Wednesday, May 14, 2014

STEMI versus NSTEMI: misunderstood, misapplied, revisited

I have written a number of posts about the binary distinction of “STEMI versus NSTEMI” for acute coronary syndrome. In those posts I have cited many examples of unintended consequences of this terminology and developed the premise that it's an artificial distinction which is often misapplied. Despite some push back and numerous questions I stand by the premise. The idea is not original with me. It was this paper from a fewyears ago, which I have cited several times since, that first alerted me to the problem.

My last post on this topic, judging form a nice Facebook avalanche I received, garnered some attention. Now might be a good time to revisit the issue.

If the question stirs debate in some minds perhaps there are a few basic problems with “STEMI/NSTEMI” we can at least agree about as starting points:

The terms STEMI and NSTEMI are simple surrogates to denote complex pathologic processes.

Flaws are inherent in the simplistic use of surrogates even though they can be clinically useful at times.

STEMI and NSTEMI are descriptive terms which lead to diagnosis based on simple pattern recognition.

Diagnosis by pattern recognition tends to ignore complexities of electrophysiology which are clinically important.

While electrocardiographic patterns can provide powerful clues they do not equate to pathologic processes in simple fashion.

The late J. Willis Hurst, master clinician and teacher of electrocardiography, published many articles on the subject. In this one from the American Journal of Cardiology he offered several suggestions for addressing the problem. One was that the electrocardiographic interpretation should not stop with pattern description but go on to include a list (differential diagnosis) of conditions associated with the pattern.

STEMI is a surrogate for acute coronary occlusion. But when the above exercise in differential diagnosis is carried out acute coronary occlusion will appear in the interpretation of many NSTEMI electrocardiograms. This was illustrated in a post from a couple of years ago at Dr. Smith's ECG blog.

Here are some of the points he made in that post:

STEMI and NonSTEMI are arbitrary terms that may confuse the clinician.
"STEMI" should mean "coronary occlusion" (or near occlusion, without good collateral circulation -- in other words, it needs thrombolytics or emergent angiogram with PCI).

NonSTEMI should mean "MI without occlusion."
"STEMI-equivalent" is a good term for "coronary occlusion".
Many STEMI-equivalents have no significant ST elevation, as you may have seen from many of my posts.
In some STEMI-equivalents (posterior STEMI, lateral STEMI, posterolateral STEMI), ST depression is the only, or most visible, feature of the ECG.

These are points I have made many times before, often via citation from Dr. Smith's posts. The difficulty lies in the fact that when using the electrocardiogram for emergency decision making we need something simple that we can use at a glance. The unfortunate reality is that in today's performance driven world we've made STEMI/NSTEMI too simple.

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