Biochemical Markers in Cardiac Diseases

8/11/2019 Biochemical Markers in Cardiac Diseases

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Biochemical Markers in Cardiac

Disease

Dr/Ehsan Mohamed Rizk


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ACUTE CORONARY SYNDROME

ACS)

Ischemic heart diseases (acute coronary syndrome) includes:

1-Angina

2-Unstable angina

3-Myocardial infarction: most serious form of ischemia thatleads 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-Hyperlipidemia5-Smoking

6-Hypertension

7-Diabetes

8-Obesity

9-High plasma homocysteine levels


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CRITERIA FOR DIAGNOSIS OF ACS

Triad of criteria:

Clinical picture

Severe & prolonged chest painAtypical pain (epigastric)

Silent ischemia.

ECG changes consistent with acute MIElevated serum cardiac MARKERS

Diagnosis requires at least two of them.


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CARDIAC MARKERS MUST BE:

Located in the myocardium.

Released in cardiac injury.

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.


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THE IDEAL CARDIAC MARKER

HIGH SENSITIVITY

High concentration in myocardium

Released after myocardial injury:

Rapid release for earlydiagnosis

Long half-life in blood for late

diagnosis

HIGH SPECIFICITY

Absent in non-myocardial tissue

Not detectable in blood of non-

diseased subjects

CLINICAL CHARACTERISTICS

fk

Ability to influence therapy

Ability to improve patient outcome

ANALYTICAL

CHARACTERISTICS

Measurable by cost-effective

method

Simple to perform

Rapid turnaround time

Sufficient precision & accuracy

The ideal cardiac

marker does

NOT yet exist

Scand J Clin Lab Inves 1999;59 (Suppl 230):113-123


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CARDIAC MUSCLE CELL

Size and subcellular distribution of myocardial proteins determines time

course of biomarker appearance in the general circulation


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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 riskfactors


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PATHOPHYSIOLOGY OF ACS

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


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BIOCHEMICAL MARKERS IN

MYOCARDIAL ISCHAEMIA / NECROSIS

RECENT

CK-MB (mass)

c.Troponins (I or T)

Myoglobin

Traditional

AST activity

LDH activity

LDH isoenzymes CK-Total

CK-MB activity

CK-IsoenzymesFUTURE:

Ischaemia Modified Albumin Glycogen Phosphorylase BB

Fatty Acid binding Protein

Highly sensitive CRP.


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LACTATE DEHYDROGENASE

LDH)

LDH is a hydrogen transfer enzyme that catalysis theoxidation of L-Lactate to Pyruvate.

It is composed of 4 subunits of 2 types

M type encoded by a gene on ch 11H 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)


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LDH

Both total and LDH isoenzymes are elevatedin myocardial injury.

Level of LD-1 are elevated 10 12 after

acute myocardial infarction, peak in 2 daysand return to normal in 7 -10 days

Usually the amount of LD-2 in the blood ishigher than amount of LD-1. Patient with AMIhave 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 ofapproximately 75% - 90% for detection of

AMI.


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CREATINE KINASE

CK is a dimeric enzyme that regulates high energy phosphate

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.


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CREATINE KINASE

NORMAL VALUES:

Vary according to

age sex

race

physical condition

muscle mass

PATHOLOGICAL INCREASES:

Myocardial infarction or injury

Skeletal muscle injury or disease

Hypothyroidism

IM injections

Generalised convulsions Cerebral injury

Malignant hyperpyrexia

Prolonged hypothermia


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CREATINE KINASE: CK-MB

In normal population CK-MB < 6% Total CKSensitive 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 CK


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CK-MB RELATIVE INDEX AND CK-MB mass:

CK-MB MASS:

Measure the concentration of CK-MB

protein is now available using sandwichtechnique with a detection limit < 1g/dl.

More sensitive than measurement ofactivity.

MB Index = (CKMB /total CK) x 10

Combined use with MB Index helps to rule-

out patients with skeletal muscle injury


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CK-isoforms:

Both M and B subunits have N-terminal lysine residues butonly M subunit is hydrolyzed by carboxypeptidase-N enzymefound 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 isoformsare used as markers of recent myocardial damage (elevatedCK-MM3/CK-MM2 and CK-MB2/CK-MB1/CK-MB1 indicatesa rise in tissue isoforms caused by recent release).


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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 predictorof myocardial injury

2 samples 2 4 hours apart with no rise in levels virtually

excludes AMI

Rapid, quantitative serum immunoassays


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THE TROPONIN REGULATORY

COMPLEX


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1. Cardiac Troponin I (cTnl) is acardiac muscle protein with amolecular weight of 24 kilo-Daltons.

2. The human cTnl has a additional

amino acid residues on its N-terminal that are not exist on theskeletal form.

3. The half life of cTnI is estimated tobe 2~4 hours.

4. Serum increase is found between

2-8 hours and returns to normal7~10 days after AMI.

