A 78-year-old man presents with a rectal adenocarcinoma in the upper rectum. He is scheduled for a robotic low anterior resection. His carcinoembryonic antigen (CEA) is normal, and staging reveals no evidence of distant metastasis. He has chronic kidney disease and baseline creatinine level is 2.1 mg/dL. He takes only metformin for his diabetes and has hypertension that is well controlled on amlodpine and metoprolol. Which of the following is an independent predictor of a perioperative cardiac complication during his surgery?