Approach to ECGs - VT vs. SVT - Wide Tachycardias
DDx = VT vs. SVT with BBB
All of the below are specific but not sensitive for VT:
- No RS complexes (i.e. entirely positive or negative) in V1 -V6
- Absence of typical RBBB or LBBB morphology
- Extreme axis deviation ("northwest axis") — QRS is positive in aVR and negative in I + aVF.
- Very broad complexes (> 160ms)
- AV dissociation (P and QRS complexes at different rates)
- Capture beats- a QRS complex of normal duration.
- Fusion beats - a sinus and ventricular beat coincides to produce a hybrid complex.
- Brugada's sign - The distance from the onset of the QRS complex to the nadir of the S-wave is > 100ms
- Josephson's sign - Notching near the nadir of the S-wave
- RSR' complexes with a taller left rabbit ear. This is the most specific finding in favour of VT. This is in contrast to RBBB, where the right rabbit ear is taller.
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