Serum Enzyme Determinations
in the Diagnosis and Assessment
of Myocardial Infarction
By BURTON E. SOBEL, M.D.,
AND
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DIAGNOSTIC ENZYMOLOGY has grown
exponentially since elevated serum
amylase was first associated with pancreatitis in 19081 and Karmen, Wroblewski,
LaDue, and their associates demonstrated in
1954 that SGOT* and LDH activity in serum
increased following myocardial infarction.2
Following Markert's elucidation of the nature
of LDH isoenzymes3 their importance in
differential diagnosis was emphasized.4 Serum
CPK elevations following myocardial infarction were first reported by Dreyfus and his coworkers5 in 1960, and soon confirmed by Hess
and MacDonald.6 Determination of SGOT,
LDH, and CPK activity rapidly became
cornerstones in the laboratory diagnosis of
acute myocardial infarction in man.
Activity of many enzymes including aldolase, malic dehydrogenase, isomerase, and
ICD may increase following myocardial infarction.7 Serum GGT, a lysosomal enzyme,
exhibits increased activity late, reaching a
peak within 8 days and returning to normal
approximately 1 month following the initial
insult.8 SPK contrary to CPK is not elevated
following intramuscular injections,9 while serum GAPDH elevation may precede increases
in conventional enzymes and aid detection of
extension of myocardial necrosis.10 However,
since SGOT, LDH, and CPK determinations
have become established criteria in the
laboratory diagnosis of acute myocardial
infarction in man, material to follow will
concern those three enzymes primarily.
General Considerations
Meaningful interpretation of serum enzyme
determinations should be based upon several
considerations:
1. Elevated serum enzyme activity associated with disease is generally assumed to
reflect activity of enzyme released from
injured tissue. In most conditions, the same
enzymes with which an injured organ is richly
endowed are those exhibiting elevated activity
in serum following organ injury.2 4 The time
course of depletion of enzyme activity from a
damaged organ parallels the time course of
increase of activity of the same enzyme in
serum following the insult."' 12 Following
experimental coronary artery occlusion, a
significant although small myocardial arteriovenous difference of enzyme activity can be
demonstrated.'3 On the other hand, peak
elevation of serum enzyme activity may not
correlate closely with the magnitude of tissue
damage,14 and some enzymes, such as ICD,
which decrease in ischemic myocardium and
increase in coronary sinus blood following
experimental coronary artery occlusion, may
not increase concomitantly in serum.15 These
disparities are reconciled when the rate of
disappearance of enzyme activity from serum,
the rate of release of enzyme from ischemic
*Abbreviations: SGOT = serum glutamic oxaloacetic transaminase; LDH = lactic dehydrogenase;
CPK = creatine phosphokinase; ICD = isocitric dehydrogenase; GGT = gamma-glutamyl transpeptidase;
SPK = serum pyruvate kinase; GAPDH = glyceraldehyde phosphate dehydrogenase; OCT = ornithinecarbamyl transferase; SGPT= serum pyruvic transaminase; and NADP = nicotinamide-adenine dinucleotide phosphate.
From the Department of Medicine, School of
Medicine, University of California at San Diego, La
Jolla, California.
Supported in part by U. S. Public Health Service
Myocardial Infarction Research Unit Contract PH-4368-1332, Project Grant HE 12373, Research and
Career Development Award 1-K4-HE-50, 179-01, and
Special Fellowship 1 F03 HE 46505-01.
Circulation, Volume XLV, February 1972
WILLIAM E. SHELL, M.D.
471
472
myocardium, the fraction of myocardial enzyme undergoing local denaturation, and the
distribution of enzyme released from the heart
in body fluids are taken into account. Thus,
ICD activity is not substantially elevated in
serum following experimental myocardial infarction because the enzyme's disappearance
rate from the circulation is very rapid.1Furthermore, when serial changes in serum
CPK activity following experimental myocardial infarction are analyzed according to a
model based on these considerations, the
correlation between myocardial enzyme depletion and increased serum enzyme activity is
close (r=0.96) over a wide range of infarct
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size. 12
2. The relative value of enzyme determinations in the diagnosis of a specific disease
entity should be assessed on the basis of both
specificity and sensitivity of the test. True
positives (instances of a positive result in a
patient with the disease), false positives
(instances of a positive result in a patient
without the disease), and false negatives
(instances of a negative result in a patient
with the disease) should be considered. An
enzyme test is highly specific when the ratio of
true positives to false positives is high. It is
highly sensitive when the ratio of true
positives to false negatives is high and the
incidence of false negatives is low. Obviously,
sampling time and frequency will influence
the apparent specificity and sensitivity of the
determination.
3. Enzyme determinations are assays of
activity, not of amount or concentration of a
specific protein in serum. Accordingly, the
apparent activity may be influenced by the
presence of inhibitors, cofactors, activators, or
unusual amounts of substrate or product in
the serum sample.16
4. The nature of the assay procedure used
may influence results profoundly. Since only
initial velocity is a reflection of enzyme
activity, kinetic assays are generally superior
to assays based on a single determination of
product concentration and less prone to error
introduced by nonspecific chromogens in
biologic material.
SOBEL, SHELL
5. Other factors related to sampling, storage, and laboratory technique may impair the
validity of enzyme determinations.
6. The normal range of activity of each
serum enzyme must be defined under the
assay conditions employed and is usually
defined as the mean ± 2 SD of values from a
control population.-' 4 When a skewed distribution is observed in control samples, "normality" may be defined with a log normal
curve.'7 These definitions of normality mean
that the value obtained in a sample from a
normal individual will fall within the normal
range 95% of the time. Stated in another way,
abnormal values for serum enzyme activity
will be obtained in 5% of normal individuals.
