Localizing Ventricular Tachycardia: Simplified ECG Approach

Localizing the origin of Ventricular Tachycardia from a 12-lead ECG is a critical skill for planning ablation and identifying the underlying pathology. While many algorithms exist, a stepwise simplified approach focusing on the “Four Directions” of the heart is often the most practical. To find where the VT is coming from, think of the heart as a 3D box. You use different ECG leads to check Left vs. Right, Superior vs. Inferior, and Base vs. Apex.

Step 1: Left vs. Right (Lead V1)

This is based on the Bundle Branch Block (BBB) morphology.

• LBBB Pattern (Negative V1): Origin is likely the Right Ventricle or the Interventricular Septum.
• RBBB Pattern (Positive V1): Origin is likely the Left Ventricle.

Step 2: Superior vs. Inferior (Frontal Axis – Leads II, III, aVF)

• Inferior Axis (Positive in II, III, aVF): The impulse travels downward, so the origin is Superior (e.g., Outflow Tracts).
• Superior Axis (Negative in II, III, aVF): The impulse travels upward, so the origin is Inferior (e.g., the Diaphragmatic wall).

Step 3: Base vs. Apex (Precordial Transition)

Look at where the QRS flips from mostly negative to mostly positive (the transition lead).

• Early Transition (V1–V2): Origin is Basal (posterior part of the heart).
• Late Transition (V4–V6): Origin is Apical (near the tip of the heart).

Step 4: Septum vs. Free Wall (QRS Width & Lead I)

• Septal Origin: Often has a narrower QRS because it accesses the conduction system faster.
• Free Wall Origin: Often has a wider QRS (>160ms) and specific polarity in Lead I (Positive I = Septal; Negative I = Lateral/Free Wall).

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