Serum lactic dehydrogenase isoenzymes and serum hydroxy butyric dehydrogenase in myocardial infarctionDS Kanekar, PN Sawant, Saroj P Taskar
Cordiovascular and Thoracic Centre, K.E.M. Hospital and Seth G.S. Medical College, Parel, Bombay 400012, India
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 458744
Source of Support: None, Conflict of Interest: None
Total serum lactate dehydrogenase activity in cases of myocardial infarct is difficult to interpret as abnormal values can occur in diseases of liver, kidney and skeletal muscle. The estimation of its isoenzymes is of better diagnostic help because of its tissue specificity. Serum LDH isoenzymes were studied in patients o f myocardial infarction and results are quantitated by densitometry. As LDH 1 represents serum hydroxybutyric dehydrogenase when 2-oxylbutyrate is used as substrate, serum hydroxybutyric dehydrogenase was also estimated in above patients. Greater specificity in diagnosis is achieved with SHBDH because of its myocardial nature and lower incidence of false positive results.
Large number of enzymes have been introduced for the diagnosis of myocardial infarction. Selection of a suitable enzyme system becomes crucial when electrocardiographic findings are not contributory in the presence of clinical symptoms. Most commonly and widely used enzyme remains to be serum glutamic oxaloacetic transaminase (SGOT) but the diagnostic specificity of this enzyme in myocardial infarction is limited because of its elevations in liver diseases and in patients with right heart failure and shock.  The use of SGOT determination for the detection of myocardial infarction also suffers from the major disadvantage that elevation following infarction is rapid and transient. An increase in serum lactate dehydrogenase following infarction is on the other hand slow and more prolonged. This is helpful in establishing a diagnosis in cases first seen several days after the event. However, the raised activity of serum lactate dehydrogenase is also difficult to interpret as the abnormal values can occur in diseases of the liver, kidney or of skeletal muscle. Since Wroblewski and Gregory  and Wieme and Van Maercke  demonstrated that LDH isoenzymes I and II originate specifically from the cardiac muscle, LDH fractionation has become a better diagnostic aid than the determination of total lactic dehydrogenase and SGOT. As serum hydroxybutyric dehydrogenase represents the activity of LDHI fraction of the total LDH, the same specificity in diagnosis can probably be achieved by determining serum hydroxybutyric dehydrogenase using 2-oxybutyrate as the substrate. As very meagre data on LDH iso-enzymes in myocardial infarction in Indian population is available in literature, attempt has been made in this paper to quantitate LDH isoenzymes and to correlate them with the levels of hydroxybutyric dehydrogenase.
One hundred and five patients belonging to both the sexes between the age group of 35 and 60 years who had had an attack of myocardial infarction diagnosed by W.H.O. criteria and admitted to the Intensive Cardiac Care Unit of K.E.M. Hospital were selected for the present study. The controls selected were 40 healthy normals between the same age group. Blood was collected in heparin bulbs by venepuncture soon after the acute episode of myocardial infarction. Haemolysis was avoided while separating the plasma which was immediately subjected to the enzyme assay. The blood samples were collected serially upto three days and a week from the day of infarction.
Total lactic acid dehydrogenase was estimated by a colorimetric method. 
Lactate dehydrogenase isoenzymes were fractionated by agarose gel electrophoresis as described by Cawley and Eberhard.  The stained slides were scanned on Chromoscan at 520 mix and the percentages of the fractions were quantitated.
Serum hydroxybutyrate dehydrogenase activity was estimated by the method of Rosalki. 
The mean values of total serum lactic dehydrogenase with S.E. and range in normals and in patients with myocardial infarction are shown in [Table 1]. Follow-up study of these patients shows that enzyme activity is elevated within the first 24 hours from the time of the episode and reaches a maximum on the second day and then declines towards the normal level after a week.
[Table 2] shows the details of results of lactate dehydrogenase isoenzymes in normal subjects, and in patients with myocardial infarction. In healthy normals largest fraction was found to be that of LDH 2 isoenzyme followed by LDH 1 isoenzyme then LDH 3 and LDH 4 isoenzymes. LDH 5 isoenzyme was found to be the smallest fraction. On serial determination of LDH isoenzymes, in patients with myocardial infarction it was observed that on the first day, LDH 1 enzyme rises sharply. The rise is greater than LDH 2 with simultaneous decrease in LDH 3 and LDH 4 isoenzymes. On the second day of the infarct, LDH 1 isoenzyme reaches maximum and LDH 2 isoenzyme is found to be minimal along with a decrease in LDH 3 , and LDH 4 isoenzymes. On the third day of the infarct, LDH 1 isoenzyme decreases with slight increase in LDH 2 , LDH 3 and LDH 4 isoenzymes and after a week, LDH 1 isoenzyme still decreases with an increase in other isoenzyme fractions tending towards the normal.
[Table 3] demonstrates the mean ratio of LDH 1 /LDH 2 in normal subjects and in patients with myocardial infarction.
[Table 4] shows serum hydroxy butyric dehydrogenase activity in normals and in patients suffering from myocardial infarction
The results obtained in the present study indicate that serum lactic dehydrogenase enzyme activity increases 4-5 folds in the first 24-72 hours after the onset of clinical infarction with a peak on the second day. It then declines gradually towards the normal within two weeks. Thus, determination of total serum LDH is valuable if patients present themselves for clinical check up even after a week from the day of infarct in contrast to SGOT. Although the contribution of myocardium to total serum lactic dehydrogenase is large, its interpretation becomes difficult if the diseases of other organs such as liver, kidney, etc. co-exist.
Electrophoretic separation of serum enzymes characterized by tissue specific isoenzyme patterns are more specific for laboratory diagnosis. Out of the various supporting media such as paper, agar, starch gel, polyacrylamide used for gel electrophoresis, agarose gel was found to have distinct advantage over the others. The staining as well as the separation is better and the scanning on densitometer is easier. (See [Figure 1] and [Figure 2] on page 56A) .
The five isoenzymes present in the :serum of normal subjects are in the following typical relative concentrations. LDH 2 > LDH 1 > LDH 3 > LDH 4 > LDH 5 . From [Table 2] and [Table 3], it is seen that LDH 1 , isoenzyme increases during the clinical course of myocardial infarction and LDH 1 :LDH 2 , ratio shifts towards more than unity. Elevated values of LDH 1 and LDH i :LDH 2 ratio above unity persist even after a week unlike those of total serum LDH. Determination of LDH 1 /LDH 2 , is particularly useful when total LDH values are on the higher side of normal or slightly above the normal. This ratio extending beyond unity is a definite indication of myocardial infarction. The greater sensitivity and specificity of SHBDH compared to LDH in detecting myocardial injury stems from the facts that only myocardial enzyme is being measured and that there is a low incidence of false positive results.
The authors wish to thank Dr. C. K. Deshpande, Dean, Seth G.S. Medical College and K.E.M. Hospital, Bombay for all facilities and Dr. (Smt.) S. G. Kinare, Professor of Pathology, Seth G.S. Medical College for her keen interest and valuable guidance in the work.
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]