Thus, an "abnormal" value does not necessarily imply that the patient from whom it was
obtained harbors disease.
Enzyme values vary with age, sex, and
activity.'X Accordingly, if a normal range were
established based on samples from 18-year-old
student nurses, its application to interpretation
of values in serum samples from 60-year-old
male patients in a coronary care unit would be
inappropriate and misleading.
Serum Enzymes in the Diagnosis
of Acute Myocardial Infarction
SGOT-Sensitivity and Specificity. In a
typical patient with acute myocardial infarction, SGOT activity exceeds the normal range
within 8 to 12 hours following the onset of
chest pain, reaches a peak elevation of two- to
tenfold in 18 to 36 hours, and declines to the
normal range within 3 to 4 days. As with all
serum enzymes the duration of elevated
activity depends in part on the maximum
value attained. When other disease processes
account for elevated SGOT, the time course
often differs. In an extensive review of
literature through 1960 by Agress and Kim,19
1692 cases of acute transmural myocardial
infarction diagnosed clinically and electrocardiographically were tabulated. True-positive
SCOT elevations occurred in 97%. Myocardial
infarction was proven by autopsy in 119 cases.
In 115 of these, SGOT had been abnormal. In
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experimental myocardial infaretion in animals,
SGOT elevations are seen consistently.
SGOT may increase in association with a
variety of disease processes, although often
the time course of elevated enzyme activity
contrasts with that seen typically in patients
with acute myocardial infaretion. Hepatic
congestion, primary liver disease, skeletal
muscle disorders, and shock may contribute to
marked and sometimes sustained SGOT elevations. In 224 patients with cardiac disease
excluding myocardial infaretion and shock,
SGOT activity was increased in 12%.2o Patients
with congestive failure exhibit an even higher
proportion of false-positive SGOT elevations
apparently in proportion to the severity of
failure. However, congestive heart failure in
the absence of overt hepatic decompensation
is infrequently associated with striking elevations of SGOT.
Myocarditis may lead to SGOT elevations,
which frequently parallel the activity of the
disorder and are not precluded by steroid
administration.2' In pericarditis, SGOT is
elevated in less than 15% of patients and those
elevations may reflect subepicardial injury.7
Although early reports indicated that SGOT
did not generally increase in patients with
pulmonary embolism,22 it has become clear
that this conclusion is not justified. Coodley
noted that four of 17 patients with definite
pulmonary embolism and 17 of 25 patients
with probable pulmonary embolism manifested increased SGOT activity.23 In other reports, between 25 and 50% of patients with
emboli proven angiographically exhibited increased SCOT.24
Increased SGOT activity follows tachyarrhythmia in more than 50% of cases when the
heart rate exceeds 140 beats/min for at least
30 min in the absence of acute myocardial
infarction. Since OCT is often elevated in such
cases,25 the SGOT appears to reflect hepatic
decompensation secondary to hemodynamic
consequences of the arrhythmia. Accordingly,
CPK does not rise nearly as frequently.7 On
the other hand, the incidence of arrhythmia
within the first 24 hours following myocardial
infarction correlates with the magnitude of
Circulation, Volume XLV, February 1972
473
SGOT elevation26 perhaps because both
SGOT and the incidence of arrhythmia reflect
the extent of myocardial injury.
Approximately 25% of patients treated with
direct-current countershock (electrical cardioversion) may exhibit increased SGOT activity
usually less than threefold above normal.
Since SGPT and isoenzymes of LDH identified with liver are not elevated in such
patients,27 and since OCT, an enzyme identified almost exclusively with liver, does not
increase28 it appears that the SGOT rise is due
to enzyme release from skeletal muscle. CPK
elevations, commonly seen, are both more
frequent and more marked than SGOT
elevations in this setting.28
Several other conditions, frequently of
interest to the cardiologist, may be associated
with elevated SGOT activity. Patients with
disease of the biliary tract who receive
intravenous or intramuscular narcotic injections may exhibit transient increases in SGOT
activity.29 Usually, the time course of elevation
is much shorter and the magnitude much less
than that seen typically following myocardial
infarction. Concomitantly increased alkaline
phosphatase activity is a valuable confirmatory sign indicating that the enzyme elevation
is related to cholestasis potentiated by narcotic
administration rather than to myocardial
damage.
Approximately 11% of females taking oral
contraceptive medication exhibit increased
SGOT, usually late in the menstrual cycle,3j'
and SGOT may be increased in patients
treated with clofibrate. SGOT and CPK
increased in 8% of 60 patients treated with
large doses of clofibrate, and elevated enzyme
activity and an associated myalgia waxed and
waned with drug administration or its discontinuance, respectively.31 False-positive SGOT
elevations following erythromycin administration are a problem only when the colorimetric
enzyme assay is employed.32
SGOT may increase following cardiac catheterization. In both adults and children, the
magnitude of serum enzyme elevations appears to be related to the duration and extent
of dissection required during the procedure.33
474
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Typically, SGOT rises following operation in
the experimental animal and in as many as 95%
of patients following general surgical procedures.34 Although increased SGOT may result
from hepatic damage by anesthetic agents in
some cases, 34 its magnitude appears to depend
primarily on the extent of dissection.
