2.3 Principles of Myocardial Infarction on an ECG

Question 1

List 3 basic changes that could indicate an MI on an ECG.

Answer 1

1. ST depression
2. ST elevation
3. T-wave inversion

Question 2

Describe the correlation between leads on the ECG and the region of the heart they measure.

Answer 2

• II, III, aVF - Inferior or posterior of heart
• V1, V2 - Anterior-septal regions
• V3, V4 - Main anterior wall of heart
• V5, V6 - Antero-lateral region
• I, aVF - Lateral region

Question 3

Which has the worst prognosis, STEMI or NSTEMI?

Answer 3

NSTEMI.

Question 4

Which ECG finding is found in STEMI?

Which ECG finding is found in NSTEMI?

Which of these is reversible?

Answer 4

STEMI - ST elevation.

NSTEMI - ST depression. Reversible, e.g. also seen in angina during an exercise stress test.

Question 5

The degree of ST depression can indicate the severity of the pathology.

Imagine what an ischaemic ST depression would look like, e.g. angina, compared to the ST depression in an NSTEMI, then look at the image on the card to see if you’re right.

Answer 5

The minor amounts of ST depression in the first image is seen in ischaemia, e.g. reduced O2 to heart muscle, such as seen during an EST.

The larger amounts of ST depression seen in the second image is what you would see with more significant damage to the heart, such as in an infarct.

Question 6

Describe the correlation between region of the heart and supplying blood vessel.

Answer 6

General Rules

1. II, III, aVF (Inferior)
   
   • 90% patients - RCA
   • 10% patients - LCX
2. V1-V6 (Anterior, Septal, Anterolateral)
   
   • LAD
3. I, aVL (‘Pure’ Lateral)
   
   • LCX

Question 7

Visualise the leads on an ECG and how they correlate anatomically to a lesion on a heart.

Answer 7