VT vs SVT with Aberrancy
- 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
- 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
- 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.
- Negative lead I
- Negative lead aVF
- Wide QRS ≥120ms
- Broad R wave in lateral leads (I, aVL, V5, V6)
- Absent Q waves in I, V5 and V6
- Initial R wave >30ms
- Josephson’s sign - notching of the S wave
- RS interval >100ms in precordial leads
- Q waves in V6
- 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
- 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)
- The presence of P waves that are regular are not associated with QRS complexes is highly suggestive of VT.
- Positive concordance - all precordial leads are positive
- Negative concordance - all precordial leads are negative
- Positive concordance:
- Negative concordance:
- Concordance, and particularly negative concordance, is highly suggestive of VT.
RS Interval in Precordial Leads
- 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
- 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
- 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.
- If present in the context of a wide complex tachycardia, fusion and capture beats are suggestive of VT.