Explain to me in detail from Braunwald and latest guidelines considering I a DrNB Cardiology Resident how to calculate and tell the origin of a VPC and the axis in a Ventricular Tachycardia from ECG only
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"ventricular tachycardia" AND "ECG localization" AND "site of origin"
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VPC VT ECG localization algorithm site of origin Braunwald 2024 guidelines
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"ventricular tachycardia" AND "12-lead ECG" AND "localization"
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VT VPC ECG localization site of origin axis LBBB RBBB outflow tract algorithm
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This is a comprehensive synthesis directly from Braunwald, Fuster/Hurst's The Heart (15th ed.), and Harrison's (22nd ed.) with the key diagrams fetched. Here's a quick orientation of what was covered:
What Was Covered
The 3-Plane Framework
Every VPC/VT is localized by three simultaneous ECG assessments:
- V1 (coronal plane) - LBBB = RV/septal origin; RBBB = LV origin
- Frontal axis (limb leads) - Inferior axis = superior exit (outflow/base); Superior axis = inferior wall exit
- Precordial transition (Z-plane) - Early (V1-V2) = posterior/basal; Late (V5-V6) = anterior/apical
Key Entities with ECG Signatures
| VT Type | V1 | Axis | Transition | Clue |
|---|---|---|---|---|
| RVOT | LBBB | Inferior | V3-V5 | Lead I for septal vs free wall |
| LVOT / Aortic cusp | LBBB but with r in V1, or RBBB | Inferior | V1-V3 (early) | V2 transition ratio ≥0.6; positive aVL |
| LCC | RBBB or transitional | Inferior | Early | III/II ratio >0.9 |
| Posterior fascicular (Belhassen) | RBBB | Left superior | Mid | QRS <140 ms; verapamil-sensitive |
| Bundle branch reentry | LBBB | Variable | Variable | Rapid, pre-existing LBBB, DCM |
| Ischemic scar VT | Variable | Depends on exit | Variable | Multiple morphologies, broad QRS |
| Papillary muscle | RBBB | Superior (posteromedial) or inferior right (anterolateral) | Mid | S waves V4-V6 for posteromedial |
The mnemonic that ties it all together: "Inferior axis = superior exit, Superior axis = inferior exit" - activation moves away from origin, so what you see is the opposite of where it starts.
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