Serum enzyme elevations may become
clinically important indices of rejection following cardiac transplantation. In a recent
experimental study, discrete SGOT and CPK
elevations appeared to provide sensitive criteria of incipient rejection in the dog.35
LDH-Senrsitivity and Specificity. In a
typical patient with acute myocardial infarction serum LDH activity exceeds the normal
range within 24 to 48 hours, reaches a peak
elevation of two- to tenfold in 3 to 6 days, and
declines to the normal range within 8 to 14
days.36 True-positive LDH elevations occurred in 86% of 282 patients with myocardial
infarction diagnosed clinically and in all 39
patients with myocardial infarction proven at
autopsy.19 Results in other series are similar.37
The specificity of LDH as an index of acute
myocardial infarction depends on the population at risk. Increased LDH occurs in 30% of
patients with congestive heart failure,20 and its
time course may resemble that following acute
myocardial infarction.
Serum LDH activity may increase markedly
under the following conditions: hemolysis, in
the sample, or in vivo; megaloblastic anemia
or anemia associated with ineffective erythropoiesis; leukemia; acute and chronic liver
disease; and renal disease, especially renal
infarction. Striking serum LDH elevations are
seen in many patients with neoplastic disease,
and elevations in cerebrospinal, pleural, or
ascitic fluid may be indicative of local
neoplasm. LDH increases even more commonly than SGOT following pulmonary embolism.22-24 In the dog, increased serum LDH
activity is a concomitant of acute pulmonary
embolism produced by administration of
autologous thrombus despite the absence of
pulmonary infarction and underlying heart
disease.38 Many conditions associated with
SOBEL, SHELL
SCOT elevation including cardiac catheterization, myocarditis, and shock may give rise to
increased serum LDH activity as well. In
addition, LDH may increase following severe
exercise apparently because of release of
enzyme not only from skeletal muscle but also
from liver and myocardium..39 LDH does not
increase as commonly as SGOT following
electrical cardioversion, but it may be released
from skeletal muscle and/or liver judging by
the serum isonenzyme profile seen.27' 28
CPK-Sensitivity and Specificity. In a
typical patient with acute myocardial infarction, serum CPK activity exceeds the normal
range within 6 to 8 hours, reaches a peak of
two- to tenfold in 24 hours, and declines to the
normal range within 3 to 4 days following the
onset of chest pain. The upper limit of normal
CPK in females is only about two thirds of
that in males.40 CPK is a sensitive index of
acute myocardial infarction, but results vary
markedly with the assay technique employed.
Both sensitivity and the incidence of false
positives increase when thiol activation is
used. Nevertheless, such activation is essential
to assure reproducibility and prevent rapid
decay of CPK activity in serum.17 Unfortunately, interpretation of CPK results from
some studies are clouded by other difficulties
including use of the forward instead of the
back reaction. When CPK is assayed by the
back reaction with thiol activation, the sensitivity of CPK is impressive, of the order of 90%
or more. On the other hand, when CPK is
assayed by other techniques sensitivity suffers.
As with other enzymes, specificity of CPK
elevation as an index of acute myocardial
infarction is far from unequivocal. Myocardium, skeletal muscle, brain, and thyroid
contain complements of CPK. Because of the
paucity of CPK in other parenchymal organs,
CPK offered promise as a relatively specific
index if cardiac injury. However, serum CPK
is markedly increased in most patients with
muscular dystrophy, inflammatory disease of
muscle, alcohol intoxication with or without
delerium tremens, diabetes mellitus with or
without ketoacidosis, convulsions, psychosis,
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SERUM ENZYMES IN MI
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and intramuscular injections, apparently because of muscle release.4' 4 Serum CPK is
rarely affected by renal disease.
Contrary to SGOT and LDH, CPK activity
usually remains normal in patients with
neoplastic disease. However, X-ray therapy
involving the heart consistently produced
CPK elevations in serum. CPK did not
increase in patients exposed to comparable
amounts of radiation(2000-5000 rads within 5
weeks) confined to regions excluding the
myocardium but including skeletal muscle.45
Serum CPK does not generally increase in
patients with uncomplicated congestive heart
failure.17 It may increase with pericarditis; but
elevations are rare and those that do occur are
usually slight.17 46 In myocarditis increased
CPK activity often parallels the underlying
severity of the inflammatory process.'6' 17
CPK has been considered an effective
discriminant in the differential diagnosis between acute myocardial infarction and acute
pulmonary embolism. However, even in early
clinical reports, occasional patients with pulmonary embolism exhibited increased serum
CPK activity.'7' 46 When CPK activity is
assayed with thiol activation, increased activity can be detected frequently.47 Perkoff
focused attention on this in a report of three
of seven patients with acute pulmonary
embolism who exhibited increased serum CPK
activity. CPK activity is demonstrable in lung
extracts from man and experimental animals.47
In experimental pulmonary thromboembolism
in dogs, serum CPK activity increases consistently two- to threefold despite only transient
and minimal hemodynamic changes and the
absence of pulmonary infarction.48 Thus,
modest, transient serum CPK elevations are
probably relatively frequent following acute
pulmonary embolism.
