Wednesday, June 10, 2009

Acute anterior STEMI from LAD occlusion, or Benign Early Repolarization (BER)???

For another fascinating related ECG, click here
Acute MI from LAD occlusion, or early repolarization? 

Case:

This is a 46 yo male with acute onset of chest pain, in distress, who called the ambulance. He arrived and had this ECG recorded at 0118 AM. 

A followup ECG and the answer is below.

There is 1 mm of ST elevation in V2 and V3, so this meets the criteria for reperfusion by the ACC/AHA guidelines. Unfortunately, the majority of patients who meet such "criteria" do not have MI. The most common reason for ST elevation is early repolarization.

(In this case, the limb leads are suggestive of ischemia as well, with some subtle ST depression inferiorly, suggesting pending ST elevation in aVL due to lateral MI from proximal LAD occlusion.)

I have developed a decision rule to differentiate Anterior STEMI from BER in patients who present to the ED with chest pain. These rules only apply when the DDx is Anterior MI vs. BER. A simple rule is the R-wave rule, which depends on the fact that, in BER, the R-wave is always well developed:

If the mean R-wave amplitude from V2-V4 is less than 5 mm, then it is almost certainly MI. If greater than 5 mm, it is probably BER. A cutoff of 5 mm gives a sensitivity for MI of about 70%, but a specificity of greater than 95%.

There are a couple other more complex rules, one of which uses QTc-B, R-wave amplitude in lead V4, and ST elevation at 60 ms after the J-point in lead V3.

Another equally accurate one, also derived using logistic regression, uses QTc and 2 averages: mean ST elevation at the J point (STEJ) from V2-V4 and mean R-wave amplitude from V2-V4.

Both rely on the findings that the mean ST elevation was higher in the MI group, and the mean QTc in BER is shorter (mean = 390 ms), and mean R-wave amplitude is greater.

If the formula: (1.553 x mean STEJ in mm) + (.0546 x QTc in ms) - (0.3813 x mean RA in mm, not mV) is > 21, vs. less than or equal to 21, then it represents MI with high sensitivity and specificity.

In this case, the values are (1.553 x 1.0) + (.0546 x 420) - (.3813 x 1.17) = 1.553 + 22.93 - 0.3813 = 24.1

Thus, the rule predicts that this is anterior MI.

The clinicians were suspicious of MI, so they were smart to obtain serial ECGs. They obtained the second ECG at 0143:

This shows unequivocal straightening of the ST segments, compared to the first ECG. This ST straightening results in T waves which are fattened and "hyperacute". This is diagnostic of anterior STEMI.

In case you can't see this difference in the straightening of the ST segment, here they are side-by-side:


He had a 100% proximal thrombotic LAD occlusion with TIMI-0 flow. It was opened and stented.

The followup ECG might give an idea of what this patient's T-waves looked like before his occlusion:

10 comments:

  1. Dr. Smith -

    You wrote:

    "If the mean R-wave amplitude from V2-V4 is less than 5 mm, then it is highly unlikely to be BER. If greater than 5 mm, it is probably MI. A cutoff of 5 mm gives a sensitivity for MI of about 70%, but a specificity of greater than 95%."

    Is this a typo?

    If the R-wave amplitude is greater than 5 mm, then it's probably MI? Or did you mean to say that it's probably BER?

    I have two cases of anterior STEMI vs. BER, and in both cases, it turned out to be anterior STEMI.

    In the first case, the mean R-wave amplitude in V2-V4 is less than 5 mm.

    In the second case, the mean R-wave amplitude in V2-V4 is greater than 5 mm.

    Would it be safe to say that the second case shows anterior STEMI in the presence of BER?

    Thanks for another great teaching point!

    Tom

    ReplyDelete
  2. Tom,

    Thanks for pointing out the typo. I have corrected it.

    Your case with good R wave amplitude is a very interesting one, and points out that neither decision rule is perfect (and the senstivities and specifities were not perfect in the study, either).

    Fortunatel for your patient, the diagnosis of STEMI is clear from ST elevation in aVL, with reciprocal ST depression in inferior leads.

    But the anterior leads sure do look like early repol, and even have the characteristic J wave!

    Thanks,

    Steve Smith

    ReplyDelete
  3. Excellent example. I've never heard of the method you described. You didn't mention the use of the R/S ratio to r/o early repol. Is this something that you advocate?


    I've been following your blog for a while and have yet to comment, so I figured I would. Great blog by the way.

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    ReplyDelete
  4. wow that was a great post, glad i pciked the STEMI but still dont have my head around the BER thing...back to the books :P

    ReplyDelete
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    ReplyDelete
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    ReplyDelete
  7. Hi!

    I have been applying the more complex rule mentioned above to the prehospital ECG of a patient we admitted last week.

    Mean STEJ = (2+1+1)/3 = 1.33mm
    QTc 392
    Mean R-amplitude 0.9mV (9mm)

    This gave a score of (1.553 x 1.33) + (.0546 x 392) - (.3813 x 0.9) = 2.06 + 21.4 - 0.343 = 23.12 - which would indicate AMI

    The patient received prehospital thrombolysis. However all three troponin measurements were negative... The ECG changes were static over time, and are thought to represent BER.

    The post states that the mean QTc in BER is 390, which would alone give a score of 21.29. And as the mean R amplitude is multiplied with a very small factor (0.3813) even larger R amplitudes would deduct very little from this score.

    Or is there some problem with the units? Should the mean RA be in mm rather than mV?

    Sincerely, Tor Pedersen (EMT and, now also, medical intern)

    ReplyDelete
  8. the rule is almost 90% sensitive and 90% specific when comparing subtle MI to BER. This was true in both a derivation group and validation group. But it's not perfect. Your very small R-wave amplitude (mean of 0.9 mm?!!) is very unusual for BER and is the reason for the false positive.

    And now I see the reason for the misunderstanding. It is mm, not mV!! I should have clarified that. Sorry.

    In my series of BER, only 5% had a mean R-wave V2-V4 less than 5mm. And probably none had a mean of 0.9mm, not mV!!

    ReplyDelete
  9. Dr. Smith,

    Besides the STD and junctional rhythm, there was also a pathological Q-wave in lead III on the first that is not present anywhere else. Is this due to misplacement? Also is a prolonged QTc sensitive for Anterior MI vs. BER? And one last question, I noticed that after reperfusion the R-wave progression is still poor. How long does it take usually until the R-wave progression becomes intact again?

    ReplyDelete
  10. Troy, very good points. It may be lead misplacement. The QRS axis on the first 2 ECGs is about 15 and then 90 on the last. Not sure how to figure which leads were misplaced. On the other hand, acute MI can alter the axis. The QTc is more prolonged in anterior STEMI than in BER, but by itself does not lead to a good cutoff value.

    Recovery of R-waves is very variable. There may have always been poor progression in this patient, even before LAD occlusion. The point is just as much that early repol always has good R-wave progression as that in MI R-wave progression may be lost.

    ReplyDelete