VT versus SVT

Features that favour VT are
- QRS > 140 ms
- cannon a waves on JVP (suggest AV dissociation)
- fusion and/or capture beats
- concordance of QRS complexes in chest leads
- dissociated p waves
- history of ischemic heart disease
- RBBB with left axis deviation
- HR >170bpm

2 algorithms are proposed for prediction of VT versus SVT

i) Brugada
- absence of RS complexes in precordial leads
- RS duration of more than 100ms in any precordial leads
- ventriculoatrial dissociation in any of 12 leads
- certain QRS morphologies, such as QR or QS in V6

ii) Vereckei
- presence of an initial R wave in aVR
- width of an inital r or q wave > 40ms in aVR
- notching on the initial downstroke of a predominantly negative QRS complexes in aVR
- ventricular activation-velocity ratio (Vi/Vt) less than or equal to 1