What are the characteristic electrocardiogram findings of an anterior‑wall myocardial infarction?

ECG Findings of Anterior Wall Myocardial Infarction

Anterior wall MI is diagnosed by new ST elevation ≥2 mm (0.2 mV) in men or ≥1.5 mm (0.15 mV) in women in leads V2–V3, and/or ≥1 mm (0.1 mV) in other contiguous chest leads, measured at the J point in at least 2 contiguous leads. 1

Primary Diagnostic Criteria

ST-Segment Elevation Thresholds

Men ≥40 years:

• Leads V2–V3: ≥2 mm (0.2 mV) 1
• All other leads: ≥1 mm (0.1 mV) 1

Men <40 years:

• Leads V2–V3: ≥2.5 mm (0.25 mV) 1
• All other leads: ≥1 mm (0.1 mV) 1

Women (all ages):

• Leads V2–V3: ≥1.5 mm (0.15 mV) 1
• All other leads: ≥1 mm (0.1 mV) 1

Lead Distribution Patterns

The specific leads showing ST elevation localize the occlusion site within the left anterior descending (LAD) artery, which invariably causes anterior wall MI. 1

Anatomic Localization by ECG Pattern

Proximal LAD Occlusion (Above First Septal and First Diagonal)

ST elevation in V1–V4, I, aVL, and often aVR indicates proximal LAD occlusion involving the basal left ventricle, anterior and lateral walls, and interventricular septum. 1

Key features:

• ST elevation in V1 (≥2.5 mm strongly predicts proximal-to-S1 occlusion) 2
• ST elevation in aVR 2
• Reciprocal ST depression in II, III, aVF, and often V5 1
• More ST elevation in aVL than aVR 1
• More ST depression in lead III than lead II 1
• Complete right bundle branch block suggests proximal occlusion 2
• ST depression in V5 predicts proximal-to-S1 occlusion 2

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

When occlusion occurs between the first septal and first diagonal branches, the basal septum is spared and V1 shows no ST elevation. 1

Key features:

• ST elevation in aVL 1, 2
• ST depression in lead III 1
• No ST elevation in V1 1
• Abnormal Q-wave in aVL indicates occlusion proximal to D1 2

Distal LAD Occlusion (Below First Septal and First Diagonal)

Distal occlusion spares the basal left ventricle, directing the ST-segment vector more inferiorly. 1

Key features:

• No ST elevation in V1, aVR, or aVL 1
• No ST depression in II, III, or aVF 1
• May show ST elevation in II, III, and aVF due to inferior vector orientation 1
• Abnormal Q-waves in V4–6 predict distal-to-S1 occlusion 2
• ST depression in aVL suggests distal-to-D1 occlusion 2
• Absence of inferior ST depression predicts distal occlusion 2

Isolated Mid-Anterior Wall MI (First Diagonal Occlusion)

A rare pattern (1.7% of anterior MIs) shows ST elevation in non-consecutive leads aVL and V2, with two types of ST depression. 3

Key features:

• ST elevation with positive T-wave in aVL and V2 3
• "True reciprocal" ST depression with negative T-wave in III and aVF 3
• "Subendocardial ischemia" pattern (ST depression with positive T-wave) in V4–5 3
• ST in V3 is isoelectric or depressed 3
• Caused by first diagonal branch occlusion without LAD involvement 3

Additional Diagnostic Features

Reciprocal Changes

Reciprocal ST depression in inferior leads (II, III, aVF) strongly suggests proximal LAD occlusion and indicates higher-risk anatomy. 1, 2

• Inferior ST depression ≥1.0 mm strongly predicts proximal LAD occlusion 2
• Absence of inferior ST depression predicts distal occlusion 2

Right Ventricular Involvement

ST elevation in lead V3R (right-sided lead) correlates with ST elevation in V1 and indicates a small conal branch of the right coronary artery. 4

• ST elevation ≥1.5 mm in V1 is associated with ST elevation in V3R (92% sensitivity) 4
• Small conal branch (not reaching interventricular septum) present in 83% of cases with V1 elevation ≥1.5 mm 4
• Absence of V1 elevation suggests large conal branch providing double circulation to septum 4

Hyperacute T-Wave Changes

Tall, peaked (hyperacute) T-waves may appear in the very early phase of STEMI before ST elevation develops. 1

Q-Wave Evolution

The majority of anterior STEMI patients will evolve ECG evidence of Q-wave infarction. 1

High-Risk ECG Patterns Indicating Multivessel Disease

In Anterior Wall STEMI

The following algorithm predicts three-vessel disease with 88.4% sensitivity and 100% specificity: 5

1. ST elevation >4 mm in at least one precordial lead AND QRS interval >120 ms 5
2. THEN flat T-wave in aVR, OR aVL with flat T-wave/ST depression in lead I, OR Q-wave in all leads II, III, and aVF 5

Critical Pitfalls to Avoid

Do not assume that inferior ST elevation with anterior changes always represents "wrapped LAD"—it may indicate true anterior MI with atypical ECG patterns not explained by standard coronary anatomy. 6

New or presumably new left bundle branch block should not be considered diagnostic of acute MI in isolation, as most cases at presentation are "not known to be old" due to lack of prior ECG for comparison. 1

Baseline ECG abnormalities (paced rhythm, LV hypertrophy, Brugada syndrome) may obscure ST-segment interpretation and require transthoracic echocardiography to identify focal wall motion abnormalities. 1

A single ECG provides only a snapshot of a dynamic process—obtain serial ECG tracings to increase diagnostic accuracy and detect evolving changes. 1