Is It Advisable To Change Pacemaker During Chemo Treatments For Breast?

My Metronic pacemaker is 6 yrs. old. Was told it might last 2 more yrs. I will start Chemo treatments soon for maybe 5 months. I have HER2+ fast growing cancer in breast/lymph nodes. Next will be breast surgery, followed by a year of radiation. Question: About the time I will be taking radiation, perhaps the chest might get burned somewhat, and now it s time to get a new pacemaker. What are my chances of getting an infection or getting a pacemaker then? I am 77, good health, have a coronery artery disease.. The breast may,maynot be removed in 6 months.