Cardiac troponin I levels after cardiac surgery as predictor for in-hospital mortality

Abstract

Purpose: Troponin is a specific marker of myocardial damage. Increased troponins, however, are observed after almost all cardiac surgery. The clinical significance of this elevation is controversial. The aim of this study was to evaluate if troponin I (cTnI) measured 1 h after cardiac surgery provides additional information to identify patients at risk for hospital mortality.

Methods: Nine hundred and thirty-eight patients undergoing cardiac surgery between October 2006 and June 2008 served as development set. This group included 688 isolated CABGs and 250 valvular (+CABG) operations, and cTnI levels were measured 1 h (cTnI) after surgery. Hospital mortality, defined as death occurring at the Radboud University Nijmegen Medical Centre (UMCN) at any time after surgery, is the studied outcome. To assess the value of cTnI as a predictor for hospital mortality, receiver-operator characteristic (ROC) curves were used. The Youden-index was used for identifying the best cut-off point. Five hundred and seventy-nine patients undergoing cardiac surgery between July 2008 and February 2009 served as validation set.

Results: The median cTnI level was 1.3 microg/l, 75% inter-quartile range (IQR) 0.68-2.59 microg/l. Ten patients (1.1%) died, cTnI release of the dead, median: 6.8 microg/l was significantly higher than the measured values in the group of survivors, median: 1.3 microg/l (P<0.001). Regression analysis showed a significant correlation between cTnI and hospital mortality (P<0.001). The ROC indicates a cTnI level of 4.25 microg/l with a ROC of 0.80 as optimal cut-off point for predicting hospital mortality, with a sensitivity of 70% and a specificity of 89%. Addition of type of surgery, isolated CABG vs. valve surgery, acute vs. elective surgery and EuroSCORE class did not improve the ROCs. In the validation set, the median cTnI level was 1.17 microg/l. Fifty-six patients had a cTnI level >4.25 microg/l. Of the 579 patients, 11 patients (1.8%) died, six of them had a cTnI level >4.25 microg/l.

Conclusion: Postoperative cTnI level, measured within the first hour after cardiac surgery, can identify a subgroup of patients with increased risk for hospital mortality. These patients may benefit from better monitoring, eventually with specific diagnostic and therapeutic interventions.