Anterior Myocardial Infarction – ECG

1. Introduction

Anterior myocardial infarction (MI) is an infarction pattern involving the anterior and/or septal left ventricular territories. In the acute setting, anterior STEMI most commonly results from acute occlusion of the left anterior descending (LAD) coronary artery.

Recognition matters because the LAD supplies a substantial proportion of the left ventricle. A proximal occlusion may jeopardise a large myocardial territory, producing severe left ventricular dysfunction, acute heart failure, cardiogenic shock, and malignant ventricular arrhythmias. The supplied reference describes anterior MI as carrying a particularly poor prognosis compared with other infarct locations.

The ECG is a rapid, repeatable tool for identifying acute coronary occlusion and directing urgent reperfusion. Interpret it with the clinical presentation, previous tracings, serial ECGs, biomarkers, and haemodynamic status; do not use a single tracing in isolation.

Clinical framing: This page focuses on anterior STEMI and LAD-related ECG patterns. “Anterior”, “anteroseptal”, and “anterolateral” are practical ECG descriptors, not precise anatomical diagnoses.

2. Electrophysiology and Pathophysiology

Acute interruption of LAD flow causes regional myocardial ischaemia. Ischaemic cells develop altered resting membrane potentials and action-potential characteristics, creating injury currents between affected and relatively normal myocardium. These voltage gradients produce ST-segment deviation on the surface ECG.

Early ischaemia: regional T-wave prominence or hyperacute T waves may precede diagnostic ST elevation.
Acute injury pattern: ST elevation appears in leads facing the affected territory; reciprocal ST depression may appear in electrically opposite leads.
Evolution: persistent injury may be followed by loss of R-wave amplitude, development of pathological Q waves, and evolving T-wave inversion.
Electrical instability: ischaemic myocardium may support premature ventricular complexes, ventricular tachycardia, or ventricular fibrillation.

The distribution depends on the site of occlusion, coronary dominance and branching, collateral supply, and individual anatomy. Proximal LAD occlusion before major septal or diagonal branches generally places a larger myocardial territory at risk.

3. Characteristic ECG Features

Core pattern

ST-segment elevation in contiguous anterior precordial leads, commonly V1–V4 and often extending to V5–V6.
Hyperacute, broad-based T waves may be an early feature.
Reciprocal ST depression may occur in inferior leads, particularly III and aVF, especially when high-lateral leads I and aVL show ST elevation.
Progressive loss of R-wave amplitude and subsequent Q-wave formation may occur as infarction evolves.
ST elevation in I and aVL suggests extension into the high-lateral territory.

Rhythm, PR interval, QRS duration, axis, and QT interval should still be assessed, but they are not defining criteria for anterior STEMI. New bundle branch block or fascicular block may indicate extensive injury and complicate ST-segment interpretation.

Authentic 12-lead ECG showing hyperacute anteroseptal STEMI with ST elevation in V2 to V4 and high-lateral changes — **Example 1 — Hyperacute anteroseptal STEMI.** The source describes ST elevation and hyperacute T waves in V2–V4, ST elevation in I/aVL with reciprocal depression in III, and septal Q waves in V1–V2. Source: *Anterior Myocardial Infarction.pdf*, PDF page 3.

Common ECG distribution labels

Pattern label in the source	Leads with maximal ST elevation	Interpretive note
Septal	V1–V2	Septal-predominant pattern
Anterior	V2–V5	Anterior precordial pattern
Anteroseptal	V1–V4	Septal and anterior pattern
Anterolateral	V3–V6, I, aVL	Anterior with lateral extension
Extensive anterior / anterolateral	V1–V6, I, aVL	Broad precordial and high-lateral involvement

Nomenclature limitation: The supplied PDF explicitly cautions that ECG-based wall labels correlate imperfectly with precise infarct location on imaging or autopsy. Use these terms descriptively rather than assuming exact myocardial anatomy.

