Serum enzyme and isoenzyme alterations in myocardial infarction

Elevation of serum creatine phosphokinase and its MB isoenzyme during normal labor and early puerperium

BACKGROUND

Chest pain or discomfort are infrequent complaints among women during labor and early puerperium, but when present they raise the suspicion of myocardial ischemia. The diagnosis of the latter is based upon serum elevatIon of certain enzymes, such as aspartate amino transferase, lactate dehydrogenase and creatine phosphokinase. Nevertheless, the normal patterns of these enzymes in the serum during labor and early puerperium have not been characterized well.

OBJECTIVE

To determine serum creatine phosphokinase, lactate dehydrogenase and aspartate amino transferase levels in late pregnancy, and throughout labor and early puerperium.

METHODS

Fifty women having normal pregnancies followed by uneventful vaginal deliveries were prospectively studied for serum lactate dehydrogenase, aspartate amino transferase and creatine phosphokinase including its MB isoenzyme before, during and after labor. Cardiac status was evaluated in all women using serial electrocardiographic and physical examinations.

RESULTS

All women were found to have low to normal antepartum serum enzymes levels. However, during labor total creatine phosphokinase increased markedly, reaching a peak of 2-4 fold baseline levels 24 hours postpartum. It then declined gradually back to baseline. Nulliparous women reached substantially higher levels than multiparous women. The MB or so-called cardio-specific isoenzyme was found to be an important contributor to creatine phosphokinase surge in most women. Correlation was demonstrated between length of the active phase of labor and both total and MB creatine phosphokinase activity. There was no clinical or electrocardiographic evidence for cardiac muscle damage in any of the study patients. Serum lactate dehydrogenase and aspartate amino transferase were not altered during or after labor.

CONCLUSIONS

Serum total creatine phosphokinase and its MB isoenzyme increase substantially during normal vaginal labor without evidence of myocardial ischemia. The uterus and placenta, two organs which were reported to embody substantial amounts of these enzymes, and which participate actively in the process of labor, are thought to release these enzymes to the circulation during labor. Knowing the normal patterns of these enzymes in the serum during labor and puerperium may prevent erroneous diagnoses of myocardial ischemia or infarction. Lack of electrocardiographic abnormalities and low lactate dehydrogenase and aspartate amino transferase levels may assist in excluding such diagnoses.

On the determination of isozyme levels in preparations containing cytoplasmic and mitochondrial aspartate aminotransferase

A spectrophotometric assay has been developed for the determination of the content of each isozyme of aspartate transaminase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) in physiological fluids or tissue extracts. The methods relies on the ability of adipate, at low pH and ionic strength to inhibit the cytoplasmic isozyme but not the one from mitochondria. Two assays are necessary, one at pH 8.0 which measures the content of both isozymes and another at low pH which measures primarily the amount of mitochondrial isozyme. Results obtained by this simple procedure match those in which each isozyme is inhibited by its antibody. The validity of the results obtained by the new method was tested at different ratios of cytoplasmic:mitochondrial isozyme and with tissue extracts. Since the amounts of each isozyme determined by radial immunodiffusion match those values gathered by following enzymatic activity, it is concluded that the quantity of each isozyme obtained from its respective catalytic activity must represent the total protein content of each isozyme in a given sample.

Metabolic consequences of glucose-insulin-potassium infusion in treatment of acute myocardial infarction

Eighteen patients treated with glucose-insulin-potassium infusion for anaerobic support of acutely ischemic myocardial tissue were studied to ascertain the metabolic consequences of this therapy, for acute myocardial infarction. Twelve patients with acute myocardial infarction were treated in a conventional manner and served as control subjects. The glucose-insulin-potassium solution was composed of 300 g of glucose, 50 units of regular insulin and 80 mEq of potassium ion per liter, and was infused at a rate of 1.5 ml/kg per hour through the right atrial port of an indwelling Swan-Ganz thermodilution catheter. Serial measurements of serum electrolytes, cardiac and hepatic enzymes, glucose and osmolality were obtained every 4 to 6 hours for 4 days. Twenty-four urinary volume and potassium levels were measured daily. Pulmonary arterial end-diastolic pressure was measured hourly and the cardiac index daily for the duration of the study. Serum potassium increased to 5 mEq/liter during the infusion and to more than 6 mEq/liter after infusion in 28 percent of patients. No recognizable complications or arrhythmias accompanied this transient hyperkalemia. Potassium balance studies revealed a net total body potassium ion gain of 120 MEq during the study. The second most frequent finding was an elevation of serum glucose (mean 175 mg/100 ml); in all instances this was controlled with supplemental administration of insulin. The serum osmolality and fluid balance remained normal in all patients during the study. Serum glutamic oxaloacetic transaminase (SGOT) and fraction 5 of lactic dehydrogenase (LDH) were increased in 34 percent of the patients during the last 12 to 18 hours of the glucose-insulin-potassium infusion. Characterization of these enzymes suggested a hepatic origin for these changes. This study suggests that glucose-insulin-potassium infusion is a relatively safe procedure in which postinfusion hyperkalemia is the most serious potential complication.

