What is OMI (Occlusion Myocardial Infarction)?

What is OMI (Occlusion Myocardial Infarction)?

OMI (Occlusion Myocardial Infarction) is an acute myocardial infarction caused by complete or near-complete coronary artery occlusion (TIMI 0-2 flow) requiring immediate reperfusion therapy, regardless of whether ST-elevation criteria are met on the ECG. 1

Defining OMI

OMI represents a paradigm shift from the traditional STEMI/NSTEMI classification system. The critical distinction is that OMI focuses on the underlying pathophysiology—acute coronary occlusion—rather than ECG criteria alone. 1, 2

Diagnostic Criteria for OMI

OMI is defined by angiographic findings:

• Acute culprit lesion with TIMI 0-2 flow (complete or near-complete occlusion), OR 1
• Acute culprit lesion with TIMI 3 flow that was intervened upon AND highly elevated troponin (cTnI > 10.0 ng/mL or hs-cTnI > 5000 ng/L) 1

The Critical Problem: STEMI Criteria Miss 40% of OMI Cases

The most important clinical implication is that 40% of patients with acute coronary occlusion do not meet traditional STEMI criteria on their presenting ECG. 1 This creates a dangerous treatment gap:

• Only 11% of STEMI(-)OMI patients receive PCI within 12 hours, compared to 77% of STEMI(+)OMI patients (p < 0.001) 1
• Despite delayed treatment, STEMI(-)OMI patients require PCI at similar rates (89% vs 93%, p = 0.496) 1
• STEMI(-)OMI patients develop mechanical complications at rates identical to STEMI(+)OMI (46.4% vs 46.8%) 1

Why the Traditional STEMI/NSTEMI Classification Falls Short

The Universal Definition of Myocardial Infarction classifies MI into types based on etiology, with Type 1 MI resulting from atherosclerotic plaque rupture/erosion with intraluminal thrombus. 3 However, this classification system relies heavily on ST-elevation criteria that were designed for sensitivity, not specificity for acute occlusion. 4

Traditional STEMI criteria require:

• ST elevation ≥0.25 mV in men <40 years, ≥0.2 mV in men ≥40 years, or ≥0.15 mV in women in leads V2-V3 4
• ST elevation ≥0.1 mV in other leads 4
• Must be present in at least two contiguous leads 4

The problem: Many acute occlusions present with subtle or atypical ECG findings that don't meet these thresholds, including:

• Hyperacute T-waves without sufficient ST elevation 5
• ST depression in anterior leads representing posterior OMI 4
• Minimal ST elevation with terminal QRS distortion 5
• The "shark fin" pattern (fusion of QRS, ST-segment, and T-wave) 6

Clinical Outcomes and Mortality

In-hospital mortality data demonstrates the severity of OMI:

• Overall mortality: 5.7% 1
• STEMI(+)OMI: 4.2% 1
• STEMI(-)OMI: 0.9% 1
• Mechanical complications occur in approximately 46% of all OMI patients, regardless of STEMI criteria 1
• Electrical complications occur in 18.5% of STEMI(+)OMI and 13.1% of STEMI(-)OMI 1

Emerging Diagnostic Tools

Machine learning algorithms show superior performance in identifying OMI compared to traditional STEMI criteria:

• AI-driven ECG interpretation achieved an AUC of 0.953 for OMI detection 7
• AI algorithms reduced false positive activations by 34% while missing zero OMI cases, compared to STEMI criteria which missed 6 OMI cases (5%) 2
• Machine learning models outperform practicing clinicians and commercial ECG interpretation systems 5

Practical Clinical Approach

When evaluating a patient with suspected acute coronary syndrome:

1. Obtain a 12-lead ECG within 10 minutes of first medical contact 4

2. Look beyond traditional STEMI criteria for signs of OMI:

   • Hyperacute T-waves 5
   • ST depression in V1-V3 suggesting posterior OMI (consider V7-V9 leads) 4
   • ST depression in ≥8 leads with ST elevation in aVR/V1 (left main or multivessel disease) 4
   • Shark fin pattern (wide triangular QRS-ST-T fusion) 6
   • New or presumed new LBBB with concordant ST changes 4

3. Recognize high-risk features requiring immediate catheterization:

   • Ongoing chest pain despite medical therapy 3
   • Hemodynamic instability or cardiogenic shock 3
   • Electrical instability with ventricular arrhythmias 3
   • Highly elevated troponin (hs-cTnI > 5000 ng/L) with dynamic changes 1

4. Do not delay catheterization in STEMI(-)OMI patients based solely on absence of ST elevation if clinical suspicion is high 1, 2

Common Pitfalls

Critical errors to avoid:

• Relying solely on automated ECG interpretation or STEMI criteria to determine need for emergent catheterization 2, 5
• Misinterpreting the shark fin OMI pattern as ventricular tachycardia, which can lead to inappropriate treatment and delayed reperfusion 6
• Failing to obtain posterior leads (V7-V9) in patients with isolated anterior ST depression, missing posterior OMI 4
• Delaying catheterization in circumflex artery occlusions, which frequently present without classic STEMI criteria 4
• Assuming NSTEMI patients can wait for catheterization when they may have acute coronary occlusion 1

The Future: OMI vs NOMI Classification

The proposed reclassification system divides acute MI into:

• OMI (Occlusion MI): Acute coronary occlusion requiring immediate reperfusion 1
• NOMI (Non-Occlusion MI): Myocardial infarction without acute occlusion 1

This classification better aligns treatment urgency with underlying pathophysiology rather than ECG patterns, potentially improving outcomes by ensuring all patients with acute coronary occlusion receive timely reperfusion therapy. 1, 2