15. Acute myocardial infarction

Question 1

What is meant by an acute myocardial infarction (AMI)?

Answer 1

I.e. a heart attack

This occurs when blood flow to the heart stops to a part of the heart and causes damage to the heart muscle

Generally occurs following the rupture of an atheromatous plaque which can cause blood clots further down

Question 2

What are the different classifications used for AMI?

Answer 2

STEMI - ST elevation Myocardial Infarction

NSTEMI - Non-ST elevation Myocardial Infarction

Question 3

Give the pathophysiology of NSTEMI

Answer 3

Ruptured coronary plaque results in subocclusive thrombus i.e. the artery is not completely blocked but there is some form of blockage that prevents blood flow

Question 4

How does an NSTEMI show in an ECG and how is it diagnosed?

Answer 4

For an NSTEMI, the ECG may be normal or may show ST depression or pathological T waves

For an NSTEM, the ECG is not diagnostic and you must await troponin analysis

Question 5

Give the pathophysiology for a STEMI

Answer 5

The ruptured coronary plaque results in an occlusive thrombus - the artery is completely blocked and blood flow is hence completely blocked

Question 6

How does a STEMI appear on an ECG and how is this diagnosed?

Answer 6

For a STEMI, the ACG shows an ST elevation

For a STEMI, the ECG is diagnostic

Question 7

Why is it important to determine whether the AMI is STEMI or NSTEMI?

Answer 7

The treatment for both of these are different to each other SO should know which one the patient has

Question 8

Why might an AMI be STEMI vs. NSTEMI and vice versa?

Answer 8

Whether the AMI is STEMI or NSTEMI is dependent on the type of blood of the patient
I.e. if a patient smokes, their blood is more likely to be sticky and this is more likely to result in a STEMI
If the patient is on anti-platelets e.g. aspirin, then the patient is more likely to present with NSTEMI (this is how aspirin works as a secondary prevention drug)

Question 9

What are the clinical manifestations of an AMI?

Answer 9

Ischaemic myocardial injury can result in chest pain, a 4th heart sound, low grade fever (this is due to the leakage of proteins which stimulates an inflammatory response), leak of component trononin

Autonomic disturbance due to massive symaptho-adrenal response leading to tachycardia and also activation of vagus leading to sweating and vomiting and maybe bradycardia

Question 10

Describe the prognosis of AMI and the major cause of death in these patients

Answer 10

Not a good prognosis
40% of patients are dead after the first year of their AMI
Due to left ventricular failure, cardiogenic shock is a major cause of their death
NB. the development of this is dependant on how bad the damage is i.e. the size of the block and the level of ischaemia (SO need to limit the amount of damage in these patients to provide them with a better prognosis)

Question 11

What is meant by cardiogenic shock?

Answer 11

Inadequate circulation of blood and insufficient perfusion of tissue to meet oxygen demands - this can lead to cardiac arrest which is the cause of death

Question 12

What is meant by cardiac arrest?

Answer 12

A sudden stop in effective blood flow due to a failure of the heart to contract effectively

Question 13

What are the two main treatment methods to treat STEMI?

Answer 13

Reduce the infarct size

Reperfusion therapy

Question 14

What treatment is used for STEMI to reduce the infarct size?

Describe these

Answer 14

Use of thrombolytic drugs -these drugs work to dissolve blood clots
There are two main types - streptokinase and tissue plasminogen activator (tPA)

Streptokinase lysis the fibrin in the thrombus directly
tPA converts plasma protein plasmolinogen to plasmin which then lysis the fibrin in the thrombus

This lysis results in restoration of the blood flow

Beta Blockers should also be administered to improve rate of survival after the infarction (should be started upon admission)

Question 15

What is the main complication associated with thrombolytic drugs?

Answer 15

Bleeding and haemorrhage - haemorrhagic stroke

This can occur at the injection site (of drug), the GI tract or elsewhere

Can then lead to hypotension

Question 16

When should streptokinase be administered and what is the main concern with this drug?

Answer 16

Should be administered up to 12 hours after the onset of symptoms via IV infusion

Streptokinase can only be used once due to the development of autoantibodies against the drug which can result in an allergic reaction and anaphylaxis

Question 17

Describe the use of reperfusion therapy to treat STEMI

Answer 17

Primary PCI is used - primary percutaneous coronary intervention
Involves placing a wire down and across the blockage and inserting a stent to allow the coronary artery to open up
This needs to be done immediately once the patient comes into the hospital wth STEMI

Should also be given anti-platelet drugs e.g. aspirin/heparin as they are about to have PCI

Question 18

What is the main treatment for NSTEMI and why does this differ to STEMI?

Answer 18

Treatment for STEMI differs to NSTEMI because as the artery is not completely occluded, the main priority is not preventing the block but instead is looking at keeping the artery open and preventing further blockages

Give anti-platelets e.g. aspirin and tricagrelor

Provide anti-ischaemic drugs for the pain

Then administer a PCI - SO still need the same treatment but the urgency for this is not the same as it was for STEMI - dependant on the clinical situation

Question 19

Give some common anti-platelet drugs that can be used (generally)

Answer 19

Aspirin
Heparin
Tricagrelor
Warfarin

Question 20

Describe different treatment types for secondary prevention of an AMI

Answer 20

Secondary prevention lifestyle:
Smoking
Diet
Exercise

Secondary prevention drugs:
Aspirin
Tricagrelor
Statin
B-blocker
ACE-I

Secondary prevention devices:
ICD (implantable cardioverter-defibrillator)