Mortality prediction using high-sensitivity troponin after coronary artery bypass surgery
Authors: Kaura A , Chan W X , Galasko G , Herbert C , Townend J , Grant S , Johnson T , Squire I , Curzen N , O'gallagher K , Kharbanda R , Patel R , Perera D , Channon K , Mayet J 
Published: November 2023

Abstract

Introduction
Recommendations regarding the threshold levels of cardiac troponin elevations for the definition of peri-operative myocardial infarction and clinically important peri-procedural myocardial injury in patients undergoing cardiac surgery range widely (&gt;10 to ≥70x the upper limit of normal (ULN)) (1,2). Limited evidence is available to support these recommendations.
In a recent multicentre cohort study, Devereaux and colleagues (3) characterised appropriate thresholds of high-sensitivity troponin-I (hs-TnI) for defining myocardial injury within 3 days after cardiac surgery. The threshold associated with an increased risk of 30-day mortality after coronary artery bypass grafting (CABG) was 218 xULN (95% confidence interval (CI), 40-318) of the hs-TnI assay. There have been no large studies assessing this threshold using high-sensitivity troponin-T (hs-TnT). Furthermore, the long-term prognostic value of troponin following CABG is unknown.

Purpose
The aim of our study was to assess the threshold associated with an increased risk of 30-day and 5-year mortality using hs-TnI assays, and to compare these thresholds to those using hs-TnT assays.

Methods
A retrospective cohort study was carried out using the National Institute for Health Research Health Informatics Collaborative Cardiovascular dataset (4,5) of all consecutive patients who had a troponin measured at five hospitals between 2010 and 2017. Patients who had a troponin measurement within three days following CABG were identified. Results were analysed using multivariable adjusted restricted cubic spline Cox regression. All hazard ratios were adjusted for the following components of the European System for Cardiac Operative Risk Evaluation II (EuroSCORE II); age, gender, renal impairment, poor mobility, chronic lung disease, diabetes, left ventricular function, and pulmonary hypertension. Analyses on troponin were performed using the peak troponin level, which was the highest troponin level measured within the first three days following CABG. All troponin measurements were high-sensitivity and were standardised by using the ratio of the observed troponin value divided by the ULN for each troponin assay. The reference for hazard ratios was a troponin level of 1 xULN.

Results
A total of 1055 patients (median age 72 years (interquartile range 63 to 78), 79% male) had a troponin measured within three days post-CABG at the five centres between 2010 and 2017. The threshold for hs-TnI associated with an increased mortality risk was 196xULN (95%CI, 42-494) for predicting 30-day mortality (Figure 1A) and 157xULN (95%CI, 32-409) for 5-year mortality (Figure 1B). The thresholds were similar for hs-TnT assays (Figure 1C and 1D).

Conclusion
The currently recommended troponin thresholds for diagnosing significant myocardial injury following cardiac surgery (&gt;10 to ≥70xULN) are too low. There was good correlation between hs-TnI and hs-TnT measurements for predicting both short- and long-term mortality.Figure 1