Detection and sizing of acute myocardial infarcts with 99mTc (Sn) tetracycline

Minocycline: a bacteriostatic antibiotic with pleiotropic cardioprotective effects

Minocycline belongs to the family of tetracyclines, which are drugs traditionally approved as antibiotics. Based on preclinical animal cardiac models and clinical neurology trials, this drug has gained special attention as a promising cardiovascular therapeutic agent given its anti-inflammatory, antiapoptotic, antioxidant, and antienzymatic properties. This review focuses on the available evidence for minocycline as a cardioprotective drug, with special attention to mechanisms of action. Ongoing cardiovascular clinical trials are briefly discussed.

Myocardial scintigraphy with 99mTc-pyrophosphate in patients with unstable angina pectoris

A total of 400 patients, aged 25-82 years, admitted to the Coronary Care Unit due to clinical suspicion of acute myocardial infarction, were examined with 10 mCi 99mTc labelled to pyrophosphate. The examinations were carried out 4-120 hours post onset of symptoms, with a mobile gamma camera. Scintigrams were evaluated with regard to presence, localization and intensity of an uptake. Among 249 patients with a verified acute myocardial infarction, uptake was found in 237. Sixty-two of 85 patients with unstable angina showed a diffuse uptake with low intensity. Scintigraphy could not be used as a prognostic index of which patients would later develop an infarct. However, the scintigraphic pattern was useful as an aid in the differential diagnosis between acute myocardial infarction and unstable angina.

Non-invasive in vivo imaging of myocardial apoptosis and necrosis

Myocardial necrosis plays an important role in the pathogenesis of various cardiovascular disorders and can result from different myocardial insults. Its non-invasive identification and localisation therefore may help in the diagnosis of these disorders, as well as in prognosis and assessment of treatment response. Apoptosis, or programmed cell death, is important in the spectrum of myocardial damage since it is gradually becoming more apparent that cell death may begin as apoptosis and not as necrosis. First attempts to directly visualise the area of myocardial necrosis were based on recognition of myocardial infarction with "hot spot imaging agents" in patients with chest pain. Since then, the study of myocardial necrosis with gamma imaging agents has gone beyond the detection of myocardial infarction, and attempts have been made to diagnose other cardiovascular disorders associated with cardiac cell death such as heart transplant rejection, myocarditis, cardiotoxicity and cardiomyopathies. Traditionally, two hot spot imaging agents have been used for the detection of myocardial necrosis, (99m)Tc-pyrophosphate and (111)In-antimyosin. In addition, preliminary studies have demonstrated promising results with (99m)Tc-glucarate. Recently, (99m)Tc-annexin V has been successfully used for non-invasive gamma imaging of apoptosis after acute myocardial infarction, acute myocardial ischaemia, acute cardiac allograft rejection and malignant intracardiac tumours. This review article focusses on the characteristics of these different myocardial necrotic and apoptotic markers and compares their role in the assessment of myocardial damage.

Correlation of the size of isolated right ventricular infarction with the changes of ST segment in dogs

Vectorcardiographic, electrocardiographic, and hemodynamic changes in isolated infarction (infarct confined to the right ventricular free wall) were studied in 19 mongrel dogs. An isolated right ventricular infarction was produced by embolizing the right coronary artery with Spongel under closed chest conditions. The size of the infarct, identified by TTC staining, accounted for 6-65% (35.9 +/- 22.0%, mean +/- SD) of the right ventricular free wall. The STx, STy, STz, and the spatial magnitude of the ST segment (STM) were continuously recorded with an automated, real-time vectorcardiographic ST-segment analyzer (ST-monitor) using the Frank lead system. The cardiac index (CI) ratio (CI after embolization/CI before embolization) of all dogs with larger infarcts (infarct greater than 35% of the right ventricle) was below 1.0. In dogs with smaller infarcts (% RVI less than or equal to 35%), there were no differences in the hemodynamic data before and 4 h after embolization. In dogs with larger infarcts, however, pulmonary arterial pressure and heart rate 4 h after embolization were significantly decreased compared with those before embolization. In addition, right atrial pressure 4 h after embolization in the larger infarct group was significantly elevated compared with that in the smaller infarct group. In dogs with larger infarcts, STx, STy, and STM were significantly larger than in those with smaller infarcts both 15 min and 4 h after embolization. There were no significant correlations between infarct size and change in vectorcardiographic ST segments in the smaller infarct group.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of infarct size in acute canine myocardial infarction by single-photon emission computed tomography with technetium-99m pyrophosphate