Evolution on serial ECGs

ECG showing hyperacute T waves in V2 to V6 and reduced R-wave height — **Example 2(a) — Hyperacute anterior STEMI.** Hyperacute T waves in V2–V6, most marked in V2–V3, with loss of R-wave height. The source also describes first-degree AV block, premature atrial complexes, and multifocal ventricular ectopy. Source: *Anterior Myocardial Infarction.pdf*, PDF page 4.

Follow-up ECG showing progressive anterior ST elevation and Q-wave formation — **Example 2(b) — Evolving anterior STEMI.** The same patient's ECG approximately 40–50 minutes later shows progressive ST elevation and Q-wave formation in V2–V5, with ST elevation also in I and aVL and reciprocal depression in III. Source: *Anterior Myocardial Infarction.pdf*, PDF page 4.

ECG showing extensive anterolateral STEMI with ST elevation in V2 to V6, I and aVL — **Example 3 — Extensive anterolateral STEMI.** ST elevation in V2–V6, I, and aVL with reciprocal ST depression in III and aVF. Source: *Anterior Myocardial Infarction.pdf*, PDF page 5.

ECG showing extensive anterior STEMI with ST elevation in V1 to V6 and I and aVL — **Example 4 — Extensive anterior STEMI.** ST elevation in V1–V6 and I/aVL, Q waves in V1–V2, and reduced R-wave height in V3–V4; the source also notes an R-on-T PVC. Source: *Anterior Myocardial Infarction.pdf*, PDF page 5.

4. Systematic ECG Interpretation

1

Confirm technical quality. Check patient identity, calibration, paper speed, lead placement, artefact, and baseline stability. Compare with a previous ECG when available.

2

Assess the clinical context. Look for ongoing chest discomfort or an ischaemic equivalent, diaphoresis, dyspnoea, syncope, or haemodynamic compromise.

3

Inspect anterior leads first, then the entire tracing. Assess J-point ST elevation in V1–V6 and look for hyperacute T waves, reciprocal inferior changes, and high-lateral involvement in I/aVL.

4

Look for evolution and infarct burden. Identify loss of R-wave progression, Q-wave formation, extensive ST elevation, and dynamic changes on serial ECGs.

5

Search for high-risk associated findings. Note RBBB, fascicular block, AV block, frequent or multifocal ventricular ectopy, ventricular tachycardia/fibrillation, and signs of shock.

6

Act on the working diagnosis. If the presentation and ECG indicate acute coronary occlusion, activate the local STEMI/reperfusion pathway. Do not delay reperfusion for troponin results or non-essential imaging.

Practical rule: A nondiagnostic first ECG does not exclude evolving occlusion. Repeat the ECG promptly when symptoms persist, recur, or the patient's condition changes.

5. Diagnostic Criteria and LAD Occlusion Clues

ST-elevation thresholds

In a patient with a compatible clinical presentation, new J-point ST elevation in at least two contiguous leads supports a STEMI working diagnosis when the following thresholds are met (in the absence of confounding LVH or LBBB patterns):

Lead group	ST-elevation threshold
Leads other than V2–V3	≥1 mm in at least two contiguous leads
V2–V3, men aged 40 years or older	≥2.0 mm
V2–V3, men younger than 40 years	≥2.5 mm
V2–V3, women (any age)	≥1.5 mm

Measure at the J point using a stable baseline and appropriate calibration. Thresholds support, but do not replace, clinical judgement. Acute coronary occlusion may occur without meeting conventional STEMI thresholds, particularly with subtle or evolving patterns.

Clues to the level of LAD occlusion

The supplied source discusses the first septal (S1) and first diagonal (D1) branches as landmarks. These ECG clues may suggest proximal disease and greater jeopardised myocardium, but they are not definitive angiographic localization criteria.

Schematic illustration of LAD coronary artery with first septal and diagonal branches — **LAD branch anatomy — schematic, not an angiogram.** The source illustrates the first septal (S1) and first diagonal (D1) branches. Source: *Anterior Myocardial Infarction.pdf*, PDF page 8. Original illustration attribution is to The Radiology Assistant as credited in the supplied PDF.

