Not much. Bundle branch block happens when there is a delay in conduction across a bundle. The his purkinjie fibers break into lb and rb. When there is a block in the rb, it is called rbbb. In most cases rbbb is of minimal consequence.
Slow conduction. It just means slow conduction in the right side of the heart's wiring system.
Abnormal conduction. The signal to beat is distributed to through the heart by a specialized electrical system. The right bundle is one of the branches of this system. If conduction through the right bundle is slowed or blocked the parts of the heart it serves will contract late, seen as widening of the electrocardiographic qrs-wave. Unless the remainder of the conduction system fails, it usually isn't a problem. Read more...