ECG: Inferior Myocardial Infarction

Question 1

An inferior infarct on ECG (inferior myocardial infarction or inferior STEMI) occurs when inferior myocardial tissue is injured due to thrombosis of which of the cardiac arteries¿

Answer 1

The right coronary artery (RCA).

Question 2

When an inferior myocardial infarction extends to posterior regions as well, an associated posterior wall myocardial infarction may occur.

The ECG findings of an acute inferior myocardial infarction include:

Answer 2

1) ST segment elevation in the inferior leads (II, III, and aVF).
2) Reciprocal ST segment depression in the lateral and/or high lateral leads (I, aVL, V5 and V6).

Note: If the reciprocal ST depressions are not present, consider alternative causes of ST segment elevation such as pericarditis.

Question 3

The findings of an old inferior myocardial infarction on the ECG are pathologic Q wave in the inferior leads.

What are the criteria for pathological Q waves¿

Answer 3

In general they are:
wider than 0.04 ms (one small box)
or
at least 1/3 the height of the QRS complex.