Quantification of myocardial infarction: a comparison of single photon-emission computed tomography with pyrophosphate to serial plasma MB-creatine kinase measurements

Elevated serum uric acid affects myocardial reperfusion and infarct size in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention

AIMS

Elevated serum uric acid (eSUA) was associated with unfavorable outcome in patients with ST-segment elevation myocardial infarction (STEMI). However, the effect of eSUA on myocardial reperfusion injury and infarct size has been poorly investigated. Our aim was to correlate eSUA with infarct size, infarct size shrinkage, myocardial reperfusion grade and long-term mortality in STEMI patients undergoing primary percutaneous coronary intervention.

METHODS

We performed a post-hoc patients-level analysis of two randomized controlled trials, testing strategies for myocardial ischemia/reperfusion injury protection. Each patient underwent acute (3-5 days) and follow-up (4-6 months) cardiac magnetic resonance. Infarct size and infarct size shrinkage were outcomes of interest. We assessed T2-weighted edema, myocardial blush grade (MBG), corrected Thrombolysis in myocardial infarction Frame Count, ST-segment resolution and long-term all-cause mortality.

RESULTS

A total of 101 (86.1% anterior) STEMI patients were included; eSUA was found in 16 (15.8%) patients. Infarct size was larger in eSUA compared with non-eSUA patients (42.3 ± 22 vs. 29.1 ± 15 ml, P = 0.008). After adjusting for covariates, infarct size was 10.3 ml (95% confidence interval 1.2-19.3 ml, P = 0.001) larger in eSUA. Among patients with anterior myocardial infarction the difference in delayed enhancement between groups was maintained (respectively, 42.3 ± 22.4 vs. 29.9 ± 15.4 ml, P = 0.015). Infarct size shrinkage was similar between the groups. Compared with non-eSUA, eSUA patients had larger T2-weighted edema (53.8 vs. 41.2 ml, P = 0.031) and less favorable MBG (MBG < 2: 44.4 vs. 13.6%, P = 0.045). Corrected Thrombolysis in myocardial infarction Frame Count and ST-segment resolution did not significantly differ between the groups. At a median follow-up of 7.3 years, all-cause mortality was higher in the eSUA group (18.8 vs. 2.4%, P = 0.028).

CONCLUSION

eSUA may affect myocardial reperfusion in patients with STEMI undergoing percutaneous coronary intervention and is associated with larger infarct size and higher long-term mortality.

Relationship between fragmented QRS and no-reflow, infarct size, and peri-infarct zone assessed using cardiac magnetic resonance in patients with myocardial infarction

BACKGROUND

The relation between fragmented QRS complex (fQRS) and cardiac magnetic resonance parameters is poorly documented in ischemic cardiopathy.

METHODS

Among 209 consecutive patients, those with fQRS were compared with those without fQRS. Cardiac magnetic resonance studies with late gadolinium-enhanced sequences were done during the week after acute myocardial infarction.

RESULTS

fQRS was present in 113 (54%) patients, and associated with a significantly lower left ventricular ejection fraction, increased left ventricular volumes, a larger infarct size (IS), and a larger peri-infarct zone. Microvascular obstruction was more frequent in patients with fQRS (62% vs 45%; P = 0.014) and the extent of the microvascular obstruction was significantly larger (1.6% [range, 0.0-4.4] vs 0.0 [range, 0.0-2.1]; P = 0.004). Finally, the transmurality score in the 2 study populations was identical (48% vs 47%; P = 0.895). In multivariate logistic regression analysis, only IS (odds ratio [OR], 1.06; 95% confidence interval [CI], 1.03-1.09; P < 0.001), systolic blood pressure (OR, 1.02; 95% CI, 1.01-1.04; P < 0.001), and left ventricular end-systolic volume (OR, 1.02; 95% CI, 1.00-1.03; P = 0.013) remained independent predictors of fQRS.

CONCLUSIONS

This study revealed that fQRS was associated with increased IS, myocardial perfusion abnormalities, decreased left ventricular ejection fraction, and increased left heart volumes. These findings show that fQRS is a reliable marker of infarct size and acute ventricular remodelling.

