Simple Electrocardiographic Criteria for Rapid Identification of Wide QRS Complex Tachycardia: the new Limb Lead Algorithm

Authors, Journal, Affiliations, Type, DOI

• Authors: Qiong Chen, Jinyi Xu, Carola Gianni, Chintan Trivedi, Domenico G. Della Rocca, Mohammed Bassiouny, Ugur Canpolat, Alfredo Chauca Tapia, J. David Burkhardt, Javier E. Sanchez, Patrick Hranitzky, G. Joseph Gallinghouse, Amin Al-Ahmad, Rodney Horton, Luigi Di Biase, Sanghamitra Mohanty, Andrea Natale
• Journal: Heart Rhythm, 2019 (ahead of print; DOI published September 2019)
• Affiliations: Texas Cardiac Arrhythmia Institute, St. David's Medical Center, Austin, TX; Henan Provincial People's Hospital, China; Albert Einstein College of Medicine at Montefiore Hospital, New York; Dell Medical School, Austin; Scripps Clinic, San Diego; Stanford University
• Type: Prospective two-centre original article
• DOI: https://doi.org/10.1016/j.hrthm.2019.09.021

Overview

Chen and Natale et al. introduce the Limb Lead Algorithm (LLA) — a purely frontal-plane, measurement-free, single-step WCT diagnostic tool evaluated in 528 EP-confirmed WCTs (397 VT, 131 SVT) from two international EP centres. VT is diagnosed if any one of three criteria is present: monophasic R in aVR; predominantly negative QRS in leads I/II/III; or the novel Opposing QRS in Limb leads (OQL) pattern — all inferior leads concordantly monophasic AND remaining limb leads concordantly monophasic with opposite polarity. The LLA achieved 88.1% accuracy with the highest specificity (90.8%) and PPV (96.7%) and best interobserver agreement (κ=0.98) of any algorithm tested, but lower sensitivity (87.2%) than Brugada (94.0%) and Vereckei (92.4%). The paper also delivers the most quantified independent validation of Brugada specificity failure: 59.5% overall, 48.1% for RBBB-pattern WCTs, driven entirely by Step 4 misclassifying SVT with RBBB+LAFB as VT.

Keywords

Wide QRS complex tachycardia, electrocardiography, ventricular tachycardia, algorithm, opposing QRS complex in limb leads, limb lead algorithm, frontal plane

Key Takeaways

Background and Motivation

• Existing WCT algorithms (Brugada, Vereckei, Pava/RWPT) fail to achieve consistent sensitivity and specificity when applied by independent authors — the likely cause is complexity: multiple steps, difficult measurements (Vi/Vt), hard-to-recall morphological criteria
• All major prior algorithms rely heavily on the horizontal plane (precordial leads); the frontal plane is underutilised
• Precordial leads may be unavailable or unreliable in telemetry/Holter recordings, intra-procedural monitoring, or non-standard electrode placement
• Goal: develop a simple, measurement-free, frontal-plane algorithm with high specificity and reproducibility

Methods

• Study population: 528 monomorphic WCTs with EP-confirmed diagnoses
  • 397 VT (75.2%), 131 SVT (24.8%)
  • Mean age 54.1 ± 17.3 years; 70.4% male
• Centers: St. David's Medical Center, Austin TX (January 2015 – December 2018) + Henan Provincial People's Hospital, China (de-identified data)
• Algorithm development (OQL origin): retrospectively derived from 130 WCTs at Henan Hospital; then combined with two additional criteria (aVR monophasic R; predominantly negative I/II/III) to form the LLA
• Validation: 528 WCTs analysed prospectively by two blinded EP observers; disagreements resolved by a third EP
• Comparators: Brugada 4-step (sources/vt-brugada-circ-1991), Vereckei aVR 2008 algorithm, RWPT (Pava ≥50 ms lead II)

The Limb Lead Algorithm (LLA) — Three Criteria

VT diagnosed if ANY ONE of the following three criteria is present. No measurements required.

Criterion 1 — Monophasic R wave in lead aVR:

• Definition: QRS in aVR consists of a single, entirely positive R wave with no preceding q or following s deflection
• Represents extreme right-superior electrical axis → VT originating from the inferior-left ventricle activating superiorly
• Similar to Vereckei's "initial R in aVR" but more restrictive: requires fully monophasic R, not just an initial positive deflection (excludes qR, RS, rS patterns)
• Present in Figure 1-A examples

Criterion 2 — Predominantly negative QRS in leads I, II, AND III simultaneously:

• Definition: the QRS is predominantly negative (net negative voltage) in ALL THREE standard limb leads at the same time
• Represents extreme northwest axis deviation (axis −90° to ±180°) — activation propagates from inferior-left ventricle superiorly and rightward, away from all three standard limb lead axes
• Note: this requires ALL THREE of leads I, II, and III to be predominantly negative — differs from simple "right superior quadrant" axis criterion which requires only the net axis to fall in that quadrant
• The two limb lead criteria (1 and 2) together capture VTs with extreme axis — outflow tract VTs, apical VTs, inferior wall VTs

Criterion 3 — Opposing QRS complex in Limb leads (OQL):