Possible level / territory	ECG clues described in the source	Clinical interpretation
Occlusion proximal to S1	ST elevation in aVR; ST elevation in V1 >2.5 mm; complete RBBB; ST depression in V5	Suggests basal septal involvement and a very proximal LAD lesion.
Occlusion proximal to D1	ST elevation or Q-wave formation in I and aVL; reciprocal ST depression ≥1 mm in II, III, or aVF	Suggests high-lateral involvement.

The source reports that aVR ST elevation in anterior STEMI was 43% sensitive and 95% specific for LAD occlusion proximal to S1 in the cited study context. This is a source-specific estimate, not a stand-alone diagnostic test; predictive value depends on population and clinical context.

ECG example of very proximal LAD occlusion with septal STEMI, RBBB and left anterior fascicular block — **Example 8 — Very proximal LAD occlusion pattern.** The PDF describes septal STEMI maximal in V1–V2, new bifascicular block (RBBB plus LAFB), marked V1 ST elevation, and aVR elevation. The accompanying narrative reports angiographic ostial LAD occlusion. Source: *Anterior Myocardial Infarction.pdf*, PDF page 9.

ECG showing acute anteroseptal STEMI with RBBB, aVR and aVL ST elevation and inferior ST depression — **Example 9 — Acute anteroseptal STEMI with proximal LAD clues.** The source lists RBBB, ST elevation in aVR and aVL, and more than 1 mm ST depression in inferior leads. Source: *Anterior Myocardial Infarction.pdf*, PDF page 10.

6. Differential Diagnosis

Differential	Potential overlap	Features that help distinguish it
Early repolarization	Precordial J-point/ST elevation	Often stable on prior ECGs, commonly concave ST elevation with J-point notching/slurring; clinical context and dynamic change are essential.
Acute pericarditis / myopericarditis	ST elevation and T-wave changes	Often widespread rather than confined to an LAD distribution; PR depression may occur. Reciprocal changes are generally limited (e.g. aVR/V1), but exceptions exist.
LV aneurysm after prior MI	Persistent anterior ST elevation with Q waves	Prior infarction, stable persistent ST elevation and unchanged serial tracings support chronicity; compare old ECGs and assess clinically. Do not assume chronicity in a symptomatic patient.
Brugada pattern	ST elevation in V1–V3	Coved or saddleback morphology in right precordial leads, often with characteristic terminal T-wave changes; evaluate in the context of syncope, fever, and family history.
Takotsubo syndrome	ST elevation, T-wave inversion, QT prolongation	Can mimic ACS; diagnosis requires clinical assessment and imaging/coronary evaluation. Do not use ECG appearance alone to exclude coronary occlusion.
LVH / conduction abnormality	Secondary ST-T changes	Voltage criteria, discordant repolarization, LBBB or paced rhythm may obscure standard STEMI thresholds. Apply appropriate criteria and integrate symptoms and prior ECGs.

Do not over-rely on morphology. No single ECG feature reliably excludes acute coronary occlusion. When the clinical picture is concerning, seek expert review, obtain serial ECGs, and proceed with appropriate ACS evaluation.

7. Clinical Significance and Complications

Anterior STEMI can involve a large proportion of the left ventricular myocardium. The supplied reference cites higher rates of in-hospital mortality, total mortality, heart failure, ventricular ectopy, and lower admission ejection fraction in anterior compared with inferior MI in the study it discusses. These historical cohort figures should not be interpreted as an individualized contemporary risk estimate.

LV systolic dysfunctionLarge infarct burden may cause acute pulmonary oedema and persistent reduced ejection fraction.

Cardiogenic shockParticularly concerning with extensive or very proximal LAD occlusion.

Ventricular arrhythmiasFrequent/multiform PVCs, R-on-T phenomenon, VT, or VF may accompany acute ischaemia.

