Right bundle branch block (RBBB) in lead V1. A 12 lead ECG with right bundle branch block, left axis (LAFB)(and left atrial enlargement). Again, watch V1. In right bundle branch block (RBBB) the conduction in the bundle to the right ventricle is slow. As the right ventricles depolarizes, the left ventricle is often halfway finished and few counteracting electrical activity is left. The last electrical activity is thus to the right, or towards lead V1.