The location and extent of myocardial infarction (MI) are important predictors of patient course. The current study tests the hypothesis that MI size could be measured accurately using rotating gamma camera single-photon emission computed tomography ( SPECT ) and technetium-99m pyrophosphate (PPi) and that the accuracy of these measurements was independent of MI location and transmural or nontransmural distribution. SPECT was performed in 38 dogs 48 hours after ligation of the left anterior descending coronary artery (14 dogs) or left circumflex coronary artery (LC) (24 dogs) at the mid-level or below. Projection images were corrected for center-of-rotation and field nonuniformity and processed with a 1-dimensional low-pass filter to diminish rib activity. Sixteen 0.5-cm-thick transverse sections, including the entire left ventricle, were reconstructed by filtered backprojection , low-pass filtered, contrast enhanced and processed with a 3-dimensional boundary enhancement operator. The boundary of PPi uptake in each slice was marked automatically using an algorithm that combined a directional derivative and a threshold, and required continuity of the boundary in 3 dimensions. The total number of volume elements that showed abnormal tracer uptake were summed, corrected to absolute volume, and multiplied by the specific weight of cardiac muscle. Scintigraphic MI weight was compared with pathologic MI weight. There was an excellent correlation between scintigraphic and pathologic MI weight. The poorer correlation for nontransmural compared with transmural MIs is most likely a function of size alone, since MIs that weighed less than 10 g (n = 12, range 1.3 to 9.5 g), both transmural and nontransmural, showed a similar correlation: S = 1.07 X P + 0.56 (r = 0.81, standard error of the slope = 0.245).(ABSTRACT TRUNCATED AT 250 WORDS)

Macroscopic and microscopic measurement of myocardial infarct size. A comparison

Infarct size measured by microscopic method is consistently larger than that measured macroscopically, indicating that certain areas of infarction are missed when observed macroscopically. Existence of a good correlation between the two methods, however, suggests that macroscopic estimation of infarct size would be enough for initial screening of the interventions designed for salvation of ischemic myocardium, as it is an easy method. An additional advantage of this method is that it can be utilized to measure infarct size as early as 72 h after production of infarction. Comparison of weight and volume method of macroscopic estimation of infarct size has shown that they do not give significantly different results. Weight method being less cumbersome and less time-consuming, may be adopted for initial screening of cardioprotective agents.

Accuracy of localization of acute myocardial infarction by 12 lead electrocardiography

Until recently, ECG accuracy in localizing acute myocardial infarction (AMI) could be assessed only by comparing the ECGs with autopsy findings. This approach, however, preselected patients, including only those who died. It is possible that this postmortem group of patients would be different from the whole population of patients with AMI. Myocardial imaging with 99mTc-pyrophosphate offers the advantage of directly localizing the region of injured myocardium in the acute phase of AMI. In 34 patients with confirmed AMI and focal uptake of 99mTc-pyrophosphate, serial ECGs were obtained and interpreted by two independent observers. The sensitivity and specificity of serial ECGs in determining the location of AMI in the five left ventricular (LV) wall segments were determined: (1) in the anterior wall sensitivity was 86.7% and specificity was 89.5%; (2) in the lateral wall sensitivity was 73.7% and specificity was 80.0%; (3) in the high lateral wall sensitivity was 80.0% and specificity was 87.5%; (4) in the inferior wall sensitivity was 87.5% and specificity was 100%; (5) in the "true" posterior wall sensitivity was 83.3% and specificity was 86.4%. Overall, in the 170 LV wall segments (five per patient) examined, scans localized with a sensitivity of 81.9% and a specificity of 88.8%. After four patients with LBBB were excluded, sensitivity increased to 87.1%. Overall, localization of AMI by serial ECG was accurate in 85.9% of the 34 patients included in the study.

