Inferior Myocardial Infarction
An inferior infarct on ECG (inferior myocardial infarction or inferior STEMI) occurs when inferior myocardial tissue supplied by the right coronary artery (RCA), is injured due to thrombosis of that vessel. 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:
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.
The findings of an old inferior myocardial infarction on the ECG are pathologic Q wave in the inferior leads. In general, if the Q wave is wider than 0.04 ms (one small box) or at least 1/3 the height of the QRS complex, then inferior Q waves are thought to represent an old myocardial infarction.
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