Wide Complex Tachycardia
On this page:Distinguishing Between VT and SVT with AberrancyExtreme Axis DeviationAtypical LBBBAtypical RBBBAV DissociationConcordanceRS Interval in Precordial LeadsR Wave Peak Time in Lead IIFusion & Capture Beats
Overview
- 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
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 Findings
- Initial R wave >30ms
- Josephson’s sign - notching of the S wave
- RS interval >100ms in precordial leads
- Q waves in V6
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 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)
AV Dissociation
- The presence of P waves that are regular are not associated with QRS complexes is highly suggestive of VT.
Concordance
- 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:
- 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.
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.
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.
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