Biochemical Markers in Cardiac
Disease
Dr/Ehsan Mohamed Rizk
ACUTE CORONARY SYNDROME
(ACS)
 Ischemic heart diseases (acute coronary syndrome) includes:
1-Angina
2-Unstable angina
3-Myocardial infarction: most serious form of ischemia that
leads to injury or even death of myocardium.
 The most common cause of myocardial ischemia is atherosclerosis.
 Risk factors for Coronary Artery Disease:
1-Age
2-Gender
3-Family history
4-Hyperlipidemia
5-Smoking
6-Hypertension
7-Diabetes
8-Obesity
9-High plasma homocysteine levels
CRITERIA FOR DIAGNOSIS OF ACS
 Triad of criteria:
 Clinical picture
Severe & prolonged chest pain
Atypical pain (epigastric)
Silent ischemia.
 ECG changes consistent with acute MI
 Elevated serum cardiac MARKERS
 Diagnosis requires at least two of them.
CARDIAC MARKERS MUST BE:
 Located in the myocardium.
 Released in cardiac injury.
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Myocardial infarction
Non-Q-wave infarction
Unstable angina pectoris
Other conditions affecting cardiac muscle
(trauma, cardiac surgery, myocarditis etc.)
 Can be measured in blood samples.
THE IDEAL CARDIAC MARKER
HIGH SENSITIVITY
HIGH SPECIFICITY
High concentration in myocardium
Released after myocardial injury:
Absent in non-myocardial tissue
Rapid release for early
diagnosis
Not detectable in blood of nondiseased subjects
The ideal cardiac
marker does
ANALYTICAL
CLINICAL CHARACTERISTICS
CHARACTERISTICS NOT yet exist!
fk
Long half-life in blood for late
diagnosis
Measurable by cost-effective
method
Simple to perform
Rapid turnaround time
Sufficient precision & accuracy
Scand J Clin Lab Inves 1999;59 (Suppl 230):113-123
Ability to influence therapy
Ability to improve patient outcome
CARDIAC MUSCLE CELL
Size and subcellular distribution of myocardial proteins determines time
course of biomarker appearance in the general circulation
CLASSIFICATION OF LABORATORY
TESTS IN CARDIAC DISEASE
 Markers of cardiac tissue damage
 Markers of myocardial function
 Cardiovascular risk factor markers
 Genetic analysis for candidate genes or risk
factors
PATHOPHYSIOLOGY OF ACS
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Proinflammatory Cytokines
 IL-6
Plaque Destabilization
 MPO
Plaque Rupture
 sCD40L
Acute Phase Reactants
 hs-CRP
Ischemia
 IMA
Necrosis
 cTnT
 cTnI
Myocardial Dysfunction
 BNP
 NT-proBNP
BIOCHEMICAL MARKERS IN
MYOCARDIAL ISCHAEMIA / NECROSIS
RECENT
 CK-MB (mass)
 c.Troponins (I or T)
 Myoglobin
FUTURE:
 Ischaemia Modified Albumin
 Glycogen Phosphorylase BB
 Fatty Acid binding Protein
 Highly sensitive CRP.
Traditional
 AST activity
 LDH activity
 LDH isoenzymes
 CK-Total
 CK-MB activity
 CK-Isoenzymes
ASPARATATE
AMINOTRANFERASE (AST)
 An enzyme that catalysis the transfer of amino
group from amino acid to keto acid which is
important for providing α keto acid for tricarboxylic
acid cycle (energy production) and providing
amino acid for urea cycle.
 It is widely distributed in hear, liver, skeletal
muscle, kidney and RBCs.
 AST activity is increased after myocardial
infarction
 It is elevated in other conditions as:
 Liver disease: hepatitis, liver cirrhosis, neoplasia
 Muscle diseases: muscular dystrophy and
dermatomyositis
LACTATE DEHYDROGENASE
(LDH)
 LDH is a hydrogen transfer enzyme that catalysis the
oxidation of L-Lactate to Pyruvate.
 It is composed of 4 subunits of 2 types
M type encoded by a gene on ch 11
H type encoded by a gene on ch 12.
