Re-evaluating the electro-vectorcardiographic criteria for left bundle branch block

Authors, Journal, Affiliations, Type, DOI

• Authors: Andrés Ricardo Pérez-Riera, Raimundo Barbosa-Barros, Rodrigo Daminello-Raimundo, Luiz Carlos de Abreu, Marcos Célio de Almeida, Jani Rankinen, Fabio Baeub Soler, Kjell Nikus
• Journal: Annals of Noninvasive Electrocardiology (Ann Noninvasive Electrocardiol)
• Affiliations: ABC Faculty of Medicine (Brazil); de Messejana Hospital (Brazil); University of Brasília (Brazil); Tampere University Hospital (Finland); Soler Clinic (Brazil)
• Type: Review article
• DOI: https://doi.org/10.1111/anec.12644

Overview

This review critically re-evaluates ECG and vectorcardiographic (VCG) criteria for complete left bundle branch block (CLBBB), particularly in the context of CRT patient selection. The central debate contrasts conventional AHA criteria (QRS ≥120 ms) with Strauss' strict criteria (QRS ≥140/130 ms men/women + mid-QRS notching/slurring in ≥2 contiguous leads), which better identify "true" LBBB and CRT responders. Approximately 1/3 of conventionally-defined LBBB cases may not represent true LBBB, contributing to the ~30% CRT non-responder rate. The review introduces clinically important prognostic distinctions between discordant LBBB (appropriate discordance, ~70%) and concordant LBBB (~28–32%), and proposes VCG as a decisive tool for distinguishing true from pseudo-LBBB.

Keywords

cardiac resynchronization therapy, concordant and appropriate discordance, left bundle branch block, QRS duration, QRS notched/slurred R waves in lateral leads

Key Takeaways

1. Electrocardiographic LBBB Criteria Analysis

Conventional vs Strict Criteria — QRS Duration:

• Conventional AHA/ACCF/HRS criteria (Surawicz 2009): QRS ≥120 ms (adults ≥18 yr); ≥100 ms (4–17 yr); ≥90 ms (<4 yr) — used in major CRT trials (COMPANION, CARE-HF, RAFT)
• Strauss' strict criteria (Strauss 2011): QRS ≥140 ms (men) or ≥130 ms (women) >18 yr, plus QS or rS in V1–V2, plus mid-QRS notching or slurring in ≥2 contiguous leads of V1, V2, V5, V6, I, aVL
• ~1/3 of patients diagnosed with LBBB by conventional criteria may have pseudo-LBBB (likely LVH + LAFB combination)
• Three key studies demonstrated this false-positive problem
• AHA/ACCF/HRS Class I CRT recommendation (Epstein 2013): QRS ≥150 ms with LBBB morphology
• ESC Class I CRT recommendation (Brignole 2013): QRS ≥120 ms with QS/rS in V1, wide R in I/aVL/V5–V6, no q waves in V5–V6

Variable CRT Trial QRS Thresholds:

Additional LBBB ECG Criteria:

• Supraventricular command: PR ≥120 ms if sinus rhythm
• Dominant S wave or QS in right precordial leads V1–V2: rS (~70%), QS (>29%), qrS (<1%)
• Initial r wave ≥1 mm in V1 suggests intact left-to-right septal activation and identifies LBBB patients at low risk of complete heart block during right heart catheterization; found in ~28% of conventionally-defined LBBB; proposed as new exclusion criterion for CLBBB
• Broad mid-QRS notching or slurring R wave in I, aVL, V5–V6 (rule)
• R-wave peak time (VAT) ≥60 ms in V5–V6 but normal in V1–V3
• Delayed QRS transition (V5 or beyond) is a novel SCD risk marker

2. Ventricular Repolarization in CLBBB

Discordant vs Concordant LBBB:

• Discordant LBBB (dLBBB) = "appropriate discordance": ST segments and T waves in polarity opposite to main QRS deflection — present in ~68–70% of CLBBB cases
• Concordant LBBB (cLBBB): T-wave orientation concordant with QRS complex (positive/diphasic T wave in ≥2 of leads I, V5, V6) — present in ~28–32% of cases

• Discordant LBBB associated with more severe CAD (Khalil 2016) and worse prognosis even in patients receiving CRT-D (Padeletti 2018)

