One of the most important things to learn about medicine is how to know when someone is really having a heart attack. Especially, a STEMI (ST Elevation Myocardial Infarction). Those are the deadliest and heart muscle has died and is dying as we speak.
If you learn anything in all of medicine, please learn to recognize a STEMI. Why? STEMIs have to go to the cath lab and the artery needs to be opened up within 90 minutes. That saves heart muscle and saves lives!
Below is a quick review of all the various parts of an EKG. We are mainly looking at the ST segment.
So what is a STEMI?
The ST segment of an EKG will be elevated by more than 2 mm in the precordial leads and by more than 1 mm in the limb leads. Further, in the precordial leads, the shape should be convex up (like a tombstone). The shape matters more than the amount of elevation in some cases. You may have minimal elevation, but the shape is convex up, that could be considered a STEMI.
In the limb leads, the shape does not matter, just the elevation. Anything more than one small box, and you have a STEMI! Pretty straight forward. Unless, of course, it is an early repol!
So why do people get confused? And what is Early Repolarization?
There is an entity known as normal variant early repolarization that can give you ST segment elevation. But this is not a STEMI. It is a normal finding.
So how can you tell the difference? Look at the shape of the ST segment take off (the J point), it will usually be a notch and does not take off flat across. See the example below.
Above you see the first example on the right. The notch on the J point gives it away as early repol. In the far left example, you see the notch again in one of the precordial leads, usually V2 or V3. This is early repol, not a STEMI.
Here is an Early Repol EKG:
So what about pericarditis?
Pericarditis ST elevations look like the concave upwards ST elevations of early repol, but do not have the notch. Further, you may have PR segment depression in lead II. There will be no reciprocal changes or ST depressions anywhere.
Good example of pericarditis EKG:
Notice the ST elevations all over the place with no reciprocal changes.
Below is a good example of an Inferior STEMI.
Notice the reciprocal changes in the anterior leads. You see depressions. While it is not necessary to have reciprocal changes, they can happen, and it helps clinch your diagnosis.
Below is an anterior STEMI, without reciprocal changes.
Below is another Anterior STEMI with the perfect tombstone pattern. No reciprocal changes.
Here is a nice table comparing the various EKG findings in STEMI, early repol, and pericarditis.
|Comparison of ECG Changes Associated with Acute Pericarditis, Myocardial Infarction and Early Repolarization|
|ECG finding||Acute pericarditis||Myocardial infarction||Early repolarization|
|ST-segment shape||Concave upward||Convex upward||Concave upward|
|Q waves||Absent||Sometimes Present||Absent|
|Reciprocal ST-segment changes||Absent||Sometimes Present||Absent|
|Location of ST-segment elevation||Limb and precordial leads||Area of involved artery||Limb and Precordial leads|
|ST/T ratio in lead V6*||>0.25||N/A||<0.25|
|Loss of R-wave voltage||Absent||Present||Absent|
|PR-segment depression||Sometimes in Lead II||Absent||Absent|
If you are unsure if it is a STEMI or not, KEEP GETTING EKGs! PLASTER THE WALLS WITH EKG PAPER! STEMIs evolve! They don’t look the same. If you have 10 EKGs in the last hour, and they all look the same…. it’s not a STEMI!