MI - Physiology and Pathophysiology

Question 1

Basic description of the heart as a pump

Answer 1

Muscular organ that pumps blood around the body.

Right side it takes in deoxygenated blood from the superior and inferior vena cava and delivers it to the lungs for oxygenation.

Oxygenated blood returns to the left side of the heart before being pumped out of the aorta and into the various arteries which transport the blood throughout the body

Question 2

Basic description of blood supply to heart

Answer 2

To remain functioning the heart needs a blood supply (coronary circulation/perfusion).

Most coronary perfusion happens in the diastole phase (heart muscles relaxing).

Blood vessels encircle the heart to supply its different regions.

This begins with the coronary arteries starting at the ascending aorta (through openings called coronary ostia), above the aortic valves.

Question 3

Division of coronary arteries

Answer 3

The RCA supplies the right atrium, the right ventricle as well as the sino-atrial node and av node.

The LMCA divides into 2 branches:

• The LAD supplies the anterior portion of the left side of the heart
• The Circumflex supplies the posterior portion of the heart.

Question 4

Definiton of MI and causes

Answer 4

An MI is caused by lack of oxygenated blood getting to the tissues of the heart. The lack of oxygenated blood causes the cardiac tissue to become ischaemic (not enough oxygen) and if uncorrected it then results in infarction (irreversible cell death).

causes:
Blood clot
Plaque build up and then clot
Cornary spasm or disease

Question 5

Types of MI

Answer 5

1. Subendocardial (typically non-STEMI) that involves infarction of the myocardium below the endocardium and not the epicardium. The thrombus may then break off before transmural infarction can occur. This would result in ST depression and T-wave inversion.
2. Transmural (typically STEMI) – if the thrombus remains, the infarction is likely to become transmural (develop through all 3 layers of the heart (endo, myo, epi). This usually causes ST elevation.

Question 6

MI by region

Answer 6

• Cx – Lateral MI
• LCA – Antero-lateral
• LAD – Antero-septal
• RCA – Posterior/Inferior MI