Rate, Rhythm and Frontal Plan Axis

The rate will be 120-250 bpm and the rhythm regular. Rates of around 150 bpm or well-tolerated rates above 200 bpm should suggest the possibility of a supraventricular origin masquerading as a VT.

Frontal plane axis

The axis in a VT is frequently outside the normal range of -30^o to 90^o as the wave of depolarisation frequently moves in the opposite direction to normal.

A wave of depolarisation originating from the apex of the heart and moving to the base may give rise to wildly abnormal axis determinations such as a positive deflection in lead aVR (-210^o).

A monomorphic tachycardia with a positive complex in aVR suggests the axis is bizarre and is very suggestive of a ventricular origin.

Learning Bite

If the QRS is positive in aVR, the axis is bizarre.