Synthesis and preliminary evaluation of mono-[123I]iodohypericin monocarboxylic acid as a necrosis avid imaging agent

Hypericin monocarboxylic acid was synthesized in an overall yield of 25% in four steps and radiolabelled with iodine-123 in good yield (>75%). The resulting mono-[(123)I]iodohypericin monocarboxylic acid was evaluated in normal mice and in rats with ethanol induced liver necrosis. In this model, tracer concentration in necrotic liver tissue was 14 times higher than in the viable liver tissue as quantified by autoradiography at 24h post injection. The results indicate the feasibility of visualization of necrotic tissue with the novel tracer.

Early positive biomarker in relation to myocardial necrosis and impaired fatty acid metabolism in patients presenting with acute chest pain at an emergency room

BACKGROUND

Measurement of circulating biomarkers has enabled early diagnosis and risk assessment of acute coronary syndrome. This study sought diagnostic values of the first single-point data of biomarkers obtained soon after patient arrival by comparing with scintigraphically quantified myocardial injury in patients presenting with acute chest pain at an emergency room.

METHODS AND RESULTS

Serial blood samples were taken soon after arrival in an emergency department in 74 patients with suspected acute coronary syndrome to quantify blood levels of troponin-T (TnT), heart-type fatty acid-binding protein (H-FABP), myocardial-bound creatine kinase (CK-MB), and myoglobin. Myocardial perfusion and metabolic defects were scintigraphically quantified. The first single-point data had high positive predictive values for detecting the defects (80-100%) but low negative predictive values (15-41%). CK-MB and TnT had higher specificities (73-100%) but significantly lower positive rates (22-27%) than the others (61-68%), resulting in greater sensitivities of H-FABP and myoglobin (75-80%) than those of CK-MB and TnT (29-35%). Among biomarkers, TnT peak concentrations most closely correlated with scintigraphic abnormalities.

CONCLUSION

H-FABP can contribute to early detection of myocardial injury and TnT is most likely to correlate with injured myocardial mass. The differential features of biomarkers are complementary in patients with acute chest pain presenting at an emergency room.

Enzyme estimates of infarct size correlate with functional and clinical outcomes in the setting of ST-segment elevation myocardial infarction

Background

Cardiac biomarkers are routinely obtained in the setting of suspected myocardial ischemia and infarction. Evidence suggests these markers may correlate with functional and clinical outcomes, but the strength of this correlation is unclear. The relationship between enzyme measures of myocardial necrosis and left ventricular performance and adverse clinical outcomes were explored.

Methods

Creatine kinase (CK) and CK-MB data were analyzed, as were left ventricular ejection fraction (LVEF) by angiogram, and infarct size by single-photon emission computed tomography (SPECT) imaging in patients in 2 trials: Prompt Reperfusion In Myocardial-infarction Evolution (PRIME), and Efegatran and Streptokinase to Canalize Arteries Like Accelerated Tissue plasminogen activator (ESCALAT). Both trials evaluated efegatran combined with thrombolysis for treating acute ST-segment elevation myocardial infarction (STEMI).

Results

Peak CK and CK area-under-the-curve (AUC) correlated significantly with SPECT-determined infarct size 5 to 10 days after enrollment. Peak CK had a statistically significant correlation with LVEF, but CK-AUC and LVEF correlation were less robust. Statistically significant correlations exist between SPECT-determined infarct size and peak CK-MB and CK-MB AUC. However, there was no correlation with LVEF for peak CK-MB and CK-MB AUC. The combined outcome of congestive heart failure and death were significantly associated with CK AUC, CK-MB AUC, peak CK, and peak CK-MB measurements.

Conclusion

Peak CK and CK-MB values and AUC calculations have significant correlation with functional outcomes (LVEF- and SPECT-determined infarct size) and death or CHF outcomes in the setting of STEMI. Cardiac biomarkers provide prognostic information and may serve as valid endpoint measurements for phase II clinical trials.

Usefulness of rapid quantitative measurement of myoglobin and troponin T in early diagnosis of acute myocardial infarction

BACKGROUND

New equipment, the Cardiac Reader(TM), which can measure blood concentrations of troponin T (T) and myoglobin (M) in only 15 min at the bedside was evaluated for early diagnosis of acute myocardial infarction (AMI).

METHODS AND RESULTS

A total of 34 consecutive patients with AMI who came to hospital within 24 h after onset were studied. Blood samples were collected from the patients at admission and 6, 12, 24, 48 h after onset to qualitatively and quantitatively measure T, M and creatine kinase-MB fraction. There were 20 patients with positive results by qualitative troponin T test and 29 with positive results by quantitative test. Of the patients who visited hospital within 3 h of onset, 17% were positive by the qualitative test and 67% cases had positive results in the quantitative test. The patients were divided into 2 groups according to the flow grade in the infarct-related coronary artery. In the TIMI 0-1 group (n=28), serum myoglobin concentrations were higher than in the TIMI 3-4 group (n=6) at admission and at their peak.

