A 63-year-old woman with diabetes is recovering in the ICU after receiving a CABG for coronary artery disease. On the sixth postoperative day, she starts complaining of chest pain. Her temperature is 101.4 ° F, blood pressure is 108/ 72 mmHg, and pulse is 125/ min. On physical exam, there is drainage from her sternal wound, and there is a crunching sound heard with a stethoscope over the precordium during systole. The sternum feels somewhat unstable to palpation. Her laboratory examination is significant for an elevated white blood count (16.7 × 103/ μL). What is the most likely diagnosis?
(A) Acute pericarditis
(B) Postoperative MI
(C) Empyema
(D) Acute mediastinitis
(E) Pneumonia