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

The impact of viability assessment using myocardial perfusion imaging on patient management and outcome

BACKGROUND

Prior studies show that ischemic cardiomyopathy (ICM) patients with substantial viable myocardium have better survival with coronary revascularization (CR) than medical therapy (MT). When myocardial perfusion imaging (MPI) is used, the analysis is often based on visual scoring. We sought to determine the value of automated quantitative viability analysis in guiding management and predicting outcome.

METHODS

We identified 246 consecutive ICM patients who had rest-redistribution gated SPECT thallium-201 MPI. Size and severity of perfusion defects were assessed by automated method. Regions with <50% activity vs normal were considered nonviable. Mortality was verified against the social security death index database.

RESULTS

Of the 246 patients, 37% underwent CR within 3 months of MPI. The initial images showed a total perfusion defect size of 32 +/- 17%, redistribution of 3.5 +/- 4.6% and nonviable myocardium of 13 +/- 14%LV. Using multivariate logistic regression analysis, independent predictors of CR included chest pains (OR 2.74) and rest-delayed transient ischemic dilatation (OR 4.49), while a prior history of CR or ventricular arrhythmias favored MT. The cohort was followed-up for 41 +/- 30 m during which 111 patients (45%) died. Survival was better with CR than MT (P < .0001). For CR, survival was better for those with a smaller area of nonviable myocardium (risk of death increased by 5%/1% increase in size of nonviable myocardium, P = .009) but this was not seen in MT. CR had a mortality advantage over MT when the area of nonviable myocardium was

CONCLUSIONS

Automated quantitative analysis of MPI is useful in predicting survival in ICM, but the decision for or against CR is a complex one as it depends on multiple other factors and "viability testing" is just one variable that needs to be incorporated in the decision-making process.

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MESH Headings

• Cardiac-Gated Single-Photon Emission Computer-Assisted Tomography
• Cardiomyopathies/diagnostic imaging
• Cardiomyopathies/etiology
• Cardiomyopathies/physiopathology
• Cardiomyopathies/surgery
• Coronary Artery Bypass
• Female
• Humans
• Kaplan-Meier Estimate
• Male
• Middle Aged
• Myocardial Ischemia/complications
• Myocardial Perfusion Imaging
• Proportional Hazards Models
• Radioisotopes
• Stroke Volume
• Thallium Radioisotopes

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Affiliation(s)

Fadi G Hage Division of Cardiovascular Disease, University of Alabama at Birmingham, Zeigler Research Building 1024, 1530 3rd AVE S, Birmingham, AL 35294, USA.
Rajesh Venkataraman
Wael Aljaroudi
Paco E Bravo
Joel McLarry
Michael Faulkner
Jaekyeong Heo
Ami E Iskandrian

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Coronary vasodilator reserve: a clue to the explanation of (201)Tl redistribution patterns early after successful primary stenting for acute myocardial infarction

OBJECTIVES

We sought to assess the mechanism and significance of different (201)Tl redistribution patterns after successful primary stenting following acute myocardial infarction (AMI).

BACKGROUND

The mechanism of (201)Tl reverse redistribution and the impact of different redistribution patterns on the recovery of contractility after successful reperfusion therapy for AMI remain unclear.

METHODS

We studied 41 consecutive patients with successful primary stenting for a first AMI. Patients underwent predischarge and six-month follow-up dipyridamole stress-reinjection single photon emission tomography (SPECT), coronary and left ventricular angiography. Intracoronary Doppler assessment of coronary flow reserve (CFR) was performed before discharge.

RESULTS

Four patient groups were identified according to predischarge SPECT: patients with I: nonreversible defects (n = 8), II: redistribution (n = 7), III: reverse redistribution (n = 21), IV: no defect (n = 5). At follow-up contractility recovery increased in a stepwise fashion from groups I to IV (19 +/- 41%, 40 +/- 53%, 70 +/- 28%, 78 +/- 33%, p = 0.01). Compared with patients with redistribution, those with reverse redistribution had lower infarct-related artery (IRA) CFR (2.2 +/- 0.5 vs. 2.8 +/- 0.9, p = 0.03) but higher contractility recovery.

CONCLUSIONS

Variable (201)Tl redistribution patterns, early after successful stenting for AMI, may predict different degrees of late contractility recovery. The lower IRA CFR and the higher contractility recovery in areas with reverse redistribution suggest more severe microvascular dysfunction and less severe myocardial injury in such areas compared with those with redistribution.

