ECG Criteria for RVOT Ventricular Tachycardia
RVOT VT characteristically demonstrates a left bundle branch block (LBBB) pattern with inferior axis, tall R waves in inferior leads (II, III, aVF), and a later R/S transition (typically at V3-V4) compared to left-sided outflow tract origins 1.
Core Diagnostic Features
QRS Morphology
- LBBB pattern with inferior axis (positive QRS in leads II, III, aVF)
- QRS duration: Typically 140-145 ms or less for superior RVOT origins 2
- Broader QRS (>145 ms) suggests inferior RVOT location 2
Precordial Lead Characteristics
Lead V1-V2 Analysis:
- R wave amplitude in V2 ≤30% of total QRS amplitude is highly predictive of RVOT origin (95% positive predictive value, 100% negative predictive value) 3
- Predominantly negative QRS complex in V1
- Small or absent R waves in V1-V2
Precordial Transition:
- R/S transition typically occurs at V3 or V4 (later than LVOT origins which transition at V1-V2) 1
- Earlier transition (V1-V2) with LBBB pattern suggests LVOT or aortic cusp origin instead
Limb Lead Features
- Tall R waves in inferior leads (II, III, aVF)
- For inferior RVOT origins specifically: R wave amplitude in lead II <1.35 mV, lead III <1.35 mV, and aVF <1.15 mV 2
- Superior RVOT origins typically have taller R waves in these leads
Advanced Discriminatory Criteria
When distinguishing RVOT from LVOT origins in cases with V3 transition:
V2 Transition Ratio
V2 transition ratio = (R/R+S)VT ÷ (R/R+S)sinus rhythm
- Ratio <0.60 indicates RVOT origin (91% accuracy) 4
- Ratio ≥0.60 suggests LVOT origin
V2S/V3R Index
V2S/V3R = S-wave amplitude in V2 ÷ R-wave amplitude in V3
- Index >1.5 indicates RVOT origin (89% sensitivity, 94% specificity) 5
- This criterion outperforms other indices regardless of transition zone location
RV1-V3 Transition Ratio
RV1-V3 ratio = (RV1+RV2+RV3)PVC ÷ (RV1+RV2+RV3)sinus
- Ratio <0.9 suggests RVOT origin (94% sensitivity, 73% specificity) 6
- Ratio ≥0.9 indicates LVOT origin
Clinical Context
Presentation Patterns
- Shorter cycle lengths and higher likelihood of syncope compared to LVOT arrhythmias 1
- Multiple PVC morphologies more common with inferior RVOT origins (24% vs 7% for superior RVOT) 2
- Sustained VT (≥30 seconds) arising from outflow tract origins is exclusively RVOT in location 7
Important Caveats
- Epsilon waves (if present) suggest arrhythmogenic right ventricular cardiomyopathy rather than idiopathic RVOT VT—these have very low sensitivity (12%) but high specificity (98%) 8
- T-wave inversions in V1-V3 may indicate structural disease (ARVC) rather than benign idiopathic RVOT VT 8
- Always exclude structural heart disease before labeling as "idiopathic" RVOT VT
Practical Algorithm
- Confirm LBBB pattern with inferior axis → suggests outflow tract origin
- Check R wave in V2: If ≤30% of QRS amplitude → RVOT highly likely 3
- Assess transition zone: V3-V4 transition → RVOT; V1-V2 transition → consider LVOT/aortic cusp
- If V3 transition present, calculate V2S/V3R index: >1.5 confirms RVOT 5
- Check QRS duration: >145 ms suggests inferior RVOT location 2
- Evaluate for structural disease markers (epsilon waves, extensive T-wave inversions) to exclude ARVC