Conduction disturbancesNew RBBB, fascicular block, or AV block may signal extensive septal injury.

Red flags requiring urgent escalation

Persistent or recurrent ischaemic symptoms with evolving anterior ST changes.
Extensive ST elevation across V1–V6 and I/aVL, especially with hypotension or signs of poor perfusion.
New RBBB or bifascicular block in a compatible acute ischaemic presentation.
Frequent ventricular ectopy, R-on-T beats, sustained VT, VF, or resuscitated cardiac arrest.
Acute pulmonary oedema, cardiogenic shock, syncope, or rapidly deteriorating haemodynamics.

ECG with massive tombstone-shaped ST elevation throughout precordial and high lateral leads — **Example 6 — Extensive anterior MI with tombstone morphology.** Massive ST elevation across V1–V6 and I/aVL is described in the PDF as a pattern associated with a large territory infarction and high risk of LV dysfunction and shock. Source: *Anterior Myocardial Infarction.pdf*, PDF page 7.

8. Clinical Evaluation and Management Principles

Management is determined by the working diagnosis of ACS, symptom timing, haemodynamic status, contraindications, and local reperfusion pathways. ECG recognition should trigger urgent action rather than delay for completion of every investigation.

Immediate assessment: ABCs, vital signs, oxygen saturation, focused history, physical examination, 12-lead ECG, and prompt clinician interpretation (goal within 10 minutes of first medical contact).
Activate the STEMI pathway: arrange immediate transfer to a PCI-capable centre and primary PCI when indicated. If timely primary PCI cannot be achieved, assess eligibility for fibrinolysis according to current guidelines and local protocols.
Monitoring and access: continuous ECG/rhythm monitoring, defibrillation capability, intravenous access, and prompt treatment of life-threatening arrhythmias or shock.
Laboratory evaluation: obtain high-sensitivity cardiac troponin and other baseline tests, but do not delay reperfusion in a patient with a convincing STEMI presentation.
Assess LV function and complications: echocardiography is useful for LV function, regional wall-motion abnormalities, shock, and suspected mechanical complications, provided it does not delay reperfusion.
After reperfusion: continue monitored care, assess complications and LV function, and institute guideline-directed secondary prevention and rehabilitation.

Time-critical point: In a patient with a convincing STEMI ECG and compatible presentation, reperfusion is urgent. Biomarker confirmation, routine echocardiography, or additional imaging should not postpone emergency reperfusion unless a specific alternative diagnosis or immediate management decision requires it.

Current guidelines recommend ECG acquisition and interpretation within 10 minutes, serial ECGs when the first tracing is nondiagnostic and suspicion remains high, and prompt reperfusion triage for STEMI. For patients with STEMI, primary PCI is preferred; fibrinolysis is considered when timely PCI cannot be delivered and the patient is eligible.

9. Common Interpretation Pitfalls

Waiting for Q waves: Q waves are not required for acute STEMI; hyperacute T waves and early ST changes may be the first clues.
Missing dynamic change: a single early ECG may be subtle or nondiagnostic. Repeat it when symptoms persist or evolve.
Over-interpreting reciprocal changes: inferior ST depression may be small or absent, particularly without high-lateral involvement.
Assuming lead labels define anatomy: ECG wall nomenclature does not map perfectly to imaging-defined myocardial segments.
Assuming aVR elevation proves proximal LAD occlusion: aVR is a contextual clue, not a definitive culprit-vessel locator.
Calling persistent ST elevation a new STEMI without comparison: prior MI with LV aneurysm morphology can produce persistent elevation; however, new symptoms require urgent reassessment.
Ignoring conduction and rhythm findings: new RBBB, bifascicular block, AV block, or ventricular ectopy may indicate extensive ischaemia and increased risk.
Using troponin as a gatekeeper: do not wait for a positive troponin when the ECG and clinical presentation establish a STEMI working diagnosis.