Relationship between T-wave normalization on exercise ECG and myocardial functional recovery in patients with acute myocardial infarction

BACKGROUND

Several studies suggested that T-wave normalization (TWN) in exercise ECG indicates the presence of viable myocardium. But the clinical implication of this phenomenon in patients with acute myocardial infarction who received proper revascularization therapy was not determined. Precisely the aim of this study was to investigate the relationship between TWN in exercise ECG and myocardial functional recovery after acute myocardial infarction.

METHODS

We studied 30 acute myocardial infarction patients with negative T waves in infarct related electrocardiographic leads and who had received successful revascularization therapy. Exercise ECG was performed 10-14 days after infarct onset using Naughton protocol. Patients were divided into 2 groups according to presence (group I; n = 14) or not (group II; n = 16) of TWN in exercise ECG. Exercise parameters and coronary angiographic findings were compared between groups. Baseline and follow-up (mean 11 months) regional and global left ventricular function was analyzed by echocardiography.

RESULTS

Exercise parameters were similar between groups. There was no difference in baseline ejection fraction and wall motion score between group I and II (EF; 56 +/- 12% vs 52 +/- 11%, p = ns. WMS; 21 +/- 3 vs 23 +/- 4, p = ns) and it was improved at the tenth month by similar magnitude (group I/group II, EF% change = 12 +/- 12% vs 7 +/- 6%, p = ns, WMS% change = 6 +/- 6% vs 7 +/- 5%, p = ns). The finding of no relation between TWN and functional recovery was observed also when the patients were analysed according to infarct location and presence or absence of Q-waves.

CONCLUSION

As the exercise-induced TWN in patients with acute myocardial infarction was not related with better functional recovery of dysfunctional regional wall motion and ejection fraction, TWN does not appear to be an indicator of myocardial viability.

Myocarditis in patients with clinical presentation of myocardial infarction and normal coronary angiograms

OBJECTIVES

The aim of this study was to assess the diagnosis of myocarditis in patients presenting with acute myocardial infarction (MI) and normal coronary angiograms.

BACKGROUND

Most often in these patients, the etiologic diagnosis remains unclear once they are found to have normal coronary arteries. The diagnosis of myocarditis mimicking MI is clinically relevant, because numerous arguments suggest a relation between myocarditis and dilated cardiomyopathy. Myocardial indium-111 (111In)-antimyosin antibody (AMA)/rest thallium-201 (201Tl) imaging allows noninvasive detection of myocarditis.

METHODS

Forty-five patients admitted to three intensive care units for suspicion of acute MI, with normal coronary angiograms, were investigated. Indium-111-AMA planar images and then a dual-isotope rest AMA/201Tl tomographic study were performed. Six-month echocardiographic follow-up was obtained in 80% of the patients with initial left ventricular (LV) wall motion abnormalities.

RESULTS

In eight patients, AMA and 201Tl scintigraphy were negative. In two patients, a matched 201Tl defect and focal AMA uptake suggested acute MI (due to prolonged vasospasm or spontaneously reperfused coronary occlusion). In 17 patients, diffuse AMA uptake over the whole LV suggested diffuse myocarditis. In 18 patients, focal AMA uptake with a normal 201Tl scan suggested diffuse but heterogeneous, or focal myocarditis. Complete functional recovery was observed in 81% of the patients with a pattern of myocarditis.

CONCLUSIONS

Among 45 patients presenting with acute MI and normal coronary angiograms, 38% had diffuse myocarditis and 40% had a scintigraphic pattern of heterogeneous or focal myocarditis. Short-term follow-up showed complete LV functional recovery in 81% of these patients.

The current role of infarct avid imaging

Tc-99m pyrophosphate is the grandfather of infarct avid agents. Its value is its clinical availability and ease of use. However, its shortcomings are the delay of 2 to 3 days for reliable interpretation in nonreperfused myocardial infarction (MI) and the overarching bone activity. Antimyosin provides exquisite specificity for the detection of myocardial necrosis irrespective of the cause of the injury. Therefore, diagnosis of equivocal MI or confirmation of diffuse myocardial necrosis would benefit from the availability of In-111 labeled antimyosin Fab. The drawback of antimyosin, like that of Tc-99m pyrophosphate, is the delay, in this case because of the protracted blood clearance of the antibody protein macromolecules. Tc-99m glucaric acid, on the other hand, may fulfill the original role envisioned for antimyosin, which was to enable early, rapid diagnosis of acute MI. However, the window for the use of Tc-99m glucaric acid appears to be limited to within the first day of the acute event. Therefore, there is a potential use of both Tc-99m glucaric acid and In-111 antimyosin in tandem with Tc-99m glucaric acid, which would not only facilitate early detection and diagnosis of acute MI and diagnosis of equivocal MI, but also may permit stratification of the infarct age.

