Diagnosis of acute myocardial infarction in a community hospital: significance of CPK-MB determination

A mutant of the Buthus martensii Karsch antitumor-analgesic peptide exhibits reduced inhibition to hNav1.4 and hNav1.5 channels while retaining analgesic activity

Scorpion toxins can kill other animals by inducing paralysis and arrhythmia, which limits the potential applications of these agents in the clinical management of diseases. Antitumor-analgesic peptide (AGAP), purified from Buthus martensii Karsch, has been proved to possess analgesic and antitumor activities. Trp³⁸, a conserved aromatic residue of AGAP, might play an important role in mediating AGAP activities according to the sequence and homology-modeling analyses. Therefore, an AGAP mutant, W38G, was generated, and effects of both AGAP and the mutant W38G were examined by whole-cell patch clamp techniques on the sodium channels hNa_v1.4 and hNa_v1.5, which were closely associated with the biotoxicity of skeletal and cardiac muscles, respectively. The data showed that both W38G and AGAP inhibited the peak currents of hNa_v1.4 and hNa_v1.5; however, W38G induced a much weaker inhibition of both channels than AGAP. Accordingly, W38G exhibited much less toxic effect on both skeletal and cardiac muscles than AGAP in vivo The analgesic activity of W38G and AGAP were verified in vivo as well, and W38G retained analgesic activity similar to AGAP. Inhibition to both Na_v1.7 and Na_v1.8 was involved in the analgesic mechanism of AGAP and W38G. These findings indicated that Trp³⁸ was a key amino acid involved in the biotoxicity of AGAP, and the AGAP mutant W38G might be a safer alternative for clinical application because it retains the analgesic efficacy with less toxicity to skeletal and cardiac muscles.

Racial differences in serum creatine kinase levels

Total creatine kinase was measured in serum samples obtained from 307 asymptomatic healthy subjects, 112 men and 195 women, during screening visits to the Yale University Hypertension Clinic or the Yale-New Haven Hospital Primary Care Center or during pre-employment physical examinations at the Yale-New Haven Hospital Personnel Health Clinic. The group consisted of 147 blacks, 132 whites, and 28 Hispanics. Blood pressure was measured in all patients, and weight, height, and serum potassium and creatinine levels were determined in most. Any subject who had engaged in any vigorous exercise in the 12 hours prior to the visit was excluded. The mean total creatine kinase level for black men was 146.5 +/- 136.9 units/liter (median, 108 units/liter), the mean level for white men was 60.8 +/- 26.1 units/liter (median, 51 units/liter), and the mean level for Hispanic men was 84.5 +/- 70.6 units/liter (median, 57 units/liter). The mean level for black women was 66.4 +/- 50.0 units/liter (median, 53 units/liter), the mean level for white women was 37.0 +/- 18.2 units/liter (median, 32 units/liter), and the mean level for Hispanic women was 41.5 +/- 36.0 units/liter (median, 30 units/liter). Using the testing laboratory's normal values for total creatine kinase (8 to 80 units/liter for men and 5 to 50 units/liter for women), 37 black men (64.9 percent) and 49 black women (54.4 percent) had abnormal values for total creatine kinase. Although sex, race, diastolic blood pressure, serum creatinine level, and presence of hypertension correlated significantly with total creatine kinase levels in the entire population, only sex did so in blacks. Multivariate analysis using linear regression techniques clearly demonstrated that sex and race were the only variables that independently predicted the total creatine kinase level. These findings show that healthy asymptomatic blacks have higher total creatine kinase levels than whites or Hispanics, with the majority having values in the abnormal range. Thus, different normal values should be used for blacks, just as they are for men and women, and elevated total creatine kinase levels should be interpreted with considerable caution.

The diagnostic value of different enzymes and standard ECG in acute myocardial infarction

Serum (S) enzyme activity of aspartate aminotransferase (ASAT, E.C. 2.6.1.1.), heat stable lactate dehydrogenase (LD, E.C. 1.1.1.27.), creatine kinase (CK, E.C. 2.7.3.2.) and CK-B subunit and the respective standard electrocardiograms (ECG) were compared in 463 patients with suspected acute myocardial infarction (MI) in order to evaluate sensitivity and specificity. Serum ASAT was analysed daily for 3 days, S-heat stable LD every 12 h for 48-108 h, S-CK and S-CK-B every 6 h for 48 h and ECG once daily for 3 days. All four enzymes had a high sensitivity, varying from 99% for LD to 97% for CK-B. The highest specificity was observed for CK-B and CK (98%) as compared with heat stable LD (91%) and ASAT (74%). Standard ECG showed a high specificity (96%) and a low sensitivity (80%).

