Postoperative troponin I values: Insult or injury?

Background: Troponin I(TnI) is increasingly employed as a highly specific m arker of acute myocardial ischemia. The value of this marker after cardiac surgery is unclear. Hypothesis: The purpose of this study was to measure serum TnI levels prosp ectively at 1, 6, and 72 h after elective cardiac operations. In addition, TnI levels were measured from the shed mediastinal blood at 1 and 6 h posto peratively. Serum values were correlated with cross clamp time, type of ope ration, incidence of perioperative myocardial infarction, as assessed by po stoperative electrocardiograms (ECG) and regional wall motion, as documente d by intraoperative transesophageal echocardiography (TEE). Methods: Sixty patients underwent the following types of surgery: coronary artery bypass graft (CABG) (n = 45), valve repair/replacement (n = 10), and combination valve and coronary surgery (n = 5). Myocardial protection cons isted of moderate systemic hypothermia (30-32 degrees C), cold blood cardio plegia, and topical cooling for all patients. Results: Of 60 patients, 57 (95%) had elevated TnI levels, consistent with myocardial injury, 1 h postoperatively. This incidence increased to 98% (59 /60) at 6 h postoperatively. There was a positive correlation between the l ength of cross clamp time and initial postoperative serum TnI (r = 0.70). T here was no difference in the serum TnI values whether or not surgery was f or ischemic heart disease (CABG or CABG + valve versus valve). There were n o postoperative myocardial infarctions as assessed by serial ECGs. There wa s no evidence of diminished regional wall motion by TEE. Levels of TnI in the mediastinal shed blood were greater than assay in 58% (35/60) of the patients at 1 h and in 88% (53/60) at 6 h postoperatively. P atients who received an autotransfusion of mediastinal shed blood (n = 22) had on average a 10-fold postoperative increase in serum TnI levels between 1 and 6 h. Patients who did not receive autotransfusion average less than doubled their TnI levels over the same interval. At 72 h, TnI levels were b elow the initial postoperative levels but still indicative of myocardial in jury. Conclusion: Postoperative TnI levels are elevated after all types of cardia c surgery. There is a strong correlation between intraoperative ischemic ti me and postoperative TnI level. Further elevation of TnI is significantly e nhanced by reinfusion of mediastinal shed blood. Despite these postoperativ e increases in TnI, there was no evidence of myocardial infarction by ECG o r TEE. The postoperative TnI value is even less meaningful after autotransf usion of shed mediastinal blood.