Although SCOT and LDH elevations following tachyarrhythmia appear to be due to
enzyme from liver, recent observations in 12
patients demonstrated increased serum CPK
activity49 suggesting possible myocardial enzyme release. Since tachycardia increases
myocardial oxygen consumption and infarct
size experimentally,50 CPK elevations may
Circulation, Volume XLV, February 1972
475
reflect occurrence of some myocardial necrosis
in patients with tachyarrhythmia. Increasing
heart rate by means of ventricular pacing in
otherwise normal dogs to two and one half
times the control rate failed consistently to
increase serum CPK activity. However, increasing heart rate from 100 to 180 beats/min
augmented infarct size and led to associated
elevations in serum CPK in five of six
conscious dogs with coronary artery occlusion.51 Electrical cardioversion produces twoto threefold increases of serum CPK activity in
up to 75% of cases.28
CPK elevations occur in several other
conditions of particular interest to the cardiologist. Selective coronary angiography33 may
increase serum CPK. Following cardiac catheterization the incidence and magnitude of
serum CPK elevations appear to depend on
the extent of muscle dissection involved in the
procedure.33' 5'2
Two- to threefold CPK elevations are
frequent following intramuscular injections of
narcotics, phenothiazines, barbiturates, antibiotics, diuretics, and analgesics even without
overt signs of inflammation.44 4 CPK, like
other serum enzymes, may increase with
severe exercise apparently because of altered
properties of cell membranes.53
LDH Isoenzymes-Sensitivity and Specificity. LDH isoenzyme determinations have
enhanced diagnostic accuracy remarkably.
The five common LDH isoenzymes are named
in order of rapidity of migration toward the
anode in an electrophoretic field. Accordingly,
LDH1 is the fastest and LDH5 the slowest in
conventional systems. Each isoenzyme is a
tetrameric unit composed of four subunits of
two possible types. The physical properties of
individual isoenzymes are determined by the
relative percentages of each type of subunit
contained.3 Extracts of heart contain primarily
LDH1, while those from liver or skeletal
muscle contain mostly LDH4 and LDH5.
Characteristic LDH isoenzyme profiles in
specific tissues may be related to the degree of
aerobic metabolism typical of the organ. Since
LDH1 and LDH2 are susceptible to inhibition
47.6
by pyruvate, this substrate may be preferentially shunted into mitochondria and metabolized aerobically in organs rich in these
isoenzymes, such as heart. However, it is not
clear that this mechanism operates in vivo,54
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and myocardial LDH profiles may change
under altered physiologic states.+5
Following acute myocardial infarction increased serum LDH1 activity frequently precedes increased total LDH and, in fact, is
typically present in the first available blood
sample obtained from patients hospitalized for
acute myocardial infarction.'0 Since many
patients with increased LDH, exhibit total
LDH activity remaining within the normal
range, increased LDH, activity is a moresensitive, early index of acute myocardial
infarction than is total LDH. Its sensitivity
exceeds 95%.
In most other conditions in which total
serum LDH is increased the isoenzyme profile
differs considerably from that seen following
acute myocardial infarction. While LDH1 is
the most prominent serum isoenzyme following infarction, LDH-, is typically increased
when congestive failure occurs without infarction.4 The isoenzyme profile typical of acute
myocardial infarction is rarely seen following
acute pulmonary embolism usually associated
with elevated LDH9 and LDH3.16 When
experimental pulmonary embolism is produced by administration of autologous thrombus, increased activity of LDH3 accounts for
most of the elevated total serum LDH
activitv.38
In cardiac patients, hemolysis associated
with jet lesions or prosthetic valves frequently
leads to increased serum LDH1. LDH, may
increase in patients with muscular dystrophy,
since myopathic tissue contains an unusual
proportion of LDH1. Furthermore, LDH1
increases in patients with renal disease,
especially renal infarction.5 6
The ratio of LDH, to LDH2 is increased in
young females, particularly during pregnancy,
compared to postmenopausal females or to
males.'8 Furthermore, physical activity of the
subject may influence isoenzyme profiles. In
well-conditioned males, LDH5 increases fol-
SOBEL, SHELL
lowing exercise,57 presumably because of
release of enzyme from skeletal muscle.
LDH1, LDH,, and LDH.5 increase in exercised
rats, probably because of release from heart,
skeletal muscle, and liver since tissue LDH
decreases in all three organs.P."
Although patients with arrhythmia may
exhibit increased total serum LDH activity,
the isoenzyme profile is quite different from
that seen following acute myocardial damage.
Thus, LDH, activity did not increase in any of
29 patients with tachyarrhythmia.-- Directcurrent countershock may increase total LDH
activity because of release of skeletal muscle
comiponents, but LDH, remains normal.28
LDH, is usually not elevated in patients with
pericarditis, but in approximately 25% of
patients with myocarditis LDH, activity in
serum may increase.4 In patients with heart
transplants, rejection episodes are frequently characterized by increased LDH1/LDH2
ratios in serum.589 Cardiac catheterization, with
or without coronary angiography, usually does
not lead to significantly increased total or
"heart" LDH isoenzyme activity.33 Thus, LDH
isoenzyme analysis may be particularly valuable in assessing the presence or absence of
concomitant myocardial infarction in patients
with arrhythmia or pericarditis, or those undergoing electrical cardioversion or cardiac
catheterization.
Most conditions in which total LDH
activity is significantly increased including
liver disease, skeletal muscle injury, and shock
with skeletal muscle and hepatic ischemia are
readily distinguishable from acute myocardial
infarction since the isoenzyme profile typically
shows predominance of slow components.
When coexistent myocardial infarction occurs
in patients with these disorders, increased
LDH, may be diagnostically useful in the
absence of marked changes in total LDH.
Activities of many serum enzymes are
elevated in patients with myxedema.9 Two
mechanisms appear to account for this phenomenon: (1) enzyme release from myopathic muscle, and (2) diminished catabolism of
circulating enzyme. The LDH isoenzyme
pattern seen in serum from patients with
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myxedema typically exhibits elevated LDH4
and LDH5. Thus, the pattern is readily
distinguishable from that seen with ischemic
myocardial injury.
