Following Criteria Exactly, even the Modified Sgarbossa Criteria, Can Be Deadly

This was sent by a reader:

Dear Dr Smith,

I am an EM resident and a rather new reader of your blog.  I am writing to ask for your opinion on an ECG one of my colleagues recently came across.

The patient was a 70-something yo previously healthy male on no medications who presented to the ED with epigastric pain, onset over a few hours.  He denied chest pain of any sort and his vitals were all normal.  

Our triage nurse therefore ordered an ECG for him (which is standard in our dept for epigastric pain patients):
What do you think?

Smith interpretation: There is LBBB with all discordant ST segments (in the opposite direction of the QRS).  The Smith modified Sgarbossa criteria diagnose OMI if there is an ST segment that is at least 25% of the preceding S-wave.  Measurement is made at the J-point relative to the QRS onset (PQ junction).

Look at lead III. In the first complex, I measure 3.0 mm with a 15 mm S-wave, for a ratio of 20%.  In the 2nd complex, I measure 3.5 mm with a 15.5 mm S-wave, for a ratio of 22.6%.  Not quite 25%.  If you somehow measure 3.0 mm STE and 15.5 mm S-wave, you still get a ratio of 19.4%, very close to 20%  

The mean maximal ST/S ratio in non-ischemic LBBB is about 0.11.  Any value over 15% is abnormal.  So 0.19 (19%) is abnormal.

In our validation study of the Modified Sgarbossa Criteria for diagnosis of acute coronary occlusion, we found that a cutoff of 20% performed similarly well to the cutoff of 25%:

Sensitivity and Spec at 20%: 84% and 94%
Sensitivity and Spec at 25%: 80% and 99%

So even at a ratio of 0.19, there is still a high probability of occlusion.

Moreover, the J-point in lead V2 is slightly depressed.  This should never happen in LBBB; the J-point should always have some discordant ST elevation.  This greatly increases the probability of OMI 

Thus I would be extremely worried about inferior OMI and obtain serial ECGs and stat echo, or just activate the cath lab.

Case continued:

“There was no old ECG for comparison and the inferior leads may show a little excessively discordant ST change but the patient was otherwise well and therefore admitted to the surgical ward.

A 2nd ECG was recorded several hours later, after admission: 
Now there is clearly excessively discordant STE in inferior leads, with excessively discordant reciprocal ST depression in aVL

Unfortunately, this was not appreciated, and the patient  went into ventricular fibrillation approximately 30 min after the 2nd ECG, and could not be resuscitated.

Learning Points:
Epigastric pain can be due to inferior OMI
Beware any discordant ST elevation that is greater than 15%.  If greater than 20%, it is very likely OMI, even if it does not meet the 25% criterion.
Criteria of any kind are only guidelines and not to be strictly followed!
The modified Sgarbossa criteria are only 80% sensitive for OMI!!
The STEMI criteria in normal conduction are only 75% sensitive for OMI!!
The 4-variable LAD occlusion formula is 80-90% sensitive at a cutoff of 18.2!!!

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