What are the electrocardiographic criteria for left ventricular outflow tract ventricular tachycardia?

ECG Criteria for Left Ventricular Outflow Tract Ventricular Tachycardia

LVOT ventricular tachycardia typically demonstrates an inferior axis with early precordial transition at V1/V2 and either left bundle branch block (70% of cases) or right bundle branch block (30% of cases) morphology. 1

Key Distinguishing Features

Primary Morphologic Criteria

The hallmark ECG pattern for LVOT-VT includes:

• QRS morphology: Left bundle branch block pattern (most common) or right bundle branch block pattern
• QRS axis: Inferior axis (positive in leads II, III, aVF)
• Precordial transition: Early R/S transition occurring at V1 or V2 1

This early transition is the critical distinguishing feature from RVOT tachycardia, which shows a later transition at V4 1.

Quantitative ECG Algorithms for LVOT vs RVOT Differentiation

When distinguishing LVOT from RVOT origins, several validated algorithms exist:

V2S/V3R Index (highest accuracy):

• Calculate: S-wave amplitude in V2 ÷ R-wave amplitude in V3
• V2S/V3R ≤ 1.5 predicts LVOT origin with 89% sensitivity and 94% specificity 2
• This outperforms other criteria, particularly when precordial transition occurs at V3

V2 Transition Ratio (useful for V3 transition cases):

• Calculate: [(R/R+S) during VT ÷ (R/R+S) during sinus rhythm] in lead V2
• V2 transition ratio ≥ 0.60 predicts LVOT origin with 91% accuracy 3
• A PVC transition occurring later than sinus rhythm transition excludes LVOT origin with 100% accuracy

Combined Diagnostic Model:

• Formula: Y = -1.15 × (transition zone index) - 0.494 × (V2S/V3R)
• Y ≥ -0.76 predicts LVOT origin with 82% sensitivity and 86% specificity 4

Specific LVOT Subsites

Aortic Cusp Origin (20% of outflow tract VTs)

• Broad QRS with early transition at V1-V2 1
• Most commonly from left coronary cusp, followed by right coronary cusp
• Cannot be reliably distinguished from other LVOT sites by surface ECG alone—requires electrophysiologic mapping 1

Four-Step Algorithm for LVOT Subsite Localization

A recent algorithm differentiates specific LVOT origins 5:

1. QS duration in aVL > 134 ms: Distinguishes aortomitral continuity/LV summit from aortic root (80% sensitivity, 76% specificity)
2. R duration in lead II > 155 ms: Differentiates LV summit from aortomitral continuity (67% sensitivity, 56% specificity)
3. Ratio of III/II < 0.9: Discriminates right coronary cusp from left coronary cusp/junction (82% sensitivity, 63% specificity)
4. QS duration in aVR > 130 ms: Distinguishes left coronary cusp from left-right coronary cusp junction (75% sensitivity, 62% specificity)

Critical Clinical Context

Important caveat: The 2015 ESC Guidelines emphasize that "the close anatomical proximity of the RVOT, LVOT and great cardiac veins limits precise localization of the VT origin based on QRS morphology except for classic RVOT tachycardia." 1 Therefore, while these ECG criteria guide initial assessment, precise localization requires activation mapping and/or pace-mapping during electrophysiology study 1.

Differential Diagnosis Warning

LBBB morphology ventricular arrhythmias with an inferior axis (R wave positive in II and III, negative in aVL) require careful differentiation from benign RVOT tachycardia, which is not familial and rarely life-threatening 6. Conversely, LBBB morphology with superior axis is typical of arrhythmogenic right ventricular cardiomyopathy and warrants different evaluation 6.

Clinical Presentation

LVOT arrhythmias clinically differ from RVOT:

• Longer cycle lengths compared to RVOT-VT 1
• Less likely to cause syncope than RVOT-VT 1
• May be incessant and provoked by exercise 7
• More common in men, typically presenting in third to fifth decades 7