STEMI/NSTEMI Findings

Using the Fourth Universal Definition of Myocardial Infarction (2018), findings that are suggestive of myocardial ischemia include ST elevation, ST depression, or T wave inversions. However, not all ST elevation, depression, or T wave inversions are indicative of ischemia and the potential presence of occlusion depends on where and how much change there is.

Contiguous Leads

To be classified as a STEMI or NSTEMI, the changes need to occur in at least two contiguous leads - leads that have views that are adjacent to each other. Recall that in the 12-lead ECG, certain leads can be grouped together because they have the "same" view:

• Anterior Leads: leads V1-V4. When leads V1-V2 are both involved, it could also indicate septal involvement.
• Lateral Leads: leads I, aVL, V5-V6
• Inferior Leads: leads II, III, aVF

ST Elevation

Per the Definition of MI, ST elevation must be in at least 2 contiguous leads. The ST elevation must be greater than 1mm in all leads except V2-V3, where it is age or gender-dependent.

The fulfillment of this criteria would technically meet the definition of a STEMI. Notice in the following example that there is ST elevation in leads V1-V4. Since this correlates to the anterior views, we would indicate that this shows an anterior STEMI.

ST Depression and T-Wave Inversions

Signs of an Acute Coronary Syndrome could be indicated by either ST depression or T-Wave inversions as well. ST depression that is at least 0.5 mm, or T-wave inversions in at least 2 contiguous leads could indicate an NSTEMI.

However, the "mirror" or reciprocal view of a lead that shows ST elevation may show ST depression. For example, the inferior leads are reciprocal to the anterior leads. Notice in the anterior STEMI example above that there is ST depression in the inferior leads III and aVF.

Example: Inferior STEMI

Here is an illustration of an inferior STEMI. Notice the elevation in the inferior leads (II, III, aVF), and the reciprocal depression in some of the lateral (I, aVL) and anterior (V2-V3) leads.

Example: Posterior STEMI

Examine the following 12-lead ECG illustration. Notice that there's clear horizontal ST depression in the anterior leads (V1-V4) but no ST elevation in any other lead of the 12-lead ECG.

As the anterior view is reciprocal to the posterior view, it's possible that there's actually ST elevation in those views. To confirm this, we'll need to get an ECG reading that involves views that look at the back of the heart. This is the 15-lead ECG, and can easily be done by moving leads V4-V6 to the positions of V7-V9 in the back of the chest.

Now, notice in the updated 15-lead ECG illustration that ST elevation is present in the posterior leads, V7-V9.

Example: Right-Sided STEMI

Examine the following 12-lead ECG illustration. This one's a bit tricky. Here, we have clear ST elevation in the inferior leads (II, III, aVF) and reciprocal changes in the lateral leads (I, aVL, V6) - usually indicative of an inferior STEMI. Notice this time, however, that there's also ST elevation in V1 (yet ST depression in V2).

Something to note is that V1 looks slightly "off" to the right-hand side of the chest, so in the standard 12-lead ECG it's the only lead that looks at the right-side of the heart. This gives us a hint that there might be a STEMI to the right ventricle. To confirm this, we'll need to do a right-sided ECG, which is also easily done by moving leads V3-V6 to the opposite (but equivalent) side of the chest to form leads V3R, V4R, V5R, and V6R.

Now, notice in the updated right-sided ECG illustration that there's ST elevation in the right-sided leads, V4R-V6R.