Waveform Studio · methodology note
Mapping ECG leads to myocardial territories
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
| Territory | Leads | Anatomic basis |
|---|---|---|
| Septal | V1, V2 | overlie the interventricular septum |
| Anterior | V3, V4 | anterior wall and apex |
| Anteroseptal | V1–V4 | septum and anterior wall together (proximal LAD) |
| Lateral | I, aVL, V5, V6 | high (I, aVL) and low (V5, V6) lateral wall |
| Inferior | II, III, aVF | inferior wall |
| Inferobasal (posterior) | V1–V3 (± V4), reciprocal | mirror of the inferobasal wall; confirm with V7–V9 |
| Anterolateral | V3–V6, I, aVL | extensive anterior plus lateral |
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
A standalone “septal” label. Part II lists Anteroseptal MI but no separate Septal MI, so isolated V1–V2 involvement would fall under the anteroseptal statement. EKGLab keeps a septal localization label because V1 and V2 overlie the septum and the distinction is standard teaching. It is a localization label, not a claim of a distinct Part II statement.2
Non-overlapping territories. Many bedside charts define anterior as V1–V4 and anteroseptal as V1–V3, so the two share leads V1–V3, and a tracing with ST elevation there fits both labels. EKGLab defines the territories so no two share a lead (septal V1–V2 only, anterior V3–V4 only, anteroseptal both), which gives a single answer per tracing. This matters for the quiz, which needs one correct territory to score a student’s response; a clinician at the bedside resolves the same overlap with judgment.
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
- Kligfield P, Gettes LS, Bailey JJ, et al. Recommendations for the standardization and interpretation of the electrocardiogram: Part I: The electrocardiogram and its technology. Circulation. 2007;115(10):1306–1324.
- Mason JW, Hancock EW, Gettes LS, et al. Recommendations for the standardization and interpretation of the electrocardiogram: Part II: Electrocardiography diagnostic statement list. Circulation. 2007;115(10):1325–1332.
- Wagner GS, Macfarlane P, Wellens H, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: Part VI: Acute ischemia/infarction. Circulation. 2009;119(10):e262–e270.
- Thygesen K, Alpert JS, Jaffe AS, et al. Fourth Universal Definition of Myocardial Infarction (2018). Circulation. 2018;138(20):e618–e651.
- Bayés de Luna A, Wagner G, Birnbaum Y, 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.
- Cerqueira MD, Weissman NJ, Dilsizian V, et al. Standardized myocardial segmentation and nomenclature for tomographic imaging of the heart. Circulation. 2002;105(4):539–542.