Myocardial cell damage during attacks of vasospastic angina in the absence of persistent electrocardiographic changes

We have investigated whether vasospastic anginal attacks might be associated with myocardial cell damage even when permanent ORS or ST-T changes are absent. We obtained serum time-activity curves of creatine kinase MB, of myoglobin, and of alpha hydroxybutyrate dehydrogenase in 15 patients with vasospastic angina admitted to our Coronary Care Unit (CCU). A slight but consistent rise and fall of both myoglobin and creatine kinase MB was observed in 7 patients (4 presented a definitive myocardial uptake of 99mTc pyrophosphate, and I had a faint deposition). A similar pattern was observed for myoglobin alone in 3 patients (1 presented a negative myocardial scan), while no consistent changes were found in the remaining 5 patients (2 presented a faint deposition of 99mTc pyrophosphate). No significant change of alpha hydroxybutyrate dehydrogenase was observed in any of the patients. The coherent rise and fall of the levels of myocardial cytosolic components after prolonged episodes of vasospastic angina suggests that cell damage may occur even in the absence of persistent QRS and ST-T changes.

Subcellular binding of 99Tcm-gluconate in infarcted myocardium in dogs

Binding of 99Tcm-gluconate on the subcellular level in myocardial infarct tissue in the dog was investigated by means of a fractionated centrifugation technique. High isotope activity/g protein was recorded in the mitochondrial fraction indicating the 99Tcm-gluconate binds preferentially to a protein structure localized in the mitochondria.

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.

Acute myocardial infarct scintigraphy with infarct-avid radiotracers

The selective uptake of radiopharmaceuticals by acutely infarcted myocardium has emerged as an independent, noninvasive technique to aid in the detection, localization, and quantification of myocardial necrosis.

Value and limitations of technetium-99m stannous pyrophosphate in the detection of acute myocardial infarction

Technetium-99m stannous pyrophosphate (99mTc-PYP) myocardial imaging was performed in 436 consecutive patients for the evaluation of chest pain and suspected acute myocardial infarction (AMI). Scintigrams were assessed independently by three observers with a 90% interobserver agreement. In 134 patients with documented AMI (97 TRANSMURAL, 37 NONTRANSMURAL), THE SENSITIVITY OF 99MTc-PYP imaging was significantly lower in patients with nontransmural AMI (41%) than in patients with transmural AMI (78%), 99mTc-PYP imaging correctly localized the site of transmural infarction in 53 patients (70%). A diffuse 99mTc-PYP uptake was found in nine (10%) of 91 patients with positive scintigrams: six of these had a transmural AMI and three nontransmural AMI. In 226 patients without AMI, the specificity of infarct imaging was 95%. A false-positive scintigram was found in 0%, 8%, 9%, and 2% of patients with unstable angina, progressive angina, stable angina, and noncardiac chest pain, respectively. A diffuse uptake was found in six (54%) of 11 patients with false-positive scintigrams. No patient with the clinical diagnosis of noncardiac chest pain showed discrete uptake. In 76 patients with uncertain diagnosis for AMI, 99Tc-PYP imaging was considered of value in 11 patients with ventricular conduction defects (two patients with WPW syndrome, nine patients with LBBB). These data suggest that: 1. 99mTc-PYP imaging is moderately sensitive in detecting and localizing transmural AMI and is insensitive in detecting nontransmural AMI; 2. A discrete 99mTc-PYP uptake is highly specific for AMI; 3. a diffuse uptake is neither sensitive to, nor specific for AMI. Myocardial imaging with 99m-Tc-PYP is of clinical value when the standard electrocardiographic and enzymatic techniques are inadequate for an accurate diagnosis of AMI.

