Which coronary artery occlusion leads to which pattern of myocardial infarction?

Coronary Artery Occlusion and Myocardial Infarction Patterns

The specific coronary artery occluded determines the ECG pattern and myocardial territory affected: LAD occlusion causes anterior MI with ST elevation in V1-V6, RCA occlusion causes inferior MI with ST elevation in II/III/aVF, and left circumflex occlusion causes posterior/lateral MI often presenting without ST elevation. 1

Left Anterior Descending (LAD) Artery Occlusion

Proximal LAD Occlusion (Above First Septal and Diagonal Branches)

This is the "widowmaker" pattern with the highest mortality risk. 2

• ST elevation in leads V1-V4, I, aVL, and often aVR 1
• Reciprocal ST depression in leads II, III, aVF, and often V5 1
• More ST elevation in aVL than aVR, and more ST depression in lead III than lead II (leftward injury vector) 1, 2
• Involves the basal left ventricle, anterior and lateral walls, and interventricular septum 1

Mid-LAD Occlusion (Between First Septal and Diagonal Branches)

• No ST elevation in V1 (basal septum spared) 1
• ST elevation in aVL with reciprocal depression in lead III 1
• The basal interventricular septum is not involved 1

Distal LAD Occlusion (Below Both Septal and Diagonal Branches)

• ST elevation more prominent in V3-V6, less in V2 1
• No ST elevation in V1, aVR, or aVL 1
• No ST depression in II, III, or aVF - may actually show ST elevation in inferior leads due to "wraparound" anatomy 1, 3
• ST vector oriented inferiorly 1

Right Coronary Artery (RCA) Occlusion

Typical Inferior MI Pattern

• ST elevation in leads II, III, and aVF 1
• ST elevation greater in lead III than lead II (sensitivity 99%, specificity 100% for RCA) 4
• ST depression in leads I and aVL 4
• Upright T wave in lead V4R 4

RCA with Right Ventricular Involvement

• ST elevation in right-sided leads V3R and V4R 3
• Record right-sided leads immediately, as ST elevation resolves within 10 hours in 50% of patients 3
• Higher mortality risk despite smaller infarct size 3
• High risk for ventricular septal rupture 3

Critical Pitfall

When ST elevation appears in both anterior (V2-V4) AND inferior (III, aVF) leads, consider distal LAD wraparound occlusion as the most common cause, though proximal RCA with RV extension is possible 3

Left Circumflex (LCx) Artery Occlusion

This is the most frequently missed culprit vessel because it often presents without ST elevation. 1, 5

Typical Presentation

• Only 43-48% present with ST elevation (compared to 71-72% for RCA/LAD) 6, 5
• 38% have no significant ST changes on admission 6
• Isolated ST depression ≥0.05 mV in leads V1-V3 represents posterior MI and should be treated as STEMI 1

Posterior/Lateral MI Pattern

• Use posterior leads V7-V9: ST elevation ≥0.05 mV (≥0.1 mV in men >40 years) 1
• ST elevation in leads I, aVL, and V4-V6 when lateral wall involved 6
• Abnormal R waves in lead V1 (96% specificity for LCx vs RCA, but only 21% sensitivity) 6

Inferior MI from LCx

• ST elevation greater in lead II than lead III (sensitivity 93%, specificity 100% for LCx) 4
• No ST depression in lead I 4
• No upright T wave in V4R 4

Clinical Impact

• LCx occlusion accounts for 19.5% of acute MI requiring PCI 5
• Patients are significantly less likely to receive PCI within 24 hours (70% vs 80-83% for other territories) 5
• Higher troponin levels in non-STEMI presentations (median 2.5 ng/ml vs 1.3-1.4 ng/ml) 5
• Emergency angiography is indicated for ongoing ischemic symptoms despite absence of ST elevation 1

Left Main Coronary Artery Occlusion

This is a catastrophic presentation requiring immediate recognition. 1, 7

• ST elevation in aVR and/or V1 1, 7
• ST depression >0.1 mV in eight or more surface leads 1, 7
• Hemodynamic compromise (hypotension, shock, pulmonary edema) is common 7
• 31% in-hospital mortality, 59% have severe multivessel disease 7
• Immediate catheterization laboratory activation without waiting for troponin results 7

Special Considerations

Wellens Syndrome (Pre-infarction LAD Warning)

• Deep symmetric T-wave inversions (≥0.5 mV) in V2-V4 with QT prolongation 2
• Indicates severe proximal LAD stenosis with high risk of imminent anterior MI 2
• Perform emergent angiography within 2 hours regardless of TIMI risk score 2

Atypical Presentations Requiring Emergency Angiography

• LBBB with ongoing ischemic symptoms 1
• Ventricular paced rhythm preventing ST interpretation 1
• Persistent ischemic symptoms despite absence of diagnostic ST changes 1
• Hyperacute T waves preceding ST elevation (very early presentation) 1