UMEM Educational Pearls

Category: Cardiology

Title: Early repolarization vs. STEMI

Keywords: early repolarization, ST segment elevation, STEMI, ST elevation (PubMed Search)

Posted: 10/17/2010 by Amal Mattu, MD
Click here to contact Amal Mattu, MD

ECG early repolarization (or sometimes referred to as "benign early repolarization" or BER) is a common finding on ECGs, especially in young patients. It is a common "confounding" pattern when trying to identify STEMI. Here are some pearls that help in distinguishing BER vs. true STEMI. Remember at the outset, though, nothing in medicine is 100%....and that getting old ECGs or getting serial ECGs can be incredibly helpful.

1. BER is ONLY allowed to have STE that is concave upwards. If you ever see STE that is convex upwards (like a tombstone) or horizontal, it MUST be a STEMI.
2. BER should not have ST-segment depression, except maybe in aVR and V1. If there is ST depression in any of the other 10 leads, it is almost definitely a STEMI.
3. If you see STE in the inferior leads, compare the STE in lead II vs. lead III. If the STE in lead III is greater than the STE in lead II, it rules out BER....gotta be STEMI.
4. STE from BER is usually maximal in the mid precordial leads. You CAN have STE in the inferior leads with BER also, but you really shouldn't have STE isolated to the inferior leads. In other words, BER can have (1) STE in the precordial leads alone, or (2) STE in the precordial + inferior leads, but it should never have STE isolated to the inferior leads, and also the STE in the precordial leads should be more prominent than the STE in the inferior leads.
5. BER should usually not have STE > 5 mm. However, I've seen some occasional exceptions when the patient has large voltage QRS complexes.

Note that despite what I've said above, STEMI can occasionally produce STE in II > III (left circ lesion), STEMI often can give concave upward STE, and STEMI does not always produce reciprocal changes. So in other words, the rules above are  very good for ruling in STEMI (ruling out BER), but there are no good rules that rule out STEMI (or definitely ruling in BER). The rules above are pretty darn reliable, though nothing in medicine is 100%. But I'd say these are pretty close.
Once again, I'll emphasize that whenever there is even a trace of doubt, go the extra mile to get an old ECG for comparison, and/or get serial ECGs. It's much harder to defend a miss without those efforts.