.1%, n = 6). In the same group of animals, indium-111 antimyosin antibody scans showed intense positive myocardial accumulation on day 10 (in six of six mice) and only slight accumulation on day 20 (in one of five mice). In the chronic stage, two of five mice on day 30 and two of six mice on day 150 still showed positive uptake. The antimyosin scan myocardium to lung uptake ratio (expressed as mean count density [mean counts/pixel of the region] ratio) increased greatly on day 10 (p less than 0.001 versus values in uninfected control mice) but not subsequently. Biodistribution studies of the indium-111 antimyosin antibody showed that the heart to blood count ratio was significantly higher on day 10 (p less than 0.001 versus values in control mice) but not on days 20, 30 and 150. Pathologic examination showed active and ongoing severe myocardial necrosis with dilated ventricles on day 10. On day 20, there was less active necrosis and healing had appeared to begin. On days 30 and 150, myocardial fibrosis increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of indium-111 antimyosin antibody and technetium-99m pyrophosphate localization in reperfused and nonreperfused myocardial infarction

Recent imaging studies suggest that technetium-99m (Tc-99m) pyrophosphate yields a considerably larger estimate of myocardial infarct size than does indium-111 (In-111) monoclonal antimyosin antibody. To determine whether Tc-99m pyrophosphate may be taken up by reversibly injured myocytes, particularly in the setting of coronary reperfusion, the tissue localization of Tc-99m pyrophosphate and antimyosin antibody was compared in 11 dogs 24 to 68 h after anterior descending coronary artery occlusion (4 dogs with permanent occlusion, 7 with reperfusion). Technetium-99m pyrophosphate and In-111 antimyosin antibody content was determined in serial 2 to 3 mm wide endocardial and epicardial samples taken through the infarct zone in multiple short-axis left ventricular slices. The number of samples with increased In-111 antimyosin antibody (defined as greater than or equal to mean + 2 SD of normal) was not significantly different from that with increased Tc-99m pyrophosphate. This was true in both reperfused and nonreperfused infarcts. However, the intensity of uptake of Tc-99m pyrophosphate exceeded that of In-111 antimyosin antibody, particularly in the border zones of reperfused infarcts, and the area with moderate to marked increase in tracer uptake (greater than or equal to 2 times normal) was significantly larger with Tc-99m pyrophosphate than In-111 antimyosin antibody (p less than 0.001). A specific zone of abnormal Tc-99m pyrophosphate with normal In-111 antimyosin antibody content could not be identified. Histologic evidence of myocardial necrosis was found in virtually every sample with increased In-111 antimyosin antibody, Tc-99m pyrophosphate, or both.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-tumor applications of radioimmune imaging

The application of radioimmune imaging techniques to the evaluation of non-neoplastic disease is largely based on the same principles as tumor imaging; specificity and high affinity of antibodies. Currently the most common non-tumor applications of antibody imaging are the detection of clots (peripheral and pulmonary emboli), myocardial necrosis (myocardial infarction, myocarditis and cardiac transplant rejection) and focal sites of infection/inflammation. In the area of injection imaging, both antigen-specific and non-specific properties of antibodies have been successfully exploited in imaging studies. While the number of non-tumor applications of antibodies are far fewer than the number of tumor studies, in many cases, they appear to be more reliable. The basis for the reliability of antibodies for detecting non-neoplastic lesions is probably related to the availability of abundant antigen, lack of antigen modulation and enhanced permeability at the lesion site. These observations suggest that there will be rapid proliferation of work in this area.

Early Indium-111 antimyosin scintigraphy for assessment of regional wall motion asynergy on discharge after myocardial infarction

To assess the relation between early Indium-111 monoclonal antimyosin antibody scintigraphy and degree of regional asynergy on discharge, 38 patients with a first acute myocardial infarct were studied (18 anterior, 20 inferoposterior infarctions). In 21 patients thrombolytic therapy was administered. On the first day of myocardial infarction, 80 MBq Indium-111 Antimyosin was injected. Planar images, anterior, lateral and left anterior oblique, were made 24 hours later. Localized myocardial uptake was present in 37/38 patients, and was evaluated for Count Density Index (count density of infarct zone/left lung count density) in the left anterior oblique images, which displayed the infarct zone well. Regional asynergy on discharge was evaluated by cross-sectional echocardiography and defined mild (hypokinesia) or severe (akinesia or dyskinesia). Count density index was significantly lower in 15 patients with mild asynergy, compared with 22 patients with severe asynergy (1.61 +/- 0.25 vs. 2.42 +/- 0.40, p less than 0.001). This difference was present in both patient groups treated with or without thrombolysis. We conclude that early count density index, reflecting the amount of local necrosis, is highly correlated to the ultimate degree of wall motion impairment.

