Hi, My 71 Year Old Mom Had A Pacemaker Implanted,

Hi, my 71 year old mom had a pacemaker implanted, because of myocardial infarction, arrhythmia, and experiencing mild heart attack. Her heart rate had gone down to about 35/36. She was also given Lisinipril to control her high blood pressure. My question is, does the pacemaker help, when the beta blocker is slowing the heart rate? It just seems like too much contradiction to me. And why would they not inplant a difibilllator instead of a plain pacemaker if they are concerned about cardiac arrest?