The 4 independent preoperative risk factors predictive of the composite end point were ( 1 ) a history of heart failure ( odds ratio , 2.9 ) ; ( 2 ) increasing age ( odds ratio , 1.033 per decade ) ; ( 3 ) a history of peripheral vascular disease ( odds ratio , 1.6 ) ; and ( 4 ) receiving aspirin before coronary artery bypass grafting ( odds ratio , 0.5 ) , which was protective .