I am so very sorry. Dementia is so, so, hard. (My mother had a terrible time with my grandmother, and there were two of her.)
Fuck that cardiologist. Can your husband or brother complain to the hospital or HMO that employs him?

ETA: I meant my mother has a twin sister, so she didn't have the terrifying sense of doing this outrageously hard thing by herself. Only one of my grandmothers had dementia.