CONCLUSION

The rapid quantitative test of T and M is useful for early diagnosis of AMI and as an indicator of its severity, which can be evaluated from the myoglobin concentration in the hyper-acute phase.

Assessment of left ventricular function using serum cardiac troponin I measurements following myocardial infarction

The prognosis and extent of injury to the myocardium have previously been assessed by increased serum creatine kinase (CK) MB levels. We report findings from 39 consecutive, acute myocardial infarction (AMI) patients presenting 4.5 h (range, 0.7-12.1 h) after the onset of chest pain. We compared CK MB mass (upper reference limit, 5.0 ng/ml) and cardiac troponin I (cTnI; upper reference limit, 0.8 ng/ml) (Stratus II, Dade International) in serial serum specimens obtained over 36 h after chest pain from AMI patients; within 6 h after onset of chest pain. While the appearance of the kinetics of CK MB and cTnI were similar during the initial 24 h following the onset of chest pain, cTnI was increased significantly (p < 0.05) over CK MB after 9 to 12 h. Half-life determinations (mean+/-S.D.) in 22 of the 39 AMI patients demonstrated a significantly (p < 0.01) shorter half-life in non-Q-wave infarcts [t1/2 6.8 h (+/-5.6)] vs. Q-wave infarcts [t1/2 20.4 h (+/-10.7)]. Further serial time versus marker (mean+/-S.D.) results were significantly correlated (p < 0.001, r = 0.66). Sixteen of twenty patients assessed by echocardiography had an abnormal left ventricular ejection fraction (LVEF); mean 37.6 (S.D. 15.2)%, ranging from 15.4 to 67.6%. LVEF was significantly and inversely correlated to peak CK MB (r = .50, p = 0.03), as well as to peak cTnI (r = 0.46, p = 0.04). Based on these findings, cTnI shows excellent promise as a useful marker of infarct size, for the assessment of left ventricular function, and may potentially replace CK MB as the cardiac-specific marker for AMI detection.

Cumulative troponin T release after acute myocardial infarction. Influence of reperfusion

For troponin T a characteristic biphasic change in the plasma time-concentration curve has been described, especially in patients with early reperfusion after thrombolytic therapy. As troponin T is bound to myofibrillar structures, treatment strategy or treatment outcome could influence the cumulative plasma release of this protein in a different way compared to the cumulative release of free cytoplasmic cardiac enzymes. The present study is the first study comparing the total quantity of troponin T released by the heart during the first 168 hours after acute myocardial infarction, both in patients treated with thrombolytic therapy (n = 16) and in patients not treated with thrombolytic therapy (n = 7). On the basis of clinical symptoms and coronary arteriogram within 24 hours, the patients treated with thrombolytic therapy were divided into two groups, reperfused (n = 9) and non-reperfused (n = 7). In the patients not treated with thrombolytic therapy, absence of spontaneous early reperfusion was judged only from clinical symptoms. Cumulative troponin T release into plasma was compared to the cumulative release of the cytoplasmic cardiac enzymes creatine kinase (EC 2.7.3.2) and hydroxybutyrate dehydrogenase (EC 1.1.1.27). Cumulative release, i. e., infarct size, was calculated using a two-compartment model for circulating proteins. Mean tissue contents, per gram wet weight, of 156 U/g for hydroxybutyrate dehydrogenase, 2.163 U/g for creatine kinase and 234 microg/g for troponin T, were used to express infarct size in gram-equivalents of healthy myocardium per litre plasma (g-eq/l). Release rates were represented by the ratio of cumulative quantities released in 10 hours and 72 hours for creatine kinase and hydroxybutyrate dehydrogenase and in 10 hours and 168 hours for troponin T.

CONCLUSIONS

- Plasma time-concentration curves and release rates of troponin T in patients treated with thrombolytic therapy showing reperfusion differ significantly from those of patients not treated with thrombolytic therapy, showing no reperfusion. - Creatine kinase and hydroxybutyrate dehydrogenase release is completed within 72-100 hours in all patients, whereas troponin T release still continues after 168 hours. - Cumulative troponin T release at 168 hours is only a fraction (around 8%) of cumulative cytoplasmic enzyme release and the percentage released is not influenced by the treatment strategy or outcome, i. e., vessel patency. - Although troponin T release is only a fraction of the cumulative enzyme release (infarct size) there is a highly significant correlation between both, independent of the treatment strategy or treatment outcome.

