Listener Tom Adds to the STEMI Imitators Tips

Listener Tom gave me permission to share this with the rest of you following the recent episode on STEMI imitators last week.

Jamie -

Thank you for bringing attention to this important issue on your recent podcast.

It’s actually not that difficult to rule out the STE-mimcs if you know what you’re looking for. Identifying acute STEMI in the presence of an STE-mimic is a little bit more difficult, but certainly not impossible.

It’s critically important that paramedics develop their 12-lead ECG interpretation skills if we are to grow as a profession and liberate ourselves from ECG transmission and/or computerized interpretations.

Let’s take them one at a time.

S-T Elevation Myocardial Infarction (STEMI) Imitators

Left ventricular hypertrophy

We should remember with LVH that we’re only talking about the so-called “strain pattern” (or repolarization abnormality) that shows ST-segment elevation in the right precordial leads (V1, V2, and  V3).

This is generally an anterior STEMI mimic, and the degree of ST-segment elevation is proportional to the depth of the S-wave. In other words, the deeper the QRS complex, the more severe the ST-T wave abnormality in the opposite direction of the QRS complex. That’s the key to identifying the strain pattern with LVH.

Left bundle branch block

This one is especially important because so many heart failure patients are walking around with non-acute LBBB. Speaking of “false positive” cardiac cath lab activations, in one study, almost 50% of patients with LBBB had no culprit artery. I think we can all agree that this is unacceptable.

So what is needed is some way to determine whether or not a LBBB is “old” or “new” or an algorithm to detect acute STEMI in the presence of LBBB. Such an algorithm exists, and it’s called “Sgarbossa’s Criteria” which came from the GUSTO investigators. Essentially the criteria says that patients with concordant ST-segment elevation (same direction as the QRS complex), patients with concordant ST-segment depression (same direction as the QRS complex), and patients with discordant ST-segment elevation > 5 mm (opposite the main deflection of the QRS complex) are presumed to have acute STEMI.

This last criterion has raised the most controversy, because as we saw with LVH, the deeper the S-wave the higher the ST-segments, and that’s the same for LBBB. That’s why others like Dr. Smith at Hennepin County Medical Center (and editor of Dr. Smith’s ECG Blog) propose a variation of Sgarbossa’s criteria that looks at the percentage of ST-segment elevation and says that discordant ST-segment elevation > 0.25 the depth of the QRS complex indicates acute STEMI.

Can paramedics learn this? Absolutely! But we need to get over the anxiety of learning something new. We also need to get over the fact that many physicians, ED physicians included, don’t know Sgarbossa’s Criteria.

As a side-note, Sgarbossa’s Criteria also works for typical paced rhythms (single pacing lead in the apex of the right ventricle).

Bengin Early Repolarization / Pericarditis

I’m listing these two together because they have many features in common, including upardly concave ST-segment elevation and a “notched” J-point, not to mention an absence of reciprocal changes. With pericarditis, you will generally see PR-segment depression.

One of the best tips I’ve ever heard for pericarditis is that you will see ST-segment elevation in leads I and II (two leads that are normally reciprocal to one another). That’s not to say you will never see a STEMI with ST-segment elevation in leads I and II, but it’s rare.

For these patients (really for all patients) serially obtained ECGs is the key to a STEMI diagnosis because a moving ST-segment and T-wave changes indicate dynamic supply vs. demand characteristics seen with acute coronary syndromes.

Final Thoughts on STEMI Imitators

They key to all of the STE-mimics is practice, practice, practice, not to mention case reviews. Any and all “false positive” cardiac cath lab activations should be sent back to the paramedics as case studies. In my experience, paramedics are devastated when they make a mistake, so this has to be handled the right way. For any QA/QI effort, mistakes have to be decriminalized and a “blame-free” culture needs to be fostered. We all want to do the right thing and make sure the right patients receive the right care at the right time. This is totally achieveable through multidisciplinary STEMI committees so that all key stakeholders can come to the table and design systems that benefit the patient.