AMI

1. ACUTE ISCHAEMIC EVENT
05/07/2010
Learning Objectives
• Pathogenesis of atherosclerosis
• Pathophysiology of myocardial ischaemia
• Prevalence and interaction of risk factors for vascular disease
• Presentations of acute myocardial infarction
• Treatment principles of acute myocardial infarction
• Potential complications of acute myocardial infarction
• Long term therapy following acute myocardial infarction
Pathogenesis of Atherosclerosis
1. Intimal accumulation of lipoprotein particles. Lipoprotein modification (oxidised) depicted by darker
colour
2. Local cytokine production.
3. Increase expression of adhesion and chemoattractant molecules.
4. Blood monocytes, enter artery wall, augmented scavenger receptor expression.
5. Uptake of modified lipoprotein particles leads to development of foam cells. Produce further
cytokines and effector molecules (e.g. hypochlorous acid, superoxide anion (O2-), and matrix
metalloproteinases.
6. Smooth muscle cell migration from media.
7. Proliferation and elaboration of extracellular matrix. The fatty streak evolves into a fibrofatty lesion.
8. Later, calcification may occur (not depicted) and fibrosis continues. Smooth muscle cell death
(including apoptosis) may occur producing a relatively acellular fibrous capsule surrounding a lipid-
rich core that may contain dying or dead cells and their detritus.

2. Pathophysiology of Myocardial Ischaemia / Angina
Angina/MI occurs when the Oxygen demand outweigh the oxygen supply. So, this imbalance might be
contributed by increased requirement or reduced supply compared to normal conditions.
Factors affecting the oxygen requirement include :
Heart rate
Contractility
Wall tension (Systolic pressure and volume)
Factors affecting the oxygen supply, thus coronary blood flow include :
Muscle spasm
Diastolic Time > Heart Rate
Aortic Pressure- Left Ventricular End-Diastolic Pressure Gradient
Local autoregulation
* In relieving angina pectoris, nitrates exert favorable effects by reducing O2 requirements and increasing
supply. Although a reflex increase in heart rate would tend to reduce the time for coronary flow, dilation of
collaterals and enhancement of the pressure gradient for flow to occur as the left ventricular end-diastolic
pressure (LVEDP) falls tend to increase coronary flow.
Presentation of AMI
Sudden death
Resuscitated collapse
Pain/ Discomfort :
o S : Central chest , Below Maxilla, Above Umbilicus
o O : Gradual onset

3. o C : Indigestion , Squeezing, chest discomfort
o R : Left Arm, Left side of Neck
o A :
o T : Often last <12h (myocardium dead afterwards)
o E :
o S :
Shortness of Breath (Dysponea) /Pulmonary Oedema
Shock
Arrhythmia
Palpitation (Sense of impending doom)
Nausea and Vomiting
Dizziness/Lightheadedness/Weakness
Sweating
Anxiety
Shock
None/Incidental
DDx of Acute Chest Pain
System Syndrome Clinical
Cardiac Stable Angina Retrosternal chest pressure, burning/heaviness, radiating
to the neck/jaw/epigastrium/shoulder/left arm
Unstable Angina Same as angina but more severe
AMI Same as angina but more severe
Pericarditis Sharp, pleuritic pain aggrevated by changes in position,
duration variable
Vascular Aortic dissection Excruciating, ripping pain of sudden onset of anterior
chest pain radiating to the back
Pulmonary embolism Sudden onset of SOB/dysponea and pain, pleuritic with
pulmonary infarct
Pulmonary hypertension Substernal chest pressure exarcebated by exertion
Pulmonary Pleuritis +/- pneumonia Pleuritic pain, usually brief, localized area of lung involved
Tracheobrochitis Burning discomfort of midline
Spontaneous pneumothorax Spontaenous unilateral pleuritic pain + dysponea
GIT GORD Burning substernal and epigastric discomfort, 10-60min
duration
Peptic ulcer Prolonged epigastric and substernal pain
Gallbladder disease Prolonged epigastric / RUQ pain
Pancreatitis Prolonged intense epigastric and substernal pain
Musculoskeletal Costochondritis
Cervical Disc Disease
Infectious Herpes Zoster Prolonged burning pain in dermatome distribution
Psychological Panic disorder Chest tightness/aching, accompanied by SOB, duration >
30min, unrelated to exertion/movement
Treatment principles of acute myocardial infarction