Troponin I concentrations of shed blood might influence monitoring of myocardial injury after coronary operations.

In a prospective study we evaluated the concentration of cardiac troponin I (cTnI) and creatine kinase activities (CK) in shed mediastinal blood in the early postoperative period after coronary artery bypass grafting (CABG). Forty seven patients who underwent first time elective CABG were studied. CTnI levels and CK activities in arterial blood and shed mediastinal blood were measured after admission to the intensive care unit (ICU) and 6 h after unclamping the aorta. Mediastinal shed blood samples were drawn from 23 patients (group A) before the filter of the cardiotomy reservoir and from 24 patients (group B) behind. Additionally, both markers were measured in blood samples collected from the cell-saver. There were no significant differences between both groups (A and B) with regard to perioperative parameters. Mean loss of mediastinal shed blood in all patients was 207 +/- 127 ml within the first 6 h after operation. There was a positive correlation between CK activities and cTnI concentrations in serum and mediastinal shed blood, but shed blood contained significantly higher concentrations of cTnI as well as CK activities than the circulating blood after admission to the ICU and 6 h after unclamping the aorta. At both time points the cTnI-concentrations and CK activities in shed blood in group B were lower than those in group A but much higher than in serum. The effects of the use of a blood filter diminishes with time. Mediastinal shed blood contains extremely high cTnI concentrations and CK activities. Retransfusion of higher quantities of shed blood might lead to false-positive diagnosis of perioperative myocardial infarction.