Accumulation of 99Tcm-gluconate in isolated rat cardiac myocytes and hepatocytes during anoxia

The accumulation of 99Tcm-gluconate in the myocardium and liver of the rat during anoxia has been investigated on the cellular level and compared with the histopathologic changes. The conclusion is drawn that the uptake of isotope runs a course similar to that registered in vivo in human myocardial infarction.

Clinical value of delayed thallium-201 myocardial imaging in suspected acute myocardial infarction

Fifty patients with acute chest pain had thallium-201 myocardial imaging performed three to six days after emergency admission to hospital. The image was abnormal in 20 out of 22 patients with acute transmural myocardial infarcts but in only 1 of 5 with acute subendocardial infarcts. Indistinguishable scan abnormalities caused by old infarcts were seen in 7 patients, and caused by myocardial ischaemia in 1 patient. A single thallium-201 myocardial scan some days after the onset of symptoms appears to be of little value in the clinical assessment of patients with suspected acute myocardial infarction.

Early quantification of experimental myocardial infarction with technetium-99m glucoheptonate: scintigraphic and anatomic studies

Recent advances in understanding of the pathophysiology of myocardial necrosis indicate the need for a noninvasive method that will allow detection and quantification of infarcts in the first few hours after the onset of infarction. Myocardial infarct scintigraphy using technetium-99m glucoheptonate is capable of detecting infarction in dogs and man within 4 to 6 hours of onset. Studies were performed in 45 dogs with acute myocardial infarction: 28 with with an anterior infarct, 5 with an inferior infarct, 6 with an anterior infarct studied after infusion of mannitol and 6 with ligation of the left anterior descending coronary coronary artery and reperfusion of the ischemic area. The dogs were given 20 m Ci of technetium-99m glucoheptonate 1 hour after coronary occlusion, subjected to imaging 5 to 9 hours later and then killed. The experiments revealed that (1) scintigraphic infarct size correlated with infarct weight for anterior (r = 0.85) and inferior (r = 0.88) infarcts; (2) technetium-99m glucoheptonate also concentrated in a rim of myocardium around the infarct that probably represented the ischemic zone; and (3) technetium-99m glucoheptonate uptake by infarcted myocardium could be greatly increased with mannitol and reperfusion.

The prognostic implications of acute myocardial infarct scintigraphy with 99mTc-pyrophosphate

The predictive value of the myocardial scintigraphy with 99mTc-pyrophosphate was studied in 100 patients admitted to the coronary care unit with suspected acute myocardial infarction. None of the 21 patients with normal scintigrams had acute myocardial infraction by other criteria. Fifty-five percent of patients with diffuse uptake (pattern B), 73% of patients with focal uptake (pattern C) and all patients with intense focal uptake (pattern D) and massive uptake (pattern E) had acute infarction. The complication rate in the hospital and after discharge (mean followup: 6.1 months) for patients with pattern E was 88% compared to 42% for D, 30% for C, 36% for B and 10% for patients with normal scintigrams (A). For patients with acute infarction with patterns C, D and E, the complication rate rose with increasing size of the myocardial uptake of 99mTc-pyrophosphate. In addition to its diagnostic potential, scintigraphy provides prognostic information which is useful for patient triage and for therapeutic decisions early in the evolution of the infarct.