Relationship between normalization of negative T waves on exercise ECG and residual myocardial viability in patients with previous myocardial infarction and no post-infarction angina

The usefulness of normalization of negative T waves in exercise ECG was investigated as an index of myocardial viability in patients with previous myocardial infarction with no symptoms or ischemic ST-segment change during exercise test. A total of 39 patients, 20 with T-wave normalization (POS group) and 19 without T-wave normalization (NEG group) on exercise ECG. were studied. Myocardial viability was evaluated by thallium-201 single-photon emission computed tomography (SPECT) during exercise or at rest. We also assessed left ventricular ejection fraction (LVEF) by contrast ventriculography before (n=39) and after percutaneous transluminal coronary angioplasty (PTCA) (n=17). SPECT detected myocardial viability in 16 (80%) of the 20 patients in the POS group and in 4 (21%) of the 19 patients in the NEG group (p<0.01). LVEF increased after successful PTCA in the POS group (from 53+/-13% to 63+/-8%, p<0.025), but fell in the NEG group (from 57+/-10% to 51+/-8%). It is concluded that normalization of negative T waves on exercise ECG is a useful, simple index of myocardial viability in patients with previous myocardial infarction with no symptoms or ischemic ST-segment change during exercise testing.

Antibody imaging in the evaluation of cardiovascular diseases

Antimyosin antibody was originally developed for in vivo detection of acute myocardial infarction. However, its utility has expanded to include diagnosis of various cardiovascular diseases in which myocyte necrosis constitutes an obligatory component of the disease. Thus antimyosin has also been used clinically for noninvasive diagnosis of acute myocarditis, heart transplant rejection, drug-induced cardiotoxicity, and other cardiomyopathies. This first-generation monoclonal antibody, antimyosin, has opened the way for the second-generation monoclonal antibodies such as antifibrin and antiplatelet for in vivo diagnostic use in the detection of deep venous thrombosis and pulmonary embolism and antiatherosclerotic lesion-specific antibody for diagnosis of metabolically active lesions. Whether the third generation of antibodies will include ultrasmall antigen-binding units or negative charge-modified antibodies must await future studies.

Transcapillary exchange of indium 111-labeled anticardiac myosin Fab and thallium 201 in isolated reperfused rabbit hearts

BACKGROUND

The physiologic mechanisms of 111In-labeled anticardiac myosin antibody [111In]-AM) imaging are fairly well established. However, to better understand the transcapillary exchange characteristics of normal and reperfused myocardium, a standard first-pass, indicator-dilution analysis was undertaken in hearts subjected to global no-flow and low-flow ischemia.

METHODS AND RESULTS

The first-pass myocardial transport of 201Tl and [111In]-AM was evaluated in an in vitro rabbit model of no-flow ischemia/reperfusion with indicator-dilution analysis during normal and ischemic flows and whole-blood perfusate. The maximum extraction fraction (Emax) of 201Tl was dominated by flow rate as expected and averaged 0.75 (+/- 0.009) and 0.57 (+/- 0.008) during ischemic and normal flows, respectively (p < 0.01). Emax values for [111In]-AM, which were 0.02 or less in all hearts at control, increased to 0.06 or greater at moderate to longer perfusion times after 50 or more minutes of no-flow ischemia. Permeability surface area (in milliliters per minute per gram) tended to decline for 201Tl with longer reperfusion periods in both ischemic and normal flow groups and paralleled the changes observed for Emax for [111In]-AM.

CONCLUSIONS

These data demonstrate that the first-pass extraction of [111In]-AM is quite low in this model of acute coronary occlusion and reflow and enhanced only in severe ischemia-reperfusion treatment. Therefore in this model there appears to be no significant [111In]-AM uptake in either normal or mildly ischemic myocardium. Consequently, [111In]-AM uptake into myocardium must depend on tracer recirculation, as well as sarcolemmal cell wall disruption, to achieve specific and sufficient [111In]-AM uptake for localization of clinical imaging.

