STEMI versus NSTEMI---meaningless distinction??

Brendan Phibbs, ever the towering intellect and still in possession of a steel trap mind at over 90 years of age, continues to contribute to the medical literature. His latest paper, in the July 2010 issue of Annals of Noninvasive Electrocardiography, is quite remarkable. It is titled Differential Classification of Acute Myocardial Infarction into ST- and Non-ST Segment Elevation Is Not Valid or Rational. Phibbs is being true to form. Never one for weasel words, he makes strong declarative statements. I don't have access to the full text of the paper, but let's look at the abstract:

Background: The distinction between ST elevation and nonST elevation infarcts is widely accepted and is employed as a guide to management...

Finding: The pathology of the two subsets is identical as are the morbidity, mortality and clinical course. Non-ST elevation infarcts are likely to be subsequent, to occur in older patients and to involve the circumflex artery: this subset therefore includes a high-risk group. ST deviation in any part of the electric field of the heart will predictably be accompanied by reciprocal deviation if the entire field of the heart is mapped. Further, ST deviation of infarction is often transient, resolving in minutes so that infarcts will be predictably misclassified. ST deviation per se is therefore not a rational basis for classification of infarcts. In fact, invasive therapy is indicated in both subsets with identical results.

Conclusion: The distinction between ST elevation and non-ST elevation infarcts is baseless. The high risk subgroup included in the non-ST elevation infarct set should not be denied the benefit of early invasive therapy.

So here's what he's saying: In his review of the world's literature, clinical and pathological correlations do not support a meaningful electrocardiographic distinction between STEMI and NSTEMI. At first that seems counterintuitive but as I think about it I can think of several explanations for why the distinction would be artificial. He's not arguing that there's no such thing as a STEMI or a NSTEMI (after all, some MI patients have ST elevations and some don't), but that the distinction is not clinically or pathologically meaningful. There might be a number of reasons.

First, many circumflex occlusions (epicardial coronary artery occlusion was long believed to be the pathologic correlate of STEMI) are associated with no or subtle ST elevation. Second, the presence or absence of ST elevation often depends on time to presentation with ST segments elevated one minute and isoelectric the next in the same patient, or vice versa, reflecting the unstable coronary plaque in a dynamic state of thrombosis and lysis. Third, there are several known “STEMI equivalents” which represent acute coronary occlusion without ST elevation, such as “true posterior” infarctions and hyperacute T wave infarctions seen in the very early stages of coronary occlusion. Finally, certain conditions which displace the ST segments such as bundle branch block and left ventricular strain may play “tug-o-war on the stylus” and mask ST elevation.

So do ST segment elevations have meaning at all? Of course. They are the most powerful initial diagnostic finding in acute MI. Often they help localize the culprit lesion and predict outcome. But if the distinction is meaningless how does one know whether to send the patient to the cath lab? In Phibbs' line of reasoning, absent contraindications, all patients with acute MI should go promptly to the cath lab. But in the real world it's usually only the ones who declare their diagnosis at the door who are eligible---and who are those patients? The ones with ST segment elevation! So is this paper of any practical importance? Maybe, in that it informs us that we should not be so rigid in our categorization. Furthermore, some patients without ST segment elevation but with a strong clinical picture or early biomarker elevation should be sent to the lab (remember what Grunt Doc did).

I think the distinction between STEMI and NSTEMI will persist for a while, just out of convenience. After all, once Phibbs' view gains traction it will open up a can of worms. The guidelines, which now lump NSTEMI with unstable angina, will have to be reorganized.

But I have a feeling it will eventually gain traction, because I think Phibbs is right. We wrestled with Phibbs in the area of electrocardiographic classification of MI once before and he won. In 1999 he published a paper demonstrating that the distinction between Q wave and non Q wave MI was meaningless. That view was not immediately accepted either, and Phibbs published several more papers on the subject over the next several years, until the concept of Q wave versus non Q wave infarction became obsolete. R.I.P.