Myocardial scintigraphy with technetrium-99m pyrophosphate during the early phase of acute infarction

To determine the sensitivity of myocardial scintigraphy with technetium-99m pyrophosphate during the early phase of acute myocardial infarction, 31 patients admitted to the coronary care unit with prolonged ischemic pain underwent imaging within 4 to 8 hours and again at 24 hours after the onset of symptoms. In 11 of 15 patients with documented acute myocardial infarction, increased focal myocardial uptake was demonstrated on early myocardial scintigraphy. Focal uptake was observed in only 2 of 16 patients with unstable angina pectoris. Three or four patients with normal early scintigrams had massive transmural myocardial infarction. Normal early scintigrams in these three patients may have reflected poor perfusion because the images were abnormal at 24 hours. In four patients the extent of technetium-99m pyrophosphate uptake increased more than 20 percent at 24 hours without other evidence of infarct extension. In the other seven patients, there was no significant change in the area of the abnormal radioactive uptake between early and delayed scintiscans. This study suggests that technetium-99m pyrophosphate scintigraphy can defect acute myocardial infarction as early as 4 hours after the onset of symptoms although the sensitivity rate (73 percent) is less than that at 24 hours.

The measurement and control of myocardial infarct size

Direct, chemical, electrocardiographic and radio-isotopic methods are described for the estimation of myocardial infarct size in animals and man. Their relative points and failings are discussed. The effects of interventions, physical, metabolic and pharmacological, upon the size of myocardial infarcts, are examined and work attempting to reduce myocardial infarct size in man reviewed.

Uptake of 99Tcm-gluconate and early histologic findings in induced myocardial infarcts in dogs

A new isotope, 99Tcm-gluconate, for detection of myocardial infarction has been investigated experimentally. Great differences in isotope uptake between infarcted myocardium and normal myocardium were found in dogs. A close correlation was found between the isotope uptake and the uptake of basic fuchsin (HBFP) at microscopy in early myocardial infarcts.

"Hot spot" myocardial scanning: experiences with a mobile nuclear camera in a coronary care unit

Twenty-nine patients with suspected or actual myocardial infarction have had myocardial "hot spot" scans with technietium 99m pyrophosphate, using a mobile nuclear camera in a coronary care unit. Nine patients with transmural infarcts had positive scans. Nine out of 12 patients thought to have had endocardial infarction had positive scans. Two patients who had had intramuscular injections presented with chest pain and abnormally high serum enzyme levels, but had negative scans. Myocardial radionuclide scanning with a mobile nuclear camera is a rapid, easy, repeatable, non-invasive method of helping to confirm or exclude the diagnosis of myocardial infarction and, used together with other available tests, is a valuable additional diagnostic aid.

Follow-up technetium-99m stannous pyrophosphate myocardial scintigrams after acute myocardial infarction

Technetium-99m stannous pyrophosphate (99mTc-PYP) myocardial scintigrams were obtained in 68 patients during acute myocardial infarction (AMI) and at follow-up 15.9 +/- 8.8 weeks later. All patients with AMI had a positive scintigram (2+ or greater); only one of 46 control patients (2%) had a positive (2+) scintigram. At follow-up scintigraphy 6 to 37 weeks following AMI, 57% of patients had a persistently positive scintigram even though recurrent AMI was suspected in only one of these patients. Patients with persistently positive scintigrams tended to have more severe disease as evidenced by compensated congested heart failure (41%) persistent angina (77%), and ECG evidence of ventricular dyssynergy (51%), We conclude that 1) in patients with prior AMI, a 2+ abnormality on 99mTc-PYP scintigram may not represent new AMI; 2) a persistently positive 99mTc- PYP scintigram may have prognostic implications since it occurs predominantly in patients with severe symptomatic coronary disease.

