Differentiating Right- and Left-Sided Outflow Tract Ventricular Arrhythmias: Classical ECG Signatures and Prediction Algorithms
Authors, Journal, Affiliations, Type, DOI
- Anderson RD, Kumar S, Parameswaran R, Wong G, Voskoboinik A, Sugumar H, Watts T, Sparks PB, Morton JB, McLellan A, Kistler PM, Kalman J, Lee G
- Circulation: Arrhythmia and Electrophysiology, 2019;12:e007392
- Department of Cardiology, Royal Melbourne Hospital; Westmead Hospital; Alfred Hospital, Victoria, Australia
- Review article
- DOI: 10.1161/CIRCEP.119.007392
Overview
Outflow tract ventricular arrhythmias (OTVAs) are the most common idiopathic VAs, arising from the RVOT (70–80%), LVOT (15–25%), and LV summit (~12%). This review comprehensively summarizes published 12-lead ECG morphological signatures for 11+ anatomic OTVA sites and evaluates 18 published ECG prediction algorithms to differentiate right- from left-sided origins. The combined transition zone (TZ) + V₂S/V₃R index yields the highest diagnostic accuracy (Youden index 0.77), while the novel V₃R/V₇ index achieves the highest AUC (0.95). A stepwise localization algorithm incorporating both standard and alternative ECG configurations is proposed.
Keywords
Algorithms, cardiac arrhythmia, catheter ablation, electrocardiography, outflow tract, PVC, ventricular tachycardia
Key Takeaways
Anatomy
- RVOT: tubular, anterior and leftward; divided into free wall (anterior), septal (posterior), left, right portions; pulmonary valve 1–2 cm above aortic valve
- LVOT: central; bounded by aortic root, aortomitral continuity (AMC), superior basal septum, LV summit; RCAS and LCAS adjacent to pulmonary infundibulum; NCAS posterior (near atrial septum)
- LV summit: most superior epicardial LV; bounded by triangle of Brocq and Mouchet (LAD, LCx, arc anterior to first septal perforator); GCV divides it into accessible (lateral) and inaccessible (superior, near coronaries) zones
- Posterior RVOT is directly anterior to LVOT/anterior interventricular septum, separated by the ventriculo-infundibular fold — explaining close ECG overlap
Classical ECG Signatures by Site
RVOT:
- All RVOT: LBBB + inferior axis (monophasic R in II, III, aVF; QS in aVR)
- Free wall (anterior): late transition (≥V4), wider QRS, notching in ≥2 inferior leads; negative lead I; QRS ≥140 ms + notching → sensitivity 74%, specificity 93%
- Septal (posterior): earlier transition (≤V3), taller inferior R waves, narrower, no notching; positive lead I
- Lead I negative → anterior site; positive/isoelectric → posterior; aVL negative → cranial (near pulmonary valve)
Pulmonary Valvular Sinuses (~4%):
- Right cusp (PSC RC): larger R wave in lead I, notching inferior leads, smaller aVL/aVR ratio
- Left cusp (PSC LC): negative lead I, taller R amplitude inferiorly, larger aVL/aVR ratio
- Pulmonary artery: tallest inferior R waves, greatest aVL/aVR ratio
Parahisian (~3%):
- Narrow LBBB, QS in V1 (early precordial transition), inferior axis, lead II R > lead III R, R wave in aVL ± notching, lead I positive
LVOT — Aortic Sinuses:
- General: longer R-wave duration, earlier R/S transition than adjacent RVOT sites
- RCAS: LBBB, rS in V1/V2, transition V3; lead I positive (more rightward)
- LCAS: LBBB, rS or RS in V1/V2, transition ≤V2; multiphasic M or W pattern in V1; R wave >50% QRS duration + R/S ratio >30% predictive
- RCAS/LCAS junction: qrS in V1–V3; QS in V1 with notched downstroke; transition at V3 (79% of cases)
- NCAS: very rare (lack of myocardial sleeves, atrial proximity)
LVOT — Annular:
- AMC: RBBB + inferior axis; qR in V1; positive precordial concordance; no S wave in V6; unique initial leftward activation from left fibrous trigone
- Anterolateral MA: RBBB + right inferior axis; monophasic R in V1; late phase notching inferior leads; long QRS; negative lead I
Epicardial:
- LV summit (accessible — GCV): RBBB, early transition; V2 pattern break (R in V2 < R in V1 and V3); slurred intrinsicoid (pseudodelta); initial R in lead I predicts endocardial approach feasibility
- LV summit (inaccessible — distal GCV): LBBB; left superior axis; V2–V3 transition; more negative aVL > aVR
- Crux: RBBB + left superior axis; positive concordance V2–V6; slurred intrinsicoid
ECG Prediction Algorithms (RVOT vs LVOT)
| Algorithm | Cutoff | Prediction | Sensitivity | Specificity | Notes |
|---|---|---|---|---|---|