Blood flow-dependent uptake of indium-111 monoclonal antimyosin antibody in canine acute myocardial infarction

OBJECTIVES

The relation of myocardial blood flow and indium-111 (111In) antimyosin antibody uptake was studied by inducing myocardial infarction in 18 dogs, 8 with closed chest left anterior descending artery balloon occlusion for 3 h followed by reperfusion (group A) and 10 dogs with open chest left anterior descending artery ligation (without reperfusion, group B).

BACKGROUND

The relation of antimyosin uptake to myocardial injury has been documented. However, its relation to tracer delivery by myocardial blood flow has not been studied and has been assumed to be independent.

METHODS

Indium-111 antimyosin antibody, 2 mCi, was injected 20 min after reperfusion and 3 h after coronary artery ligation in groups A and B, respectively. Regional blood flows were determined by radiolabeled microspheres during occlusion and 24 h later in both groups. On day 2, dogs were killed after risk zone delineation with gentian violet. The heart was excised and stained with triphenyltetrazolium chloride solution and graded for increasing severity of tissue injury based on extent of staining. Microsphere activity and 111In antimyosin activity were measured in control tissue (grade 1), noninfarct tissue at risk (grade 2), mixed tissue (grade 3), infarct tissue (grade 4) and hemorrhagic infarct tissue (grade 5, present only in group A dogs). Count activity was normalized to that of the mean value in control tissue (grade 1) and expressed as a ratio of activity.

RESULTS

Indium-111 antimyosin activity was high in triphenyltetrazolium chloride grade 4 tissue in both groups but was attenuated in grade 4 tissue in group B dogs (10.6 +/- 5.1 vs. 5.0 +/- 4.5; p < 0.05 group A vs. group B), which had lower blood flow on day 2 (0.51 +/- 0.36 vs. 0.23 vs. 0.22; p < 0.01). Normalizing 111In antimyosin activity for blood flow on day 2 resulted in equivalent 111In antimyosin uptake for infarct tissue (32.6 +/- 21.6 vs. 36.6 +/- 29.8 for group A vs. group B; p = NS).

CONCLUSIONS

Thus, 111In antimyosin uptake is a specific marker of necrotic tissue with a high signal ratio in reperfused tissue. However, its uptake is dependent on residual blood flow in the infarct territory. Indium-111 antimyosin could potentially serve as a suitable tracer for infarct sizing if myocardial blood flow in the same region were factored simultaneously.

Cardiac imaging after acute myocardial infarction. Identification of patients at continued risk

Diagnostic imaging performed early in the course of acute myocardial infarction provides anatomic and functional information that is useful in assessing patients at risk for future cardiac events and premature death. Early identification of left ventricular dysfunction or complications of myocardial infarction allows appropriate and timely management of high-risk patients and early transfer of stable patients from the intensive care environment. Noninvasive predischarge functional imaging to unmask patients with jeopardized myocardium identifies high-risk patients who may need invasive studies and surgical or interventional treatment. Postdischarge risk stratification with diagnostic imaging provides vital prognostic information in high- and low-risk patients, allowing for appropriate allocation of medical resources.

Circulating myosin light chain I levels after coronary reperfusion: a comparison with myocardial necrosis evaluated from single photon emission computed tomography with pyrophosphate

This study was performed to assess the influence of coronary reperfusion on the serial serum myosin light chain (LC)I levels and to evaluate the relationship between the peak LCI level and the infarct size calculated from single photon emission computed tomography (SPECT) with technetium-99m pyrophosphate (Tc-99m PYP) in 11 patients who underwent coronary reperfusion. Blood was drawn before reperfusion, immediately after reperfusion, and once a day for 14 days, to estimate the time course of serum LCI release. The infarct size estimated by Tc-99m PYP ranged from 7.3 to 62.4 ml. The LCI levels obtained before reperfusion were less than 2.5 ng/ml but those obtained immediately after reperfusion were much higher. The value ranged from 2.7 to 9.7 ng/ml and that expressed as a percentage of peak LCI (% peak LCI) ranged from 19 to 83%. Collateral circulation, reperfusion arrhythmia and the degree of residual stenosis had no influence upon the % peak LCI. The correlation between peak LCI levels and SPECT-determined infarct size was good, with a correlation of 0.76 (p less than 0.01, regression line by least squares method y = 3.31 + 1.53x). Early serum LCI might be influenced by coronary reperfusion but the peak LCI value reflected acute myocardial necrosis in patients who underwent coronary reperfusion.