Antimyosin antibody cardiac imaging: its role in the diagnosis of myocarditis

Right ventricular endomyocardial biopsy currently remains the procedure of choice for identifying patients with symptomatic heart failure due to myocarditis from the larger population with idiopathic dilated cardiomyopathy. Despite its specificity, the sensitivity of right ventricular biopsy remains uncertain because of the focal or multifocal nature of the disease. Because myocyte necrosis is an obligate component of myocarditis, the use of indium-111 antimyosin imaging was evaluated in 82 patients with suspected myocarditis. Seventy-four patients had dilated cardiomyopathy of less than 1 year's duration (mean left ventricular ejection fraction 0.30 +/- 0.02); eight patients had normal left ventricular function (mean ejection fraction 0.59 +/- 0.03). Symptoms at presentation included congestive heart failure (92%), chest pain mimicking myocardial infarction (6%) and life-threatening ventricular tachyarrhythmias (2%). All patients underwent planar and single photon emission computed tomographic (SPECT) cardiac imaging after injection of indium-111-labeled antimyosin antibody fragments and right ventricular biopsy within 48 h of imaging. Antimyosin images were interpreted as either abnormal or normal and correlated with biopsy results. On the basis of the right ventricular histologic examination, the sensitivity of antimyosin imaging was 83%, specificity 53% and predictive value of a normal scan 92%. Improvement in left ventricular function occurred within 6 months of treatment in 54% of patients with an abnormal antimyosin scan compared with 18% of those with a normal scan (p less than 0.01). Antimyosin cardiac imaging may be useful for the initial evaluation of patients with dilated and nondilated cardiomyopathy and clinically suspected myocarditis.(ABSTRACT TRUNCATED AT 250 WORDS)

Infarcted heart uptake and biodistribution of radiolabelled anti-myosin monoclonal antibody in rat and dog myocardial infarct models

A new mouse monoclonal antibody that recognizes alpha- and beta-heavy chains of human atrial and ventricular myosin and beta-heavy chain of human slow skeletal muscle myosin was obtained. The 125I- and 111In-labelled antibody, and its F(ab')2 and Fab fragments localize in isoproterenol induced infarcted rat heart, with the F(ab')2 fragment showing the highest uptake. Comparison with 99Tc-pyrophosphate uptake in infarcted dog heart, induced by selective obstruction of a coronary artery, suggest that the 111In-labelled F(ab')2 localizes specifically in infarcted myocardium only.

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.

The role of antimyosin antibodies in acute myocardial infarction

Antimyosin is an Fab fragment of a monoclonal antibody that binds with human myosin exposed in myocytes irreversibly damaged by an ischemic event. Labeled with 111In, the antibody is taken up into acutely necrotic tissue and can be imaged by planar or single photon emission computed tomography (SPECT) techniques. A large, multicenter clinical trial has demonstrated a high degree of both sensitivity for detecting infarction and specificity for excluding a recent ischemic event in patients admitted with chest pain syndrome. No allergic reactions to antibody injection have occurred, nor have there been documented significant increases in human antimouse antibody titers postinjection. Due to relatively slow blood clearance, the optimal imaging time is 24 to 48 hours post-injection. Between 13% and 21% of 24-hour scans are nondiagnostic due to persistent blood pool activity. In two thirds of these patients, 48-hour scans confirm negative tracer uptake. Moderate to intense cardiac uptake occurs in greater than 80% of scans. Faint tracer uptake, which occurs in a small minority of patients, is associated with inferoposterior infarct location and an occluded infarct vessel. Potential clinical uses include both diagnostic and prognostic areas. A negative scan in a patient with chest pain syndrome and no ECG changes rules out a recent significant ischemic event. The extent of antimyosin uptake (infarct size), measured semiquantitatively from planar scans or quantitatively from SPECT reconstructions, has been shown to correlate with future cardiac events. Relative patterns of distribution of indium-antimyosin and 201TI on simultaneous dual isotope SPECT reconstructions may identify patients with residual myocardium at further ischemic risk.

Measurement of acute Q-wave myocardial infarct size with single photon emission computed tomography imaging of indium-111 antimyosin

Myocardial infarct size was measured by single photon emission computed tomography (SPECT) following injection of indium-111 antimyosin in 27 patients (18 male and 9 female; mean age 57.4 +/- 10.5 years, range 37 to 75) who had acute transmural myocardial infarction (MI). These 27 patients represent 27 of 35 (77%) consecutive patients with acute Q-wave infarctions who were injected with indium-111 antimyosin. In the remaining 8 patients either tracer uptake was too faint or the scans were technically inadequate to permit infarct sizing from SPECT reconstructions. In the 27 patients studied, infarct location by electrocardiogram was anterior in 15 and inferoposterior in 12. Nine patients had a history of prior infarction. Each patient received 2 mCi of indium-111 antimyosin followed by SPECT imaging 48 hours later. Infarct mass was determined from coronal slices using a threshold value obtained from a human torso/cardiac phantom. Infarct size ranged from 11 to 87 g mean 48.5 +/- 24). Anterior infarcts were significantly (p less than 0.01) larger (60 +/- 20 g) than inferoposterior infarcts (34 +/- 21 g). For patients without prior MI, there were significant inverse correlations between infarct size and ejection fraction (r = 0.71, p less than 0.01) and wall motion score (r = 0.58, p less than 0.01) obtained from predischarge gated blood pool scans. Peak creatine kinase-MB correlated significantly with infarct size for patients without either reperfusion or right ventricular infarction (r = 0.66). Seven patients without prior infarcts had additional simultaneous indium-111/thallium-201 SPECT studies using dual energy windows.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis of acute myocardial infarction by indium-111 antimyosin antibodies and correlation with the traditional techniques for the evaluation of extent and localization