Efforts directed toward detecting "heart"
LDH isoenzymes by rapid chemical procedures rather than electrophoretic techniques
exploit properties of the dominant LDH
subunit seen in heart LDH isoenzymes
including heat stability, susceptibility to inhibition by pyruvate, resistance to inhibition by
urea, and affinity for alpha-hydroxybutyric
acid as a substrate. Alpha-hydroxybutyric
dehydrogenase (a-HBD) should not be
viewed as a specific enzyme but rather as
enzymatic activity residing in that fraction of
LDH with high affinity for alpha-hydroxybutyric acid.
Electrophoretic analysis of LDH isoenzymes continues to provide a more-sensitive
and specific diagnostic index compared to the
chemical techniques. However, precautions
required include assay of enzyme activity
within the range of linearity of the staining
procedure used and control of temperature
throughout the supporting medium. The
major difficulty with chemical methods is that
specific isoenzymes are not identified. Apparent enzyme activity with the chemical methods depends on total LDH activity and total
subunits of each type rather than the isoenzyme profile per se. Thus, chemical inhibition
methods may fail when total LDH activity is
high. Lack of agreement between results of
"heart" LDH isoenzyme activity estimated by
urea inhibition and that determined electrophoretically occurs in as many as 24% of
samples, with frank contradiction in as many
as 10%."10 Despite these qualifications, LDH
fractionation by chemical techniques led to
true-positive results in a combined total of 457
of 464 patients from several centers.'06 61, 62
Thus, results with chemical fractionation
techniques are more specific and sensitive
than total LDH determinations, while those
obtained with isoenzyme separation by electrophoresis surpass both.
Circulation, Volume XLV, February 1972
477
Activity of Serum Enzymes in Patients
with Coronary Insufficiency
Insufficient coronary blood flow may be
associated with several clinical syndromes and
pathologic consequences. Yet, elucidation of
the relationships between each of these
syndromes and changes in serum enzymes has
been difficult. In order to examine these
relationships, it is useful to consider four
syndromes of apparently decreasing severity:
(1) definite transmural myocardial infarction
with evolution of Q waves; (2) prolonged
chest pain due to myocardial ischemia and
associated with transient S-T-segment and Twave changes; (3) prolonged chest pain due
to ischemia but associated with no electrocardiographic changes; and (4) typical angina
pectoris. Compilation of data from several
studies indicates that 92, 58, 27, and 5% of
patients in these four categories, respectively,
exhibit elevated SGOT, CPK, LDH, and/or
LDH1.4 7, 8, 10, 16, 17, 19, 46, 60, 61, 63-65
Several conclusions appear warranted. The
incidence and extent of enzyme elevations
vary widely in patients with insufficient
coronary blood flow without transmural myocardial infarction, probably because criteria
for patient classification vary. The incidence
of increased serum enzyme activity is greatest
in patients with transmural myocardial infarction, decreases in those with chest pain and
associated electrocardiographic changes, and
is least in those with prolonged chest pain or
angina pectoris without any electrocardiographic changes. This trend is consistent with
the possibility that prevalence of myocardial
necrosis in these patient groups follows the
same trend and that enzyme elevations reflect
necrosis.
Enzyme elevations that do occur are modest
in patients with insufficient coronary blood
flow without transmural myocardial infarction.16' 19 Mortality following definite myocardial infarction parallels, in general, the
magnitude of peak enzyme elevation acutely.66 Thus, available clinical data are consistent with the interpretation that serum
enzyme elevations following myocardial isehemia are indicative of myocardial necrosis.
SOBEL, SHELL
4 78
Clearly, the wide spectrum of necrosis seen
clinically may include massive infarction on
the one hand, and miniscule islands of
myocardial-cell death on the other, with
profoundly different prognostic and therapeutic implications.
Quantitative Relationships between
the Extent of Myocardial Necrosis
and Changes in Serum Enzymes
In unselected patients with acute infarction
when SGOT, LDH, and/or CPK activity
increases more than tenfold, mortality rises
markedly.;6' 67 This correlation may result
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from a general dependence of both mortality
and peak enzyme activity on the extent of
myocardial necrosis. In one large autopsy
series, infarcts were graded as small, medium,
and large by morphologic criteria. The median
peak SGOT and LDH values in patients
falling into these respective groups increased
correspondingly.68 Infarct size is large in
patients dying with cardiogenic shock associated with myocardial infarction.6" Under
certain circumstances inflammatory or regenerative responses within a damaged organ
may increase serum enzyme activity beyond
that anticipated from the amount of enzyme
initially present in the entire damaged organ.
However, this phenomenon does not appear
to occur with myocardial damage.12
Although peak serum enzyme activity correlates with infarct size in groups of animals
despite inprecision in anatomic criteria leading to scatter, the correlation may not be close
in the same animal.15 70 In order to elucidate
the basis of this apparent disparity, we have
studied serum and myocardial CPK activity
following experimental myocardial infarction.
