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ECG Localization of VPC/VT Origin: A DrNB Cardiology Reference

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The Core Principle: 3 Spatial Planes on the 12-Lead ECG

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Step 1 - Determine the Bundle Branch Block Pattern (V1)

LBBB Pattern in VPC/VT (rS or QS in V1)

• The left ventricle activates late → depolarization travelling from right to left
• Origin is in the RV, septum (right side), or RVOT
• The classic example: RVOT VT - LBBB + inferior axis

RBBB Pattern in VPC/VT (rsR', qR, or dominant R in V1)

• The right ventricle activates late → origin in the LV free wall or LV outflow tract
• Classic: Idiopathic LV fascicular VT (Belhassen/verapamil-sensitive) - RBBB + left superior axis

"Arrhythmias that originate from the right ventricle or septum result in late activation of much of the left ventricle, thereby producing a prominent S wave in V1 referred to as a left bundle branch block-like configuration. Arrhythmias that originate from the free wall of the left ventricle have a prominent positive deflection in V1, thereby producing a right bundle branch block-like morphology in V1."

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Step 2 - Determine the Frontal Axis (Limb Leads)

Inferior Axis (positive R in II, III, aVF)

• Initial activation of the cranial/superior portion of the ventricle
• Exit site is basal or outflow tract (apical activation happens last → inferior forces)
• LBBB + inferior axis = RVOT origin (classic)

Superior Axis (negative in II, III, aVF; S or QS in aVF)

• Initial activation of the inferior wall
• Exit site is the inferior, apical, or diaphragmatic surface
• RBBB + superior axis = LV posterior fascicle / posteroinferior wall (Belhassen VT)

Right Superior Axis (negative I, II, III, aVF)

• Exit from RV anterior free wall or apical septum
• Seen in ischemic VT from anterior MI (RBBB + right superior axis)

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Step 3 - Determine the Precordial Transition (Z-plane / Basal-to-Apical)

• Transition V3 or earlier → raises strong suspicion for LVOT, aortic sinus cusp, or left-sided origin (despite LBBB appearance)
• Transition V4-V6 → RVOT (right-sided)
• The V2 transition ratio (Betensky criterion): If V2-transition ratio ≥0.6 → LVOT origin (86% specificity)

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The 3-Dimensional Framework Applied to Specific Origins

A. RVOT (Right Ventricular Outflow Tract) VT/PVC

• LBBB morphology in V1
• Inferior axis (tall R in II, III, aVF)
• Late precordial transition (V3-V5)
• Tall, monophasic R waves in inferior leads
• Predominantly negative or isoelectric in aVL
• Lead I: positive (free wall) or negative/isoelectric (septal origin)

"Outflow origin PVCs and VT have a characteristic pattern on the 12-lead ECG, with an LBBB morphology and inferior axis." - Fuster & Hurst (15th ed.)

• Septal RVOT: isoelectric or negative lead I, narrower QRS, earlier transition
• Free wall RVOT: positive lead I, broader QRS

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B. LVOT / Aortic Sinus Cusp VTs

• RBBB-like or transitional in V1 (dominant R)
• Inferior axis
• Negative aVL (R-wave in aVL rules out LCC, RCC, or junction origin)

• R-wave amplitude ratio III/II > 0.9 → LCC
• R-wave amplitude ratio III/II ≤ 0.9 → RCC

• Deeper S in aVL, later transition than LCC/RCC

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C. LV Fascicular (Verapamil-Sensitive / Belhassen) VT

• RBBB pattern in V1 (dominant R or rsR')
• Left superior axis (negative in II, III, aVF; left axis deviation)
• Relatively narrow QRS (<140 ms) - reflects near-normal conduction via Purkinje system
• QRS often <120 ms in the posterior fascicular form
• Sensitive to IV verapamil (terminates the tachycardia)
• Inducible by atrial pacing
• Occurs in young adults with structurally normal hearts

"Left fascicular reentrant tachycardia...the most common form involves the LV posterior fascicle giving rise to an RBBB-like tachycardia with a superior left axis." - Braunwald (block7, line 3028)

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D. Bundle Branch Reentry VT (BBR-VT)

• LBBB morphology (most common): circuit goes anterograde down RBB, retrograde up LBB
• RBBB morphology (rare reverse circuit)
• Often rapid (>200 bpm)
• Often occurs in patients with pre-existing LBBB or interventricular conduction delay during sinus rhythm
• Associated with severe LV dysfunction (DCM, ischemic CMP)
• Ablation of the RBB is curative

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E. Ischemic/Scar-Related VT (CAD)

"In almost all patients who have VT associated with ischemic heart disease, the arrhythmia, regardless of its configuration on the surface ECG, arises in the left ventricle or on the left ventricular side of the interventricular septum."

