Anterior Infarction: Causative Artery
Anterior myocardial infarction is invariably caused by occlusion of the left anterior descending (LAD) coronary artery. 1
Anatomic Basis
The LAD supplies the anterior wall of the left ventricle, and its occlusion produces a characteristic pattern of ST-segment elevation in the precordial leads (V1-V6), with the specific leads affected depending on the location of the occlusion within the vessel 1.
Location-Specific Patterns
The site of LAD occlusion determines the extent and distribution of myocardial injury:
Proximal LAD Occlusion (Above First Septal and Diagonal Branches)
- Produces the most extensive anterior infarction involving the basal left ventricle, anterior and lateral walls, and interventricular septum 1
- ST-segment elevation appears in leads V1-V6, I, aVL, and often aVR 1
- Reciprocal ST-segment depression occurs in inferior leads (II, III, aVF) 1
- Typically shows more ST elevation in aVL than aVR, and more ST depression in lead III than lead II 1
Mid-LAD Occlusion (Between First Septal and First Diagonal)
- The basal interventricular septum is spared, so lead V1 shows no ST elevation 1
- ST-segment elevation in aVL with depression in lead III 1
Distal LAD Occlusion (Below Septal and Diagonal Branches)
- The basal left ventricle is not involved 1
- No ST elevation in V1, aVR, or aVL 1
- No ST depression in inferior leads (II, III, aVF) 1
- ST elevation may be more prominent in leads V3-V6 and less prominent in V2 1
High-Risk ECG Pattern
A critical subset of patients presents with deeply inverted T waves (>0.5 mV) in leads V2-V4 with QT prolongation, which indicates severe stenosis of the proximal LAD with collateral circulation. 1 These patients are at extremely high risk for extensive anterior wall infarction if not promptly revascularized 1.
Rare Anatomic Variants
In exceptional cases, a "wrap-around" or hyperdominant LAD can extend beyond the apex to supply the posterior-inferior wall, potentially causing posterior-inferior infarction patterns despite being an LAD occlusion 2. However, this represents an anatomic variant rather than the typical pattern.