My husband had a CABG 7 years ago and continues to get rare, mild chest pain, back pain at pinpoint areas lasting anywhere from a few seconds to several hours. It does not spread to any other areas during the pain. No other cardiac symptoms. Unrelieved w/ntg. He takes lisinopril, asa, plavix, metoprolol, simvastatin. What is causing this? His cardiologist tells him to monitor it.