5. Cardiac TnI levels provide usefulprognostic information.

6. Reference range: cTnI


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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


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ISCHAEMIA-MODIFIED ALBUMIN(IMA)

Serum albumin is altered by free radicals released from ischaemic

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 baselinewithin 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)


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Glycogen phosphorylase BB GPBB):

Glycogen phosphorylase (GP) is a glycolytic enzyme whichplays an essential role in the regulation of carbohydratemetabolism.

It functions to provide energy supply for muscle contraction

Three GP isoenzymes are found in human tissues:

o GP-LL in liver

o GP-MM in muscle

o GP-BB in brain.

GP-BB is the predominant isoenzyme in myocardium. With theonset 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 afterAMI.

However it is not cardiac specific.


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BIOCHEMICAL MARKERS IN ACS:

RELEASE, PEAK AND DURATION OF ELEVATION

Marker start Peak Duration ofelevation

LD-1 2447 h 4872 h 710 days

Total CK 38 h 1230 h 34 days

CK-MB 46 h 24 h 4872 h

CK-MB

isoforms

23 h 18 h < 24 h

cTnI 6 h 24 h 710 dayscTnT 6 h 1248 h 710 days

Myoglobin 2 h 67 h 24 h

IMA Few minutes 24 h 6 h


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BIOCHEMICAL MARKERS IN ACS:

RELEASE, PEAK AND DURATION OF ELEVATION


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BIOCHEMICAL MARKERS IN ACSUNSTABLE ANGINA PECTORIS (UA)

Characterised by chest pain at rest

? Caused by disruption of liquid-filled atheroscleroticplaque with platelet aggregation & thrombus formation

Variable degree of ischaemia resulting in reversible orirreversible injury

Non-occlusive plaques may produce sufficient ischaemiafor release of low molecular weight markers

cTnI & cTnT are often elevated in patients with unstableangina pectoris without additional clinical signs (ECG) orclassical laboratory signs of acute MI (elevated CK-MB)

These patients have a very high risk of cardiac events


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CARDIAC TROPONINS INUNSTABLE ANGINA PECTORIS (UA)

Does an elevated Troponin level in the absence of

other signs reflect irreversible myocardial damage?

Epidemiological studies

Animal experiments

Clinical trials

Sensitive imaging techniques

Say

YES!

MImust be REDEFINED!

QUESTION:


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ACS REDEFINED

If Troponins are not available, best alternative is CK-

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


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BIOCHEMICAL MARKERS IN AMIASSESSMENT OF REPERFUSION

Washout phenomenon

enzymes & proteins have

direct vascular access when

occluded coronary circulation

becomes patent

Peak concentrations earlier &

at higher levels if reperfusion

successful

Due to short plasma half life (t = 10 min) Myoglobin is considered the

best re-perfusion marker

Time

MarkerLevel

Successful

reperfusion

Unsuccessful

reperfusion


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BIOCHEMICAL MARKERS IN ACSCURRENT RECOMMENDATIONS

AMI Routine diagnosis Troponins (CK-MBmass)

Retrospective diagnosis Troponins

Skeletal muscle pathology Troponins

Reinfarction Mb, CK-MBmass

Reperfusion Mb, Tn, CK-Mbmass

Infarct size Troponins

Risk stratification in UA Troponins


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BIOCHEMICAL MARKERS OFMYOCARDIAL FUNCTION

CARDIAC NATRIURETIC PEPTIDES:

(ANP, BNP & pro-peptide forms)

Family of peptides secreted by cardiac atria (+ ventricles)with potent diuretic, natriuretic & vascular smooth musclerelaxing activity

Levels of these neuro-hormonal factors can be measuredin blood

Clinical usefulness (especially BNP/N-terminal pro-BNP) Detection of LV dysfunction

Screening for heart disease

Differential diagnosis of dyspnea


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CARDIOVASCULAR RISK FACTORS

ESTABLISHED RISK FACTORS EVIDENCERaised serum low density lipoprotein cholesterol ++

Decreased serum high density lipoprotein cholesterol ++

Smoking ++

High Blood pressure ++

Increased plasma glucose concentrations +

Physical inactivity +

Obesity +

Advanced age +

EMERGING RISK FACTORS

Inf lammatory Markers

Sensitive C-reactive protein +

Interleukins +

Serum amyloid A +

Pregnancy-associated plasma protein A ?

Chronic infection (Chlamydia pneumoniae, ?

Helicobacter pylori, etc)Procoagu lant Markers

PlasmaHomocysteine +

Tissue plasminogen activator +

Plasminogen activator inhibitor +

Lipoprotein A +

Process Markers

Fibrinogen +

D-dimer ?

Coronary artery calcification ?

Boersma et al, Lancet, 2003:361,p849

++ Clear evidence, and modification

of the risk factor decreases the risk of

cardiovascular disease

+ Clear evidence, but less clear

whether modification of the risk factor

decreases the risk of cardiovascular

disease

? Risk factor under scrutiny


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GENETIC ANALYSIS OF CANDIDATE GENESOR RISK FACTORS FOR CARDIOVASCULARDISEASE

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 underassessment

Technology is still complex & expensive but is developing

very rapidly


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Biochemical Markers in Cardiac Diseases