CPK was chosen because this enzyme is not
present to a significant extent in cells participating in the inflammatory response in myocardium. In initial studies in rabbits, depletion
of myocardial CPK correlated closely with
infarct size assessed morphologically 24 hours
after coronary artery occlusion.7' CPK depletion in selected regions from dog hearts 24
hours after coronary artery occlusion corre-
lated closely with the extent of acute cellular
injury in the same site measured independently with the use of epicardial electrocardiographic recordings.-" A method based solely
on serial changes of serum CPK activity was
then developed for quantitative assessment of
infarct size in the conscious animal.12 CPK
released from the infarct was determined
solely on the basis of serial serum CPK
measurements analyzed with a model accounting for the rate of CPK disappearance from
serum, the rate of release of CPK from
myocardium undergoing infarction, the fraction of myocardial CPK degraded locally in
the heart, and the distribution space into
which CPK is diluted following release into
the circulation, all of which were determined
independently. Infarct size calculated on the
basis of observed changes in serum CPK
activity was compared with infarct size
determined directly by analysis of myocardial
CPK depletion in 22 animals. The correlation
wvas close in each case. Results from all
experiments fit a regression line with narrow
confidence limits and a correlation coefficient
of 0.96.12 These findings are consistent with
the bulk of earlier experimental work and
clinical observations that support the hypothesis that elevation of serum enzyme activity
following myocardial infarction is a reflection
of enzyme release from myocardial cells
undergoing necrosis. Thus, although the relationship between changes in serum enzyme
activity and infarct size is complex it appears
to be quantitative. Accordingly, analysis of
changes in serum enzyme activity following
myocardial infarction should permit the accurate assessment of the extent of myocardial
necrosis and its progression, so that the potent
surgical tools becoming available for the
patient with coronary artery disease can be
focused effectively. 2
Conclusions
SCOT, LDH, CPK, and LDH isoenzyme
determinations are of immense value in the
assessment of patients with coronary artery
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disease. Meaningful interpretation of such
determinations requires knowledge of sampling technique, assay conditions, and physiologic and pathologic states capable of influencing serum enzyme activity. The time course,
magnitude, and pattern of serial changes are
helpful in identifying responsible etiologic
factors. Following acute myocardial infarction, serum LDH1, CPK, and SGOT rise
promptly. Total LDH activity increases later
and appears to be a somewhat less-sensitive
index. All enzymes suffer from some lack of
specificity. Total LDH and LDH1 are particularly prone to spurious elevations when
hemolysis is present in vivo or in vitro. LDH1
and CPK are less likely than SCOT and total
LDH to increase in patients with congestive
heart failure. LDH1 is particularly useful in
differentiating acute myocardial infarction
from acute pulmonary embolism and in
excluding myocardial injury in patients treated with direct-current countershock or studied
invasively in whom serum activity of SGOT,
CPK, and LDH derived from skeletal muscle
may increase. Extensive evidence supports the
conclusion that serum enzyme elevations
following myocardial ischemia are related
quantitatively to enzyme release from irreversibly injured cells. Continued elucidation of
changes in serum enzyme activity should be of
considerable practical value in detecting and
assessing the extent of infarction and its
progression in individual patients with coronary artery disease.
References
1. WOHLGEMUTH J: Uber eine neue Methode zur
quantiativen Bestimmung des diastatischen
Ferments. Biochem Ztschr 9: 1, 1908
2. KARMEN A, WROBLEWSKI F, LADUE JS: Transaminase activity in human blood. J Clin Invest
34: 126, 1954
3. MARKERT CL: Lactate dehydrogenase isozymes:
Dissociation and recombination of subunits.
Science 140: 1329, 1963
4. COHEN L, DJORDJEvrICH J, ORNIISTE V: Serum
lactic dehydrogenase isozyme patterns in
cardiovascular and other diseases, with particuCirculation, Volume XLV, February 1972
479
lar reference to acute myocardial infarction. J
Lab Clin Med 64: 355, 1964
5. DREYFUS JC, SCHAPIRA G, RESNAIS J, SCEBAT L:
Le creatine-kinase serique dans le diagnostic
6.
7.
8.
9.
10.
de l'infarctus myocardique. Rev Franc Etudes
Clin Biol 5: 386, 1960
HESS JW, MACDONALD RP: Serum creatine
phosphokinase activity. Mich Med 62: 1095,
1963
XVEST M, ESHCHAR J, ZIMMERMAN HJ: Sertum
enzymology in the diagnosis of myocardial
infarction and related cardiovascular conditions. Med Clin N Amer 50: 171, 1966
HEDWORTH-WHITTY
WHITFIELD
RB,
JB,
RICHARDSON RW: Serum -y-glutamyl transpeptidase activity in myocardial ischaemia. Brit
Heart J 29: 432, 1967
SHAFT FR, BAN RW, IMFELD H: Serum pyruvate
kinase in acute myocardial infarction. Amer J
Cardiol 26: 143, 1970
KARLINER JS, GANDER MP, SOBEL BE: Elevated
serum glyceraldehyde phosphate dehydrogenase activity following acute myocardial infarction. Chest 60: 318, 1971
1 1. JENNINGS RB, KALTENBACH JP, SMETTERS GW:
Enzymatic changes in acute myocardial ischemic injury. Arch Path (Chicago) 64: 10,
1957
12. SHELL WE, KJEKSHUS JK, SOBEL BE: Quantitative assessment of the extent of myocardial
infarction in the conscious dog by means of
analysis of serial changes in serum creatine
phosphokinase (CPK) activity. J Clin Invest.
In press
13. PASYK S, BLOOR CM, KHOuRI EM, GREGG DE:
Systemic and coronary effects of coronary
artery occlusion in the unanesthetized dog.
Amer J Physiol 220: 646, 1971
14. WROBLEWSKI F: Seruim enzyme and isoenzyme
alterations in myocardial infarction. Progr
Cardiovasc Dis 6: 63, 1963
15. STRANDJORD PE, THOMAS KE, WHITE LP:
Studies on isocitric dehydrogenase in experimental myocardial infarction. 3 Clin Invest 38:
2111, 1959
16. BATSAKIS JG, BRIERE RO: Interpretive Enzymology. Springfield, Illinois, Charles C Thomas, 1967
17. HESS JW, MACDONALD RP, FREDERICK RJ, JONES
RN, NEELY J, GROSs D: Serum creatine
4x80
18.
