Left bifascicular block with normally conducting middle fascicle.

A case of aortic insufficiency showing an ECG pattern of left ventricular hypertrophy and strain has been followed over time. One year after the initial observation, the ECG and VCG recordings showed the appearance of a left bifascicular block, due to involvement of the anterior and posterior fascicles, with normal septal activation. It is suggested that the normally functioning middle fascicle activates the inferior two-thirds of the septum. This hypothesis is discussed in light of recent experimental data.