The Case:

A 75-year-old male with a past medical history of hypertension and ESRD on HD presents to the ED for 2 hours of generalized chest pain prior to arrival. The patient was brought to the ED via EMS and was given aspirin 325 mg PO en route. He has no known cardiac history but has poorly controlled hypertension on triple therapy. He denies any radiation of chest pain to the shoulder, back, or jaw, or shortness of breath. An ECG (Figure 1) was obtained on arrival.

Interpretation:

Rate: 66 bpm; Rhythm: normal sinus rhythm; Axis: left axis deviation (I: pos, II: eqv., aVF: neg); Intervals: PR: 160, normal; QRS: 100, normal; QT: 420, normal; P-Waves: present and associated with every QRS; QRS Complex: poor R wave progression in precordial leads; ST Segment/T-waves: mild concave ST elevation (1.5mm) in aVF with reciprocal ST depression (1mm) in aVL

Work-up:

Additional work-up included a CBC, CMP, troponin, and a chest x-ray. A repeat ECG was ordered for 1 hour along with serial troponins. Lab results were significant only for a moderately elevated troponin at 0.086 ng/mL. The HEART score was 7 (high, risk of MACE 12–65%). The index ECG fails to meet STEMI criteria as there is no ST elevation in two consecutive leads. Cardiology was consulted for NSTEMI. While awaiting Cardiology recommendations, the repeat ECG was obtained (Figure 2).

Interpretation:

Rate: 54 bpm; Rhythm: sinus bradycardia; Axis: indeterminate axis (I: pos, II: eqv., aVF: eqv.); Intervals: PR: 160, normal; QRS: 100, normal; QT: 420, normal; P-Waves: present and associated with every QRS; QRS Complex: RSR’ in leads II, III, aVF, and aVL; ST Segment/T-waves: evolving ST elevation in II (2mm), III (3mm), and aVF (3mm) with reciprocal depression in aVL (2mm)

Cardiology took the patient to the cath lab where he was found to have an RCA occlusion. A stent was placed and the patient was admitted to the Cardiology service.

Discussion:

The patient was ultimately diagnosed with severe coronary artery disease with type I myocardial infarction. This patient presented with classic symptoms of myocardial infarction in the setting of multiple cardiac risk factors (age, hypertension, and hyperlipidemia); notably his HEART score even before the troponin resulted was 6 which falls in the moderate risk category with a 12-16.6% chance of MACE. However, none of the ECGs obtained ever demonstrated classic STEMI criteria (or even a so-called “STEMI equivalent”) which is what emergency physicians classically use to diagnose myocardial infarction.

In 2018, the terms “OMI” (Occlusive Myocardial Infarction) and “NOMI” (Non-Occlusive Myocardial Infarction) were proposed by Meyers, Weingart, and Smith to replace the classic terminology of STEMI/NSTEMI (1-3). Their reasoning for this paradigm shift is threefold: 1) under current STEMI/NSTEMI criteria, 25-30% of patients diagnosed with NSTEMI are consistently found to have missed acute coronary occlusion, 2) physicians across all specialties have poor accuracy and poor inter-rater reliability for detecting acute coronary occlusion (ACO), and 3) physicians cannot agree on where and how to measure the ST segment.

The DIFOCCULT Study, published in 2020, further supported this paradigm shift. Their study analyzed patients who presented to the ED with clinically likely ACS and were diagnosed to have an MI with or without subsequent coronary intervention (4). Patients were subdivided into STEMI, NSTEMI, and ACS-excluded (control) groups. 28.2% of patients classified as NSTEMI using traditional criteria were re-classified as having ACO using OMI/NOMI classification on ECG. Within the reclassified NSTEMI group, 60.7% were found to have ACO (compared to the STEMI group which had an ACO rate of 85.3%, and the non-reclassified NSTEMI groups which had an ACO rate of 25.3%). The study data demonstrated the OMI/NOMI classification (Figure 3) has superior diagnostic accuracy in the prediction of ACO and long term mortality compared to STEMI/NSTEMI criteria.

Suggested ECG changes to detect OMI include:

Hyperacute or small hyperacute T-waves
Pathologic Q-waves with subtle STE which cannot be attributed to old MI
Terminal QRS Distortion that does not extend to baseline, with absence of both a J-wave and an S-wave
Reciprocal STD and/or T-wave Inversion
Subtle STE not Meeting Criteria
STD Maximal in V2 – V4 Indicative of Posterior OMI
Any STE in Inferior Leads with any STD/T-Wave Inversion in aVL (5)

The patient’s ECG in this case initially demonstrated ST elevation in the inferior lead aVF with ST depression in aVL. Per classic STEMI/NSTEMI criteria, with a positive biomarker, this patient would be diagnosed with NSTEMI and admitted to cardiology for serial troponins and a delayed cardiac catheterization. But, per the OMI/NOMI classification, this patient meets criteria for emergent cardiology consultation and consideration of urgent PCI.

OMI/NOMI Educational Resources:

● Dr. Hedayati on RebelEM: Time to Evolve – Redefining Coronary Ischemia – The OMI/NOMI Paradigm

● The OMI Manifesto

● OMI Cheat Sheet

● LITFL Replacing the STEMI Misnomer

Take Away Points:

● Do not focus solely on the ST segment when analyzing an ECG for signs of ACS.

● When your patient has ECG changes that do not meet STEMI criteria but are suggestive of ischemia in the correct clinical setting (refer back to Suggested EKG changes to detect OMI list), consider early cardiology consultation.

● Rather than asking, “Does this patient have a STEMI?” think, “Does the patient have an acute coronary occlusion that would benefit from immediate intervention?”

Authored by Michael Hohl, MD.

References:

McLaren, J. (2019, November 19). Subtle inferior mi: ECG cases: Em cases. Emergency Medicine Cases. Available at: https://emergencymedicinecases.com/subtle-inferior-mi/
Meyers, P., Weingart, S., & Smith, S. The OMI Manifesto. Dr. Smith’s ECG Blog & EMCrit. Available at: The OMI Manifesto PDF 3.29.18.pdf
Buttner, R., Cadogan, M., & Cadogan, R. (2023, August 10). Omi: Replacing the stemi misnomer. Life in the Fast Lane • LITFL. Available at: https://litfl.com/omi-replacing-the-stemi-misnomer/
Aslanger EK et al.Diagnostic Accuracy of Electrocardiogram for Acute Coronary Occlusion Resulting in Myocardial Infarction (DIFOCCULT Study). Int J Cardiol Heart Vasc 2020. PMID: 32775606
Salim R. "Upping Our ECG Game: OMI vs STEMI", REBEL EM blog, May 10, 2021. Available at: https://rebelem.com/upping-our-ecg-game-omi-vs-stemi/.

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