 There are 5 isoenzymes:
LD-1 (4 H subunits)
LD-2 (3 H and 1 M sumunits)
LD-3 (2 H and 2 M sumunits)
LD-4 (1 H and 3 M sumunits)
LD-5 (4 M subunits)
LDH
 Both total and LDH isoenzymes are elevated
in myocardial injury.
 Level of LD-1 are elevated 10 – 12 after
acute myocardial infarction, peak in 2 days
and return to normal in 7 -10 days
 Usually the amount of LD-2 in the blood is
higher than amount of LD-1. Patient with AMI
have more LD-1 than LD-2 (ratio > 1) this is
called "Flipped Ratio".
 An elevated level of LD=1 with flipped ratio
has a sensitivity and specificity of
approximately 75% - 90% for detection of
AMI.
CREATINE KINASE
 CK is a dimeric enzyme that regulates high energy phosphate
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production and utilization in contractile tissues.
It is composed of two subunits:
M subunit encoded by a gene on chromosome 14.
B subunit encoded by a gene on chromosome 19.
There are different isoenzymes:
CK1 (CK-BB): the predominant isoenzyme found in brain.
CK2 (CK-MB): represent 20 – 30 % of total CK in diseased cardiac
tissue
CK3 (CK-MM): 98% in skeletal muscles and 1% in cardiac muscles.
CK-mitochondrial (CK-Mt): located in mitochondria and encoded by a
different gene on chromosome 15.
Macro-CK: CK complexed with Igs.
CREATINE KINASE
NORMAL VALUES:
Vary according to –
 age
 sex
 race
 physical condition
 muscle mass
PATHOLOGICAL INCREASES:
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Myocardial infarction or injury
Skeletal muscle injury or disease
Hypothyroidism
IM injections
Generalised convulsions
Cerebral injury
Malignant hyperpyrexia
Prolonged hypothermia
CREATINE KINASE: CK-MB
 In normal population CK-MB < 6% Total CK
 Sensitive marker with rapid rise & fall:
Serum CK-MB levels rise within 2~8 hours after AMI.
CK-MB values return to normal 2~3 days after the
event.
 More specific than total CK but has limitations:
False elevations in:
-perioperative patients without cardiac injury
-Skeletal muscle injury
-Marathon runners
-Chronic renal failure
-Hypothyroidism
MB Index = (CKMB /total CK) x 100
Combined use with MB Index helps to rule-out patients with
skeletal muscle injury
CK-MB RELATIVE INDEX AND CKMB mass:
 MB Index = (CKMB /total CK) x 10
Combined use with MB Index helps to ruleout patients with skeletal muscle injury
 CK-MB MASS:
 Measure the concentration of CK-MB
protein is now available using sandwich
technique with a detection limit < 1µg/dl.
 More sensitive than measurement of
activity.
CK-isoforms:
 Both M and B subunits have N-terminal lysine residues but
only M subunit is hydrolyzed by carboxypeptidase-N enzyme
found in blood.
 CK-MM is present in three isoforms:
CK-MM3: tissue form.
CK-MM2: (one lysine residue is removed).
CK-MM1: (both lysine residue are removed)
 CK-MB has two isoforms:
CK-MB2: tissue form.
CK-MB1: circulating form.
 The ratio of tissue isoforms and plasma modified isoforms
are used as markers of recent myocardial damage (elevated
CK-MM3/CK-MM2 and CK-MB2/CK-MB1/CK-MB1 indicates
a rise in tissue isoforms caused by recent release).
MYOGLOBIN (Mb)
 Low MW protein
 Skeletal & cardiac muscle Mb identical
 Serum levels increase within 2h of muscle damage
 Peak at 6 – 9h
 Normal by 24 – 36h
 Excellent NEGATIVE predictor of myocardial injury
– 2 samples 2 – 4 hours apart with no rise in levels virtually
excludes AMI
 Rapid, quantitative serum immunoassays
CARDIAC TROPONINS
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1.
2.
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It consists of 3 subunits troponin C, I, and T.
The complex regulates the contraction of
striated muscle.
TnC binds to calcium ions.
TnI binds to actin and inhibits actin-myosin
interaction.
TnT binds to tropomyosin, attaching to thin
filament.
