Features favoring VT   

Features favoring SVT w/aberrancy

AV dissociation

Consistent onset of tachycardia with PACs

Fusion/Dressler (capture) beats

Short RP interval (<0.1 sec)

2:1 ventriculoatrial block

1:1 ventriculoatrial relationship

Slightly irregular R-R intervals

Regular R-R intervals

Triphasic pattern in V₁

QRS concordance in the precordial leads similar to normally conducted beats   

Initial vector of abnormal QRS complex

Predominantly negative QRS complexes in V₄ - V₆

QR complexes present in V₂ - V₆

R-S width > 100ms in at least one precordial lead

QRS duration > 140ms

Extreme left superior axis deviation

Net area under QRS negative in leads I and II

Features favoring VT   

Features favoring SVT w/aberrancy

RBBB pattern:   

RBBB pattern:

• Monophasic R or biphasic qR, QR, or RS in V₁

• Triphasic rSR' in V₁

•    S > R or QS in V₆  

• Triphasic rSR' in V₆

• R > S in V₆
  

LBBB pattern:   

LBBB pattern:

• Broad R wave or wide R-S length (> 30msec) in V₁ or V₂

• No R in V₁

• Notched downstroke of S-wave in V₁ or V₂

• Small narrow R in V₂

• > 60msec to nadir of S in V₁ or V₂   

• No slurring of S-wave downstroke

• qR or QS pattern in V₆  

• Monophasic R in V₆

• Presence of septal Q in I & V₆