Download Myocardial infarction

Myocardial Infarction
 Ischemic heart muscle necrosis.
 significant cause of death worldwide.
 33% -50% die before they can reach the
hospital lethal arrhythmia  Sudden
Cardiac Death
 Arrhythmias are caused by electrical
abnormalities of ischemic myocardium
and conduction system.
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• Most common coronary involved is
proximal left anterior descending (LAD)
artery (40% to 50% of all MI).
infarction of anterior wall of left
ventricle + anterior two thirds of the
ventricular septum + heart apex
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 frequency of MIs rises with
increasing age and presence of other
risk factors such as hypertension,
smoking, and diabetes.
 10% of MIs occur in people younger
than 40 years.
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Clinical Features of MI
1) Severe, crushing substernal
chest pain radiating to neck,
jaw, epigastrium, or left arm.
• MI can be entirely asymptomatic
in 10% to 15% (silent infarcts)
common in:
1- diabetes mellitus (peripheral
neuropathies)
2- in the elderly
2- rapid and weak pulse.
5- nausea (posterior-MI).
6- cardiogenic shock
(massive MI >40% of left
ventricle)
7- dyspnea (impaired myocardial
contractility & dysfunction of
mitral valvepulmonary
congestion and edema).
Evaluation of MI
• Clinical signs and symptoms
• Electrocardiographic(ECG)
abnormalities
• Laboratory evaluation:
- blood levels of molecules leaking out
of injured myocardial cells through
damaged cell membranes.
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Cardiac enzymes in MI
• These molecules include :
1- myoglobin.
2- cardiac troponins T and I (TnT, TnI): 
the best markers for acute MI.
3- creatine kinase (CK, specifically
myocardial-specific isoform= CK-MB)
4- lactate dehydrogenase
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Microscopic changes of MI and its
repair.
(<24 hr) coagulative necrosis and wavy
fibers.
2- to 3-day old - infarct Dense neutrophil
infiltrate
(7 to 10 days) phagocytic macrophages
removal of necrotic myocytes
up to 14 days Granulation tissue.
several weeks dense collagenous scar.
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Microscopic features of myocardial
infarction and its repair (detailed) .
(<24 hr)
coagulative
necrosis and
wavy fibers
Necrotic cells
are separated by
edema fluid
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Microscopic features of myocardial infarction
and its repair. (detailed)
2- to 3-day old infarct Dense
neutrophil
infiltrate
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Microscopic features of myocardial
infarction and its repair. (detailed)
7 to 10
days)
complete
removal of
necrotic
myocytes by
phagocytic
macrophages
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Microscopic features of myocardial
infarction and its repair.
up to 14 days
Granulation
tissue = loose
connective tissue
(blue) and
abundant
capillaries (red)
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Microscopic features of myocardial
infarction and its repair.
several weeks
Healed
myocardial
infarct consisting
of a dense
collagenous
scar (blue)
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Consequences and Complications of
MI
 1- Death:
 50% of the deaths: pts never reach the
hospital (due to arrhythmias)
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Consequences and Complications
of MI (cont.):
 2- cardiogenic shock.
- (10% to 15%) after acute MI
- large infarcts ( >40% of Left
ventricle).
- 70% mortality rate; (2/3 of in-hospital
deaths).
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Consequences and Complications of MI
(cont.):
3-Myocardial rupture
Complications of myocardial rupture include:
(1) rupture of free wall hemopericardium &
cardiac tamponade (usually fatal)
(2) rupture of septum VSD and left-to-right
shunt
(3) papillary muscle rupture severe mitral
regurgitation
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myocardial rupture
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Consequences and Complications of MI
(cont.):
 4-Pericarditis.
- 2 to 3 days post-transmural MI
- spontaneously resolves with time
- immunologic mechanism.
 5-Infarct expansion.
- stretching, thinning, and dilation of the
infarct region
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Consequences and Complications of MI
(cont.):
 6-Mural thrombus.
-local loss of contractility (stasis) +
endocardial damage
 7-Ventricular aneurysm.
- A late complication
- large infarct heals with the formation of
thin scar tissue
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Ventricular
aneurysm
Complications of
ventricular
aneurysms
include:
1-mural thrombus
2-arrhythmias
3-heart failure
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Consequences and Complications of MI
(cont.):
 8-Papillary muscle dysfunction (postinfarct mitral regurgitation )
 9-Progressive late heart failure
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Long-term prognosis after MI
depends on many factors, the most
important of which are:
- left ventricular function
- severity of atherosclerosis of remaining
viable myocardium.
Mortality rate within the first year =30%
• Thereafter, the annual mortality rate is 3%
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Chronic Ischemic Heart Disease
• post-infarction cardiac decompensation
• exhaustion of the hypertrophic viable
myocardium = progressive heart failure
(CHF)
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Sudden Cardiac Death (SCD)
• Definition: unexpected death from cardiac
causes either without symptoms or within 1 to
24 hours of symptom onset .
• The most common mechanism is ventricular
fibrillation (arrythmia).
• The most common underlying cause is
Coronary artery disease
• With younger victims, other non-atherosclerotic
causes are more common:
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Other non-atherosclerotic causes of
SCD
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Congenital coronary arterial abnormalities
Aortic valve stenosis
Mitral valve prolapse
Myocarditis
Dilated or hypertrophic cardiomyopathy
Pulmonary hypertension
Hereditary or acquired abnormalities of the
cardiac conduction system.
• Isolated myocardial hypertrophy.
• unknown ??.
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