99mTc-antimyosin antibody imaging for the detection of acute myocardial infarction in human beings

111In-antimyosin imaging is a highly sensitive and specific technique for the detection of myocardial necrosis. Two new methods of labeling antimyosin with 99mTc have been developed, and were compared with the standard 111In-antimyosin imaging technique in 29 patients with acute myocardial infarction. Fourteen patients (group I) received directly labeled 99mTc-antimyosin, and 15 (group II) were given RP-1 conjugated 99mTc-antimyosin. 99mTc-antimyosin imaging was performed at 6, 12, and 24 hours, and 111In-antimyosin imaging was done at 24 and 48 hours following injection. The images were interpreted by three blinded observers. In group I, 99mTc-antimyosin uptake could be detected in 3, 6, and 12 cases at 6, 12, and 24 hours, respectively, compared with only 8 cases at 24 hours with 111In-antimyosin. At 48 hours all patients showed 111In-antimyosin uptake. In group II, 99mTc-antimyosin uptake could be detected in 2, 3, and 6 cases at 6, 12, and 24 hours, respectively, compared with 8 and 12 cases at 24 and 48 hours, respectively, with 111In-antimyosin. Gated blood pool studies could be obtained in all patients following 99mTc-antimyosin injection and could be used to identify regional wall motion abnormalities. The plasma half-lives of 99mTc-antimyosin in group I and group II were 2.67 +/- 0.3 hours and 4.23 +/- 0.3 hours, respectively, and the plasma half-life of 111In-antimyosin was 6.3 +/- 0.4 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

The noninvasive assessment of myocardial viability

The major objective of noninvasive imaging for detection of myocardial viability is to assist in the improved selection of patients with coronary artery disease and severe left ventricular dysfunction who would benefit most from revascularization. The techniques most commonly used to identify viable myocardium are thallium-201 (201Tl) scintigraphy, positron emission tomography (PET) using a flow tracer in combination with a metabolic tracer, technetium-99m (99mTc) sestamibi imaging, and dobutamine echocardiography. On stress 201Tl scintigraphy, asynergic regions showing normal thallium uptake, an initial defect with delayed redistribution at 3-4 h, late redistribution at 24 h, or defect reversibility after reinjection of a second dose of 201Tl at rest all suggest preserved viability. The greater the final uptake of 201Tl in areas of regional myocardial dysfunction preoperatively, the greater the improvement in ejection fraction after coronary revascularization. Demonstration of uptake of fluoro-18 deoxyglucose (FDG) in regions of diminished blood flow on PET imaging also correlates well with improved systolic function after revascularization. 99mTc sestamibi may also be useful for assessment of myocardial viability, particularly after thrombolytic therapy for acute myocardial infarction. Dobutamine echocardiography has good positive predictive value for viability determination, but absence of systolic thickening in an akinetic zone in response to intravenous infusion of the drug may still be associated with viable myocardium in 25-50% of segments. Of all the techniques cited above, quantitative resting 201Tl scintigraphy may be the best approach for distinguishing between viable and irreversibly injured myocardium.

Quantitative planar rest-redistribution 201Tl imaging in detection of myocardial viability and prediction of improvement in left ventricular function after coronary bypass surgery in patients with severely depressed left ventricular function

BACKGROUND

Although many patients with multivessel coronary artery disease (CAD) and severely depressed left ventricular (LV) function will benefit from coronary artery bypass graft surgery (CABG), surgeons may be reluctant to perform CABG on these patients without evidence of myocardial viability in regions of severe asynergy. We hypothesized that quantitative planar rest-redistribution 201Tl imaging would identify viable myocardium and predict improved regional and global function after revascularization in patients with depressed LV function and CAD.

METHODS AND RESULTS

Twenty-one patients (mean LV ejection fraction, 0.27 +/- 0.05) were studied. Regional and global LV functions were evaluated before and 8 weeks after CABG with radionuclide ventriculography. Segments were prospectively classified as showing normal, mildly reduced, or severely reduced viability on the basis of quantitative analysis of defect severity and redistribution on planar resting 201Tl imaging. By 201Tl criteria, 90% of hypokinetic segments were classified with normal or mildly reduced viability. Among akinetic or dyskinetic segments, 20% had normal 201Tl uptake, 53% had mildly reduced viability, and only 27% had severely reduced viability. 201Tl viability criteria identified segments that improved function after CABG. Sixty-two percent of severely asynergic segments with normal viability and 54% with mildly reduced viability improved function after surgery, but only 23% with severely reduced viability improved function (p = 0.002). When only adequately revascularized segments were considered, the predictive value of a positive preoperative viability scan for functional improvement was 73%. The greatest improvement in global LV function after CABG occurred in patients with the greatest number of asynergic segments classified as viable before surgery (p < 0.01). In 10 patients with more than seven viable, asynergic segments, mean LV ejection fraction increased significantly after CABG (0.29 +/- 0.07 to 0.41 +/- 0.11, p = 0.002). In 11 patients with seven or fewer viable, asynergic segments, mean LV ejection fraction remained unchanged after revascularization (0.27 +/- 0.05 to 0.30 +/- 0.08, p = NS).