This clinical study evaluated the accuracy of planar myocardial scintigraphy with antimyosin monoclonal antibodies radiolabeled with indium-111 (AMA-Fab) in the detection and localization of acute myocardial infarction (AMI). Fifty-seven patients admitted for suspected AMI were studied; 17 patients underwent thrombolytic therapy with intravenous streptokinase and 11 had clinical signs of reperfusion; 9 had had a previous myocardial infarction. Fifty of 57 patients were discharged from the coronary care unit with a confirmed diagnosis of AMI. The AMA-Fab study results were positive for AMI in 49 patients (98%) and negative in 1 (2%). Among the 7 patients without AMI, 5 had unstable angina, 1 had Prinzmetal's variant angina and 1 had acute pancreatitis. AMA-Fab results were negative in 6 of 7 patients (85%) and positive in 1 (15%). Therefore, the sensitivity and specificity of AMA-Fab scintigraphy were 0.98 and 0.85, respectively. To assess accuracy in defining the extent and location of AMI, AMA-Fab results were compared with those of the electrocardiogram, echocardiogram, technetium-99m pyrophosphate myocardial scintigraphy and coronary angiography and left ventriculography. AMA-Fab scintigraphy showed a good concordance with the traditional techniques in the topographic definition of the infarcted regions. No uptake of AMA-Fab was seen in the regions of previous old infarcts. Ten healthy volunteers also underwent AMA-Fab scintigraphy. No evidence of myocardial tracer uptake was noted in them. No adverse reactions or side effects were noted after injection of AMA-Fab in any patient. It is concluded that planar myocardial scintigraphy with AMA-Fab is a reliable method for AMI detection and location.

Identification of cardiac rejection in heterotopic heart transplantation using 111In-antimyosin

It is important in heart transplantation to evaluate precisely the extent and location of cardiac rejection. At present, right ventricular endomyocardial biopsy has been used as the gold standard, however, establishment of noninvasive, simple, and easy diagnostic procedure is desired. The canine donor heart, in which atrial septal defect and tricuspid regurgitation had been produced beforehand, was heterotopically transplanted into the recipient's chest cavity. In seven dogs, two to three mCi of 111In-antimyosin was injected intravenously upon cardiac rejection before the heart was excised. 111In-antimyosin myocardial imaging was then performed using a gamma camera. In the same slice, a histopathological rejection score was calculated and divided into mild, moderate or severe injection. The uptake of 111In-antimyosin was significantly higher in moderate and severe rejected myocardium, since this agent produced a specific and selective localization and concentration in areas of myocardial damage. Therefore, this new technique allows the evaluation of therapeutic intervention upon cardiac rejection and may replace right ventricular endomyocardial biopsy.

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

A definitive diagnosis of myocarditis requires right ventricular biopsy. Despite its specificity, however, right ventricular biopsy may lack sensitivity due to the focal nature of the disease. Because indium 111-monoclonal antimyosin antibody imaging can be used to detect myocardial necrosis, this procedure was performed on 28 patients clinically suspected of having myocarditis, 25 of whom had left ventricular ejection fractions of less than 45%, and the results were compared with those of right ventricular biopsy performed within 48 hr of the scan. Antimyosin scans were positive in nine patients who had evidence of myocarditis on right ventricular biopsy, and negative in 11 who had no evidence of myocarditis by biopsy. The remaining eight had positive antimyosin scans but showed no evidence of myocarditis on right ventricular biopsy. On the basis of a right ventricular biopsy standard, the sensitivity of this method was 100%, the specificity 58%. We conclude that antimyosin antibody imaging is a reliable screening method for the evaluation of patients suspected of having myocarditis, and that a positive antimyosin scan indicates the need for right ventricular biopsy to establish the histologic diagnosis.

