Persistent posterobasal forces usually comes off a reading of an EKG. It has to do with the way the heart directs the electrical impulses around the heart. Though it can be seen in some cases of right bundle branch block, it is usually a normal variant, and of minimal significance.
You should discuss this with your cardiologist. He/she will be able to give you a more thorough explanation, in correlation with the rest of your history, symptoms, physical examination, and the rest of the EKG study.