CONCLUSIONS

In patients with CAD and severely depressed LV function, preoperative quantitative planar rest-redistribution. 201Tl imaging identifies viability in many asynergic myocardial segments, and these segments frequently improve function after CABG. The presence of numerous asynergic but viable myocardial segments before surgery correlated significantly with improvement in global LV function after bypass surgery.

Myocardial thallium-201 scintigraphy for assessment of viability in patients with severe left ventricular dysfunction

Many patients with ischemic heart disease and depressed left ventricular (LV) function have asynergic zones with sustained microcirculatory perfusion and myocardial metabolic activity that exhibit improved systolic function after coronary revascularization. The 2 predominant noninvasive techniques used to determine myocardial viability in patients with severely depressed LV function are thallium-201 (201Tl) scintigraphy and positron emission tomography (PET). Myocardial extraction of 201Tl is unaltered under experimental conditions of myocardial stunning or short-term hibernation (characterized by decreased flow and ischemic dysfunction). Akinetic or dyskinetic LV wall segments can exhibit normal or near normal 201Tl uptake as long as some residual flow is present. 201Tl scintigraphy can identify viable asynergic segments when performed on patients with severe coronary artery disease who are in the resting state. Many of these patients have initial resting defects that demonstrate delayed redistribution, or mild persistent defects that show improved perfusion and function after revascularization. There is a direct correlation between the extent of 201Tl uptake in zones of severe regional myocardial asynergy and the magnitude of improvement in resting LV ejection fraction after coronary bypass surgery. Rest 201Tl scintigraphy may help in the selection of patients with coronary artery disease and severely depressed LV function who would benefit the most from revascularization.

Assessment of postreperfusion myocardial hemorrhage using proton NMR imaging at 1.5 T

BACKGROUND

Intramyocardial hemorrhage occurs frequently after reperfusion of acute myocardial infarction. However, its significance has not yet been established, mainly because of the lack of methods for detecting such hemorrhage. The following ex vivo study was carried out to assess the potential of nuclear magnetic resonance (NMR) imaging to detect and quantitate postreperfusion intramyocardial hemorrhage.

METHODS AND RESULTS

Sixteen adult mongrel dogs underwent 3 hours of coronary occlusion followed by 1 hour of reperfusion, and three dogs underwent 4 hours of occlusion without reperfusion. Radiolabeled microspheres and 51Cr-labeled red blood cells were used to assess flow and evaluate the extent of hemorrhage. These results were later compared with both NMR and histology. Spin-echo NMR imaging was performed on the excised hearts using a 1.5-T system. Macroscopic assessment of the sliced myocardium revealed the existence of hemorrhage in 14 of the 16 dogs that underwent reperfusion but in none of those with occlusion only. In all 16 dogs with reperfusion, zones of increased signal intensity (SI) ratio (1.68 +/- 0.41 compared with control, p less than 0.05) were seen in regions relating to the distribution of the occluded coronary artery, whereas in 13 of the 16 dogs, areas of decreased SI within the zone of increased SI ratio (0.81 +/- 0.16 compared with control, p less than 0.05) were also seen, corresponding to regions with macroscopic hemorrhage. In contrast, in the three dogs without reperfusion, no macroscopic hemorrhage was observed, and likewise, no NMR zones of reduced SI were detected. Hemorrhage size by NMR (decreased SI zones), correlated well with hemorrhage size calculated from tissue slices (r = 0.96, SEE = 0.92%, p less than 0.01), or by 51Cr labeling (r = 0.78, SEE = 1.5, p = 0.1). In the reperfusion group, T2 relaxation times in the infarcted hemorrhagic zone (58 +/- 9 msec) were significantly lower than the infarcted zones without hemorrhage (98 +/- 13 msec, p less than 0.001). In contrast, when compared with control (964 +/- 72 msec), T1 relaxation times were significantly increased in both infarct zones, either with (1,284 +/- 176 msec) or without (1,266 +/- 103 msec) hemorrhage. The selective shortening of T2 relaxation times in the hemorrhagic regions is consistent with the paramagnetic effects of deoxyhemoglobin.

CONCLUSIONS

NMR imaging may provide a noninvasive approach for the detection and quantitation of intramyocardial hemorrhage. This observation may provide a means to further characterize pathological processes associated with acute myocardial infarction and assess the role of myocardial hemorrhage after reperfusion therapy.