19.
20.
21.
Downloaded from http://circ.ahajournals.org/ by guest on June 15, 2017
22.
23.
24.
25.
26.
27.
28.
29.
SOBEL, SHELL
phosphokinase (CPK) activity in disorders of
heart and skeletal muscle. Ann Intern Med 61:
1015, 1964
COHEN L, BLOCK J, DJORDJEVICH J: Sex related
differences in isozymes of serum lactic dehydrogenase (LDH). Proc Soc Exp Biol Med
126: 55, 1967
AGRESS CM, KIM JHC: Evaluation of enzyme
tests in the diagnosis of heart disease. Amer J
Cardiol 6: 641, 1960
WEST M, GELB D, PILZ CG, ZIMMERMAN HJ:
Serum enzymes in disease: Significance of
abnormal serum enzyme levels in cardiac
failure. Amer J Med Sci 241: 350, 1961
NYDICK I, TANG J, STOLLERMAN GH, WRoBLEWSKI F, LADUE JS: The influence of
rheumatic fever on serum concentration of the
enzyme glutamic oxalacetic transaminase. Circulation 12: 795, 1955
WACKER WEC, ROSENTHAL M, SNODGRASS PJ,
AMADOR E: A triad for the diagnosis of
pulmonary embolism and infarction. JAMA
178: 8, 1961
COODLEY EL: Enzyme profiles in the evaluation
of pulmonary infarction. JAMA 207: 1307,
1969
HILDNER FJ, ORMOND RS: Accuracy of the
clinical diagnosis of pulmonary embolism.
JAMA 202: 567, 1967
RUNDE I, DALE J: Serum enzymes in acute
tachycardia. Acta Med Scand 179: 535,
1966
ESHWAR KP: Correlation of serum glutamic
oxaloacetic transaminase levels and arrhythmias in acute myocardial infarction. New York
J Med 69: 1041, 1969
WARBASSE JR, WESLEY JE, CONNOLLY V,
GALLUZZI NJ: Lactic dehydrogenase isoenzyme
after electroshock treatment of cardiac arrhythmias. Amer J Cardiol 21: 496, 1968
KONTTINEN A, HUPLI V, LOUHIJA A, HARTEL
G: Origin of elevated serum enzyme activities
after direct-current countershock. New Eng J
Med 281: 231, 1969
MOSSBERG SM, BLOOM A, BERKOWITZ J, Ross C:
Serum enzyme activities following morphine:
A study of transaminase and alkaline phosphatase in normal persons and those with gallbladder disease. Arch Intern Med (Chicago)
109: 429, 1962
30. LARSSON-COHN U: Transaminase activity during
oral contraceptive therapy. Acta Obstet Gynec
Scand 45: 196, 1966
31. LANGER T, LEVY RI: Acute muscular syndrome
associated with administration of clofibrate.
New Eng J Med 279: 856, 1968
32. SABATH LD, GERSTEIN DA, FINLAND M: Serum
glutamic oxalacetic transaminase: False elevations during administration of erythromycin.
New Eng J Med 279: 1137, 1968
33. MICIIE DD, CONLEY MA, CARRETITA RF,
BOOTH RW: Serum enzyme changes following
cardiac catheterizations with and without
selective coronary arteriography. Amer J Med
Sci 260: 11, 1970
34. LAURIA JI, KING BD, MARKELLO R: Transaminase values following anesthesia and surgery.
New York J Med 69: 2003, 1969
35. CLAUVEL M, SCHWAARTZ K, CREPIN Y, CACHERA
JP: Enzyme profiles after heart transplant.
Nature 220: 483, 1968
36. ERICKSON RJ, MORALES DR: Clinical use of
lactic dehydrogenase. New Eng J Med 265:
478, 531, 1961
37. COHEN L, DJORDJEVICH J, JACOBSEN S: The
contribution of isozymes of serum lactic
dehydrogenase (LDH) to the diagnosis of
specific organ injury. Med Clin N Amer 50:
193, 1966
38. BLOOR CM, SOBEL BE, HENRY PD: Autologous
pulmonary embolism in the intact, unanesthetized dog. J Appl Physiol 29: 670, 1970
39. DOTY DH, BLOOR CM, SOBEL BE: Altered tissue
lactic dehydrogenase activity after exercise in
the rat. j Appl Physiol .20: 548, 1971
40. ROSALKI SB: An improved procedure for serum
creatine phosphokinase determination. J Lab
Clin Med 69: 696, 1969
41. VELEz-GARCIA E, HARDY P, DIoso M, PERKOFF
GT: Cysteine-stimuilated serum creatine phosphokinase: Unexpected resuilts. J Lab Clin
Med 68: 636, 1966
42. LAFAIR JS, MYERSON RM: Alcoholic myopathywith special reference to the significance of
creatine phosphokinase. Arch Intern Med
(Chicago) 122: 417, 1968
43. SAVIGNANO T, HANOK A, Kuo J: Creatine
phosphokinase activity: A study of normal and
abnormal levels. Amer J Clin Path 51: 76,
1969
Circulation, Volunme XLV, February 1972
SERUM ENZYMES IN MI
44. MELTZER HY, MROZAK S, BOYER M: Effect of
intramuscular injections on serum creatine
phosphokinase activity. Amer J Med Sci 259:
42, 1970
45. MUCCIA FM, GHOSSEIN NA, HANOK A: Creatine
phosphokinase and other serum enzymes
during radiotherapy. JAMA 211: 1345, 1970
Downloaded from http://circ.ahajournals.org/ by guest on June 15, 2017
