Jen,
I don't know what PCI is and I don't know what kind of treatments your dad is going through , but if steroids are involved... prednisone or dexamethasone , you have your answer to the behavior. My husband, Mike was the kindest human being and hated to complain or make waves, but when he was on prednisone he became very agitated, aggressive and would oftentimes strike out at the ones closest to him. He would realize it later and apologize. He would tell me that it wasn't him talking , it was the drugs. Not everyone reacts like this , but many do. It's hard to be patient and understanding when someone is being hateful to you, but it just may be it is medication and not your Dad. God Bless..
Sue