• Full definition:
  • ALL THREE inferior leads (II, III, aVF) show a concordant monophasic QRS (all R waves, OR all QS waves)
  • AND two or three of the remaining limb leads (I, aVL, aVR) show a concordant monophasic QRS with the OPPOSITE polarity to the inferior leads
  • Examples: inferior leads all monophasic R + superior/lateral leads all monophasic QS; OR inferior leads all monophasic QS + superior/lateral leads all monophasic R
• Physiological basis:
  • VT (superior origin): activation front spreads from superior→inferior → predominantly inferior vector → all inferior leads monophasic R, all superior leads monophasic QS
  • VT (inferior origin): activation front spreads from inferior→superior → predominantly superior vector → all inferior leads monophasic QS, all superior leads monophasic R
  • SVT with RBBB aberrancy: vector is predominantly horizontal (left→right, toward blocked bundle); in RBBB the initial vector points left-inferior, but to complete RV depolarisation it then turns right-superior → QRS in lateral leads (I, aVL) is biphasic, mirroring the inferior leads → prevents more than 4–5 limb leads being monophasic → OQL pattern not achievable
  • SVT with LBBB aberrancy: initial vector right-anterior-superior→left-posterior-inferior; left ventricle dominates → R in lateral leads (I, aVL) but inferior leads have variable morphology (R to rS, rs, rSr depending on axis) → impossible for more than 2 inferior leads to show pure QS → OQL pattern not achievable
• Why OQL has high specificity: SVT with aberrancy produces non-monophasic morphology (at least biphasic) in the limb leads lying perpendicular to the main depolarisation vector — this breaks the monophasic concordance requirement on both sides
• Why OQL sensitivity is limited: VTs originating near the conduction system or subendocardial inferior wall may have discordant inferior leads (initial "r" wave → rS, not pure QS) — OQL not met even though VT; this is why Criteria 1 and 2 were added

Performance Results (Table 1-2)

Key comparisons (Table 2 p-values):

• LLA vs Brugada: sensitivity lower (P<0.001), specificity higher (P<0.001), PPV higher (P<0.001), accuracy NS (P=0.20)
• LLA vs Vereckei: sensitivity lower (P=0.01), specificity higher (P=0.001), PPV higher (P=0.002), accuracy NS (P=0.84)
• LLA AUC > Brugada (P<0.001) and RWPT (P<0.001); comparable to Vereckei
• Brugada vs Vereckei: specificity differs (P=0.003); sensitivity NS; Brugada has worse specificity but similar sensitivity

The high PPV of LLA (96.7%) means that when LLA diagnoses VT, it is correct in 97% of cases — the most reliable positive diagnosis of any algorithm in this comparison.

Brugada Specificity Quantified by Morphology Pattern

This paper provides the most detailed independent breakdown of Brugada specificity by QRS morphology:

• RBBB-pattern WCTs (n=314): sensitivity 97.5%, specificity 48.1% (AUC 0.73)
• LBBB-pattern WCTs (n=214): sensitivity 88.8%, specificity 75.9% (AUC 0.82)
• Overall specificity 59.5% (vs Brugada's original 96.5%)
• Root cause: RBBB+LAFB (RBBB + left anterior fascicular block) SVT has R in V1 and R/S <1 in V6 → Step 4 RBBB morphological criteria diagnose VT → massive false-positive rate
• Steps 1–3 retained good specificity (98%, 93.9%, 93.9% respectively) — Step 4 is the single point of failure
• This confirms the Vereckei 2007 finding (sources/vt-vereckei-ehj-2007): Step 4 accounted for 59% of all Brugada errors

Practical Advantages of LLA

1. No measurements required: all three criteria are pattern-recognition only; no RS interval, no Vi/Vt voltage ratio, no time-to-peak measurement
2. Highest interobserver reproducibility (κ=0.98): significantly better than Brugada (0.89) and Vereckei (0.90)
3. Applicable to Holter/telemetry recordings: only limb leads required; precordial leads not needed
4. Applicable under non-standard electrode placement: tested in some ECGs with limb electrodes on shoulders/hips — retained high specificity
5. Potentially automatable: measurement-free criteria are suited for automated arrhythmia detection algorithms

Limitations of LLA

• Fails for conduction-system VTs: para-Hisian VT, fascicular VT (including LPF-VT; see concepts/Fascicular-Ventricular-Tachycardia), moderator band VT, papillary muscle VT — inferior leads show discordant (biphasic) pattern in these VTs, so OQL is not met; Criteria 1 and 2 are also typically absent
• Fails for VTs with non-extreme axis: VTs originating subendocardially from the inferior wall may show rS (not QS) in inferior leads → OQL not fulfilled; Criteria 1/2 may also be absent
• Abnormal baseline QRS: congenital heart disease, pre-existing BBB, WPW — OQL pattern may occur in sinus rhythm, limiting specificity in these populations; not well-studied
• Electrode placement variation: some ECGs used non-standard limb electrode positions (shoulders/hips); effect on sensitivity not fully characterised
• Lower sensitivity than Brugada and Vereckei: 87.2% vs 93.95% and 92.4% — more VTs missed; in clinical practice, missing VT (false negative) may be more dangerous than over-diagnosing it

Key Concepts Mentioned

• concepts/Wide-Complex-Tachycardia — primary subject; LLA adds the highest-specificity frontal-plane algorithm to the WCT toolkit
• concepts/Fascicular-Ventricular-Tachycardia — explicitly identified as a LLA failure mode (discordant inferior leads in fascicular VT)
• concepts/ECG-Conduction-Disturbances — RBBB+LAFB aberrancy is the key source of Brugada Step 4 false positives documented in this paper

Key Entities Mentioned

• None prominent beyond the arrhythmia entities

Wiki Pages Updated

• wiki/sources/vt-chen-hrs-2019.md — created (this file)
• wiki/concepts/Wide-Complex-Tachycardia.md — algorithm table updated; LLA section added; Brugada specificity note updated with specific figures; source link added; source_count 7→8
• wiki/concepts/Fascicular-Ventricular-Tachycardia.md — LLA added to algorithm failure table
• wiki/sourceindex.md — added entry
• wiki/wikiindex.md — Wide-Complex-Tachycardia entry updated