The risk factors for postoperative atrial fibrillation by the Cox proportional hazard model were an age 70 years , emergency surgery , preoperative aldosterone level > 150 ng/mL , preoperative nonuse of angiotensin receptor antagonists , preoperative use of calcium antagonists , postoperative nonuse of - blockers , postoperative nonuse of aldosterone blockers , and nonuse of carperitide .