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!!!

Chest Pain, LBBB, and a ratio that does not quite meet the Modified Sgarbossa Criteria

Is there excessively discordant ST Elevation in this ECG with Left Bundle Branch Block?

A Fascinating Demonstration of ST/S Ratio in LBBB and Resolving LAD Ischemia

Chest pain with New LBBB: It helps to actually measure the ST/S ratio

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Comment by KEN GRAUER, MD (4/7/2019):

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Hindsight is 100% in the retrospectoscope. Our gratitude to the clinician who submitted this case — as it is one we all can learn from.

• For clarity — I’ve straightened and relabeled the initial ECG in this case ( = ECG #1, or the BOTTOM tracing in Figure-1). For illustrative purposes — I’ve added in the TOP of Figure-1 an example of LBBB without associated acute OMI ( = Exhibit A).

Figure-1: The initial ED ECG in this case ( = ECG #1) — and in the TOP of this Figure ( = Exhibit A), an example of LBBB without associated acute OMI (See text).

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COMMENT: This was a difficult case! Changes of acute OMI were readily apparent in the 2nd ECG recorded in this case, obtained several hours after admission.

• This 2nd tracing (shown above) — highlights the value of a comparison ECG, especially in cases of LBBB in which early ECG findings of acute OMI are often more challenging to recognize. Lead-to-lead comparison between the 2 ECGs obtained in this case should leave little doubt that there has been marked change (progression) in both the shape and amount of ST elevation in multiple leads.

I focus my attention on the initial ECG in this case:

• Changes suggestive of acute OMI were far more subtle for this initial tracing ( = ECG #1 in Figure-1). Recognition of this was made all the more difficult because: i) The patient had NO chest pain; and, ii) NO prior ECG was available for comparison.
• As per Dr. Smith — application of modified Smith-Sgarbossa criteria yielded an abnormal result for assessment of ECG #1 (detailed analysis by Dr. Smith above).

Qualitatively — the shape of ST segment deviations in ECG #1 of itself is suggestive of a possible acute change. Perhaps the best way to illustrate this — is by comparison with another example of LBBB not associated with acute OMI ( = Exhibit A in Figure-1). I’ll emphasize that there is great variation in the spectrum of LBBB appearance. Not all cases of LBBB look like Exhibit A. Nevertheless — I believe the example of LBBB that I’ve chosen for Exhibit A helps illustrate the qualitative principles I discuss.

• Note that there is no more than minimal J-point ST elevation in lead III of Exhibit A. The other inferior leads don’t manifest any J-point ST elevation at all.
• There is J-point ST elevation in 4 of the chest leads in Exhibit A (ie, leads V1-thru-V4). However, the J-point is not distinct — but instead, is rather “elusive”, in that there is a gradual upsloping concavity to the ST segment. Modified Smith-Sgarbossa criteria are negative for these 4 chest leads in Exhibit A — because the S waves in these leads are so very deep.
• There is ST-T wave depression in virtually all lateral leads in Exhibit A. That said, this is not ischemic — but rather a typical manifestation of LBBB.
• In summary — ST-T wave shape in Exhibit A looks benign (ie, typical for a patient with LBBB).

Qualitatively — the shape of ST segment deviations in ECG #1 is concerning:

• I’ve added short RED horizontal lines in the inferior leads to clarify the ST segment baseline. These horizontal lines facilitate recognition of how much the J-point is elevated. There is rapid ascent to this J-point — and the J-point is discrete. This same abnormality is seen in all 3 inferior leads. This ST segment shape in all 3 inferior leads looks worrisome, and may indicate primary ST elevation.
• As per Dr. Smith — there is typically some (often slight) ST elevation in anterior leads in association with LBBB. There should not be any ST depression at all in leads V2 and V3. As a result — the shape of the ST-T wave in lead V2 of ECG #1 is not normal. Given how deep the S wave is in this lead (>30mm! ) — I would expect at least slight ST elevation, and there is none.

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NOTE: Assessment for LVH is clearly more difficult in the presence of LBBB. Since LBBB changes the sequence of ventricular depolarization — the usual voltage criteria for LVH diagnosis do not pertain. In addition, the sequence of ventricular repolarization is also changed. As a result — the asymmetric (slower downslope; more rapid upslope) shape of ST segment depression that we see in both examples of LBBB in Figure-1 are expected secondary ST-T wave changes that are typically seen with this conduction defect. They cannot be assumed due to LV “strain” (and they cannot be assumed to represent ischemia).

• Virtually all patients with complete LBBB have some form of underlying heart disease. As a result — statistically, patients with LBBB make up a high-prevalence population for LVH.
• The presence of very deep S waves (ie, >25-30mm) in one or more anterior leads (ie, V1, V2 and/or V3) is highly correlated with LVH in patients with LBBB. This suggests that both of the ECGs in Figure-1 have LVH.

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BOTTOM Line: In the absence of chest pain and NO prior tracing for comparison — I was not initially certain that ECG #1 represented acute OMI. But I was suspicious — for the reasons I discuss above.

• Repeating the ECG much sooner than several hours later may have been enlightening. When in doubt about the findings on an initial tracing — repeating the ECG within ~15 minutes is advisable. Use of other modalities (ie, troponin, Echo at the bedside) may have also helped to recognize ongoing acute OMI sooner.
• FINAL Thought: Use of modified Smith-Sgarbossa criteria can very helpful in assessing patients with LBBB by the easy-to-calculate, objective rating scale that facilitates identifying patients with higher probability of acute OMI. With practice and experience — qualitative assessment of ST-T wave shape can instantly provide similar diagnostic assistance. I favor use of both methods to hone your diagnostic skills!