Measurement of infarct size and percentage myocardium infarcted in a dog preparation with single photon-emission computed tomography, thallium-201, and indium 111-monoclonal antimyosin Fab

Single photon-emission tomography (SPECT) and indium 111-labeled monoclonal antimyosin Fab fragments were used to measure myocardial infarct size in 12 dogs, six subjected to balloon catheter-induced coronary artery occlusion for 6 hr (late reperfusion) and six subjected to occlusion with reperfusion at 2 hr (early reperfusion). Tomographic imaging was performed 24 hr after the intravenous injection of labeled Fab fragments with the use of a dual-head SPECT camera with medium-energy collimators. Immediately after the first tomographic scan, thallium-201 was injected into nine of 12 dogs and imaging was repeated. Estimated infarct size in grams was calculated from transaxially reconstructed, normalized, and background-corrected indium SPECT images with the use of a threshold technique for edge detection. Estimated noninfarcted myocardium in grams was calculated from obliquely reconstructed thallium SPECT images by a similar method. The animals were killed and infarct size in grams and true infarct size as a percentage of total left ventricular myocardial volume were measured by triphenyl tetrazolium chloride staining. Estimated infarct size from indium SPECT images showed an excellent correlation with true infarct size (r = .95, SEE = 4.1 g). Estimated percentage myocardium infarcted was calculated by dividing estimated infarct size from indium images by the sum of estimated infarct size plus estimated noninfarcted myocardium obtained from thallium images. Correlation between the estimated percentage of myocardium infarcted and true percentage of myocardium infarcted was excellent (r = .93, SEE = 4.4%). We conclude that dual-isotope SPECT with indium 111-monoclonal antimyosin antibodies and thallium-201 can accurately estimate infarct size and percentage myocardium infarcted.

Current status and prospects of new radionuclides and radiopharmaceuticals for cardiovascular nuclear medicine

The rapid emergence of new imaging modalities like positron emission tomography (PET) and single photon emission computerized tomography (SPECT) and their advance into the clinical arena offered new opportunities for, but also stimulated research and development of new radiopharmaceuticals suitable for cardiac imaging. While tracers of myocardial blood flow remained in the center of interest, other trends heralded possibilities of studying more comprehensively cardiac physiology and pathophysiology as, for example, metabolism, the severity of tissue injury, neural activity and membrane function. N-13 ammonia and rubidium-82 became the primary tracers for evaluating and possibly quantifying regional myocardial blood flow with PET, while cationic Tc-99m isonitrile complexes have now reached a stage where high contrast images of the human heart are obtained on planar scintigraphy and SPECT. These radiopharmaceuticals hold considerable promise for routine clinical use. Tracers of metabolism, especially those labeled with positron emitting isotopes as for example, C-11 palmitate, F-18 2-deoxyglucose, are approaching the phase of clinical use and provide information on regional myocardial substrate metabolism and oxidative processes. Less successful and more limited were developments of single photon emitting tracers of metabolism which remained largely confined to radioiodinated fatty acid analogs. Exploration and characterization of the metabolic fate of the radiolabel in tissue and its relation to the externally observed signal have been truly impressive. Tested in humans primarily in western European countries, these tracers promise to yield metabolic information on a more limited scope. Most widely applied are iodohepta- and hexadecanoic acid and, more recently, the aromatic fatty acid analog, paraiodophenylpentadecanoic acid. Labeled monoclonal antibodies rapidly advanced to the point of clinical use. Accurate identification and sizing of acute myocardial infarction is now possible with Tc-99m or indium-111 labeled specific antimyosin antibody fragments. This success stimulated new research activities for use of labeled antibody techniques in other areas as for example, scintigraphic evaluation of formation and presence of vascular thrombi. While promising, these efforts have however remained in an early stage of development. The same holds true for single photon and positron emitting tracers that are suitable for assessing sympathetic neuron densities in myocardium as well as imaging of both cholinergic and adrenergic receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Infarct size--can it be measured or modified in humans?

Despite more than 15 years of intensive experimental and clinical research in the general area of limiting infarct size, no treatment has been shown to be so efficacious and relatively free of side effects that its routine use can be recommended. In addition, there is no ideal means of measuring infarct size as yet. However, considerable progress has been made in understanding mechanisms responsible for irreversible cellular injury and in identifying factors and anatomic alterations responsible for or contributing to the development of transmural (Q wave) and non-transmural (non-Q wave) myocardial infarcts. Interventions are available that are capable of causing rapid coronary thrombolysis, and techniques are becoming available tht have increasing power to size myocardial infarcts and estimate both segmental and ventricular function. Experimental studies have also suggested a potential benefit from a combination of reperfusion therapy with selected pharmacologic intervention in reducing infarct size and preserving ventricular function. It seems likely that this general area will remain an intensive area of clinical research in the immediate future.

Scintigraphic quantification of myocardial necrosis in patients after intravenous injection of myosin-specific antibody

The Fab fragments of antimyosin antibodies, labeled with 99mTc, were used in the scintigraphic examination of 30 patients with myocardial infarction. The ability to detect necrosis and determine its extent from the antimyosin scan were compared with the results of quantitative regional wall motion analysis by contrast ventriculography at 10 to 14 days and 99mTc-pyrophosphate imaging. Antimyosin images recorded by planar and single photon-emission computed tomography (SPECT) delineated areas of myocardial necrosis in 27 of 30 patients (90%) compared with a 91% sensitivity of pyrophosphate in 21 of 23 patients. Infarct size was determined by both antimyosin and pyrophosphate SPECT images. Results by both techniques showed a significant correlation with computer-derived hypokinetic segment length (r = .79 for both, p = .002) and peak creatine kinase (r = .9 for both, p less than .01). Although sensitivity for and correlations with markers of necrosis were similar with both techniques, infarct size by pyrophosphate SPECT was 1.7 times larger than infarct size by antimyosin SPECT (p less than .01). Certain zones in the infarct area were differentially labeled; the nature and irreversibility of injury within these zones remains to be clarified.

