Figure 206-10

Wide QRS tachycardia.
A. Wide QRS complexes of at least two varieties are seen. Those showing a left bundle branch block pattern are due to conduction over an accessory pathway, while those with a right bundle branch pattern are aberrant in nature. Note the His bundle activation prior to both narrow and aberrant complexes but not before preexcited complexes.
A right posteroseptat preexcitation can be appreciated in B, with a short PR, a delta wave (d), an His to ventricle (HV) of zero, and negative delta wave in Lead V1.