Biochemical Markers for Diagnosis of Myocardial InfarctionCardiovascular BlockMedical Biochemistry CourseDr. Aida Ahmad Abd Elhamed Lecturer of Clinical Pathology

What is Myocardial Infarction?Myocardial ischemia results from the reduction of coronary blood flow to an extent that leads to insufficiency of oxygen supply to myocardial tissue

When this ischemia is prolonged & irreversible, myocardial cell death & necrosis occurs ---this is defined as: myocardial infarction is the death & necrosis of myocardial cells as a result of coronary prolonged & irreversible ischemia

Biochemical Changes in Acute Myocardial Infarction(mechanism of release of myocardial markers)ischemia to myocardial muscles (with low O2 supply)

anaerobic glycolysis

increased accumulation of Lactate

decrease in pH

activate lysosomal enzymes

disintegration of myocardial proteins

cell death & necrosis

release of intracellular contents to bloodBIOCHEMICAL MARKERS

clinical manifestations (chest pain)

ECG changes

Diagnosis of Myocardial Infarction SHOULD depend on THREE items(as recommended by WHO)

1- Clinical Manifestations 2- ECG 3- Biochemical Markers

criteria for ideal markers for myocardial infarction1- Specific: to myocardial muscle cells (no false positive)

2- Sensitive: - rapid release on onset of attack (diagnose early cases) - so, can detect minor damage - no miss of positive cases (no false negative)

3- Prognostic: relation between plasma level & extent of damage

4- Persists longer: so, can diagnose delayed admission

6- Reliable: procedure depends on evidenced principle

5- Simple, inexpensive: - can be performed anywhere by low costs - no need for highly qualified personnel

7- Quick: low turnaround time

Types of Biochemical Markers for Myocardial Infarction1- Cardiac Enzymes (isoenzymes): Total CK CK-MB activity CK-MB mass

2- Cardiac proteins: Myoglobin Troponins

BIOCHEMICAL MARKERS IN MYOCARDIAL ISCHAEMIA / NECROSISRECENTCK-MB (mass)c.Troponins (I or T)MyoglobinTraditionalAST activityLDH activityLDH isoenzymesCK-TotalCK-MB activityCK-Isoenzymes

FUTURE:Ischaemia Modified AlbuminGlycogen Phosphorylase BBFatty Acid binding ProteinHighly sensitive CRP.

Cardiac EnzymesTotal CK (sum of CK-MM, CK-MB & CK-BB) non specific to cardiac tissue (available in skeletal ms.)

CK-MB (CK-2) activity

more specific than total CK BUT: less specific than troponin I (available in sk. Ms)

appears in blood: within 4-6 hours of onset of attack peak: 12 - 24 hours returns to normal: within 2 - 3 days (no long stay in blood) Advantages: - useful for early diagnosis of MI - useful for diagnosis reinfarction

Disadvantages: not used for delayed admission (more than 2 days) not 100% specific (elevated in sk.ms damage)

CK-MB mass - appears one hour earlier than CK-MB activity (more sensitive) - So, useful for diagnosis of early cases & reinfarction - BUT: not for diagnosis of delayed admission cases & less specific than troponin I

Relative index = CK-MB mass / Total CK X 100 more than 5 % is indicative for MI

Cardiac ProteinsMyoglobin cytosolic protein

- not specific for cardiac tissue (also in sk.ms. & renal tissue) - appears in blood EARLIER than other markers (within 1-4 hours) So, with high sensitivity - BUT: Returns to normal in 24 hours So, not for delayed admission cases (after one day of onset of attack)

Cardiac Troponins

Protein complex located on the thin filament of striated muscles consists of 3 subunits: cTn T, cTnI & cTn C with different structures & functions

cTnI & cTnT are used are biomarkers for MI diagnosis

Cardiac troponins (cTn) are different from skeletal muscle tropnins So, more specific for MI diagnosis cTnI: 100 % cardiac specificWith greater sensitivity for diagnosing minor damage of MIAppears in blood within 6 hours after onset of infarctionpeak: around 24 hoursDisappears from blood after about one week (stays longer) So, useful for diagnosis of delayed admission casesPrognostic marker (relation between level in blood & extent of cardiac damage)

Recommendations for use of biochemical markers for diagnosis of myocardial infarction1- Recommended for all patients complaining of chest pain (with clinical examination & ECG)

2- Sample Type: plasma Timing: i. on admission ii. serial ( at least every one hour in a period 6-9 hours) should be referenced to admission & onset of pain

3- Test should be with low turnaround time less than one hour (accepted) less than half an hour is preferred

4- Types of Markers used: two types early markers: as Myoglobin: appears in blood early (within less 4 fours) BUT not specific & not persists for long period (less than 2 days)

definitive markers: Troponin: appears in blood later than myoglobin (within 6 hours) BUT 100% specific, prognostic & stays longer (one week)

5- Troponin is currently the marker of choice should be available in all cardiac & emergency centers (if not, CK-MB mass is the second choice)

THANK YOU

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