Levels of ventricular myosin fragments in human sera after myocardial infarction, determined with monoclonal antibodies to myosin heavy chains

Serum levels of ventricular myosin heavy chains were quantitated in patients with acute myocardial infarction using a competitive radioimmunoassay involving monoclonal antibodies to the b-type myosin heavy chains of a human ventricle. Among the seven antibodies selected for their higher affinity for ventricular myosin heavy chains, only four antibodies detected significant and variable myosin amounts in the serum samples of nineteen patients with acute myocardial infarction; the same antibodies occasionally detected, if at all, low myosin amounts in the sera of patients with no clinical sign of myocardial infarction, and no myosin in the serum of the healthy control subjects. The peak levels of myosin release were observed 4.6 +/- 0.5 days (n = 13, P less than 0.01) after myocardial infarction and correlated rather well with the measured creatine kinase peak levels (the correlation coefficients were between 0.75 and 0.81, P less than 0.01, depending on the monoclonal antibody used for myosin determination). The time courses of myosin release varied according to the complexity of the heart attack observed. It was concluded that the titration of serum myosin was probably of little clinical value for therapeutic intervention during the acute phase of myocardial infarction; it could, however be an effective tool for retroactive detection of an infarct and for late estimation of infarct size.

The role of free radical-mediated processes in oxygen-related damage in cultured murine myocardial cells

A new approach to quantifying myocyte cell death utilizing fluorescence-activated sorting of antimyosin antibody-labeled cells was used to study the effects of oxygen-generated free radicals on cell survival. Uptake of antimyosin, reflecting sarcolemmal damage, increased under conditions which promoted elevated free radical formation and decreased in the presence of increased levels of free radical-scavenging agents. Superoxide dismutase decreased antimyosin uptake at pH 6.7 and 7.5. Mannitol decreased antimyosin uptake at pH 6.5 and 6.7 but not at pH 7.5, and dimethyl sulfoxide decreased antimyosin uptake at pH 6.4 but not at pH 7.5. These data suggest that a greater portion of hydroxyl radicals are produced at higher concentrations of hydrogen ion. Mannitol, a scavenger of hydroxyl radicals, was effective in reducing antimyosin uptake at pH 7.5 in the presence of ferrous sulfate, but had no effect on antimyosin uptake in the absence of ferrous sulfate, suggesting possible iron-mediated catalysis of hydroxyl radical formation. The data suggest that oxygen-derived free radicals can cause significant loss of membrane integrity in cultured myocytes, that the species of radical formed is dependent both on pH and the concentration of iron salts, and that this injury is, at least in part, preventable by the administration of exogenous radical scavenging agents.

Monoclonal antibody to cardiac myosin: imaging of experimental myocardial infarction

Monoclonal antibody R11D10 to human cardiac myosin, which also cross-reacted with canine cardiac myosin, was used to demonstrate in vivo localization and visualization by gamma scintigraphy of experimental myocardial infarction. R11D10 Fab with a Ka of 5 X 10(8) M-1 was labeled with technetium-99m (99mTc) by the dithionite reduction method of technetium pertechnetate, via a bifunctional chelating agent, diethylene triamine pentaacetic acid (DTPA). Uptake of 99mTc R11D10 Fab in the infarct can be visualized as early as 2 h after intravenous administration. Comparison of R11D10 uptake to thallium-201, an analogue of potassium which is sequestered by normal myocardium, showed an inverse relation (r = -0.75, -0.87, -0.89), similar to that obtained with 125I labeled polyclonal antimyosin Fab. Ratios of R11D10 Fab in the infarct to normal myocardium were as high as 30:1 where access of antibody to antigen was not blood flow limited. However, with severe blood-flow restriction, the ratios were lower at about 10:1. Despite the theoretical limitation of a single epitope per myosin molecule available for binding by R11D10 Fab, the immense excess of myosin in the infarcted myocardium allowed adequate concentration of radiolabeled R11D10 for visualization of the infarct by external gamma scintiscanning.

