My 82 year old grandmother was taking a medicine in which caused kidney damage an now her heart is off rhythm what should we expect?

Depends. It would depend on what you mean by her heart is off rhythm. If it's sinus arrhytmia, infrequent premature atrial or ventricular complexes, and she has no symptoms nothing needs to be done. But if she has atrial fibrillation, she may need to be put on meds to control heart rate, to prevent stroke, and possbly control rhythm. If she is passing out due to sick sinus syndrome, a pacemaker is needed.