THE TROPONIN REGULATORY
COMPLEX
cTnI
cTns
1. Cardiac Troponin I (cTnl) is a
cardiac muscle protein with a
molecular weight of 24 kiloDaltons.
2. The human cTnl has a additional
amino acid residues on its Nterminal that are not exist on the
skeletal form.
3. The half life of cTnI is estimated to
be 2~4 hours.
4. Serum increase is found between
2-8 hours and returns to normal
7~10 days after AMI.
5. Cardiac TnI levels provide useful
prognostic information.
6. Reference range: cTnI <2 ng/ml
cTnT
1.Cardiac Troponin T (cTnT) is
present in fetal skeletal muscle.
2. In healthy adult skeletal muscle
cTnT is absent.
3. The gene of cTnT may be re
expressed in skeletal muscle
disease.
4. Biological half life and early
serum increases of cTnT are
similar to that of cTnI.
5. Peak between 12~96 hours and
return to normal 14 days after AMI.
TROPONIN SUMMARY
 Regulatory complex of striated muscle
contraction
 Early release ex cytosolic pool
 Prolonged release due degradation of
myofilaments
 Distinct skeletal & myocardial muscle forms
 High specificity for myocardial injury
 Sensitive to minor myocardial damage
ISCHAEMIA-MODIFIED ALBUMIN
(IMA)
 Serum albumin is altered by free radicals released from ischaemic
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tissue
Angioplasty studies show that albumin is modified within minutes of
the onset of ischaemia.
IMA levels rise rapidly, remain elevated for 2-4 h + return to baseline
within 6h
Clinically may detect reversible myocardial ischaemic damage
Not specific (elevated in stroke, some neoplasms, hepatic cirrhosis,
end-stage renal disease)
Thus potential value is as a negative predictor
Spectrophotometric assay for IMA adapted for automated clinical
chemistry analysers
FDA approved as a rule-out marker in low risk ACS patients (2003)
Glycogen phosphorylase BB (GPBB):
 Glycogen phosphorylase (GP) is a glycolytic enzyme which
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plays an essential role in the regulation of carbohydrate
metabolism.
It functions to provide energy supply for muscle contraction
Three GP isoenzymes are found in human tissues:
o
GP-LL in liver
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GP-MM in muscle
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GP-BB in brain.
GP-BB is the predominant isoenzyme in myocardium. With the
onset of tissue hypoxia when glycogen is broke down, GP-BB is
converted from structurally bound to cytoplasmic form.
In AMI GP-BB: Increases 1 – 4 after onset of chest pain
Peaks before CK-MB and cTnT
Return to reference interval 1 – 2 days after
AMI.
However it is not cardiac specific.
BIOCHEMICAL MARKERS IN ACS:
RELEASE, PEAK AND DURATION OF ELEVATION
Marker
LD-1
Total CK
CK-MB
CK-MB
isoforms
cTnI
cTnT
Myoglobin
IMA
Duration of
elevation
7 – 10 days
start
Peak
24 – 47 h
3–8h
4–6h
2–3h
48 – 72 h
12 – 30 h
24 h
18 h
6h
24 h
7 – 10 days
6h
2h
Few minutes
12 – 48 h
6–7h
2–4h
7 – 10 days
24 h
6h
3 – 4 days
48 – 72 h
< 24 h
BIOCHEMICAL MARKERS IN ACS:
RELEASE, PEAK AND DURATION OF ELEVATION
BIOCHEMICAL MARKERS IN ACS
UNSTABLE ANGINA PECTORIS (UA)
 Characterised by chest pain at rest
 ? Caused by disruption of liquid-filled atherosclerotic
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plaque with platelet aggregation & thrombus formation
Variable degree of ischaemia resulting in reversible or
irreversible injury
Non-occlusive plaques may produce sufficient ischaemia
for release of low molecular weight markers
cTnI & cTnT are often elevated in patients with unstable
angina pectoris without additional clinical signs (ECG) or
classical laboratory signs of acute MI (elevated CK-MB)
These patients have a very high risk of cardiac events
CARDIAC TROPONINS IN
UNSTABLE ANGINA PECTORIS (UA)
QUESTION:
 Does an elevated Troponin level in the absence of
other signs reflect irreversible myocardial damage?
