Waveform Studio · methodology note

Mapping ECG leads to myocardial territories

Rationale and sources for the lead-to-territory scheme used by the EKGLab Waveform Studio and the 12-lead ST identification quiz.

Waveform Studio renders each simulated infarct under a named territory (septal, anterior, anteroseptal, lateral, inferior, anterolateral, inferobasal), and the 12-lead ST quiz assigns the same names to real tracings. No single consensus document publishes a definitive lead-to-territory table; the scheme below is a synthesis grounded in standard electrode anatomy, the AHA/ACCF/HRS electrocardiogram-standardization statements, the Fourth Universal Definition of Myocardial Infarction, and the cardiac-magnetic-resonance reclassification of infarct location. This note documents each choice and is explicit about where the literature is unsettled.

Why there is no single standardized table

The AHA/ACCF/HRS standardization series divides the material. Part II is a controlled vocabulary of diagnostic statements (Anterior MI, Anteroseptal MI, Inferior MI, Lateral MI, Posterior MI) with no lead criteria.² Part VI supplies the ST-segment thresholds and culprit-vessel correlation but no named-territory table, and it explicitly cautions that the changes in a given lead need not localize to the region beneath that electrode.³ The Universal Definition specifies ST thresholds and Q-wave criteria, not a territory chart.⁴ The empirical lead-to-anatomy correlation was not rigorously established until cardiac MRI, which then revised several inherited names.⁵ The familiar bedside table is therefore a teaching synthesis, not a primary-document standard.

The scheme used in EKGLab

Across the anterior precordium the territories are defined so that no two share a lead: septal = V1–V2 only, anterior = V3–V4 only, anteroseptal = both. Waveform Studio builds each scenario from these lead groups and the quiz classifies real tracings by the same groups, so the boundaries are identical in both tools.

Anatomic basis

The standardized precordial electrode positions place V1 and V2 over the interventricular septum, V3 and V4 over the anterior wall and apex, and V5 and V6 over the low lateral wall; leads I and aVL view the high lateral wall.¹ This lead-to-wall correspondence is standard electrocardiographic anatomy: the wall names follow the AHA 17-segment model,⁶ and correlation of ECG patterns with cardiac MRI supports separating septal from anterior or apical involvement.⁵

Concordance with the foundational statements

• Names. Most EKGLab territories map directly to a Part II statement: Anterior (160), Anteroseptal (165), Inferior (161), Lateral (163), and Posterior (162), the last retained by Part VI.^2,3 Inferior + RV pairs the inferior statement with Right ventricular MI (174), and Part II also carries Extensive anterior MI (166) and MI in the presence of LBBB (173). Two EKGLab labels have no dedicated Part II statement: septal (discussed below) and anterolateral (a composite of the anterior and lateral statements; Section M runs 160 to 163, 165, 166, 173 and 174, with no anterolateral entry).
• Thresholds. The quiz classifies a tracing’s ST elevation by the Part VI and Universal-Definition sex- and age-stratified J-point values: ≥0.2 mV in men ≥40, ≥0.25 mV in men <40, and ≥0.15 mV in women, in V2–V3; ≥0.1 mV in the other leads.^3,4
• Inferobasal. Part VI Recommendation 1 retained the term posterior for the V1–V3 ST-depression and tall-R pattern; the 2018 Universal Definition relabelled the wall inferobasal myocardial ischemia (previously termed posterior infarction) while still calling V7–V9 the posterior leads. EKGLab uses “inferobasal (posterior)” to carry the current term and the retained one.^3,4

Deliberate choices, stated plainly

Two further points of honesty: EKGLab groups I and aVL as high-lateral, whereas cardiac-MRI work shows first-diagonal occlusion can produce a “mid-anterior” pattern in aVL; the high-lateral grouping is the standard teaching simplification.⁵ And the posterior-to-inferobasal rename remains contested, with both terms in active clinical use; EKGLab leads with the 2018 term and preserves the older one.^3,4

Summary

The EKGLab lead-to-territory scheme rests on standard precordial anatomy, uses the diagnostic vocabulary of the AHA/ACCF/HRS statements and the ST criteria of the Universal Definition, is consistent with the cardiac-MRI reclassification of infarct location, and is applied by the same rule in the Waveform Studio and the ST quiz. Its two deliberate departures, a septal localization label and a non-overlapping partition, are stated openly above. No element contradicts a primary source; where the sources are silent or unsettled, the choices follow standard localization teaching.

References