• Exit from the septum (LV side)
• Superior axis → basal or mid-septal location
• Inferior axis → mid-septal location
• Anterior MI: LBBB VTs from apical septum; inferior axis → anterior wall, superior axis → inferior wall

• Exit from the lateral or free wall (away from septum)
• Positive lead I + superior axis → mid-posterior location
• Negative lead I + superior axis → apical-posterior location
• Inferior axis + RBBB → anterior wall; Lead I positive → basal; Lead I negative → mid-anterior

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F. Inferior Wall / Diaphragmatic VT (RBBB + Superior Axis)

• RBBB + extreme left axis (negative II, III, aVF) → inferior LV
• Inferior MI-related VTs often RBBB with right superior axis (antero-apical septum)

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G. Papillary Muscle VTs

• Posteromedial papillary muscle: RBBB + superior axis + S waves V4-V6
• Anterolateral papillary muscle: RBBB + inferior rightward axis
• Often associated with mitral valve prolapse; may trigger VF

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Summary Algorithm: Step-by-Step Approach

Step 1: Is V1 → LBBB or RBBB?
  ├── LBBB → RV, septum, or RVOT
  │     Step 2: Axis in inferior leads (II, III, aVF)?
  │       ├── INFERIOR axis → RVOT / basal outflow tract origin
  │       │     Step 3: Lead I & transition?
  │       │       ├── Transition V4+ , Lead I –  → Septal RVOT
  │       │       ├── Transition V4+ , Lead I +  → Free wall RVOT
  │       │       └── Early transition V1-V3, R in V1 → LVOT / Aortic cusp
  │       └── SUPERIOR axis → Inferior LV, inferior septum, apical
  │
  └── RBBB → LV free wall or LVOT
        Step 2: Axis?
          ├── LEFT SUPERIOR axis, narrow QRS → Posterior fascicle (Belhassen VT)
          ├── LEFT SUPERIOR axis, broad QRS → Posteroinferior LV free wall
          ├── INFERIOR axis → Anterior LV or anterolateral wall
          └── RIGHT SUPERIOR axis → Antero-apical septum (ischemic)

Step 3: Precordial transition zone
  ├── Early (V1-V2) → Posterior/basal LV, aortic cusp
  ├── V3-V4 → Midventricular
  └── Late/absent → Anterior/apical

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Special ECG Clues at a Glance

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Notes on Axis Calculation

• Inferior axis (0° to +90°): dominant R in II, III, aVF → origin is superior (outflow tracts, base)
• Superior/left axis (-30° to -90°): S wave dominant in II, III, aVF → origin is inferior wall, apex, or fascicles
• Extreme axis ("northwest axis," +180° to -90°): negative in all inferior leads AND negative lead I → apex, anterior septum, or ischemic scar
• Right axis (>+90°): left lateral LV origin or anterolateral scar

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2022 ESC Guideline Context

• RVOT VT: LBBB + inferior axis → catheter ablation Class I recommendation as first-line for symptomatic patients
• Left fascicular VT: RBBB + superior axis → catheter ablation Class I recommendation
• Non-RVOT, non-fascicular idiopathic VTs: Consider CMR even with normal echo given the importance of identifying substrate

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Sources

• Braunwald's Heart Disease (Zipes et al.), Ch. 64 & 67 - Ventricular Tachycardia, Location and Ablation
• Fuster & Hurst's The Heart, 15th ed., Ch. 37 - Ventricular Tachycardia in Structural Heart Disease; Outflow Tract VT; Fascicular VT; Fig. 37-8
• Harrison's Principles of Internal Medicine, 22nd ed., Ch. 259 - Fig. 259-4, site of VT origin based on QRS morphology
• 2022 ESC Guidelines for Management of Ventricular Arrhythmias (Zeppenfeld et al.)
• Josephson ME & Callans DJ: "Using the 12-lead ECG to localize the site of origin of ventricular tachycardia" (referenced in Hurst's)
• Betensky et al. JACC 2011;57:2255 - V2 transition ratio for RVOT vs LVOT discriminationThis 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:

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What Was Covered

The 3-Plane Framework

1. V1 (coronal plane) - LBBB = RV/septal origin; RBBB = LV origin
2. Frontal axis (limb leads) - Inferior axis = superior exit (outflow/base); Superior axis = inferior wall exit
3. Precordial transition (Z-plane) - Early (V1-V2) = posterior/basal; Late (V5-V6) = anterior/apical

Key Entities with ECG Signatures