12-Lead Territories and Localisation
Lead territories help you localise where ECG changes are occurring by grouping leads that view similar areas of myocardium. The most reliable patterns involve contiguous leads showing consistent changes.
Quick Jump
Localise fastKey Concepts
Contiguous leads- Contiguous leads are leads that look at neighbouring regions of the heart (same “territory”).
- Localisation is strongest when changes occur in two or more contiguous leads.
- Always interpret localisation alongside rhythm, QRS morphology, and clinical context.
Territory Map (Quick Reference)
Lead groups| Territory | Primary Leads | Notes |
|---|---|---|
| Inferior | II, III, aVF | Looks at the inferior wall. Patterns here are often assessed alongside potential reciprocal changes in I/aVL. |
| High lateral | I, aVL | “High lateral” view in the frontal plane. Often considered with lateral chest leads (V5–V6). |
| Lateral | V5, V6 (± I, aVL) | Lateral wall in the horizontal plane. Changes may overlap with high lateral territory. |
| Septal | V1, V2 | Septal region. Also where right-sided conduction patterns (e.g., RBBB features) may be prominent. |
| Anterior | V3, V4 | Anterior wall. Often assessed together with septal (V1–V2) and lateral (V5–V6) for broader patterns. |
| Anterolateral | V3–V6 (± I, aVL) | Combined pattern across anterior and lateral leads. |
Reciprocal Changes
Opposing leadsReciprocal changes are “opposing” ECG changes seen in leads viewing the electrically opposite region of the heart. They can support localisation when a consistent pattern is present.
- Inferior patterns may show reciprocal changes in I / aVL.
- Lateral patterns may show reciprocal changes in II / III / aVF.
- Anterior patterns may show reciprocal changes as changes in inferior leads (pattern-dependent).
“Contiguous” Doesn’t Mean “Adjacent on Paper”
Same viewpointLeads are grouped by what they “look at,” not where they are printed. For example, II, III, and aVF are contiguous because they share an inferior viewpoint, even though their placement on the ECG printout depends on the machine format.
Posterior Involvement
Consider V7–V9Posterior changes may not be directly visible on a standard 12-lead because there are no posterior chest leads by default. Posterior involvement is often assessed using:
- Clues in V1–V3 (e.g., mirror-image patterns depending on context).
- Posterior leads V7–V9 when indicated for clarification.
Right Ventricular Involvement
Consider V4RStandard precordial leads are placed on the left chest. If right ventricular involvement is suspected in the right context, right-sided leads can be recorded:
- V4R is commonly used as a quick right-sided lead.
- Additional right-sided leads may be recorded depending on need and workflow.
Practical Localisation Checklist
5-step summary- Identify the abnormality (ST/T/QRS/Q waves) and confirm it’s real (artefact/lead placement).
- Find the lead group(s) with the clearest changes.
- Confirm the pattern appears in contiguous leads.
- Look for supportive “opposing” patterns (reciprocal changes) when appropriate.
- Summarise localisation: inferior / lateral / septal / anterior (or combination).