Effect of infarct size measured from antimyosin single-photon emission computed tomographic scans on left ventricular remodeling

To evaluate the effect of infarct size on left ventricular volumes and geometric remodeling, 26 patients with a first acute Q wave myocardial infarction (anterior in 14, inferior in 12) had the infarct sized from single-photon emission computed tomographic (SPECT) imaging of indium-111 antimyosin. All patients underwent gated blood pool scintigraphy before hospital discharge for determination of ejection fraction and end-diastolic and end-systolic volume indexes. Infarct size was quantitated from indium-111 antimyosin uptake in coronal slices with use of a threshold technique for edge detection. Nineteen of 26 patients had additional simultaneous acquisitions of indium-111 and thallium-201 uptake and the infarct was expressed as a percent of the total left ventricle. Infarct size was larger (59 +/- 16 vs. 33 +/- 16 g), predischarge ejection fraction lower (35 +/- 5% vs. 60 +/- 9%) and end-systolic volume index higher (57 +/- 13 vs. 36 +/- 10 ml/m2) in the group with anterior infarction. Despite these differences, predischarge end-diastolic volume index was not significantly different between the group with anterior (88 +/- 17 ml/m2) versus inferior (89 +/- 14 ml/m2) infarction. There was a significant inverse correlation between percent infarct size and ejection fraction for patients with dual isotope imaging (r = -0.90) and a significant direct correlation between infarct size and end-systolic volume index (r = 0.79, p less than 0.01). Fourteen patients without subsequent myocardial infarction or coronary artery bypass grafting had a repeat gated blood pool study late (26 +/- 15 months) after infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimating the size of myocardial infarction by magnetic resonance imaging

OBJECTIVE

To develop a method to measure myocardial infarct size by magnetic resonance imaging and to compare the results with pyrophosphate scanning by single photon emission computed tomography.

DESIGN

All patients underwent magnetic resonance imaging and pyrophosphate scanning 5-7 days after the onset of symptoms. Both measurements of infarct size were compared with the release of creatine kinase MB and with ventricular performance estimated by radionuclide ventriculography.

PATIENTS

19 patients (age 40-68 years) who had sustained their first uncomplicated myocardial infarction and who had not been treated with thrombolytic therapy.

RESULTS

The site of infarction was clearly shown by both imaging techniques and was identical in each patient. The volume of infarcted tissue measured by magnetic resonance imaging agreed well with the infarct size measured by single photon emission tomography (mean difference 2.7 cm3). Correlations of both imaging techniques with the release of creatine kinase MB were best when total release rather than peak release was used. Both imaging techniques correlated closely with the subsequent ventricular performance.

CONCLUSIONS

Magnetic resonance imaging after acute infarction allows measurement of infarct size and this may prove useful in assessing new treatments designed to salvage myocardium.

Quantitative estimation of infarct size by simultaneous dual radionuclide single photon emission computed tomography: comparison with peak serum creatine kinase activity

To test the hypothesis that simultaneous dual energy single photon emission computed tomography (SPECT) with technetium-99m (99mTc) pyrophosphate and thallium-201 (201TI) can provide an accurate estimate of the size of myocardial infarction and to assess the correlation between infarct size and peak serum creatine kinase activity, 165 patients with acute myocardial infarction underwent SPECT 3.2 +/- 1.3 (SD) days after the onset of acute myocardial infarction. In the present study, the difference in the intensity of 99mTc-pyrophosphate accumulation was assumed to be attributable to difference in the volume of infarcted myocardium, and the infarct volume was corrected by the ratio of the myocardial activity to the osseous activity to quantify the intensity of 99mTc-pyrophosphate accumulation. The correlation of measured infarct volume with peak serum creatine kinase activity was significant (r = 0.60, p less than 0.01). There was also a significant linear correlation between the corrected infarct volume and peak serum creatine kinase activity (r = 0.71, p less than 0.01). Subgroup analysis showed a high correlation between corrected volume and peak creatine kinase activity in patients with anterior infarctions (r = 0.75, p less than 0.01) but a poor correlation in patients with inferior or posterior infarctions (r = 0.50, p less than 0.01). In both the early reperfusion and the no reperfusion groups, a good correlation was found between corrected infarct volume and peak serum creatine kinase activity (r = 0.76 and r = 0.76, respectively; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Single photon emission computed tomography with technetium-99m hexakis 2-methoxyisobutyl isonitrile in acute myocardial infarction before and after thrombolytic treatment: assessment of salvaged myocardium and prediction of late functional recovery

