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1. Myocardial infarction

2. Myocardial infarction
• Infarction is defined as the process by which necrosis (cell or tissue
death) results from ischaemia
• Infarction of cardiac muscle (myocardial infarction or MI) is one of the
commonest causes of morbidity and mortality in adults living in
industrialized societies.

3. 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 blood
BIOCHEMICAL
MARKERS
clinical manifestations
(chest pain)
ECG
changes

4. Development of atheroma in coronary arteries, with
histopathological section
(bottom right).

5. Criteria for acute myocardial infarction
• The term myocardial infarction should be used when there is evidence of
myocardial necrosis in a clinical setting consistent with myocardial
ischaemia. Under these conditions the following meets the diagnosis for
myocardial infarction:
• Detection of rise and/or fall of cardiac biomarkers (preferably troponin)
with at least one of the following:
• Symptoms of ischaemia;
• ECG changes indicative of new ischaemia (new ST-T changes or new left
bundle branch block (LBBB));
• Development of pathological Q waves* in the ECG;
• Imaging evidence of new loss of viable myocardium or new regional wall
motion abnormality.

6. ECG changes following an MI. (a) Normal ECG. (b) Two hours after onset of chest pain.
Note elevated ST segment. (c) Twenty-four hours later the patient had a further episode of
chest

7. Diagnosis of Myocardial Infarction
SHOULD depend on THREE items
1- Clinical Manifestations
2- ECG
3- Biochemical Markers

8. Cardiac Enzymes
• Total 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)

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

10. Cardiac Proteins
• Myoglobin
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)

11. 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 and 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 specific
• With greater sensitivity for diagnosing minor damage of MI
• Appears in blood within 6 hours after onset of infarction
• peak: around 24 hours
• Disappears from blood after about 1-2 week (stays longer) So, useful for diagnosis of delayed admission cases
• Prognostic marker (relation between level in blood and extent of cardiac damage)
• The diagnostic sensitivity of troponin reaches 100% 12 hours after onset of symptoms

12. Recommendations for use of biochemical markers for diagnosis of myocardial
infarction
1- 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)