STEMI equivalents

We all know the classic STEMI.  When we see ST segment elevation greater/equal to 1 mm in two contiguous leads, activation of the cath lab is not far behind.  What other EKG findings should you look for that indicate acute coronary ischemia? 

In a 2010 paper from the American Heart Journal, Rokos, et al discussed 6 “STEMI equivalents” that should prompt the clinician to look harder at the EKG and either obtain a STAT cardiology consult vs activating the cath lab.  The following are the STEMI equivalents discussed in the paper:  new or presumed new LBBB, preexisting LBBB with Sgarbossa concordance, posterior MI, left main coronary occlusion (LMCO), de Winter ST/T wave complexes, and hyper-acute T waves.

The AHA guidelines have included the new or presumed new LBBB in the setting of chest pain as a STEMI equivalent; however, this recommendation will likely be demoted in future guidelines as it is not very specific.  In a single center study, >90% of LBBB patients evaluated in the ED did not have acute coronary occlusion and did not need to go to the cath lab.  The only caveat to this is if the Sgarbossa criteria are present.  The most specific of the Sgarbossa criteria is concordance of greater/equal to 1 mm in one or more leads, usually precordial.  A metanalysis showed low sensitivity for this concordance criteria (20%), but the specificity was 98%!  The other Sgarbossa criteria that is well known is ST segment discordance greater/equal to 5 mm, but this was less specific than the concordance criteria.  Don’t forget to check for concordance in your LBBB patients with chest pain.

Acute left main coronary occlusion (LMCO) is usually rapidly lethal, but many of these patients will make it to an ED to be evaluated.  You must be able to pick up on this EKG that, to the untrained eye, will look like a typical NSTEMI.  You will see diffuse ST segment depressions (6-8 leads depending on the criteria you use) with ST elevation in aVR.  The ST depressions are usually inferior although other leads will probably be involved.  The elevation in aVR will also usually be greater than in V1.  If these criteria are present, the sensitivity and specificity are 75% in one study of 75 patients with LMCO.  See that picture associated with this post for an example.

The posterior MI is another STEMI equivalent, usually presenting with ST depressions greater/equal to 0.5 mm in V1-V3.  These leads represent the reciprocal changes occurring due to posterior ischemia.  Therefore leads V7-9 should also be evaluated (the posterior ECG), looking for at least 0.5 mm of ST elevation in these leads.  Posterior MIs have been treated via non-emergent PCI recently, but some studies have shown worsened 30 day mortality in this cohort.  Cath lab activation is still indicated at this time.

The Rokos paper also discusses the de Winter ST/T wave complex, which was described in 2008.  This pattern signifies in acute LAD occlusion and presents as “1-3 mm of ST depression that is up-sloping at the J point in leads V1 through V6 and associated with persistently tall, upright, and symmetric precordial T-waves.”  The best way to learn this one is to actually look at ECGs with these findings.  The Rokos paper has an example, or you can search the internet for a few good examples as well.  Of note, they also discuss the difference between the de Winter complex, which is indicative of acute proximal LAD ischemia, with Wellens syndrome, which is indicative of chronic proximal LAD ischemia.  You should still know Wellens syndrome and the associated deep T wave inversion in V2-3 or biphasic T waves in the same leads.  These patients still need angiography, but MAYBE not as emergent as the STEMI equivalents listed here.

Hyperacute T waves are also a STEMI equivalent as they represent the earliest finding of ischemia and occur immediately following symptom onset.  This finding, however, is transient and usually no longer exists by the time the patient presents to an ED.  It should still always be in your differential, especially in a patient who starts having chest pain while in the ED/hospital.  Make sure you rule out hyperkalemia first!

In addition to the STEMI equivalents, you should also be aware of all of the STEMI mimics.  Let us know if you’d like to see a post describing all of these.  The goal for cath lab activation is to find all of the acute coronary ischemia patients while maintaining less than 5% inappropriate activation.

Goldberger A.  Electrocardiogram in the diagnosis of myocardial ischemia and infarction.  Updated Dec 19, 2011.

Rokos I, French W, Mattu A, et al.  Appropriate Cardiac Cath Lab activation:  Optimizing electrocardiogram interpretation and clinical decision-making for acute ST-elevation myocardial infarction.  American Heart Journal.  2010, 160(6):  995-1003, 1003e1-e8.


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