Single photon emission computed tomography (SPECT) with technetium-99m hexakis 2-methoxyisobutyl isonitrile was investigated as a method to evaluate the results of intravenous thrombolytic treatment in 14 patients (11 men and 3 women) with acute myocardial infarction admitted to the coronary care unit within 4 h of the onset of symptoms. All patients received an injection of 740 MBq of the tracer before starting the thrombolytic therapy, and isonitrile tomography was performed 3 to 4 h later. The tomographic study was repeated 5 days after the acute event. The results of thrombolytic treatment were independently evaluated taking into account the clinical, electrocardiographic (ECG) and enzymatic data and the findings of left ventricular and coronary angiography. Furthermore, all patients were studied with two-dimensional echocardiography on admission, 5 days later and 1 month later. The site and extent of the perfusion defects on admission scintigraphy were consonant with the ECG and echocardiographic findings. A good correlation could be established between the 5 day scintigraphic estimate of infarct dimension and the enzymatic infarct size (r = 0.907, p less than 0.00002). The comparison between pre- and postthrombolytic treatment images enabled the identification of successful and unsuccessful reperfusion even in patients whose other noninvasive findings were inconclusive. Finally, the reduction in defect size predicted late functional improvement that was demonstrated by echocardiography performed 1 month later (r = 0.89, p less than 0.00005). The results of the study suggest the feasibility and the possible usefulness of isonitrile tomography in demonstrating the presence and size of myocardial damage and in assessing the extent of myocardial salvage after thrombolytic therapy in acute myocardial infarction.

Inflammatory response, neutrophil activation, and free radical production after acute myocardial infarction: effect of thrombolytic treatment

Activated neutrophils releasing proteolytic enzymes and oxygen free radicals have been implicated in extending myocardial injury after myocardial infarction. Neutrophil elastase was used as a marker of neutrophil activation and the non-peroxide diene conjugate of linoleic acid was used as an indicator of free radical activity in 32 patients after acute myocardial infarction; 17 were treated by intravenous thrombolysis. Patients with acute myocardial infarction had higher plasma concentrations of neutrophil elastase and the non-peroxide diene conjugated isomer of linoleic acid than normal volunteers or patients with stable ischaemic heart disease. Patients treated by thrombolysis had an early peak of neutrophil elastase at eight hours while those who had not been treated by thrombolysis showed a later peak 40 hours after infarction. The plasma concentration of non-peroxide conjugated diene of linoleic acid was highest 16 hours after the infarction irrespective of treatment by thrombolysis. Quantitative imaging with single photon emission tomography showed decreased uptake of indium-111 labelled neutrophils in the infarcted myocardium (as judged from technetium-99m pyrophosphate) in those who had received thrombolysis, suggesting a decreased inflammatory response. The results indicate increased neutrophil activation and free radical production after myocardial infarction; they also suggest that thrombolysis does not amplify the inflammatory response and may indeed suppress it.

Infarct sizing by scintigraphic techniques and nuclear magnetic resonance imaging

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

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.

Myocardial infarction determined by technetium-99m pyrophosphate single-photon tomography complicating elective coronary artery bypass grafting for angina pectoris

