Myocardial infarction

Question 1

What is the normal pathophysiology of an MI?

Answer 1

Rupture of an arthrosclerotic plaque, with the development of thrombosis and total occlusion of the artery.

Question 2

What are 3 rare causes of acute coronary syndrome?

Answer 2

• Emboli
• Coronary spasm in coronary arteries
• Vasculitis

Question 3

What are the presenting symptoms of an MI?

Answer 3

• Acute central chest pain >20 mins

* Nausea, Sweatiness, Dyspnoea, Palpitations

Question 4

What is strange about 20% of MI presentations?

Answer 4

they present with no or very few symptoms.

• Normally elderly or those with diabetes or hypotension
• May present with hypotension
• Arrhythmia
• Pulmonary oedema
• Acute confusional state
• Epigastric pain → vomiting

Question 5

How is MI diagnosed?

Answer 5

Initial diagnosis is made on the basis of clinical HX. and early ECG changes.

subsequently:

• Changes ( an ↑ and then ↓) in Cardiac markers → Troponin Lvls
• Development of pathological Q waves
• Loss of myocardium on imaging

Question 6

Which ECG leads will show an inferior infarct?

Answer 6

• Lead ll, lll and aVF

Question 7

Occlusion of which arteries causes an inferior

Infarct?

Answer 7

• the vast majority (~80%) of inferior STEMIs are due to occlusion of the dominant right coronary artery (RCA).
• Less commonly (around 18% of the time), the culprit vessel is a dominant left circumflex artery (LCx).

Question 8

Where do pathological Q waves form after an inferior wall infarct?

Answer 8

• Progressive development of Q waves in II, III and aVF

Question 9

Which ECG leads will show an lateral infarct?

Answer 9

• ECG leads l, ll, and AVL

Question 10

Occlusion of which arteries causes an Lateral

Infarct?

Answer 10

•The lateral wall of the LV is supplied by branches of the left anterior descending (LAD) and left circumflex (LCx) arteries.

Question 11

Which ECG leads will show an Anterior infarct?

Answer 11

ECG leads V2, V3, V4, V5, V6

Question 12

Occlusion of which arteries causes an anterior Infarct?

Answer 12

• Anterior STEMI results from occlusion of the left anterior descending artery (LAD).

Question 13

An infarct of which region of the heart carries the worst prognosis?

Answer 13

• Anterior myocardial infarction carries the worst prognosis of all infarct locations, mostly due to larger infarct size.

Question 14

An infarct of which region of the heart carries the best prognosis?

Answer 14

• Inferior STEMI generally has a more favourable prognosis than anterior myocardial infarction (in-hospital mortality only 2-9%), however certain factors indicate a worse outcome.

Question 15

What signs might you find on examination of a patient with MI?

Answer 15

• Distress, anxiety, pallor
• ↓↑ BP and pulse
• 4th heart sound
• Pansystolic murmur
• Signs of heart failure: ↑ JVP, Heart sounds, basal crepitations
• Low grade fever
• Later development of pericardial rub or peripheral oedema

Question 16

What ECG signs of a developing MI?

Answer 16

• Hyper acute T waves on ECG
• ST elevation
• New bundle branch block

Question 17

What will the ECG show over hours and days after an MI?

Answer 17

Pathological Q wave formation and ST depression.

Question 18

What will be difficult about 20% of ECGs in MI’s?

Answer 18

They will initially be normal.

Question 19

In cases suspected of MI, What might you look for on CXR?

Answer 19

• Cardiomagaly
• Pulmonary oedema
• Widened mediastinum in aortic rupture

Question 20

What bloods would you want done in a suspected MI?

Answer 20

FBC, U+E’s, Glucose, Lipids

Question 21

What Cardiac markers/enzymes are there?

Answer 21

• Troponin (T+I). regulatory muscle proteins that are highly specific and sensitive to cardiac muscle damage.
• Creatine Kinase. Less specific and sensitive

Question 22

What is the management of a STEMI?

Answer 22

• Primary angioplasty or thrombolysis in no contraindication
• B - blocker → atenolol (contraindicated by asthma)
• ACE inhibitor in all normotensive patients
• Clopidogrel loading for 30 days

Question 23

What is the management of a NSTEMI?

Answer 23

• B-Blocker (atenolol) and IV nitrates
• An antithrombotic → fondaparinux (if low risk of bleeding and no angioplasty planned. otherwise LMW heparin → Enoxaparin
• Assess risk → GRACE score
• High risk patients → GP2b/3a agonist or bivalirudin. Clopidogrel for 12/12
• Low risk patients →Clopidogrel 12/12