L2 - Myocardial infarction (MI) by Hussein A. Abid

1. MYOCARDIAL INFARCTION
Hussein A. Abid
Iraqi Medical Laboratory Association
Scientific Affairs & Cultural Relations
Training and development center
Lecture: 2
Date: 06/08/2018

2. MYOCARDIUM (cardiac muscle)
• Is one of the three major types of muscle, the others being
skeletal muscle and smooth muscle.
• It is an involuntary, striated muscle that constitutes the main
tissue of the walls of the heart.
• The myocardium forms a thick middle layer between the outer
layer of the heart wall (the epicardium) and the inner layer (the
endocardium).
• It is composed of individual heart muscle cells (cardiomyocytes)
joined together by intercalated discs, encased by collagen fibers
and other substances forming the extracellular matrix.

3. MYOCARDIUM

4. MYOCARDIUM (cardiac muscle)
• Cardiac muscle does the work of pumping blood to circulate it
throughout the rest of the body, work that is sometimes difficult
and always unceasing.
• To do its steady work, cardiac muscle requires ample blood
supply, which is delivered by the coronary circulation.
• Diseases of heart muscle are of major importance. These include
conditions caused by a restricted blood supply to the muscle
including angina pectoris and myocardial infarction, and other
heart muscle disease known as cardiomyopathies.

6. CARDIAC (HEART) PATHOLOGY
ISCHEMIC HEART DISEASE
• Hypoxemia (diminished transport of oxygen by the blood) less
deleterious than ischemia
• Also called coronary artery disease (CAD) or coronary heart
disease (CHD)
• The cause in 90% of cases, coronary atherosclerotic arterial
obstruction.

7. CARDIAC (HEART) PATHOLOGY
ISCHEMIC HEART DISEASE (mainly four types)
1. Myocardial infarction (MI)
2. Sudden cardiac death,
3. Angina pectoris; and
4. Chronic IHD with heart failure.

8. MYOCARDIAL INFARCTION
• Myocardial infarction (MI), or acute myocardial infarction (AMI).
• Commonly known as a heart attack, occurs when blood flow
decreases or stops to a part of the heart, causing damage to the
heart muscle.
• The most common symptom is chest pain or discomfort which
may travel into the shoulder, arm, back, neck, or jaw. Often it
occurs in the center or left side of the chest and lasts for more
than a few minutes. The discomfort may occasionally feel like
heartburn.
• Other symptoms may include shortness of breath, nausea,
feeling faint, a cold sweat, or feeling tired.

9. Diagram showing the blood
supply to the heart by the two
major blood vessels, the left and
right coronary arteries (labelled
LCA and RCA). A myocardial
infarction (2) has occurred with
blockage of a branch of the left
coronary artery (1).

10. MYOCARDIAL INFARCTION
• About 30% of people have atypical symptoms.
• Women more often have atypical symptoms than men.
• Among those over 75 years old, about 5% have had an MI
with little or no history of symptoms.
• An MI may cause heart failure, an irregular heartbeat,
cardiogenic shock, or cardiac arrest.

11. A myocardial infarction (MI)
occurs when an atherosclerotic
plaque slowly builds up in the
inner lining of a coronary artery
and then suddenly ruptures,
causing catastrophic thrombus
formation, totally occluding the
artery and preventing blood
flow downstream.

12. MYOCARDIAL INFARCTION
• Most myocardial infarctions occur due to coronary artery disease
• Risk factors include high blood pressure, smoking, diabetes,
lack of exercise, obesity, high blood cholesterol, poor diet,
and excessive alcohol intake, among others.
• The complete blockage of a coronary artery caused by a rupture
of an atherosclerotic plaque is usually the underlying mechanism
of an MI.
• Is are less commonly caused by coronary artery spasms, which
may be due to cocaine, significant emotional stress, and extreme
cold, among others.

13. MYOCARDIAL INFARCTION
• A number of tests are useful to help with diagnosis, including:
1. Electrocardiograms (ECGs)
2. Blood tests, and
3. Coronary angiography
• An ECG, which is a recording of the heart's electrical activity, may
confirm an ST elevation MI (STEMI) if ST elevation is present.
• Commonly used blood tests include troponin and less often creatine
kinase MB.

14. MYOCARDIAL INJURY
• Irreversible injury typically requires 30 minutes of ischemia.
• Chronic O2 deficiency makes cells more resistant.
• Time to diagnose and therapy is critical.
After 30 – 60
minutes, cell death
starts
80% of cells at risk
die within 3 hours
Almost 100% by 6
hours of ischemia

15. ACUTE CORONARY SYNDROME

16. CLINICAL DIAGNOSIS OF MI
• Silent MI: in diabetes mellitus, elderly, cardiac transplantation
recipients.
• Typical features: rapid, weak pulse and sweating profusely
(diaphoretic), dyspnea, chest pain.

17. LABORATORY DIAGNOSIS
 Diagnostic:
 Best markers: Troponins (T & I), both sensitive and cardio-specific
 Next best: CK-MB
 Predictive
 CRP > 3 mg/ L (highest risk)

18. MI diagnosis – WHO criteria
 History of ischemic type of chest discomfort
• Evolutionary ECG changes
• Rise and fall in serum cardiac markers
 Limitations:
• 1/3 of patients with AMI don’t present with chest pain
• Only 1/2 present with Q waves or ST elevation
• 1/2 of patients with suggestive chest pain have non-diagnostic ECG
• With use of new markers, additional 1/3 are diagnosed to have MI
• Perioperative MI and post PCI MI – symptoms may be absent and
ECG changes may be non-specific

19. MYOCARDIAL INFARCTION
• Treatment of an MI is time-critical.
• Aspirin is an appropriate immediate treatment for a suspected MI.
• Nitroglycerin or opioids may be used to help with chest pain;
however, they do not improve overall outcomes.
• Supplemental oxygen is recommended in those with low oxygen
levels or shortness of breath.
• In a STEMI, treatments attempt to restore blood flow to the heart,
and include percutaneous coronary intervention (PCI), where the
arteries are pushed open and may be stented, or thrombolysis,
where the blockage is removed using medications.

20. MYOCARDIAL INFARCTION
• People who have a non-ST elevation myocardial infarction
(NSTEMI) are often managed with the blood thinner heparin,
with the additional use of PCI in those at high risk.
• In people with blockages of multiple coronary arteries and
diabetes, coronary artery bypass surgery (CABG) may be
recommended rather than angioplasty. After an MI, lifestyle
modifications, along with long term treatment with aspirin, beta
blockers, and statins, are typically recommended.
• Worldwide, about 15.9 million myocardial infarctions
occurred in 2015.

21. MYOCARDIAL INFARCTION
• More than 3 million people had an ST elevation MI and more
than 4 million had an NSTEMI. STEMIs occur about twice as
often in men as women.
• About one million people have an MI each year in the United
States. In the developed world the risk of death in those who
have had an STEMI is about 10%.
• Rates of MI for a given age have decreased globally between
1990 and 2010.
• In 2011, AMI was one of the top five most expensive conditions
during inpatient hospitalizations in the US, with a cost of about
$11.5 billion for 612,000 hospital stays.