The incidence of acute myocardial infarction (AMI) complicating coronary artery bypass grafting (CABG) has previously been based on concordance of electrocardiographic, enzymatic and scintigraphic criteria. Technetium-99m pyrophosphate (Tc-PPi) single-photon emission computed tomography now enables detection of AMI with high sensitivity and specificity. Using this technique, perioperative AMI was detected in 12 of 58 patients (21%) undergoing successful elective CABG for stable angina pectoris. Stepwise multivariate logistic regression analysis was performed to compare the predictive value of preoperative (New York Heart Association class, left ventricular ejection fraction and use of beta blockers) and intraoperative (number of grafts constructed, use of internal mammary anastomoses, use of sequential saphenous vein grafts, smallest grafted distal vessel lumen caliber and aortic cross-clamp time) variables. Preoperative New York Association class (p = 0.04) and smallest grafted distal vessel lumen caliber (p = 0.03) were significant multivariate predictors of perioperative AMI. Only 1 perioperative patient with AMI (and 1 pyrophosphate-negative patient) developed new Q waves. Serum creatine kinase-MB was higher in patients with AMI by repeated measures analysis of variance (p = 0.0003). Five AMIs occurred in myocardial segments revascularized using sequential saphenous vein grafts, and 7 in segments perfused by significantly stenosed epicardial vessels with distal lumen diameter and perfusion territory considered too small to warrant CABG. At 6-month follow-up, the mean left ventricular ejection fraction increased from 0.61 to 0.65 in Tc-PPI-negative patients (p = 0.01), but not in perioperative patients with AMI.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Quantification of area and percentage of infarcted myocardium by single photon emission computed tomography with thallium-201: a comparison with serial serum CK-MB measurements

In order to quantify the size of the infarcted myocardium, two kinds of data processing techniques were applied to single photon emission computed tomography (SPECT) with thallium-201 and its clinical reliability was evaluated by comparing it with the infarct sizing procedure with the serial serum creatine kinase-MB measurements in 14 patients with acute myocardial infarction. After maximum-count circumferential profile analysis, short axis images were reformatted into an unfolded surface map and a bull's eye view map. The SPECT-determined infarct size was defined as the area or the percentage of hypoperfused myocardium of which the profile count was less than the mean minus 2SD derived from 8 normal subjects. The infarct area was calculated from the number of pixels with an abnormal count and expressed in an unfolded surface map. The percentage was calculated from the number of abnormal profile points and displayed in a bull's eye view map. A high linear correlation was observed between the enzymatically determined infarct size and the infarct area or the percentage (r = .947, r = .872, respectively), despite underestimations in 2 patients with accompanying right ventricular infarction and overestimations in 2 patients with prior anterior infarction. Moreover, a close negative correlation was found between the left ventricular ejection fraction and the infarct area or the percentage (r = .836, r = .821, respectively). Thus, the semiautomatic techniques for processing thallium-201 SPECT images might contribute to the quantitative estimation and display of infarcted myocardium and have high clinical reliability.

Antimyosin imaging in acute transmural myocardial infarctions: results of a multicenter clinical trial

Murine monoclonal antimyosin antibody has been shown experimentally to bind selectively to irreversibly damaged myocytes. To evaluate the safety and efficacy of monoclonal antimyosin for identifying acute transmural infarction, 50 patients with acute Q wave myocardial infarction were entered into a phase I/II multicenter trial involving three clinical sites. Indium-111 antimyosin was prepared from an instant kit formulation containing 0.5 mg of diethylene triamine pentaacetic acid (DTPA)-coupled Fab fragment (R11D10) and 1.2 to 2.4 mCi of indium-111. Average labeling efficiency was 92%. Antimyosin was injected 27 +/- 16 h after the onset of chest pain. Planar or tomographic imaging was performed 27 +/- 9 h after injection in all patients, and repeat imaging was done 24 h later in 39 patients. Of the 50 patients entered, 46 showed myocardial uptake of antimyosin (sensitivity 92%). Thirty-one of 39 planar scans performed at 24 h were diagnostic; 8 showed persistent blood pool activity that cleared by 48 h. Focal myocardial uptake of antimyosin corresponded to electrocardiographic infarct localization. No patient had an adverse reaction to antimyosin. In addition, 125 serum samples, including 21 collected greater than 42 days after injection, were tested for human antimouse antibodies, and all samples were assessed as having undetectable titers. Intensity of antimyosin uptake was correlated with infarct location and the presence or absence of collateral vessels. There was a significant correlation between faint uptake and inferoposterior infarct location. In 21 patients who had coronary angiography close to the time of antimyosin injection, there was a significant correlation between faint tracer uptake and closed infarct-related vessel with absent collateral flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Early estimation of acute myocardial infarct size soon after coronary reperfusion using emission computed tomography with technetium-99m pyrophosphate

