Since the left bundle branch accepts the electrical
conduction for septal depolarization first, 
left bundle branch
blocks are described as being a disruption in the initial
depolarization of the septum. In this condition, however, the
right bundle branch accepts the first wave of electrical
depolarization making the electrical signal sweep right then
left. The second wave of depolarization remains to the left
because of the electrically dominant left ventricle.
Lead V1 - Left bundle branch blocks are represented in lead
V1 by a large negative deflection, or "QS" waveform, which is
usually 3-4 boxes wide and approximately 10 boxes deep. It
represents septal and left ventricular depolarization. No "septal
r" wave is seen because depolarization is being conducted away
from lead V1 to the septum and then the left ventricle. If the
complex is greater
than 0.10 seconds, it represents an incomplete
left bundle branch block. If the complex is greater than 0.12
seconds, it represents a complete left bundle branch block.
Lead V6 - Left bundle branch blocks are represented in lead
V6 by a 
tall, wide,
positive deflection which is usually notched
and is known as an "R" waveform. If the complex is greater than
0.10 seconds, it represents an incomplete left bundle branch
block. If the complex is greater than 0.12 seconds, it represents
a complete left bundle branch block.