coronary artery bypass cryosurgery mitral valve repair CORONARY ARTERY BYPASS It is now widely accepted that approximately 50 per cent of patients undergoing mitral valve repair and/or replacement surgery and up to 20 per cent of patients undergoing coronary artery bypass surgery (CABG) also have AF. Surgeons believe that it is appropriate to treat the patients' atrial fibrillation as a secondary outcome, while the patient is being primarily treated for mitral valve disease or coronary vessel obstruction.