Localization of 131I-labeled p97-specific Fab fragments in human melanoma as a basis for radiotherapy

33 patients with advanced malignant melanoma were studied after intravenous administration of 131I-labeled Fab fragments specific for p97, an oncofetal glycoprotein of human melanoma. In all, 47 gamma camera imaging studies were performed for the purpose of localization of metastatic deposits. In addition to tumor, 131I-Fab uptake was also seen in liver and kidney. 20 of these studies included simultaneous administration of both an 131I-labeled Fab specific for p97, and an 125I-labeled Fab not specific for p97. Blood clearance of p97-specific Fab was significantly more rapid than for nonspecific Fab. Eight of these patients had biopsies of subcutaneous nodules at 48 and 72 h postinjection in order to assess whether localization of radioactivity was antigen specific. Antigen-specific localization was observed with average ratios of specific/nonspecific uptake of 3.7 (48 h) and 3.4 (72 h); uptake was strongly correlated with tumor p97 concentration (r = 0.81, P less than 0.01). Also, imaging studies of the bio-distribution of 131I-labeled anti-p97 Fab in patients selected for high p97 tumor concentration showed avid tumor uptake and more prolonged retention of labeled Fab in tumor than in normal tissues. Based on these studies, we estimated that total 131I doses of 500 mCi could be safely given to patients before dose-limiting toxicity would be observed. Accordingly, in seven selected patients, phase I radiotherapeutic trials were begun. For improved radiation safety, we developed automated methods to label Fab fragments with up to 200 mCi of 131I. So far, a total of 12 individual therapeutic doses, ranging from 34 to 197 mCi of 131I-labeled to 5 to 10 mg of Fab, have been administered with excellent tumor localization and without major target organ toxicity. Cumulative doses ranged from 132 to 529 mCi 131I. Side effects attributable to the radiation were mild, with a transient drop slightly greater than 50% in platelet and absolute neutrophil counts being observed in the two patients who received cumulative doses greater than 500 mCi. In the combined series of 47 diagnostic and 12 therapeutic studies, four acute reactions were observed: one episode each of transient chills and fever; flushing and hypotension; and two skin rashes. All of these reactions responded promptly to symptomatic therapy. After multiple administrations of 131I-(anti-p97) Fab (IgG1), isotype-specific immunity was observed in three patients. In two of these patients it was possible to successfully reinfuse after immunity had developed with 131I-(anti-p97) Fab of a different isotype (IgG2a). Dosimetry estimates were performed based on the biodistribution of (131)I-Fab in these patients,and for every 100 mCi of (131)I-Fab given, tumor receives 1,040 rads; liver. 325 rads; and bone marrow, 30 rads. Marrow would be expected to be the critical organ, if doses >500 mCi (131)I-Fab are given. These studies demonstrated that, with proper precautions, large doses (of an (131)I-labeled murine Fab fragments immunologically specific for a human melanoma-associated antigen) could be safely given to humans by using repetitive intravenous injections.

Patterns of cellular injury in myocardial ischemia determined by monoclonal antimyosin

The development of cellular injury in the rat left ventricle resulting from left coronary artery occlusion was examined by immunofluorescence after intravenous injection of monoclonal antimyosin. Cardiac muscle cells that bound antimyosin during ischemia were localized by staining sections with fluorescein-conjugated anti-mouse IgG. Fluorescent staining was detectable within the ischemic region of the left ventricle 3 hr after occlusion and injection of antimyosin. After 6 hr of ischemia, the highly irregular margin of the ischemic zone was clearly outlined by fluorescent cells. At 3-6 hr after occlusion, marked heterogeneity in cellular staining was observed in the epicardial half of the ischemic area, with intensely fluorescent cells intermixed with cells of markedly lower fluorescence. By 24 hr, a homogeneous pattern of staining was observed throughout the ischemic zone. In nonischemic regions of the heart and in rats treated for 24 hr with antimyosin without occlusion, there were only background levels of staining. We conclude that: (i) visualization of ischemic cells via antimyosin provides a sensitive means for examining developing patterns of injury; (ii) the heterogeneity of staining during early ischemia may reflect variation in cellular resistance to deprivation; and (iii) the pattern of fluorescence at the margin of the occluded region indicates that the "border zone" is composed of interdigitating ischemic and nonischemic tissues.

Early membrane damage during coronary reperfusion in dogs. Detection by radiolabeled anticardiac myosin (Fab')2

