Factors That Alter the Relationship Between Peak Postoperative CKMB and Troponin T after CABG

INTRODUCTION: Peak postoperative creatine kinase MB fraction (CKMB) and Troponin T (TnT) levels have been measured after cardiac surgery to assess perioperative myocardial damage, evaluate myocardial protective strategies and predict adverse events. However, the relationship between peak levels of both enzymes has not been fully established in this setting. We compared peak levels of CKMB and TnT in patients after CABG to test the hypothesis that patient and operative characteristics influence the correlation between the values of these biomarkers. METHODS: Data were prospectively collected from 171 consecutive patients undergoing on-pump CABG at a single institution between July 1, 2014 and Dec 31, 2015. Peak values were selected from all serum levels of CKMB and TnT collected during the hospital stay following surgery. Clinical variables were collected based on definitions in the STS Adult Cardiac Surgery Database version 2.181. Linear regression models were used to statistically compare the slope of the linear relationship between peak postoperative CKMB and TnT for the patient cohort. Models were created to compare the slopes by pre-defined clinical variables including (1) gender, (2) age (< or >70), (3) race, (4) tobacco use, presence or absence of (3) hypertension, (4) dyslipidemia, (5) diabetes, (6) renal dysfunction (GFR<60), (7) MI within 21 days, (8) EF (< or > 40%), preoperative use of (9) ACE-inhibitors, (10) beta-blockers, and (11) anticoagulants; and operative variables including (1) cross clamp time (< or > 70 min), (2) CPB time (< or > 100 min), and (3) whether or not intra-operative blood products were received. A lower slope implies less change in CKMB compared to the change in TnT. RESULTS: Overall, the correlation between peak postoperative CKMB and TnT was robust in patients undergoing CABG (m = 19.6, r= 0.783). However, the slope of the relationship was significantly lower in males, patients > 70 years, diabetics, non-smokers, patients with renal dysfunction, patients with lower EF, patients receiving anticoagulants, and patients undergoing CABG following a recent MI. The slope was significantly greater in patients with longer clamp times and who were receiving beta blockers and ACE-inhibitors (Table I). In all other models, the slope of the relationship was similar. CONCLUSION: The relationship between CKMB and TnT following CABG appears to be influenced by patient and operative characteristics. These data do not assess which enzyme more accurately reflects myocardial injury, but does suggest conclusions about myocardial damage may be affected by the biomarker selected in the presence of certain variables. Further study to assess the association between these biomarkers and patient outcomes is warranted.