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  • Ventricular tachycardia (VT) is an imminently life-threatening arrhythmia that must be rapidly diagnosed and treated. Supraventricular tachycardia is a more benign arrhythmia that may also present as a wide complex tachycardia when combined with aberrant conduction; this can be difficult to distinguish from VT.
  • This section includes a list of causes of wide complex tachycardia, as well as a guide to key findings used to distinguish between causes.
    • Causes of Wide Complex Tachycardia

    • Regular

    • Monomorphic ventricular tachycardia
    • Supraventricular tachycardia with aberrant conduction (bundle branch block)
    • Supraventricular tachycardia with preexcitation (accessory pathway)
    • Pacemaker-mediated tachycardia - atrial tracking or endless loop tachycardia
    • Irregular

    • Polymorphic ventricular tachycardia
    • Atrial fibrillation with aberrant conduction (bundle branch block)
    • Atrial fibrillation with preexcitation (accessory pathway)
    • Other

    • Artefact - due to CPR, shivering, shaking or other movements

Distinguishing Between VT and SVT with Aberrancy

  • Several ECG features can be used to distinguish between ventricular tachycardia and supraventricular tachycardia with aberrant conduction.
    • Factors favouring VT over SVT with Aberrancy

    • Patient History

    • Structural heart disease (95% of wide complex tachycardias in patients with heart disease will be VT)
    • Normal baseline ECG - no bundle branch block or preexcitation
    • ECG Findings

    • Extreme axis deviation (-90 to 180°)
    • Atypical LBBB or RBBB morphology
    • QRS duration >140 with RBBB pattern or >160 with LBBB pattern
    • AV dissociation - visible, regular P waves (Almost 100% specific for VT)
    • Positive or negative concordance - precordial leads all positive or all negative
    • RS interval >100ms in precordial leads - from onset of R wave to deepest point of S wave
    • R wave peak time ≥50ms in lead II - from isoelectric line to peak of R wave
    • Onset and Offset

    • Wide complex tachycardia initiated by a ventricular complex
    • Fusion beats: a hybrid between a normal QRS complex and a ventricular ectopic
    • Capture beats: a normal, narrow QRS complex produced during due to a conducted atrial beat

Extreme Axis Deviation

  • Extreme axis deviation, also known as northwest axis, is highly suggestive of ventricular tachycardia.
    • Look For

    • Negative lead I
    • Negative lead aVF
    • Extreme Axis Deviation

Atypical LBBB

    • Typical LBBB

    • Wide QRS ≥120ms
    • Broad R wave in lateral leads (I, aVL, V5, V6)
    • Absent Q waves in I, V5 and V6
    • Atypical LBBB
    • Atypical Findings

    • Initial R wave >30ms
    • Josephson’s sign - notching of the S wave
    • RS interval >100ms in precordial leads
    • Q waves in V6
    • Atypical LBBB

Atypical RBBB

    • Typical RBBB

    • Wide QRS ≥120ms (complete BBB) or 110-120ms (incomplete BBB)
    • Added R wave (R’) in right precordial leads - RSR’ pattern in leads V1 or V2 (R’ taller than R) (Due to delayed conduction to right ventricle)
    • Slurred S wave in lateral leads - S wave duration > R wave duration (or >50ms) in leads I, V5 and V6
    • Atypical RBBB
    • Atypical Findings

    • Monophasic R wave
    • R wave taller than R’ (taller left rabbit ear)
    • Q wave in V1
    • QS waves in V6
    • R:S ratio <1 in V6 (S wave deeper than R wave is tall)
    • Atypical RBBB
    • Atypical RBBB
    • Atypical RBBB

AV Dissociation

  • The presence of P waves that are regular are not associated with QRS complexes is highly suggestive of VT.
    • AV Dissociation


  • Concordance, and particularly negative concordance, is highly suggestive of VT.
    • Features of Concordance

    • Positive concordance - all precordial leads are positive
    • Negative concordance - all precordial leads are negative
    • Positive concordance:
    • Positive concordance
    • Negative concordance:
    • Negative concordance

RS Interval in Precordial Leads

  • The RS interveal refers to the time from the onset of the R wave to the deepest point of the S wave in the precordial leads.
  • An RS interval >100ms in the precordial leads is suggestive of VT.
    • RS Interval in Precordial Leads

R Wave Peak Time in Lead II

  • Look for the time from the start of the depolarisation from the isoelectric line to the first deflection in the complex.
  • An R wave peak time ≥50ms in lead II is suggestive of VT.
    • R Wave Peak Time in Lead II

Fusion & Capture Beats

  • If present in the context of a wide complex tachycardia, fusion and capture beats are suggestive of VT.
  • Fusion beats are hybrid complexes that occur when a ventricular beat and a supraventricular beat coincide.
  • A capture beat occurs when a sinus impulse is normally conducted down the AV node and 'captured' by the ventricle, resulting in a normal QRS complex.
    • Fusion & Capture Beats
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