Location and size of acute transmural myocardial infarction estimated from thallium-201 scintiscans. A clinicopathological study

A clinicopathological study was performed in 23 patients who died from acute transmural myocardial infarction and who had been studied with thallium-201 during the acute phase. Twenty patients died within five days and three later than five days after scintigraphy. The scintigraphic location and the estimated size of infarction in vivo were correlated with postmortem findings. There was good agreement in 91% between scintigraphic and postmortem location of infarction and in 70% between the ECG and postmortem findings. The size of infarction as determined from computer-processed schematic drawings of postmortem slices of the heart correlated well with the size determined from processed schematic drawings of the scintiscans (r = 0.91 for anterior infarction, r = 0.97 for inferior infarction, r = 0.86 for anterior-inferior infarction). It is concluded that thallium-201 scintigraphy provided more precise location of infarction than the ECG and that the size of the scintigraphically abnormal area reflected the extent of necrotic myocardium.

Sizing acute myocardial infarcts: present limitations and potential approaches

It is now possible by scintigraphic imaging to identify the presence of acute transmural or nontransmural myocardial infarcts by noninvasive techniques and to localize acute transmural infarcts. Radionuclide blood-pool scintigraphy allows assessment of the impact of old and new myocardial damage on left ventricular function.

Favorable effects of hyaluronidase on electrocardiographic evidence of necrosis in patients with acute myocardial infarction

To evaluate hyaluronidase's effect in reducing post-infarction myocardial necrosis, we randomized 91 patients with anterior infarction to control (45) or to hyaluronidase-treatment (46) groups. A 35-lead precordial electrocardiogram was recorded on admission and seven days later. Hyaluronidase was administered intravenously after the first electrocardiogram and every six hours for 48 hours. QRS-complex changes were analyzed to assess the drug's effect. Precordial sites with ST-segment elevation (larger than or equal to 0.15 mV) on the initial electrocardiogram that retained an R wave were considered vulnerable for the development of electrocardiographic signs of necrosis. The sum of R-wave voltages of vulnerable sites fell more in the control group than in the hyaluronidase group (70.9 +/- 3.6 per cent [+/- 1 S.E.M.] vs 54.2 +/- 5.0 per cent P less than 0.01). Q waves appeared in 59.3 +/- 4.9 per cent of the vulnerable sites in control versus 46.4 +/- 4.9 per cent in hyaluronidase-treated patients (P less than 0.05). Thus, hyaluronidase reduced the frequency of electrocardiographic signs of myocardial necrosis.

Serum myoglobin level as diagnostic test in patients with acute myocardial infarction

Serum myoglobin levels were measured in normal subjects and patients by means of a newly developed radioimmunoassay. Myoglobin was identified in all of 135 sera from normal adults and ranged between 6 and 85 ng/ml (mean +/- SE 31 +/- 1.3). Raised myoglobin levels were present in 62 of 64 patients with documented acute myocardial infarction, the mean serum concentration being 528 +/- 76 ng/ml. Serial determinations in 46 patients with acute infarct showed that maximum values usually occurred within 4 hours after admission. In 19 of 42 cases, raised myoglobin levels preceded the rise in creatine kinase (CK) values; in the remaining patients, both serum myoglobin and creatine kinase were increased on admission. Only 2 of an additional 44 patients admitted with chest pain but without subsequent electrocardiographic, enzyme, or technetium-99m stannous pyrophosphate myocardial scintigraphic evidence of acute myocardial infarction had raised myoglobin levels; the mean value for this group was within the normal range (44 +/- 6 ng/ml). Serum myoglobin values also were normal in patients with congestive heart failure without acute myocardial infarction, and in patients after moderate exercise and cardiac catheterisation. Trasient myoglobinaemia appears to be one of the earliest laboratory abnormalities occurring in acute myocardial infarction and, therefore, should prove useful as a diagnostic aid in patients.

Imaging of acute myocardial infarction using technetium 99m labelled phosphate compounds

Technetium 99m pyrophosphate or polyphosphate administered intravenously soon after acute myocardial infarction produces positive images of the area and extent of myocardial necrosis. Forty-four patients have been studied of whom 39 had myocardial infarction. There was good correlation of the site and extent of infarction as indicated by the scintigram with electrocardiogram and cardiac enzyme criteria.