Acute anterior STEMI from LAD occlusion, or Benign Early Repolarization (BER)???
Posted Aug 14 2009 6:48pm
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 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%.
A more complex rule was derived using logistic regression, and involves 2 other variables: mean ST elevation at the J point (STEJ) from V2-V4, and computer measured QT-c (Bazett method). This relies on the findings that the mean ST elevation was higher in the MI group, and the mean QTc in BER is short (mean = 390 ms).
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 arefattened and "hyperacute". This is diagnostic of anterior STEMI.
He had a 100% proimal thrombotic LAD occlusion with TIMI-0 flow. It was opened and stented.
The followup ECG gives an idea of what this patient's T-waves looked like before his occlusion