Any paramedic who has studied the STEMI mimics has heard of the classic benign early repolarization pattern of a "fish-hooked" J-point with upwardly concave (smiley-faced) ST-segment, often best appreciated in lead V4.

But, as the excellent work of Stephen Smith, M.D. demonstrates, not all cases of early repolarization present this way, and it can often be very difficult to differentiate between early repolarization and LAD occlusion.

So, we took a run-of-the-mill "male pattern" early repolarization pattern, removed the computerized interpretation, and posted the ECG to our Facebook fan page.

The variety of interpretations was shocking! 

Some of the common interpretations included Wolff-Parkinsons-White syndrome, pericarditis, hyperkalemia, and (less commonly) acute anterior STEMI. Very few mentioned early repolarization.

This just goes to show how important and valuable Stephen Smith's work on this topic really is!

Here's the same ECG with the computerized interpretation.

I have a sneaking suspicion that some of the very same paramedics who rail against computerized interpretive algorithms are unconsciously influenced by the computerized interpretation whether they realize it or not.

That may not be a bad thing.

A baseline reading of "normal ECG" creates a comfort level for this normal variant. Keep in mind, ST-elevation in leads V2 and V3 for a young male is not a normal variant. It's a normal finding! But these T-waves are a little more impressive than we might expect, so I'm calling it a variant.

So what gives away that it's not hyperacute anterior STEMI?

Dr. Smith has an abstruse formula (he probably doesn't think it's abstruse but then again the man's a physicist as well as a physician) that was recently published in the Annals of Emergency Medicine.

(1.196 x STE at 60 ms after the J-point in V3 in mm) + (0.059 x computerized QTc) – (0.326 x R-wave Amplitude in V4 in mm)

A value greater than 23.4 is quite sensitive and specific for LAD occlusion.

Dr. Smith adds these qualifiers:

"It is critical to use it only when the differential is subtle LAD occlusion vs. early repol. If there is LVH, it may not apply. If there are features that make LAD occlusion obvious (inferior or anterior ST depression, convexity, terminal QRS distortion, Q-waves), then the equation MAY NOT apply. These kinds of cases were excluded from the study as obvious anterior STEMI. ST elevation (STE) is measured at 60 milliseconds after the J-point, relative to the PR segment, in millimeters." 

What does this mean for the field provider? I'm a firm believer in keeping it simple.

The bottom line (in my opinion) is that we should suspect the possibility of benign early repolarization when: 

• R-wave progression is intact (this is big)
• There is a tall R-wave in lead V4
• The QTc is on the low end of normal (in this case < 400 ms)
• There is an absence of reciprocal changes
• ST-elevation is upwardly concave
• U-waves are easily identifiable (additional tip shared by Dr. Smith in private conversation)
• There are no changes on serially obtained ECGs

None of these rules of thumb are 100% but we're trying to make a logical game-time decision and knowledge is power.

Simply knowing that the differential diagnosis is early repolarization vs. LAD occlusion would be an important improvement when faced with an ECG like this (which frankly isn't anywhere near as difficult as some others we've seen).

For example:

Here's another:

Conclusion

• Early repolarization is a common and underappreciated STEMI mimic
• It does not always present with "fish-hooked" J-points
• The ST-elevation and T-waves can often be scary with early repolarization
• The key here is knowing that the differential is LAD occlusion vs. early repolarization

I encourage everyone to read the archived early repolarization cases at Dr. Smith's ECG Blog by clicking here.