Diagnostic and prognostic significance of minimally elevated creatine kinase-MB in suspected acute myocardial infarction

CK-MB changes were studied using agarose gel electrophoresis in 244 patients admitted to a coronary care unit for suspected acute myocardial infarction (AMI). A range of minimally elevated CK-MB levels, from 1 to 24 IU/liter, was identified as representing uncertain AMI events. Positive AMI events were defined by elevations of 25 IU/liter or more documented in patients with new Q waves or abnormalities in all enzyme and isoenzyme levels. Negative AMI events were defined by elevation of 0 IU/liter, observed in all control subjects. The 1-year cardiac mortality rates in the "positive"-AMI (n = 91) and "uncertain"-AMI (n = 22) groups were identical (22%), and significantly higher than that in the "negative"-AMI group (n = 93) (6%) (p less than 0.05). However, when a larger uncertain-AMI group of 115 patients was compiled by 2 collaborating centers, the 1-year cardiac mortality rate in the 39 patients with chest pain alone was 0%, vs 33% in the 76 patients with accompanying severe medical problems such as cardiac or respiratory failure. Whether minimal CK-MB elevations represent AMI of limited extent is not clear. These elevations occur most often in association with severe medical problems, and in patients without such problems, they may not indicate a poor prognosis.

Sensitivity and specificity of MB creatine kinase activity determined with column chromatography

Several analytic techniques are used to estimate the activity of creatine kinase (CK) isoenzymes. These techniques are undergoing continual refinement because the MB CK molecule appears to be nearly cardiospecific. An improved column chromatographic assay is presented with a lower limit of analytic detection of 0.8 mlU/ml. The assay was applied to normal subjects and to patients with myocardial infarction and with complex disease states. Results of the column chromatography were compared with those of agarose and cellulose acetate electrophoresis. There was MB CK activity in all normal sera (no. = 19, mean +/- standard deviation = 2.4 +/- 7). After acute myocardial infarction the MB CK activity increased by 650 percent (no. = 86, mean +/- standard error of the mean = 158.2 +/- 12.6 mlU/ml). The sensitivity for myocardial infarction was 100 percent. The specificity, evaluated in multiple clinical states, approached 100 percent. The column assay was compared with both agarose and cellulose acetate electrophoresis, and poor correlations with these semiquantitative systems were demonstrated. Finally, peak MB CK activity was closely correlated with kinetic analyses used to estimate infarct size (r = 0.94). Thus, column chromatography is a sensitive and specific method of estimating MB creatine kinase activity and is more precise than current electrophoretic methods.

Aids to the evaluation of diagnostic performance, as applied to immunological creatine kinase-MB assay in myocardial infarction

Immunoassay of creatine kinase-MB provides numerical information, which makes it possible to estimate quantitatively the diagnostic performance following myocardial infarction. Two graphical methods for such an evaluation are presented. The relationship between technical sensitivity and specificity was analyzed using a continuous function, the receiver-operator characteristic curve. Using this function, a diagnostic threshold ("upper normal limit") was chosen, which balances both technical specificity and sensitivity on the first day following infarction. On the second and third days this threshold caused a progressive loss of technical sensitivity. The relationship between effectiveness and the prevalence of myocardial infarction in the tested population was evaluated with a nomogram correlating these two quantities. With the chosen diagnostic threshold, effectiveness is independent of prevalence on the first day, but the loss in technical sensitivity on subsequent days causes effectiveness to decay when the prevalence is high.

Creatine kinase MB isoenzyme in the evaluation of myocardial infarction

The measurement of serum CK-MB isoenzyme is a very sensitive and specific indication of myocardial injury since only myocardium has substantial amounts of CK-MB. Serum CK-MB levels are most helpful clinically when the total creatine kinase is nonspecifically elevated, as with intramuscular injections, cardiac catheterization, stroke, noncardiac surgery and electric cardioversion. Elevations of serum CK-MB occurring in Duchenne's muscular dystrophy and other neuromuscular disorders may be due to the presence of abnormal regenerative skeletal muscle fibers, which are known to contain large amounts of CK-MB isoenzyme. These examples emphasize that under normal, nonregenerative conditions, elevations of serum CK-MB are rare in the absence of myocardial injury.