There is currently great interest in acute coronary reperfusion as a therapeutic modality for severe myocardial ischemia. While some studies have demonstrated a reduction in the overall extent of necrosis by early reperfusion, other studies have identified potentially deleterious effects produced by reflow. Because membrane disruption may be an important mechanism of irreversible cell injury, we measured changes in cell membrane integrity early during reperfusion using radiolabeled anticardiac myosin (Fab')2 antibody fragments in dogs. Our method involved brief periods of exposure to the (Fab')2 so that the levels of (Fab')2 binding indicated the degree of membrane disruption at discrete times during the progression of cell injury. In the first protocol (Fab')2 fragments labeled with either 125I and 131I were injected into the left circumflex coronary artery at the onset of reflow and at 45 min of reflow after a 1-h circumflex artery occlusion. Coronary sinus flow was diverted for 5 min following each injection to prevent recirculation. The (Fab')2 binding ratio (ischemic/control) increased during the first 45 min of reflow in each of eight experiments (mean increase 170%, P less than 0.01). No significant increase in (Fab')2 binding was observed in five additional experiments in which nonspecific (Fab')2 was injected. This indicates that the increase in binding seen with antimyosin-specific (Fab')2 was due to changes in specific binding rather than to alterations in (Fab')2 delivery produced by changes in blood flow distribution. The increase in membrane damage during reflow was confirmed by a second protocol in which each animal received only a single left atrial injection of (Fab')2 followed by rapid excision of the heart. The (Fab')2 binding ratio was 1.7 +/- 0.3 (SEM) in the group that received (Fab')2 at the onset of reflow and 3.7 +/- 0.6 (SEM) (P less than 0.05) in the group that received (Fab')2 after 45 min of reflow. In a third set of experiments in which hyperosmotic mannitol was infused during reflow the mean increase in (Fab')2 binding using the first protocol was only 80 +/- 40 vs. 170 +/- 30% without mannitol (P less than 0.05). Thus, membrane damage develops early during coronary reperfusion following 1 h of circumflex coronary artery occlusion, and part of this membrane damage can be prevented by altering the conditions of reflow. A method involving brief exposure of the myocardium to antimyosin (Fab')2 is promising for detecting changes in membrane integrity during evolving ischemic injury.

Relation of immediate and delayed thallium-201 distribution to localization of iodine-125 antimyosin antibody in acute experimental myocardial infarction

Thallium-201 (TI-201) distribution in acute experimental myocardial infarction (MI) (n = 18) was compared with cardiac-specific antimyosin Fab (AM-Fab) uptake, a specific marker for myocardial necrosis. When antimyosin was injected 4 hours after ligation with TI-201 administered 23 hours 55 minutes later and measurement of myocardial distribution determined 5 minutes after intravenous administration of TI-201, (1) TI-201 distribution closely correlated with microsphere regional blood flow, and (2) an inverse exponential relation to iodine-125 (I-125) AM-Fab uptake was apparent. In another group of 4 animals, TI-201 and AM-Fab were administered intravenously 4 hours after MI, and 36 hours later myocardial distribution was measured. This delayed TI-201 distribution had a close inverse linear correlation with I-125 AM-Fab uptake. This inverse linear relation also was apparent in 28-hour-old MIs in dogs (n = 4) where collateral circulation had been established. TI-201 was administered intravenously at 27 hours after MI, and TI-201 distribution was determined 1 hour later. The present study demonstrated that whereas immediate TI-201 distribution is flow-limited, delayed TI-201 distribution is a marker of cell viability which, due to prolonged circulation time and redistribution, is not flow-limited.

Myocardial injury: quantitation by cell sorting initiated with antimyosin fluorescent spheres

Spheres coated with antibodies specific for myosin were used to detect myocardial cell membrane disruption by scanning electron microscopy. Injury in a population of cultured myocytes as then followed and measured by fluorescence-activated cell sorting. This approach provides a unique method for quantitating the evolution of myocardial injury and potentially for assessing the efficacy of interventions aimed at myocardial protection.

Immunological probes in cardiovascular disease

The immune system has long been recognised as playing a central role in the organism's defence against infectious diseases and possibly the development of neoplasia. The active stimulation of the immune system by immunisation and the passive administration of antitoxins have a venerable history in medicine. Yet the concept that antibodies may be used to modify physiological or pharmacological effects or may act as diagnostic agents in the living organisms has only recently come to be recognised. Advances, both in an understanding of the structural chemistry of the antibody molecule and in the ability to culture antibody-producing cells, now permit the selection and production of homogeneous antibodies and their smaller fragments in quantity by means other than conventional immunisation. These innovations will allow the development of a new pharmacology based on the remarkable resolving power of the antibody combining site. Antibodies or their fragments are shown to inhibit the pressor action of renin, to neutralise the pharmacological actions of digitalis, to block the beta-adrenergic receptor, and to detect and image myocardial infarcts.

Localization of anti-mitochondrial antibody in experimental canine myocardial infarcts

Alterations in cell and subcellular membrane integrity occur during evolving ischemic myocardial injury. We tested the hypothesis that an antibody against human liver mitochondria [anti-mitochondrial antibody developing in a patient with primary biliary cirrhosis] could identify altered cell membrane integrity in experimental canine myocardial infarcts. The proximal left anterior descending coronary arteries of 12 dogs were ligated and 1 hr later 131I-labeled F(ab')2 fragments from either a control human IgG (6 dogs) or anti-mitochondrial IgG (6 dogs) were injected. The 131I-labeled F(ab')2 anti-mitochondrial fragments concentrated maximally in the central infarct subendocardium [infarct-to-normal ratio of 9.2 +/- 3.5 (mean +/- SD) vs. 4.6 +/- 3.3 for control F(ab')2 IgG, P < 0.05]. There was also 1 1/2- to 2-fold greater anti-mitochondrial antibody F(ab')2 accumulation in the central infarct epicardium and the peripheral infarct subendocardium and subepicardium. Thus, an anti-mitochondrial antibody obtained from a patient with primary biliary cirrhosis concentrates in irreversibly damaged myocardium after experimental canine myocardial infarction. Presumably this occurs because of altered cell membrane integrity, which allows exposure of mitochondria to the anti-mitochondrial antibody. The F(ab')2 fragments of anti-mitochondrial antibodies labeled with suitable radionuclides should allow noninvasive scintigraphic detection of experimental acute myocardial infarcts.