Rat liver alcohol dehydrogenase isozymes: influence of infection with Trypanosoma

A study has been made of changes in alcohol dehydrogenase (ADH) isozymes in livers of rats infected with the following trypanosomes: Trypanosoma cruzi, T. rhodesiense, T. congolense, and six geographical isolates of T. lewisi. A control group of the same age was injected with saline, and another left uninjected. Liver homogenates were electrophoresed in noble agar gels followed by formazan staining according to the method of Ursprung and Leone (1965). Of a total of 25 replicates, 15 showed that the level of rat liver ADH isozymes was similar in the uninjected and saline injected animals; 6 replicates showed a slightly higher level of ADH isozymes in uninjected than saline injected control rat livers, and 4 replicates had a higher level in saline injected than in the uninjected. With either 1-octanol or ethanol as substrate, a marked elevation of ADH activity was observed beginning with day 7 post inoculation in rat livers infected with T. cruzi, T. lewisi, and T. congolense, or as early as day 4 post inoculation with T. rhodesiense. The elevation persisted 59 days or more in rat livers infected with T. lewisi, but rats infected with the pathogenic species usually died 5 to 14 days after infection. The elevation of ADH isozymes has also been demonstrated spectrophotometrically for the first 5 minutes of reaction time, using acetaldehyde as substrate. Also observed in livers infected with pathogenic species and certain strains of T. lewisi were: (1) ADH isozyme pattern changes involving an elevated level of certain isozymes only, and (2) abnormal isozyme mobilities.

ST-segment elevation in acute myocardial infarction. Prognostic importance

Four hundred and four patients who were admitted to the hospital with their first myocardial infarction within 24 hours of the onset of symptoms were studied. In 315 patients the ECG findings in 12 standards leads (I, II, aVF, aVR, aVL, V 1 -V 6 ) showed the infarction to be in the anterior wall, the inferior wall, or in multiple areas. The patients in each of these three categories were further subdivided into two groups according to the magnitude of the ST-elevation; those with major ST-elevation and those with minor ST-elevation. Occurrence of the risk factors of diabetes, hypertension, hyperlipidemias, age, and complicating chronic pulmonary and renal diseases were comparable, but since women predominated in one group (anterior wall infarction/ minor ST-elevation) the clinical course of the disease in men and women was studied separately. The patients with major ST-elevation had a more unfavorable course: cardiac arrest ( P < 0.0005), congestive heart failure ( P < 0.0005), death ( P < 0.001), atrial fibrillation ( P < 0.005), cardiogenic shock ( P < 0.005), atrioventricular (A-V) block 2°-3° ( P < 0.01), and ventricular extrasystoles and ventricular tachycardia ( P < 0.025) all occurred with significant frequency. The magnitude of ST-elevation thus gives valuable prognostic information, useful in selecting patients for prolonged monitoring.

Determination of the site, extent, and significance of regional ventricular dysfunction during acute myocardial infarction

Infarct site, extent, and the degree of associated asynergy are major determinants of the hemodynamic consequences of myocardial infarction. Although conventional electrocardiography and vectorcardiography are routinely employed in assessing the location and size of infarction, they are relatively nonspecific. The newer techniques of high-frequency electrocardiography and isopotential mapping offer promise but have yet to undergo systematic evaluation. A rough measure of the extent of infarction is obtained from serum enzyme measurements. However, they furnish no information with regard to localization.

The region of infarction may be detected by precordial scanning following the intravenous or intracoronary injection of a radioisotope. The infarct may be revealed as an area of decreased perfusion (cold spot) or as an area to which a specific radioactive label is bound (hot spot). With the availability of newer radionuclides such as 43 potassium and the use of computer techniques, a more precise means of localizing and quantifying myocardial infarction may become available.

Optimal definition of asynergy is obtained with contrast angiography. However, the risk of this procedure has limited its use, to date, in acute myocardial infarction. Apex- and kinetocardiography, chest X-ray, and fluoroscopy often suggest regional ventricular dysfunction, but these techniques are not sufficiently specific. Newer noninvasive methods for objectively evaluating regional ventricular dysfunction are ECG-gated cardiac scintiphotography and radarkymography. With ECG-gated scintiphotography, end-diastolic and end-systolic cardiac isotope images are obtained following intravenous injection of 99m technetium-albumin. From these images, assessment of asynergy and extent and location of infarct can be made. With radarkymography, heart-wall motion is assessed and quantitated by tracking segments of the cardiac silhouette visualized on a cinefluorogram. These techniques are ideally suited to the acutely ill patient. Echocardiography is another noninvasive technique with potential application to the study of asynergy. However, at present, only posterior-wall motion can be measured.

At the time of surgery regions of infarction may be localized by means of chemical indicators (fluoroscein), isotope techniques, or epicardial electrocardiographic mapping. Recently much has been learned about the hemodynamics of myocardial infarction. Through the use of the techniques described, further insight into regional ventricular abnormality and extent and localization of myocardial infarction could be obtained. With this information better approaches to therapy and prognosis could be developed.

Many students of the coronary circulation must have noted that the ventricular zone affected by ligating a large coronary branch not only appears cyanotic and dilated, but that it seems to alter in its mode of contraction. The detailed and sequential changes in contraction are not easily followed by the unaided eye and so far have not been recorded myographically. The reasons for this were the lack of an adequate and suitable myograph and a technique for the application of one to a limited ventricular surface so that records obtained represent, at least reasonably well, changes in muscle length and not predominantly artifacts due to position changes, thrusts and vibrations of the vigorously beating ventricle. 1