| Earliest QRS onset / peak in V2 (Yang) | V2 earliest → RVOT | RVOT | 92% | 88% | LBBB/inferior axis VTs |
| R-wave duration index + R/S amplitude (Ouyang/Ito) | RDI <0.5 AND R/S <0.3 | RVOT | 88% | 95% | V1 or V2 |
| V3 R-deflection >80ms + V1 R amplitude >0.3 (Cheng) | Both criteria | LVOT | 100% | 83% | For V3 transition specifically |
| V2 transition ratio ≥0.6 (Betensky) | PVC R/QRS ÷ SR R/QRS ≥0.6 | LVOT | 95% | 100% | Corrects for cardiac rotation |
| TZ index <0 (Yoshida) | TZ(PVC) − TZ(SR) <0 | LVOT | 88% | 82% | Corrects for cardiac rotation |
| V2S/V3R ≤1.5 (Yoshida) | V2 S-amp ÷ V3 R-amp ≤1.5 | LVOT | 89% | 94% | Best for V3 transition (sens 94%) |
| Combined TZ + V2S/V3R (He) | Y = −1.15×TZ − 0.494×V2S/V3R; if ≥−0.76 | LVOT | 90% | 87% | Highest Youden index (0.77); best overall |
| V1−V2 S-R difference (Kaypakli) | (V1S+V2S)−(V1R+V2R) >1.625 | RVOT | 95% | 85% | Measures proximity to V1/V2 |
RVOT Sub-localization (Septal vs Free Wall)
- QRS ≥140 ms + R-wave notching in ≥2 inferior leads → free wall (sens 74%, spec 93%) (Joshi)
- PVC QRS duration ÷ sinus QRS duration ≥1.9 → free wall (Zhang), after transition >V4 confirmed
- Lead I: negative/isoelectric → anterior; isoelectric/positive → posterior
- aVL: isoelectric/positive → caudal (>2 cm from PV)
LV Summit Sub-localization (Accessible vs Inaccessible)
- RBBB pattern (TZ <V1) + aVL/aVR ratio >1.1 + S wave in V5 or V6 → accessible zone (GCV/AIV ablation feasible); sensitivity 87%, specificity 100% (Yamada)
Alternative ECG Configurations
- Virtual right-sided leads (Syn-V3R–V5R): R>S concordance in all → LVOT; no R/S transition in all → RVOT free wall; V5R morphology Rs/rS → RVOT (sens 87%, spec 91%)
- High precordial V1/V2 positioning: superior displacement → decreased R/S (mimics RVOT); inferior displacement → increased R/S (mimics LVOT); position errors can cause misclassification
- V4/V8 index: modifies V5 to posterior position (V8); V4/V8(PVC) ÷ V4/V8(SR) >2.28 → LVOT (spec 98%, PPV 89%); superior to V2 transition ratio/V2S/V3R for V3 transition
- V3R/V7 index: ≥0.85 → LVOT; AUC 0.95 (highest of all); sens 87%, spec 96%; prospective validation accuracy 98.6%; best for cardiac rotation and V3 transition
Pitfalls and Limitations
- Preferential conduction: ~25% of aortic sinus OTVAs have earliest activation at RVOT breakout site (shared myocardial fibers); ablation at RVOT may fail despite excellent pacemap; near-field signals at adjacent LVOT site more useful
- V3 transition ambiguity: 38% of patients; most algorithms perform worst here → V2S/V3R, V4/V8, or V3R/V7 preferred
- Cardiac rotation: counter-clockwise (37%) or clockwise (13%) shifts transition lead → TZ index and V2 transition ratio normalize this
- Pacemapping limitation: spatial resolution 1.8 cm² (inferior to activation mapping 1.2 cm²); far-field capture can mislead localization
- Change in exit after RF: 4% of OTVAs change ECG morphology after initial RF → new exit site ablation succeeds in 88%
- Non-RVOT sites more likely to develop PVC-induced cardiomyopathy and have greater coupling interval variation → higher cardiac event risk
Limitations of the Document
- Review article: no original patient data; relies on summary of 18 heterogeneous studies
- Most included studies are small, retrospective, and single-center; patient numbers range from 7 to 695
- Many algorithms derived from pacemapping (spatial resolution inferior to activation mapping)
- V3 transition subgroup analyses are underpowered across most algorithms
- No direct head-to-head prospective comparison of all algorithms in a single population
- Alternative ECG configuration studies (V4/V8, V3R/V7) validated primarily in single centers; broad applicability not established
Key Concepts Mentioned
- concepts/OTVA-ECG-Localization — comprehensive algorithm and signature synthesis
- concepts/PVC-Mapping-Ablation — ablation strategy informed by ECG localization
- concepts/PVC-Induced-Cardiomyopathy — non-RVOT sites higher risk
Key Entities Mentioned
- entities/Catheter-Ablation — primary curative therapy for OTVAs
Wiki Pages Updated
wiki/sources/RVOT-LVOT-circ-ep-2019.md— created (this file)wiki/concepts/OTVA-ECG-Localization.md— createdwiki/concepts/PVC-Mapping-Ablation.md— updated ECG algorithm sectionwiki/concepts/PVC-Induced-Cardiomyopathy.md— updated with non-RVOT riskwiki/wikiindex.md— updatedwiki/sourceindex.md— updated