Sunday, December 15, 2013

Friday's post produced skeptics.....

I have been posting ECGs like this for so long that I erroneously thought everyone would see the inferior STEMI here.  I was just posting it as another example.

One reader was exasperated and said, "this is too much," implying that it is simply beyond belief that this ECG, which I will post again here, unequivocally shows inferior MI.

Remember the patient had a previous anterior MI and an LAD stent.

Here is the ECG again:
The ECG clearly shows the Q-waves in V1 and V2 from the old MI.  But that was not the focus of the post.  The combination of proportionally huge T-waves in II, III, aVF and minimal ST elevation in these inferior leads, along with T-wave inversion and minimal reciprocal ST depression in aVL, as seen here, is diagnostic of inferior MI.  The T-wave inversion in V2 is highly supportive as it suggests concomitant posterior MI because the artery that supplies the inferior wall very frequently supplies the  posterior wall as well.

First, let me try to establish some trust here:
1) I have been intensely interested in the ECG for the last 25 years, and scrutinized many tens of thousands of them.  I am provided particularly difficult ECGs by hundreds of people, continuously, over the years, and so have seen not just thousands of ECGs, but thousands of ECGs which physicians find particularly difficult to analyze.  I have always verified my readings with angiographic outcomes.

2) I have read over a thousand papers on the ECG in acute MI; some of the older ones are described in the annotated bibiliography of each of thee 38 chapters of my book.

3) I have done a lot of formal research into ECG findings of MI, and written a lot of evidence-based chapters on the ECG in MI.  Here is a list of my cardiology publications, mostly on the ECG (see the first 5 pages on this google scholar search)  Much of what I've studied is in how to identify subtle occlusion and how to differentiate the ST elevation of STEMI from that of the look-alikes.

4) There are 3 studies in the literature that I am aware of which studied the incidence of an occluded infarct-related artery in patients who rule in for MI by troponin.  These are patients who rule in and therefore get an angiogram the next day.  In these studies, 30% have an occluded infarct-related artery that was not detected on the ECG.  They have higher mortality, worse LV function, and higher biomarkers.  They were ultimately diagnosed with "NonSTEMI" (the diagnosis came after the angiogram, even though the artery was occluded).  Could these have been identified on the ECG?  I believe from my experience that many of them could have been diagnosed.

5) There are a number of studies in which ECGs are given to "experts" who are told to say whether the patient has an occluded artery or not.  In one such study, accuracy by interventionalists was very low and the interrater reliability was even worse.

In another study here, the best accuracy was among interventionalists, but still they had a mean accuracy of only 79%.  This study published all the ECGs they used, so that you can take the test yourself.  I did so, and I had 100% specificity and 92% sensitivity, far higher than the mean for any group.  I state this not to brag but to illustrate that one can train and get very sensitive at finding the subtle occlusion without sacrificing specificity.

As for this ECG:
1) I was reading a stack of ECGs and I saw this one and I instantaneously knew without any doubt that it was an inferior MI.  I said to myself: "Wow, here is an inferior MI that most physicians would not recognize as such.  I wonder what happened."  So I investigated and found that the physicians had not, in fact, recognized the hyperacute T-waves.

2) We have studied the ECG in inferior ST Elevation (STEMI vs. early repol vs. pericarditis) and are about to submit a manuscript.  In our study, no patient with any ST elevation who did NOT have any reciprocal ST depression in aVL had an MI.  Zero.  And among (admittedly select, with ultimate diagnosis of STEMI) patients with some (even minimal) inferior ST elevation, any ST depression in aVL was 99% sensitive for inferior MI.  T-wave inversion had similar sensitivity and specificity.

3) I have seen countless such cases and recognize this ECG as if it is an old enemy.  For me, this morphology brings instantaneous recognition.  I am trying to find ways to codify this subjective morphology recognition of MI, for many kinds of morphologies, so that others can recognize it equally well.

4) Proportionality is the one of the most important aspects to reading ECGs.  ST elevation or T-wave size that is out of proportion to the size of the QRS is alarming.  In this ECG, it is particularly true of lead aVF.  It is not the size of the T-wave or the height of the ST elevation that indicates MI, it is their relative size, relative to the QRS.

5) The T-wave is just as important, or perhaps more important, than ST elevation.  QRS, and R-wave is very important to the diagnosis.

6) Finally, we are only beginning to understand these relationships.  The old research is very poor and not angiographically based.  ST elevation is a crude measure of STEMI, paradoxically.  For instance, in our study comparing early repolarization to subtle anterior STEMI, the R-wave amplitude was the best differentiator, NOT ST elevation.  There are 6 rules of ST elevation cutpoints: we studied all 6 and the best accuracy was only 60%!

Finally, one must simply look at a lot of these, over and over, until they become like a recognizable face.  Perhaps one day facial recognition software will do a good job of making the diagnosis.  Until then, we need humans who have the experience, or at least the rules, to do so.

Recommended Resources