A New Approach to the Differential Diagnosis of a Regular Tachycardia With a Wide QRS Complex

Authors, Journal, Affiliations, Type, DOI

• Authors: Pedro Brugada, Josep Brugada, Lluis Mont, Joep Smeets, Erik W. Andries
• Journal: Circulation, Vol 83, No 5, May 1991, pp. 1649–1659
• Affiliations: Cardiovascular Center (P.B., L.M., E.W.A.), Postgraduate School of Cardiology, OLV Hospital, Aalst, Belgium; Departments of Physiology (J.B.) and Cardiology (J.S.), Maastricht University, The Netherlands
• Type: Prospective original article
• DOI: https://doi.org/10.1161/01.CIR.83.5.1649

Overview

The Brugada 1991 paper is the foundational prospective study establishing the four-step stepwise algorithm for differentiating ventricular tachycardia (VT) from supraventricular tachycardia with aberrant conduction (SVT-A) in regular wide QRS tachycardia (QRS ≥0.12 s). The authors analysed 554 EP-confirmed tachycardias (384 VT, 170 SVT-A) using complete 12-lead ECGs, with two independent observers blinded to the electrophysiological diagnosis. By identifying four criteria applied in sequence — absence of RS complex in all precordial leads, RS interval >100 ms, AV dissociation, and morphological criteria in leads V1/V2 and V6 — the algorithm achieved sensitivity 98.7% and specificity 96.5%, substantially outperforming all prior single-criterion approaches. This paper remains the most-cited WCT diagnostic tool in clinical cardiology.

Keywords

Wide QRS complex, ventricular tachycardia, supraventricular tachycardia, aberrant conduction, differential diagnosis, ECG algorithm, RS interval, AV dissociation, morphological criteria

Key Takeaways

Background and Motivation

• Differential diagnosis of WCT (QRS ≥0.12 s) is a common and high-stakes clinical problem: misclassifying VT as SVT with aberrancy — particularly administering verapamil — may cause haemodynamic collapse
• Prior criteria (single morphological features, concordance, rabbit ears, axis criteria) had poor specificity in prospective validation: approximately 70% specificity for RBBB-like tachycardias
• Reasons for diagnostic errors: criteria not applied in a consistent stepwise manner; reliance on morphology alone; criteria originally developed in selected populations
• Purpose of study: develop a new stepwise approach combining available criteria into a decision tree with higher sensitivity and specificity than any single criterion alone

Methods

• Population: 554 tachycardias with wide QRS complex (QRS ≥0.12 s) prospectively collected at OLV Hospital, Aalst, Belgium
  • 384 ventricular tachycardia (70%; EP-confirmed site of origin in ventricular myocardium)
  • 170 supraventricular tachycardia (30%): 97 SVT with right bundle branch block aberrant conduction (SVT-RB); 73 SVT with left bundle branch block aberrant conduction (SVT-LB)
• Diagnosis: complete 12-lead ECG recorded at 25 mm/sec for all tachycardias; electrophysiologically confirmed mechanism (intracardiac recordings)
• Observers: two independent observers unaware of EP diagnosis; retrospective analysis of both new and previously available criteria
• Part 1: Assessed currently available single criteria in 236 prospectively analysed tachycardias (Table 1 — morphology criteria sensitivity/specificity)
• Part 2: 170 SVTs and 554 VTs tested with the four-step algorithm in two independent analyses (Observers 1 and 2)

Part 1 — Analysis of Current Criteria (Morphological Criteria in 236 BCTs)

Table 1: Sensitivity and Specificity of Individual Morphological Criteria:

Key morphological VT criteria:

• RBBB-like morphology:
  • V1/V2: monophasic R wave; qR complex; or RS where R>S → VT
  • V1/V2: triphasic rSR'/rsR'/rSR' or RS where R<S → SVT with aberrant conduction
  • V6: QS, QR, or R/S ratio ≤1 → VT
  • V6: R>S → SVT with aberrant conduction
• LBBB-like morphology:
  • V1/V2: R wave width >30 ms → VT
  • V1/V2: interval from onset of R to nadir of S >60 ms → VT
  • V1/V2: notching on downstroke of S wave → VT
  • V6: any Q wave (QS or QR pattern) → VT
  • V6: no Q wave → SVT with aberrant conduction
• The frontal plane QRS axis in all precordial leads (QRS morphology in frontal plane) was NOT useful as an isolated criterion: axis is "only recognisable to the expert eye" in aVR

Table 2 — Presence of AV Dissociation, Left Axis, and Duration of QRS in 170 Prospectively Analysed BCTs:

• AV dissociation: present in 21 SVT-RB (confirmed SVT; must exclude) vs present in 82 VTs → Sp 100%, Sn variable by subgroup
• Left axis (mean frontal QRS <0°): 48/99 VTs, 17/71 SVTs — not sufficiently specific alone
• Mean QRS duration >0.14 s: 5% VTs, 1% SVTs — too insensitive

Part 2 — The Four-Step Stepwise Algorithm (Primary Contribution)

The algorithm is applied sequentially; a positive finding at any step stops further analysis and provides the diagnosis:

Step 1 — Absence of RS complex in ALL precordial leads:

