L14 - Acute MI

Question 1

What is myocardial infarction (MI)?

Answer 1

A condition caused by the interruption of blood supply to part of the heart, leading to the death of myocardial cells.

Question 2

What are the two types of myocardial infarction?

Answer 2

• NSTEMI: Partial thickness damage due to partial occlusion of a major artery or complete occlusion of a minor artery.
• STEMI: Full thickness damage due to complete occlusion of a major coronary artery.

Question 3

What are the causes of MI?

Answer 3

• Atherosclerosis.
• Plaque rupture leading to thrombus formation.
• Triggers such as exercise or stress, though plaque vulnerability plays a larger role.

Question 4

How does tissue necrosis progress in MI?

Answer 4

• Begins 20–40 minutes after occlusion.
• Proceeds in a “wavefront” from the subendocardial layer outward.
• Substantial myocardial salvage is possible if blood flow is restored within 6 hours.

Question 5

What is ventricular remodelling after MI?

Answer 5

• Changes in size and shape of the heart following injury to the left ventricle.
• Can lead to infarct expansion, thinning, and ventricular dilatation.

Question 6

What are the symptoms of MI?

Answer 6

• Chest pain (“crushing” or “someone sitting on my chest”).
• Pain radiating to the neck, arm, back, or jaw.
• Nausea, vomiting, sweating, and breathing difficulty.
• Pain not relieved by rest or sublingual GTN.

Question 7

What are the key biochemical markers for MI diagnosis?

Answer 7

• Troponin I/T: Rise within 3-5 hours, peak at 14-18 hours, and remain elevated for days.
• CK-MB: Peaks within 12-28 hours and normalises after 72-96 hours.
• Myoglobin: Elevates within 1-2 hours but is less specific for MI.
• LDH: Elevated in later stages of MI.

Question 8

What ECG changes indicate MI?

Answer 8

• Hyperacute T waves: Early sign of ischaemia.
• T wave inversion: Indicates ongoing ischaemia.
• ST elevation: Sign of transmural ischaemia.
• Pathological Q waves: Permanent evidence of myocardial necrosis.

Question 9

What is the universal definition of MI?

Answer 9

Detection of a rise or fall in troponin with at least one of the following:

1. Symptoms of ischaemia.
2. ECG changes (ST elevation or depression).
3. Imaging evidence of new loss of viable myocardium.
4. Identification of intra-coronary thrombus.

Question 10

How is myocardial infarction treated?

Answer 10

• Reperfusion therapy: PCI or thrombolysis to restore blood flow.
• Medications: Antiplatelets, beta-blockers, ACE inhibitors, statins, and nitrates.
• Lifestyle changes: Smoking cessation, healthy diet, and exercise.