Inferior Myocardial Infarction - ECG
The myocardial infarction affecting the inferior heart wall should be evaluated from leads that are perpendicular to the plane of the affected heart wall. In this case those are the leads II, III and aVF. As usual, we distinguish the STEMI and non-STEMI infarction.
In an acute STEMI we find the typical elevations of the ST intervals known as Pardee’s waves in leads II, III and aVF. Leads recording the anterior and lateral myocardial wall (V1-V6, I, aVL) usually show the “mirror” depression of ST intervals. Chest pain with these ECG changes is a clear indication to an acute coronary angiography. In subacute forms of a STEMI, the ST elevations are accompanied by gradual formation of deep Q waves that mark myocardial necrosis. These deep Q waves usually never disappear as they also mark myocardial scar.
Non-STEMI infarction is typical with ST depressions and negative T waves in II, III and aVF leads. However, this finding is unspecific and can be present also in a simple cardiac ischemia without myocardial cells necrosis. That is why the diagnosis of a non-STEMI infarction needs the elevated levels of cardiac enzymes. This ECG finding together with chest pain but without positive cardiac enzymes can be evaluated “only” as the unstable angina pectoris.
Inferior myocardial STEMI – Pardee’s waves are clearly visible in II, III, aVF (red) and mirror ST depressions in I and aVL leads (blue).
If this ECG recording is found in a patient with chest pain (ST interval depressions with negative T waves in II, II and aVF) and when the cardiac enzymes are positive, it is highly suspicious of a non-STEMI infarction of the inferior heart wall.