• If NO RS complex is present in any of V1–V6 → diagnose VT
• Sensitivity: 21%, Specificity: 100%
• Mechanism: complete lack of RS implies entirely negative or entirely positive QRS throughout precordium (concordance or qR/QS pattern throughout), reflecting purely ventricular activation without His-Purkinje involvement
• If RS complex IS present in any lead → proceed to Step 2

Step 2 — RS interval >100 ms in any precordial lead:

• RS interval = time from onset of R wave to deepest point of S wave (nadir), measured in the precordial lead where it is longest
• If RS interval exceeds 100 ms in ANY precordial lead → diagnose VT
• Sensitivity: 66%, Specificity: 98%
• Mechanism: slow muscle-to-muscle ventricular spread (VT) prolongs the time to reach the S-wave nadir; SVT with BBB has rapid initial activation via His-Purkinje → short time to S-nadir
• If RS interval ≤100 ms → proceed to Step 3

Step 3 — AV dissociation:

• If P waves present independent of QRS (AV dissociation confirmed) → diagnose VT
• Sensitivity: 82%, Specificity: 98% (0% SVT with true AV dissociation)
• Note: retrograde VA conduction occurs in ~50% of VTs, so AV dissociation will be absent in many VTs at this step; the algorithm still proceeds to Step 4
• If no AV dissociation identifiable → proceed to Step 4

Step 4 — Morphological VT criteria in V1/V2 AND V6:

• Apply RBBB or LBBB criteria (above) depending on QRS morphology in V1
• If morphological criteria for VT are met in BOTH V1/V2 AND V6 → diagnose VT
• If criteria are NOT met → diagnose SVT with aberrant conduction
• This step fulfils diagnosis for the remaining ~15% of tachycardias not classified by Steps 1–3

Algorithm Performance (554 BCTs; Figure 7):

• Sensitivity (Observer 1): 96.5%; (Observer 2): 98.7%
• Specificity (Observer 1 and 2): 96.5%
• PPV for VT (Observer 1): 0.987; PPV for SVT: 0.965
• 11 tachycardias misclassified in two-observer combined analysis (2%)
  • 5 VTs misclassified as SVT; 6 SVTs misclassified as VT
  • In 3 of these, the axis in the frontal plane was not recognisable (key limitation of Step 4 morphological criteria)

Comparison to Old Criteria

• All previously used single criteria had sensitivity/specificity combinations inferior to the new stepwise approach
• Applying the four steps reduced the average diagnostic time in the first part of the study and eliminated the most common sources of diagnostic error
• The stepwise approach addresses the fundamental problem: a single criterion applied in isolation without context leads to incorrect diagnosis when the criterion is met by chance in the minority condition

Discussion Points

• The algorithm deliberately ends with SVT-aberrant conduction as the "default negative" diagnosis — i.e., VT must be positively identified at each step; failure to identify VT → SVT
• 4% of SVTs had an RS complex absent in all precordial leads when the old criteria were applied incorrectly, causing misdiagnosis
• The authors note: "more than one criterion in any one precordial lead makes a diagnosis of VT more secure"
• RS interval >100 ms was the single most powerful step: identified 66% of total VTs independently of prior steps
• AV dissociation, though highly specific, is visible in only ~20% of VTs after Steps 1–2 have been applied
• Frontal plane morphological criteria (Step 4) were the most difficult to apply reliably; discordance between observers was highest at this step

Limitations of the Document

• Single-centre study: all tachycardias from OLV Hospital, Aalst, Belgium — referral bias expected (higher VT prevalence than community settings)
• No bundle branch reentry VT: not represented in the cohort; BBR-VT has typical BBB morphology and rapid intrinsicoid deflection — the algorithm would classify BBR-VT as SVT with aberrant conduction
• No fascicular VT: not explicitly discussed; fascicular VT has narrow-ish QRS and RS duration <80 ms, falling below the >100 ms threshold of Step 2
• No pre-excited SVT: antidromic AVRT not included; this entity produces fully pre-excited wide QRS that may meet criteria for VT
• No antiarrhythmic drug effect: class Ic agents produce bizarre QRS widening that would be indeterminate; not studied
• Observer expertise: both observers were experienced electrophysiologists at a tertiary EP centre — real-world reproducibility likely lower, particularly for Step 4 morphological criteria
• Paper speed 25 mm/sec: time-domain measurements (RS interval) may be less accurate on differently calibrated ECG recordings

Key Concepts Mentioned

• concepts/Wide-Complex-Tachycardia — primary subject; this paper is the original source of the Brugada 4-step algorithm
• concepts/ECG-Conduction-Disturbances — RBBB/LBBB morphological criteria basis

Key Entities Mentioned

• entities/Brugada-Syndrome — note: Pedro and Josep Brugada are the authors of this 1991 paper; the Brugada syndrome (BrS) ECG was later described by the same family in 1992; this paper is distinct from BrS

Wiki Pages Updated

• wiki/sources/vt-brugada-circ-1991.md — created (this file)
• wiki/sourceindex.md — added entry
• wiki/wikiindex.md — updated Wide-Complex-Tachycardia entry
• wiki/concepts/Wide-Complex-Tachycardia.md — added source link, updated source_count 4→5