OMI/NOMI — beyond ST-elevation · Course

The STEMI/NSTEMI paradigm (4th universal MI definition) classifies acute coronary syndromes by ST elevation at the J-point. It is simple, reproducible and the standard of care for decades — but systematically misses acute occlusions that fail to meet the ST-elevation threshold. The emergency-cardiology community (Meyers, Smith et al.) has therefore developed the OMI/NOMI paradigm, classifying patients by the underlying pathophysiology rather than by the ECG phenomenon.

OMI vs. NOMI — definitions

OMI (Occlusion Myocardial Infarction): acute thrombotic coronary occlusion or functional equivalent (critical sub-total stenosis with insufficient collaterals) that without immediate reperfusion leads to transmural myocardial loss.
NOMI (Non-Occlusion MI): myocardial infarction without acute occlusion — primarily plaque-disruption-triggered type-1 infarct with preserved residual perfusion or type-2 demand ischaemia.

The dividing line is not the ECG, but the answer to the question: Will this patient benefit from emergent reperfusion within 90 minutes?

Limitations of the STEMI criterion

Several observations drive the criticism:

Only about 40–60 % of angiographically confirmed acute occlusions meet the STEMI criterion (Meyers et al. 2021); conversely, up to one in four NSTEMIs has an acute occlusion (5th UDMI 2026). The remaining occlusions are classified as NSTEMI and treated late — with measurably worse prognosis.
Posterior MI is often missed on the standard 12 leads (mirror image V1–V3); V7–V9 are rarely recorded routinely.
Left bundle branch block and paced rhythm make the standard criteria unusable — Sgarbossa-Smith is not universally adopted.
Hyperacute T-waves and De Winter T-waves are early OMI phenomena without classical ST-elevation — often reported as "non-diagnostic".

OMI patterns beyond ST-elevation

Pattern	ECG features	Correlate
Hyperacute T	broad, tall, symmetric, early after pain onset	early LAD/RCA occlusion
De Winter T-waves	upsloping ST depression precordially + tall symmetric T + ST↑ aVR	acute proximal LAD occlusion
Wellens (type A/B)	biphasic or deeply inverted T in V2–V4 after pain episode	critical LAD stenosis, post-occlusive reperfusion
Sgarbossa-Smith in LBBB/Pacing	concordant ST↑ ≥1 mm; concordant ST↓ ≥1 mm V1–V3; ST/S-ratio ≤−0.25 (discordant ST elevation ≥ 25 % of the preceding S-wave depth)	OMI with bundle branch block
Isolated posterior MI	reciprocal ST↓ V1–V3 with tall R; ST↑ ≥0.5 mm in V7–V9	LCx or distal RCA occlusion
Aslanger pattern (2020)	ST↑ isolated to III (not in II/aVF) + ST↓ in at least one of V4–V6 with a positive T-wave	inferior OMI with concomitant LMCA / multi-vessel disease
South-African-Flag sign	ST↑ I, aVL, V2 + ST↓ III	high lateral OMI (D1, proximal LCx)
Subtle ST-T asymmetry	T-axis shift, increased T/QRS ratio	early OMI without classical ST change

How to interpret OMI-style

OMI interpretation requires integrative thinking instead of the binary "STEMI yes/no" question:

Clinic first — persistent ischaemic chest pain, haemodynamic instability or new heart failure are by themselves a trigger for immediate cath, regardless of the ECG.
Prior ECG — even minimal new changes are diagnostic when they correlate with the clinical picture.
Look for reciprocal changes — isolated ST↑ without reciprocal ST↓ is less likely OMI; subtle reciprocal changes support the diagnosis.
T-wave morphology — symmetry, height, axis shift. Hyperacute T is often the only early sign.
Don't forget aVR and V1 — diffuse ST↓ + ST↑ aVR (left main), De Winter pattern, Aslanger.
Use posterior and right-ventricular leads liberally when inferior or posterior involvement is suspected.
Serial ECGs every 10–20 minutes in case of persistent pain.

Clinical consequence

ESC ACS 2023 explicitly recognises STEMI equivalents (De Winter, isolated posterior MI, left main pattern) as a Class-I indication for immediate primary PCI — moving toward the OMI concept without adopting the term. ESC 2023 assigns the Wellens sign to NSTE-ACS (critical proximal LAD stenosis); the 5th UDMI 2026 lists it among the patterns that, in the right clinical context, suggest an occlusion — the consequence is urgent invasive evaluation.

In practice this means: when an OMI pattern is present, the question of whether ST-elevation cut-offs are met becomes irrelevant. Instead the underlying question is asked: is there an acute occlusion that needs opening now? This lowers the threshold for cath-lab activation and can shorten the time to reperfusion for the occlusions missed by the STEMI criterion (40–60 % of all occlusions in OMI cohorts).

What it is not

OMI does not replace the ST-elevation criteria — the formally defined STEMI thresholds (ESC 2023, 4th universal MI definition) remain the primary triage tool and the consensus for trials and reporting. OMI complements them in cases where the threshold is not met but the occlusion is clinically and electrocardiographically likely. In centres with high OMI awareness, door-to-balloon times for OMI without ST-elevation are well below the standard NSTEMI pathway — with demonstrably better outcomes.

Further learning

Smith SW. Dr. Smith's ECG Blog — case discussions with OMI focus.
Meyers HP, Bracey A, Lee D, et al. "Comparison of the ST-Elevation Myocardial Infarction (STEMI) vs. NSTEMI and Occlusion MI (OMI) vs. NOMI Paradigms of Acute MI." J Emerg Med 2021.
Aslanger E, Yıldırımtürk Ö, Şimşek B, et al. "A new electrocardiographic pattern indicating inferior myocardial infarction." J Electrocardiol 2020. doi:10.1016/j.jelectrocard.2020.04.008
Pendell Meyers H, Smith SW. "OMI Manifesto" (open-access PDF).
ESC ACS 2023 — STEMI equivalents as Class-I indication for primary PCI.

OMI/NOMI — beyond ST-elevation

Learning objectives