VT vs SVT with Aberrancy | Tachyarrhythmias - MedSchool
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Tachyarrhythmias
 
 
Tachyarrhythmias
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 contains a list of ECG findings that suggest a diagnosis of VT as opposed to SVT with aberrancy.
 

VT vs SVT with Aberrancy

 
 

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 contains a list of ECG findings that suggest a diagnosis of VT as opposed to SVT with aberrancy.
    • 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

    • Look For

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

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

RS Interval in Precordial Leads

    • Look For

    • The time from the onset of the R wave to the deepest point of the S wave in the precordial leads.
    • RS Interval in Precordial Leads
       
    • Significance

    • 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.
    • R Wave Peak Time in Lead II
       
    • Significance

    • An R wave peak time ≥50ms in lead II is suggestive of VT.

Fusion & Capture Beats

  • 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
       
    • Significance

    • If present in the context of a wide complex tachycardia, fusion and capture beats are suggestive of VT.
Last updated on December 29th, 2018
 
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