Early appearance of positive findings on a technetium-99m pyrophosphate scan has been shown to be associated with the presence of a reperfused acute myocardial infarction (AMI). Early technetium-99m pyrophosphate imaging was performed by emission computed tomography to evaluate reperfusion and to test the feasibility of estimating infarct size soon after coronary reperfusion based on acute positive tomographic findings. Twenty-seven patients with transmural AMI who were treated with intracoronary urokinase infusion followed by percutaneous transluminal coronary angioplasty underwent pyrophosphate imaging 8.7 +/- 2.1 hours after the onset of AMI. None of the 8 patients in whom reperfusion was unsuccessful had acute positive findings. Of 19 patients in whom reperfusion was successful, 17 had acute positive findings (p less than 0.001). In these 17, tomographic infarct volumes were determined from reconstructed transaxial images. The threshold for areas of increased pyrophosphate uptake within the infarct was set at 60% of peak activity by the computerized edge-detection algorithm. The total number of pixels in all transaxial sections showing increased tracer uptake were added and multiplied by a size factor and 1.05 g/cm3 muscle to determine infarct volume. The correlations of tomographic infarct volumes with peak serum creatine kinase (CK) levels (r = 0.82) and with cumulative release of CK-MB isoenzyme (r = 0.89) were good. Moreover, the time to positive imaging was significantly shorter than that to peak CK level (8.5 +/- 2.3 vs 10.4 +/- 2.2 hours, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of early myocardial technetium-99m pyrophosphate uptake to early peaking of creatine kinase and creatine kinase-MB as indicators of early reperfusion in acute myocardial infarction

The value of technetium-99m pyrophosphate (Tc-99m-PYP) scintigraphy as an indicator of reperfusion 2.8 to 8 hours after the onset of symptoms of acute myocardial infarction was compared with the value of early peak creatine kinase (CK) and CK-MB release within 16 hours after the onset of symptoms. In 29 patients who received thrombolytic therapy, recanalization was seen (group 1) and in 7 it was not (group 2). In 23 patients (79%) in group 1 scintigraphic findings were positive and in all 7 in group 2 they were negative. In 15 patients (52%) in group 1 and 1 patient (14%) in group 2, CK reached its peak level within 16 hours. In 20 patients (69%) in group 1 and 3 (43%) in group 2 the CK-MB level reached a peak within 16 hours. The sensitivity, specificity and predictive accuracy of positive results of early Tc-99m-PYP scintigraphy in predicting the reperfusion were 79%, 100% and 83%. These values are significantly higher than or similar to those of early peaking of CK and CK-MB release. In contrast to measurements of enzyme release, reperfusion data for Tc-99m-PYP scintigraphy are available immediately after thrombolytic therapy. Therefore, early Tc-99m-PYP scintigraphy (3 to 8 hours after onset of symptoms) is valuable as a noninvasive technique for early diagnosis of reperfusion.

Quantitative aspects of myocardial perfusion imaging

Computer quantitation of myocardial perfusion images has enhanced the detection of thallium perfusion abnormalities compared to visual analysis. Computer analysis is more specific than visual analysis for detection of initial defects and more sensitive for detection of redistribution. Computer analysis is equally good for detecting thallium abnormalities in the distribution of the three major coronary arteries. Measurement of absolute clearance of thallium results in an unacceptable high false-positive rate. However, when clearance in a myocardial segment is compared to the fastest clearing segment in the heart, the specificity of clearance improves significantly. Quantitation of lung:heart ratio is very useful. Increased lung:heart ratio reflects exercise induced left ventricular dysfunction and is a strong marker of prognosis. Single photon emission computerized tomography (SPECT) offers the potential of more precisely sizing the risk area. The question of whether this technique offers a significant advantage over planar thallium imaging has to be answered.

The acute inflammatory response to myocardial infarction: imaging with indium-111 labelled autologous neutrophils

The uptake of indium-111 labelled neutrophils was examined in 30 patients with acute myocardial infarction by planar imaging and single photon emission computed tomography. The time from venepuncture to reinjection of the autologous labelled neutrophils was less than 2.5 hours and imaging was carried out 24 hours later. Twenty three patients had a positive uptake of neutrophils in the myocardium and imaging was improved by single photon emission computed tomography. There was a significant difference between the intervals from the onset of chest pain to injection of labelled neutrophils between patients with positive and negative images; early reinjection was more likely to produce a positive image. Indeed, all nine patients reinjected within 18 hours of the onset of symptoms had positive images. The results suggest that the stimulus for activation and migration of neutrophils is transient; this is an important factor if neutrophil release products play a role in cell damage after coronary occlusion.

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.