Bundle Branch Block

The heart is driven by a sergeant-major chanting "left, right, left".
This is why the pattern of depolarization is "left septum, right septum, left ventricle".

The other way to think about it is that the septum is depolarized by the left bundle only. This is why depolarization goes from the left side of the septum to the right side of the septum.

So, with a RBBB, the septal depolarization proceeds normally. Then the left ventricle depolarizes normally. However, after it has finished, the RV is still being depolarized by the slow right bundle. Thus, instead of the usual 2 waves, you will see 3 waves and this third wave will be fat and always be heading towards the right.
So, what you will see is an rSR in V1, though in some people the LV is not very big and so the S wave never makes it below the baseline - in that case you get a notched R wave.

Since the normal QRS is only 100msec (2.5 small squares), an incomplete RBBB is 100-120msec, and a complete RBBB is 120msec.

With LBBB, the first phase of depolarization is reversed as the septum has to depolarize from right to left, and the second phase is prolonged. So, see a totally positive R wave in V6 and a totally negative S wave in V1 (i.e. invert your septal wave and get a prolonged normal second wave). The notching that produces the classic W and M shapes is due to the influence of the RV.

An incomplete LBBB is from 100-120msec.

What can you say if you see an rS pattern in LBBB? It means the septum is still being depolarized from left to right!

You can tell that there has been a septal infarct in the presence of a RBBB if you've lost your septal Q's in I and AVL.