MI and Cardiac Biomarkers

Question 1

What is a biomarker?

Answer 1

A naturally occurring molecule, gene, or characteristic which acts as a surrogate marker by which a particular pathological or physiological process, disease, etc. can be identified.

Question 2

What is infarction?

Answer 2

• Infarction is the death of a tissue due to inadequate oxygen supply.
• Infarction does not affect individual cells so much as the whole tissue, because adjacent cells have the same blood supply.

Question 3

What is the most probable cause of infarction?

What are other causes?

Answer 3

• Infarction usually happens because an artery is blocked and the tissue dies. Coronary artery thrombosis is the primary cause of infarction.
• It is lack of oxygen supply which determines whether the tissue dies. So, other causes of infarction include:
  
  • Blockage or partial blockage due to atherosclerosis.
  • Major blood loss causing reduced Hb.
  • Decreased oxygen (hypoxic or anaemic).
  • Increased demand for oxygen.

Question 4

What is the effect of reduced oxygen on myocardial cells?

Answer 4

Reduced oxygen causes a myocardial cell to be at risk of arrhythmias or dysrhythmias.

Question 5

What is the effect of an infarct on the tissue?

Answer 5

• When there is an infarct, there is tissue death via necrosis.
• Necrosis causes an inflammatory response:
  
  • Vasodilation
  • Neutrophil activation
  • Increased blood flow
• 7-10 days after a full thickness infarct there is necrotic tissue with inflammation around the edges and the wall of the heart ruptures.
• After a partial thickness infarct there can be dyskinesia.

Question 6

Describe Virchow’s triad.

Answer 6

1. Stasis of blood flow
2. Endothelial injury
3. Hypercoagulability

Question 7

What results from a subendocardial blockage?

Answer 7

Subendocardial blockage sets off Virchow’s triad which results in thrombus formation.

Question 8

What name is given to a dislodged thrombus?

What is the potential effect of this?

Answer 8

• Embolis
• An embolis can become dislodged and travel through the circulation up to the heart. This can result in PE.

Question 9

Describe why time is of the essence if you suspect MI.

Answer 9

• By intervening early, you can make the infarct smaller and restoration of oxygen supply decreases necrosis.
• The point of fast diagnosis is to control the final size of the infarct.
• You only have a short window to thrombolyse post-MI.

Question 10

What is the effect of late thrombolysis?

Answer 10

• Risk of reperfusion injury.
  
  • ​If you flood the cells surrounding the thrombus with oxygen if they have already become accustomed to a reduced oxygen environment, they essentially blow themselves up.
• The outcome of thrombolysis if you are late is that it may cause more problems for the patient than no intervention at all.

Question 11

What are the biomarkers which can be used to identify MI?

Answer 11

• Lactate dehydrogenase - for this to leak from a cell, the cell has to already be dead (late biomarker; not good for early assessment). It is useful to determine the extent of tissue death.
• Creatinine kinase - for this to leak out the cell has to be slightly less dead.
• Aspartate - and less again.
• Troponin - this is not necessarily a marker for a dead cell, just a leaky one (earlier marker; current gold standard biomarker for MI).
  
  • It comes up early and stays up, so gives a better picture of the whole course of an MI.
  • Troponin is specific to cardiac tissue.
• Sliding scale from dead to leaky.