46. VINCENT WR, RAPAPORT E: Serum creatine
phosphokinase in the diagnosis of acute
myocardial infaretion. Amer J Cardiol 15: 17,
1965
47. PERKOFF CT: Demonstration of creatine phosphokinase in human lung tissue. Arch Intern
Med (Chicago) 122: 326, 1968
48. HENRY PD, BLOOR CM, SOBEL BE: Increased
serum
creatine phosphokinase activity in
experimental pulmonary embolism. Amer J
Cardiol 26: 151, 1970
49. BATSAKIS JG, PRESTON JA, BRIERE RO, GIESEN
PC: Jatrogenic aberrations of serum enzyme
activity. Clin Biochem 2: 125, 1968
50. MAROKO PR, KJEKSHUS JK, SOBEL BE,
WATANABE T, COVELL JW, ROSS J JR,
BRAUNWALD E: Factors influencing infaret size
following experimental coronary artery occlusions. Circulation 43: 67, 1971
51. SHELL WE, HENRY PD, SOBEL BE: The effect of
increased heart rate on infarct size in the
conscious dog. (Abstr) Circulation 44 (suppl
II): II-61, 1971
52. CROWLEY LV: Creatine phosphokinase activity in
myocardial infaretion, heart failure, and following various diagnostic and therapeutic procedures. Clin Chem 14: 1185, 1968
53. WAGNER JA, CRITZ JB: The effect of prednisolone
on the serum creatine phosphokinase response
to exercise. Proc Soc Exper Biol Med 128:
716, 1968
54. VESELL ES: Lactate dehydrogenase isozymes:
Substrate inhibition in various human tissues.
Science 150: 1590, 1965
55. SOBEL BE, HENRY PD, EHRLICH BJ, BLOOR CM:
Altered myocardial lactic dehydrogenase isoenzymes in experimental cardiac hypertrophy.
Lab Invest 22: 23, 1970
56. BATSAKIS JG, BRIERE RO: LDH isoenzymes by
urea inhibition and substrate (lactate) modification: A clinical evaluation. Clin Biochem 2:
171, 1969
Circulation. Volume XLV, February 1972
481
57. ROSE LI, LOWE SL, CARROLL DR, WOLFSON S,
COOPER KH: Serum lactate dehydrogenase
isoenzyme changes after muscle exertion. J
Appl Physiol 28: 279, 1970
58. NORA JL, COOLEY DA, JOHNSON BL, WATSON
SC, MILAM JD: Lactic dehydrogenase isoenzymes
in human cardiac transplantation.
Science 164: 1079, 1969
59. GRIFFITHS PD: Serum enzymes in diseases of
the thyroid gland. J Clin Path 18: 660, 1965
60. LUBRAN M, JENSEN WE: Determination of LDH
isoenzymes in serum: A urea inhibition method
compared with an electrophoretic method. Clin
Chim Acta 22: 125, 1968
61. ROSALKI SB, WILKINSON JH: Serum a-hydroxybutyrate dehydrogenase in diagnosis. JAMA
189: 61, 1964
62. COODLEY EL: Evaluation of enzyme diagnosis in
myocardial infarction. Amer J Med Sci 256:
300, 1968
63. SMITH AF: Diagnostic value of serum-creatinekinase in a coronary-care unit. Lancet 2: 178,
1967
64. RATNER JT, SACKS HJ: Transaminase in coronary
artery disease. Canad Med Ass J 76: 720,
1957
65. HENDRICH F, STEJFA M, HULE V: Diagnostic
value of serum lactate dehydrogenase isoenzymes in anginal attacks. Cor Vasa 12: 8,
1970
66. KLUGE WF: Prognostic value of serum creatine
phosphokinase levels in myocardial infarction.
Northwest Med 68: 847, 1969
67. MCCALL M, HERTZ A, RAPPAPORT I, NELSON W:
Serum glutamic oxalacetic transaminase activity in acute coronary thrombosis with myocardial infarction: Relation to prognosis. Amer J
Cardiol 7: 673, 1961
68. KIBE 0, NILSSON NJ: Observations on the
diagnostic and prognostic value of some
enzyme tests in myocardial infarction. Acta
Med Scand 182: 597, 1967
69. HARNARAYAN C, BENNETT MA, PENTECOST BL,
BREWER DB: Quantitative study of infarcted
myocardium in cardiogenic shock. Brit Heart J
32: 728, 1970
70. KILLEN DA, TINSLEY EA: Serum enzymes in
experimental myocardial infarcts. Arch Surg
(Chicago) 92: 418, 1966
71. KJEKSHUS JK, SOBEL BE: Depressed myocardial
SOBEL, SHELL
482
creatine phosphokinase activity following
ex-
perimental myocardial infarction. Circ Res 27:
403, 1970
72. BRAUNWALD EB, KARLINER JS, ASHBURNT WL,
KAZAMIAS TM, Ross J JR, MAROKO PR, SOBEL
BE, BRAUNWALD NS: Research on the diagnosis and treatment of myocardial infarction.
Calif Med 114: 44, 1971
Downloaded from http://circ.ahajournals.org/ by guest on June 15, 2017
Circulation, Volume XLV, February 1972
Serum Enzyme Determinations in the Diagnosis and Assessment of Myocardial
Infarction
BURTON E. SOBEL and WILLIAM E. SHELL
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Circulation. 1972;45:471-482
doi: 10.1161/01.CIR.45.2.471
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