Quantitative 111In antimyosin antibody imaging to predict the age of myocardial infarction

To establish whether quantitative 111In antimyosin uptake can be used to predict infarct age, we studied the heart-lung ratio in 107 images from 90 patients at various intervals following a Q-wave infarction. Imaging was performed 24 hours following 111In antimyosin injection. The HLR was measured as the ratio of the maximum counts in the infarcted myocardium to the adjacent lung background. The ratio ranged from 1.26 to 3.87, and declined with increasing infarct age. Infarcts were classified on the basis of age as type I (less than 3 days old), type II (less than 14 days), and type III (less than 90 days). True positive and false positive rates (TPR and FPR), and test-likelihood ratio calculations were performed for HLR thresholds ranging from 1 to 4, for the three infarct types. A FPR of 0% and likelihood ratio of infinity was obtained at a HLR threshold of 2.3 for type I infarcts (TPR 40.8%); at a HLR threshold of 2 for type II infarcts (TPR 50.6%), and a threshold of 1.8 for type III infarcts (TPR 52.6%). The likelihood of each infarct type can be estimated directly from the HLR for values below the above thresholds. These results show that quantitative 111In-antimyosin imaging may be used to predict infarct age.

Clinical role of indium-111 antimyosin imaging

Myocyte necrosis occurs in ischaemic, inflammatory and toxic heart diseases and can be detected by indium-111 antimyosin imaging. This allows a non-invasive evaluation of the site, extent and quantitation of the severity of myocardial necrosis. Simultaneous imaging of perfusion in patients with myocardial infarction allows the differentiation of necrosed and perfused areas and the varying degrees of mismatch and overlap, which has prognostic significance. 111In-antimyosin imaging is useful in the assessment of patients with unstable angina and in those for whom the diagnosis of infarction or unstable angina is not clear. In suspected myocarditis, a positive scan indicates the necessity for endomyocardial biopsy to confirm inflammation, whereas a negative scan makes the diagnosis of myocarditis unlikely. Antimyosin imaging is not useful as a marker of rejection in the 1 year post-transplant, but uptake after this period is associated with an increased rejection rate and is therefore an important tool in planning management strategies. Most patients on anthracycline treatment have demonstrable uptake, which is related to the cumulative dose and to the ejection fraction. Its role in this situation is as yet unclear. The use of new ligands and radioisotopes (99mTc) is likely to allow earlier imaging and produce improved quality.

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.

Thallium 201 kinetics in stunned myocardium characterized by severe postischemic systolic dysfunction

The hypothesis tested in this study was that despite the presence of severe postischemic myocardial dysfunction ("stunning"), the extraction and subsequent intracellular washout of thallium 201 should be preserved as long as irreversible sarcolemmal membrane injury was avoided. To produce myocardial stunning, 19 open-chested dogs with a critical left anterior descending coronary artery (LAD) stenosis underwent 10 5-minute periods of total LAD occlusion, each interspersed by 10 minutes of reperfusion by reflow through the critical stenosis. In another 12 control dogs observed for the same time period, no LAD occlusions were performed after placement of the critical stenosis. Hemodynamics, regional myocardial thickening by quantitative two-dimensional echocardiography, and microsphere-determined regional blood flows were serially measured. In 18 stunned dogs, systolic thickening in the LAD zone was markedly reduced to 0.4 +/- 2.4% at 40 minutes after the 10th reperfusion period compared with 32.5 +/- 2.2% thickening (p less than 0.001) in 12 control dogs at a matched time. The 201Tl first-pass extraction fraction determined by a double-isotope method using intracoronary 201Tl administration was comparable after the 10th reflow in a subgroup of 13 stunned (0.78) and six control (0.79) dogs. The T1/2 for the intracellular washout rate was also not significantly different in another group of six stunned (60 +/- 13 minutes) and six control (53 +/- 14 minutes) dogs, nor was the percentage of the 201Tl dose initially distributed in the interstitial compartment (11 +/- 3% vs. 7 +/- 2%). Systemic hemodynamics and regional flows were comparable in the two groups at 40 minutes after the 10th reflow. No dog had evidence of myocardial necrosis by triphenyl tetrazolium chloride staining. Thus, normal myocardial 201Tl extraction and washout kinetics are observed in a canine model of severe postischemic dysfunction (stunning) produced by repetitive brief LAD occlusions. These findings might have important clinical implications concerning the application of rest 201Tl scintigraphy for evaluation of perfusion and viability in patients with coronary artery disease and regional myocardial asynergy that is ultimately reversible.

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.

