Is this ST depression due to OMI or due to subendocardial ischemia? This is critical to distinguish, and this is a trick case!

We just today published this very important article in the Journal of the American Heart Association:

Ischemic ST‐Segment Depression Maximal in V1–V4 (Versus V5–V6) of Any Amplitude Is Specific for Occlusion Myocardial Infarction (Versus Nonocclusive Ischemia)

full text: https://www.ahajournals.org/doi/pdf/10.1161/JAHA.121.022866

However, if the patient has atrial fibrillation with RVR, one must first cardiovert and then re-assess.  STD Max V1-V4 can be due to subendocardial ischemia (not OMI) when there is tachycardia, especially if due to atrial fibrillation with RVR.

I have long noticed this (but have not formally studied it), and just by chance I had this patient very recently who presented with chest pain and this ECG and no history of atrial fibrillation:

Notice the STD diffusely, and in precordial leads it is maximal in lead V3.  In sinus rhythm with a heart rate under 100, and in a chest pain patient, this is VERY specific for posterior OMI.  One is tempted to diagnose posterior OMI, but one should resist that temptation!

In the context of atrial fibrillation with rapid ventricular response, the correct management is to first cardiovert, then re-assess.

This is what we did.  

After giving 10 mg of etomidate (low dose propofol is fine as well), we did synchronized cardioversion with 200 J.

He converted to sinus rhythm and we recorded this 12-lead ECG immediately after:

Sinus rhythm with no evidence of OMI and some residual ischemia (ST depression), which eventually resolved.

Formal bubble contrast echo the next day was completely normal, as expected.

Learning point:

ST Depression maximal in leads V1-V4 in the context of high suspicion for ACS is posterior OMI until proven otherwise, because subendocardial ischemia manifests with STD maximal in V5-6.

This is true unless:

1.  There is tachycardia -- find the cause of tachycardia and reverse it, and also use supportive care to bring down the heart rate, then record the ECG again.

2. Especially in atrial fibrillation with Rapid Ventricular Response, there may be subendocardial ischemia which is maximal in V1-V4.