Myocardial infarct imaging of antibodies to canine cardiac myosin with indium-111-diethylenetriamine pentaacetic acid

Antibodies, by virtue of marked selectivity and affinity, may lend themselves to identification of structures of unique antigenic specificity in vivo. In experimental myocardial infarction in dogs, F(ab')2 fragments of antibodies to cardiac myosin that had been labeled with iodine-131 were shown to localize within the lesion. Because the energy characteristics of iodine isotopes are not ideal for imaging with a gamma camera, a new method for labeling antibody fragments with divalent or polyvalent radionuclides was developed. A bifunctional chelating agent, diethylenetriamine pentaacetic acid was covalently coupled, by an amide bond, to Fab fragments of antibodies to canine cardiac myosin. A stable chelate was then formed with indium-111, a nuclide that has appropriate half-life and energy characteristics for gamma imaging. Antibodies treated in this way retain their antigen-binding activity and are useful in locating myocardial infarcts in vivo.

Early imaging of experimental myocardial infarction by intracoronary administraion of 131I-labelled anticardiac myosin (Fab')2 fragments

We examined the feasibility of early imaging of myocardial infarcts by intracoronary injection of 131I-labelled cardiac myosin-specific antibody (Fab')2. The left anterior descending coronary artery was occluded for 5 hours by a balloon catheter introduced through the carotid artery in 12 dogs. The catheter was withdrawn and 1 mCi 201Tl was injected intravenously and 500 muCi of 131I antibody were injected into the main left coronary artery. Six of these animals demonstrated evidence of myocardial infarction by ECG and subsequent triphenyl-tetrazolium chloride staining, while the others did not. In each of the infarcted animals, in vivo scintograms one-half hour after injection of isotope showed uptake of 131I in the anteroapical region of the heart corresponding to the region of absent 201Tl uptake. This relationship was confirmed in the excised hearts and in heart slices. In slices, 131I uptake corresponded to regions that did not stain with triphenyltetrazolium chloride. In the six animals that did not show evidence for infarction after coronary occlusion, uptake of 131I was not demonstrated, either in vivo or in excised specimens. In four additional dogs subjected to the same procedure, 125I-labelled (Fab')2 from nonimmune IgG was injected simultaneously into the left main coronary artery with 131I-labelled canine myosin-specific antibody (Fab')2. The ratio of uptake between infarct center and normal tissue was 34.3 +/- 1.5 (mean+/-SEM) for the specific antibody fragment as contrasted to 6.6+/-0.4 for the nonimmune IgG fragment, indicating that intracoronary injection does not favor nonspecific sequestration of protein in regions of infarction. Thus, the intracoronary administration of myosin-specific antibody fragments leads to early and specific one-half hour imaging of myocardial infarcts.

Detection of serum cardiac myosin light chains in acute experimental myocardial infarction: radioimmunoassay of cardiac myosin light chains

To develop a more specific plasma test for myocardial infarction, antibodies specific for cardiac myosin light chains (CM-LC) were elicited that showed less than 3% cross-reactivity with skeletal muscle light chains. These antibodies were used to develop a radioimmunoassay for CM-LC that had a sensitivity of 20 ng (+/- 4 SD; P less than 0.001). Normal dog plasma showed no measurable concentrations of CM-LC (n = 6). Plasma samples from 10 dogs with experimental myocardial infarction produced by persistent left anterior descending coronary artery (LAD) occlusion were obtained at 0, 2, 4, 6, 24, 48 and 72 hours. CM-LC were first detectable in all 10 animals 6 hours after occlusion (97.98 +/- 14 ng/ml [mean +/- SEM]; P less than 0.001). Maximal CM-LC levels were usually obtained between 24 and 48 hours. Sham-operated open chest dogs (0--48 hours, n = 3) showed no measurable CM-LC in the plasma samples. Another group of 10 dogs were subjected to 5 hours of LAD occlusion, followed by reperfusion. In four dogs, CM-LC were detectable as early as 1 hour after reperfusion (81.88 +/- 37.75 ng/ml serum). Sera from all 10 dogs showed elevated levels of CM-LC (199.75 +/- 24.0 ng/ml) by 24 hours. Peak CM-LC concentrations were obtained in five dogs at 24 hours (247.0 +/- 35.28 ng/ml) and in another dog at 120 hours (245 ng/ml). Histochemical infarct size was determined to be 0.5--10% of the left ventricular mass at seven days by triphenyltetrazolium chloride staining. The specificity and sensitivity of this radioimmunoassay for detection of CM-LC, unique proteins to the heart, may be valuable in the diagnosis of myocardial infarction.