Relations of the myocardial imaging agents 99mTc-MIBI and 201T1 to myocardial blood flow in a canine model of myocardial ischemic insult

Myocardial imaging with thallium 201 has proven to be an important clinical procedure to assess the severity of the myocardial ischemic insult. Uptake of 201Tl is related to perfusion to and extraction by intact myocardium. Recently, a newer group of agents based on 99mTc alkyl isonitriles has been developed and appears promising for myocardial imaging. Although the distribution of this new agent has been shown to be related to myocardial perfusion, its dependence on myocardial integrity has not been established. This study compared the distribution of 99mTc-2-methoxy-isobutyl-isonitrile (99mTc-MIBI) with that of 201Tl in a clinically relevant canine model of ischemic insult. Fifteen adult dogs underwent 2 hours of occlusion by left anterior descending coronary artery ligation followed by reperfusion. In one group of dogs, 201Tl and 99mTc-MIBI were administered 5 minutes before 35 minutes of reflow (group 1, n = 5). In the other animals, the agents were given 5 minutes after onset of reflow, and dogs were killed after 10 (group 2, n = 5) and 35 minutes of reperfusion (group 3, n = 5). 99mTc-MIBI activity was significantly correlated with 201Tl activity (r = 0.91, 0.77, and 0.92, for groups 1, 2, and 3, respectively). Both 201Tl and 99mTc-MIBI activities were correlated similarly with blood flow in all models. In groups 1 and 2, 201Tl and 99mTc-MIBI activities correlated directly with microsphere-determined blood flow, whereas in group 3, they correlated inversely. The present study shows that in these models of myocardial ischemic insult, 99mTc-MIBI distribution is closely related to that of 201Tl.

Dual isotope thallium and indium antimyosin SPECT imaging to identify acute infarct patients at further ischemic risk

Forty-two patients (28 men and 14 women) with acute myocardial infarction (35 Q, seven non-Q wave) were injected with 2.0 mCi indium 111-labeled antimyosin (AM) monoclonal antibody (111In AM) within 48 hours of the onset of chest pain. Forty-eight hours later (72-96 hours after onset of chest pain), patients were injected with 2.2 mCi thallium 201, and two sets of single-photon emission computed tomography (SPECT) images were obtained simultaneously using dual energy windows set for the 247 keV indium photopeak and the 70 keV thallium peak. Seventeen patients had repeat scans at 4 hours. 111In AM uptake and 201Tl defects were localized to one or more of 24 coronal and sagittal segments. Scans with only 201Tl defects and corresponding 111In AM uptake were classified as matches; scans with unmatched 201Tl defects in addition to matching regions corresponding to electrocardiographic infarct location were classified as mismatches; and scans with 201Tl and 111In AM uptake in the same segments were classified as overlap. Scan patterns were correlated with clinical evidence for residual ischemia occurring within 6 weeks of infarct and including infarct extension, recurrent angina, and positive predischarge low-level or 6-week symptom-limited stress tests and with coronary anatomy. Fourteen patients had only matching patterns (group 1), 23 had mismatches (group 2), and five had 201Tl-111In overlap as the predominant pattern. None of the patients in group 1 had previous myocardial infarction; in each, the matched area corresponded to the Q wave location on electrocardiogram, and none had further in-hospital ischemic events or positive stress tests.(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.

Role of myocardial perfusion imaging in evaluating thrombolytic therapy for acute myocardial infarction

Myocardial thallium-201 scintigraphy is being increasingly employed as a method for assessing the efficacy of coronary reperfusion in acute myocardial infarction. New thallium uptake after intracoronary tracer administration after successful recanalization indicates that nutrient blood flow has been successfully restored. One may also presume that some myocardial salvage occurred if thallium administered in this manner is transported intracellularly by myocytes with intact sarcolemmal membranes. However, if one injects thallium by way of the intracoronary route immediately after reperfusion, the initial uptake of thallium in reperfused myocardium may predominantly represent hyperemic flow and regional thallium counts measured may not be proportional to the mass of viable myocytes. When thallium is injected intravenously during the occlusion phase the degree of redistribution after thrombolysis is proportional to the degree of flow restoration and myocardial viability. When thallium is injected for the first time intravenously immediately after reperfusion, an overestimation of myocardial salvage may occur because of "excess" thallium uptake in the infarct zone consequent to significant hyperemia. Another approach to myocardial thallium scintigraphy in patients undergoing thrombolytic therapy is to administer two separate intravenous injections before and 24 hours or later after treatment. Clinical studies have demonstrated that the improvement in defect size on serial images predicts improvement in regional function and patency of the infarct-related vessel. Finally, patients with acute myocardial infarction who receive intravenous thrombolytic therapy are candidates for predischarge exercise thallium-201 scintigraphy for risk stratification and detection of residual ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The prevalence and clinical significance of residual myocardial ischemia 2 weeks after uncomplicated non-Q wave infarction: a prospective natural history study