3. Vectorcardiographic Criteria for True CLBBB (Horizontal Plane)

• Narrow, long QRS loop usually with figure-of-8 rotation
• QRS loop duration ≥130 ms (women) or ≥140 ms (men) — 65 or 70 dashes (1 dash = 2 ms)
• Elongated and narrow QRS loop shape
• Main body of QRS loop inscribed posteriorly and to the left (−90° to −40°)
• Maximal QRS vector in left posterior quadrant (−40° to −80°) of increased magnitude (>2 mV)
• Main portions of QRS loop: clockwise rotation (counterclockwise may indicate parietal CLBBB, lateral infarction, or severe LVH)
• Middle + end conduction delay in the QRS loop: pathognomonic of true LBBB (absence distinguishes pseudo-LBBB from true LBBB)
• ST/T-wave vector directed rightward and anteriorly — QRS/ST-T angle ≥90° (discordant) or <90° (concordant)
• VCG identifies true LBBB more easily than ECG because mid-end conduction delay in the QRS loop is pathognomonic; pseudo-LBBB lacks this finding

4. Prognosis in CLBBB

• LBBB is associated with increased cardiovascular mortality, SCD, and heart failure (multiple registry studies)
• LBBB vs RBBB: worse prognosis with LBBB (Baldasseroni 2002, Freedman 1987, Hesse 2001)
• Isolated LBBB without cardiac disease: prognosis is controversial to neutral, but LBBB causes mechanical asynchrony with LV EF reduction and redistribution of circumferential shortening and myocardial blood flow even in normal hearts (Vernooy 2005 animal model)
• New-onset LBBB should always be considered pathological; may indicate acute MI (Sgarbossa concordant criteria)
• HV interval ≥70 ms (or ≥100 ms) predicts higher risk of spontaneous second- or third-degree AV block
• Chronic BBB + infranodal block (HV ≥70 ms) → significantly higher incidence of complete AV block
• Women: develop LBBB pattern at shorter QRSd and have more frequent mechanical dyssynchrony at shorter QRSd → explains better CRT response rates at shorter QRSd in women (De Pooter 2018)

5. CRT Non-Responder Problem

• ~30% of CRT recipients do not benefit (non-responders) but are subjected to device complications and costs
• Broad adoption of conventional LBBB criteria (QRS ≥120 ms) selects patients with LVH/LAFB pseudo-LBBB who do not respond
• Strict LBBB criteria (Strauss or PREDICT) associated with better echocardiographic response and lower HF hospitalization vs non-true LBBB (Mascioli 2012, Garcia-Seara 2018)
• However, Bertaglia 2017 showed stricter criteria did not improve CRT response vs current AHA definition — controversy unresolved
• Non-LBBB subgroups that may respond to CRT: prolonged PR ≥230 ms, RBBB with concomitant left-sided delay, significant RV pacing burden
• ECG imaging (ECGI) reliably detects electrical dyssynchrony and resynchronization (Bear 2018)

Limitations of the Document

• Review article — no original primary data; synthesizes multiple studies with heterogeneous designs
• Strauss strict criteria validity remains controversial (Bertaglia 2017 negative study)
• VCG criteria require specialized equipment not routinely available in most clinical settings
• The concordant/discordant LBBB data largely from observational/registry studies with potential confounding
• Gender-specific criteria (different QRS thresholds for men/women in Strauss criteria) have not been uniformly adopted in guidelines

Key Concepts Mentioned

• concepts/ECG-Conduction-Disturbances — LBBB criteria, AHA/ACCF/HRS definitions, LBBB morphology
• concepts/Cardiac-Resynchronization-Therapy — CRT patient selection, LBBB as key indicator, non-responder problem
• concepts/LBBB-Criteria — Strauss strict criteria, concordant/discordant distinction, VCG criteria (new page)
• concepts/Sgarbossa-Criteria — concordant LBBB and ACS/AMI diagnosis
• concepts/Atrioventricular-Block — HV interval and AV block progression in BBB
• entities/Vectorcardiography — VCG criteria for true LBBB

Key Entities Mentioned

• entities/Vectorcardiography — VCG as tool to distinguish true vs pseudo-LBBB

Wiki Pages Updated

• Created: wiki/sources/lbbb-evg-ane-2019.md
• Updated: wiki/sourceindex.md
• Updated: wiki/wikiindex.md
• Updated: wiki/concepts/ECG-Conduction-Disturbances.md — added Strauss strict criteria, concordant/discordant LBBB, VCG differentiation
• Updated: wiki/concepts/Cardiac-Resynchronization-Therapy.md — added true vs pseudo-LBBB in CRT selection, concordant/discordant LBBB prognosis
• Created: wiki/concepts/LBBB-Criteria.md — new dedicated concept page