Sensitive assay of creatine kinase isoenzymes in human serum using M subunit inhibiting antibody and firefly luciferase

A sensitive method for the assay of B subunit and total creatine kinase activity is described. The ATP formation in the creatine kinase reaction is continuously monitored by measuring the bioluminescence obtained with a purified firefly luciferase reagent. The B subunit activity is determined using an M subunit inhibiting antibody resulting in greater than 99.5% and approximately 50% inhibition of MM and MB isoenzymes, respectively. The bioluminescent method correlated well with a similar spectrophotometric method in the assay of B subunit as well as total creatine kinase activity (r greater than or equal to 0.98). However, the bioluminescent assay is considerably more sensitive, allowing the assay of B subunit activity in serum from healthy individuals. This is due to the inherent sensitivity of the bioluminescent assay of ATP, a reduced analytical interference from adenylate kinase and a reduced reagent blank. The within-series precision at 1 U/liter and greater than 52 U/liter corresponded to a C.V. of 14% and 3%, respectively. The method is as rapid and suitable for routine work as spectrophotometric methods. From a clinical point of view the new method is of particular interest in the early diagnosis of small acute myocardial infarctions.

[Studies of activity kinetic of isoenzyme CK-MB in serum after myocardial infarction (author's transl)]

We investigated the activity kinetics of CK-total and CK-MB in 83 patients with proven myocardial infarctions. Serial serum samples were taken at intervals of 2--6 h. The activity of isoenzym CK-MB was determined by means of the immunological inhibition method. CK-MB activity was determined in all patients. The mean peak activity of CK-MB was 65 U/l (range: 9-241 U/l). At the time of peak CK-MB activity the mean percentage CK-MB activity was 13.2% (range: 3.4--21.7%). The CK-MB activity reached its peak at 17.4 h (range: 3.0--32.5 h) after the onset of retrosternal pain. This is 1.4 h after peak CK-total activity. The mean disappearance rate constant for CK-MB (n = 31) was found to be 9.3 X 10(-4) U/min with a large individual variation. This value corresponds to a half life of 12.5 h (CK-total: 15.5 h). The determination of CK-MB activity is therefore only of diagnostic significance within 48 h of possible myocardial occurrence. Moreover, isoenzyme CK-MB is not found exclusively in myocardium. For this reason it is better to use the percentage CK-MB activity in the differential diagnosis of myocardial infarction. With 80% of the patients this value is greater than 6% within 36 h of proven myocardial infarction.

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.

The management of acute coronary insufficiency

1. Coronary insufficiency is a pathophysiologic state that can initiate lethal cardiac arrhythmias in the absence of myocardial necrosis. Patients with suspected coronary insufficiency should be monitored until they are stabilized and a diagnosis is confirmed. 2. Early and adequate intravenous antiarrhythmic prophylaxis with lidocaine to raise the fibrillation threshold in the setting of coronary insufficiency can prevent primary ventricular fibrillation. Classic "warning arrhythmias" are not predictive of ventricular fibrillation. Their persistence during adequate antifibrillatory prophylaxis does not indicate therapeutic failure. 3. The isoenzyme of creatine phosphokinase, CPK-MB, is an extremely sensitive and specific indicator of myocardial necrosis if measured serially during the 24 hours following the onset of symptoms suggesting coronary insufficiency. It may prove most useful in eliminating the false positive diagnosis of myocardial infarction in difficult clinical cases. 4. The management of heart failure in myocardial infarction requires an understanding of the relationship between ventricular preload and the cardiac output. The treatment of clinical manifestations of an elevated ventricular preload in asymptomatic patients is not justified and may be detrimental. In symptomatic patients, however, judicious manipulation of ventricular preload should be the first therapeutic consideration, and an optimal filling pressure should be achieved and maintained when other determinants of the cardiac output are manipulated. 5. Indications for the prophylactic insertion of a temporary transvenous pacing electrode for heart block associated with myocardial infarction must be individualized. Most authorities agree that prophylactic pacing may be justified in patients with evidence of new infranodal block involving two of the three fascicles. Patients with bifascicular block who progress to complete heart block transiently may benefit from permanent transvenous pacemaker insertion before discharge. 6. Hospitalized patients with persistent pain of suspected cardiac origin but without evidence of myocardial infarction can be studied safely with coronary angiography. A small percentage will be normal or have diffuse disease that is inoperable. Of those with operable disease, short-term mortality appears to be similar for medical and surgical therapy. 7. Patients with an uncomplicated myocardial infarction may be safely discharged from thehospital by day 7-10. 8. Experimental evidence indicates that modification of infarct size is possible. Application of these concepts to human subjects presently is limited by the absence of a proved method of measuring infarct size in vivo in humans.