Despite having smaller infarct size and better left ventricular function, patients with non-Q wave myocardial infarction (NQMI) appear to have an unexpectedly high long-term mortality that is ultimately comparable to that of patients with Q-wave myocardial infarction (QMI). Patients with NQMI may lose their initial prognostic advantage because there is more viable tissue in the perfusion zone of the infarct-related vessel, rendering myocardium more prone to reinfarction. We tested this hypothesis in a prospective study of 241 consecutive patients 65 years of age or younger with acute uncomplicated myocardial infarction confirmed by creatine kinase levels (MB fraction). All patients received customary care and none underwent thrombolytic therapy or emergency angioplasty. Predischarge coronary angiography, radionuclide ventriculography, 24 hr Holter monitoring, and quantitative thallium-201 (201T1) scintigraphy during treadmill exercise were performed 10 +/- 3 days after infarction. Infarcts were designated as QMI (n = 154) or NQMI (n = 87) by accepted criteria applied to serial electrocardiograms obtained on days 1, 2, 3, and 10. The baseline Norris coronary prognostic index, angiographic jeopardy scores, and prevalence of Lown grade ventricular arrhythmias were similar between groups despite evidence for less necrosis with NQMI vs QMI, reflected by lower peak creatine kinase levels (520 vs 1334 IU/liter; p = .0001, 4 hr sampling), higher resting left ventricular ejection fraction (53% vs 46%; p = .0001), fewer akinetic or dyskinetic segments (1.2 vs 2.4; p = .0001), and fewer persistent 201Tl defects in the infarct zone (0.9 vs 1.9; p = .0001). Patients with NQMI also had more patent infarct-related vessels (54% vs 25%; p less than .0001) and a shorter time from onset of infarction to peak creatine kinase level (16.9 vs 22.5 hr; p = .0001). Importantly, the prevalence and extent of quantitatively determined 201Tl redistribution within the infarct zone on exercise scintigraphy was greater in patients with NQMI vs those with QMI (60% vs 36%, p = .007; and 0.98 vs 0.53 myocardial segments, p = .0003); when the two groups were stratified on the basis of the infarct-related vessel, subset analysis revealed the same findings. During 30 months median follow-up, cardiac mortality was low, 8.4% in the QMI group and 9.2% in the NQMI group (p = NS).(ABSTRACT TRUNCATED AT 400 WORDS)

Exercise thallium-201 scintigraphy in dogs: effects of long-term coronary occlusion and collateral development on early and late scintigraphic images

To examine the effects of coronary collateral development on thallium-201 (201Tl) distribution the left circumflex coronary artery was ligated in eight dogs. Three days later these animals ran on a treadmill, and 201-thallous chloride was injected into the right atrium at peak exercise. Scintigraphic scanning was begun within 10 min and continued for 3 hr. Scanning was repeated weekly for 6 weeks. In the last week radioactive microspheres were injected into the left atrium at peak exercise to measure regional myocardial blood flow. The scintigraphically determined disparity between perfusion of the ischemic and normal myocardium was most marked at 3 days after ligation. This difference gradually lessened over the first 4 weeks until there was no difference in 201Tl distribution to normally perfused myocardium and tissue distal to the ligation. Concomitant with the improvement in the scintigrams, exercise hemodynamics also improved over this 4 week period with significant increases in cardiac output and decreases in left atrial pressure. Serial coronary angiographic studies in two animals demonstrated the appearance of collaterals in the initial weeks after coronary occlusion, and by 4 weeks the left circumflex artery distal to the obstruction was completely opacified by collateral flow. The ratio of directly measured exercise blood flow to the left circumflex and normally perfused tissues was 0.89 +/- 0.08 at 6 weeks after ligation. Scintigraphic 201Tl redistribution after 3 hr also changed over the weeks after ligation. Three days after ligation washout from the ischemic area was significantly slower than that from the normal myocardium. By 6 weeks loss of 201Tl from the two regions occurred at nearly equal rates. Thus myocardial perfusion and function during exercise after coronary occlusion are dynamic events that change with time. It is likely that coronary collateral development is responsible for these phenomena. Therefore coronary collaterals do have salutary effects in the dog.

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.