ECG features increasing the likelihood of VT

Electrocardiographic features that increase the likelihood of VT include:

Absence of typical RBBB or LBBB morphology

Extreme axis deviation (“northwest axis”): QRS positive in aVR and negative in I and aVF

Very broad complexes > 160ms

AV dissociation:

P and QRS complexes at different rates

P waves are often superimposed on QRS complexes and may be difficult to discern

Capture beats: Occur when the sinoatrial node transiently “captures” the ventricles in the midst of AV dissociation, producing a QRS complex of normal duration

Fusion beats: Occur when a sinus and ventricular beat coincide to produce a hybrid complex (see Dressler beat)