Elevated cardiac troponin (cTn) within 48 hours of coronary artery bypass graft (CABG) surgery may indicate prognostically significant perioperative myocardial injury (PMI) and need for further clinical evaluation for Type 5 MI, conclude Matthias Thielmann, MD, et. al., in a position paper published by the European Society of Cardiology (ESC) in the European Heart Journal.

PMI and Type 5 MI following CABG surgery are associated with a poorer prognosis. However, the lack of a clear definition of PMI that indicates worse clinical outcomes led the ESC Joint Working Groups on Cardiovascular Surgery and the Cellular Biology of the Heart to better define the level of cardiac biomarker elevation following CABG surgery at which PMI has prognostic significance.

PMI has been defined as an isolated elevation in creatine kinase-MB fraction (CK-MB) or cTn greater than the upper reference limit (URL) within 48 hours after CABG. However, most patients undergoing CABG have elevated biomarkers. While CK-MB elevation after CABG has been associated with increased mortality, most centers now use cTn, which has higher sensitivity and specificity for detecting PMI.

The use of cTn has been a challenge because of different cTn assays, the introduction of high-sensitive assays and the presence of renal dysfunction. Studies have demonstrated that post-CABG mortality increases as cTnT or cTnl levels increase. Further, isolated elevations of cTnT at or greater than seven-times the URL or cTnl at or greater than 20-times the URL (using standard assays) have clearly been associated with significant increases in short- and long-term mortality after CABG. These findings were independent of electrocardiographic (ECG), angiographic and imaging evidence of MI.

Based on this evidence, the Working Groups recommend that for patients with a preoperative cTN less than one-times the URL, isolated elevations of standard cTn assays (cTnT at or greater than seven-times the URL or cTnl at or greater than 20-times the URL) within 48 hours after CABG, in the absence of ECG, angiographic or other imaging evidence of MI, may indicate prognostically significant PMI and require further clinical evaluation for Type 5 MI. Early graft failure should be suspected with high postoperative cTN elevations (cTnl greater than 45-times the URL at 12 hours and greater than 70-times the URL at 24 hours). The Third Universal Definition of MI (2012) should be used to define Type 5 MI.

The authors also propose an algorithm for managing CABG patients with or without suspected graft failure based on cardiac biomarker elevations. The algorithm defines when coronary angiography should be performed and whether patients should be managed conservatively or with PCI or repeat CABG surgery.

Keywords: Coronary Angiography, Creatine Kinase, MB Form, Electrocardiography, Coronary Artery Bypass, Heart, Biomarkers, Prognosis, Algorithms, Troponin

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