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Epidemiological studies
Animal experiments
Clinical trials
Sensitive imaging techniques
MI must be REDEFINED!
Say
YES!
“ACS REDEFINED”
 If Troponins are not available, best alternative is CK
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MBmass
Degree of elevation of the marker is related to clinical risk
CK(total), AST & LDH (Cardiac Enzymes) should NOT be
used!
Combine early (myoglobin) & late (Troponins) markers
Serial testing: admission, 6 – 9 h, 12 – 24 h
An elevated Troponin level in the absence of clinical
evidence of ischaemia should prompt searching for other
causes of cardiac damage
ACS REDEFINED
Revised Criteria: Acute/Evolving/ Recent MI
 Typical myocardial necrosis-associated rise & fall of
Troponin or CK-MBmass
PLUS
 One of:
– Cardiac Ischaemia symptoms
– Q waves on ECG
– ST segment changes indicative of ischaemia
– Coronary artery imaging (stenosis/obstruction)
 OR Pathologic findings of an acute MI
BIOCHEMICAL MARKERS IN AMI
ASSESSMENT OF REPERFUSION
 “Washout”
Marker Level
Successful
reperfusion
Unsuccessful
reperfusion
phenomenon –
enzymes & proteins have
direct vascular access when
occluded coronary circulation
becomes patent
 Peak concentrations earlier &
at higher levels if reperfusion
successful
Time
Due to short plasma half life (t½ = 10 min) Myoglobin is considered the
best re-perfusion marker
BIOCHEMICAL MARKERS IN ACS
CURRENT RECOMMENDATIONS
 AMI – Routine diagnosis
 Retrospective diagnosis
 Skeletal muscle pathology
 Reinfarction
 Reperfusion
 Infarct size
 Risk stratification in UA
Troponins (CK-MBmass)
Troponins
Troponins
Mb, CK-MBmass
Mb, Tn, CK-Mbmass
Troponins
Troponins
BIOCHEMICAL MARKERS OF
MYOCARDIAL FUNCTION
CARDIAC NATRIURETIC PEPTIDES:
(ANP, BNP & pro-peptide forms)
 Family of peptides secreted by cardiac atria (+ ventricles)
with potent diuretic, natriuretic & vascular smooth muscle
relaxing activity
 Levels of these neuro-hormonal factors can be measured
in blood
 Clinical usefulness (especially BNP/N-terminal pro-BNP)
– Detection of LV dysfunction
– Screening for heart disease
– Differential diagnosis of dyspnea
CARDIOVASCULAR RISK FACTORS
ESTABLISHED RISK FACTORS
Raised serum low density lipoprotein cholesterol
Decreased serum high density lipoprotein cholesterol
Smoking
High Blood pressure
Increased plasma glucose concentrations
Physical inactivity
Obesity
Advanced age
EVIDENCE
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++ Clear evidence, and modification
+
of the risk factor decreases the risk of
cardiovascular disease
EMERGING RISK FACTORS
Inflammatory Markers
Sensitive C-reactive protein
Interleukins
Serum amyloid A
Pregnancy-associated plasma protein A
Chronic infection (Chlamydia pneumoniae,
Helicobacter pylori, etc)
Procoagulant Markers
Plasma Homocysteine
Tissue plasminogen activator
Plasminogen activator inhibitor
Lipoprotein A
Process Markers
Fibrinogen
D-dimer
Coronary artery calcification
Boersma et al, Lancet, 2003:361,p849
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?
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+
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+
+
?
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+ Clear evidence, but less clear
whether modification of the risk factor
decreases the risk of cardiovascular
disease
?
Risk factor under scrutiny
GENETIC ANALYSIS OF CANDIDATE GENES
OR RISK FACTORS FOR CARDIOVASCULAR
DISEASE
 Recent explosion of genetic analysis & micro-array
technology
 Common cardiovascular diseases are polygenic. Multiple
susceptibility loci interact with lifestyle & environment
 Single gene defects may account for some of the
cardiomyopathies, inherited cardiac arrhythmias
 Possible genetic cardiovascular risk factors under
assessment
 Technology is still complex & expensive but is developing
very rapidly