10. ECG Pearls

Hyperacute T waves may precede obvious ST elevation.
Look across V1–V6 and I/aVL rather than focusing on one precordial lead.
Inferior reciprocal depression supports an anterior/high-lateral injury pattern but is not obligatory.
Progressive ST elevation, R-wave loss, and Q-wave formation on serial ECGs suggest an evolving infarction.
ST elevation in aVR, marked V1 elevation, and new RBBB may raise concern for very proximal LAD involvement in the appropriate context.
Simultaneous anterior and inferior ST elevation may occur with a wraparound LAD.
Persistent anterior ST elevation with established Q waves may represent prior infarction with LV aneurysm; compare with prior tracings and assess symptoms.

ECG showing anterior and inferior ST elevation with hyperacute T waves and forming Q waves — **Example 7 — Anterior–inferior STEMI pattern.** The source describes ST elevation in precordial and inferior leads, hyperacute T waves in V1–V3, and Q waves forming in V1–V3, III, and aVF, suggesting a wraparound LAD pattern. Source: *Anterior Myocardial Infarction.pdf*, PDF page 7.

ECG of prior anteroseptal and lateral myocardial infarction with deep Q waves and residual ST elevation — **Example 5 — Prior anteroseptal/lateral MI.** Deep Q waves in V1–V3, reduced R-wave height, residual ST elevation in V1–V3, and T-wave abnormalities are described as a prior infarction pattern with possible LV aneurysm morphology. Source: *Anterior Myocardial Infarction.pdf*, PDF page 6.

11. Quick Reference

Question	Key point
Most common culprit artery?	Left anterior descending (LAD) coronary artery.
Typical acute leads?	V1–V4, often extending to V5–V6 and I/aVL.
Early clue?	Hyperacute T waves may precede diagnostic ST elevation.
Reciprocal changes?	Inferior ST depression, often III/aVF; may be absent.
Evolution?	Progressive ST elevation, R-wave loss, Q-wave formation, later T-wave inversion.
Proximal LAD clues?	aVR/V1 elevation, RBBB, and high-lateral involvement may be suggestive but are not definitive.
Major complications?	LV dysfunction, acute heart failure, cardiogenic shock, VT/VF, and conduction disturbances.
Immediate priority?	Urgent STEMI pathway activation and reperfusion assessment.

12. References

1. Rao SV, et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes.Circulation. 2025. doi: 10.1161/CIR.0000000000001309. Current US guideline covering ECG assessment and ACS management.

2. Byrne RA, et al. 2023 ESC Guidelines for the management of acute coronary syndromes.European Heart Journal. 2023;44(38):3720–3826. doi: 10.1093/eurheartj/ehad191.

3. Thygesen K, et al. Fourth Universal Definition of Myocardial Infarction (2018).Journal of the American College of Cardiology. 2018;72(18):2231–2264. doi: 10.1016/j.jacc.2018.08.1038.

4. Burns E, Buttner R. Anterior Myocardial Infarction.LITFL ECG Library Diagnosis. Published August 1, 2020. Supplied source PDF; includes ECG examples and cited literature. Images reproduced here from the supplied PDF with source and page attribution.

5. Arbane M, Goy JJ. Prediction of the site of total occlusion in the left anterior descending coronary artery using admission electrocardiogram in anterior wall acute myocardial infarction.American Journal of Cardiology. 2000;85(4):487–491, A10. PMID: 10728956. Reference listed in the supplied PDF.

6. Engelen DJ, et al. Value of the electrocardiogram in localizing the occlusion site in the left anterior descending coronary artery in acute anterior myocardial infarction.Journal of the American College of Cardiology. 1999;34(2):389–395. Reference listed in the supplied PDF.

7. Bayés de Luna A, et al. A new terminology for left ventricular walls and location of myocardial infarcts that present Q wave based on the standard of cardiac magnetic resonance imaging.Circulation. 2006;114(16):1755–1760. Reference listed in the supplied PDF.