Clinically important troponin I threshold for mortality after cardiac surgery

1. For patients undergoing only a coronary-artery bypass grafting (CABG) or aortic-valve operation, a troponin I level 218 times the upper reference limit was found to be associated with increased postoperative mortality.

2. For other cardiac surgery patients, the threshold for increased mortality is 499 times the upper reference limit.

Evidence Rating Level: 2 (Good)

Study Rundown: Cardiac surgery is an increasingly common and potentially life-saving treatment for many patients. Nevertheless, complications such as myocardial injury can worsen outcomes and increase mortality. Creatine kinase MB was historically used to diagnosed myocardial injuries and infarctions but has since been replaced by cardiac troponin due to availability. Recommendations suggested a troponin level ranging from 10 times to 70 times the upper reference limit as clinically important, with only limited supporting evidence. This current prospective cohort study sought to determine the troponin I thresholds that were associated with an increased risk of death within 30 days of a cardiac surgical procedure. Among patients who had isolated CABG or aortic valve procedures, the troponin threshold associated with increased mortality was 218 the upper reference limit. Among patients undergoing other cardiac surgery, this clinically important threshold was 499 times the upper reference limit. This study indicated that the clinically important cardiac troponin threshold may be significantly lower than currently suggested by consensus recommendations.

Click here to read the study in NEJM

Relevant Reading: Postoperative high-sensitivity troponin and its association with 30-day and 12-month, all-cause mortality in patients undergoing on-pump cardiac surgery

In-Depth [prospective cohort]: The article reported findings from an international prospective cohort study of 13,862 patients 18 years of age and older undergoing cardiac surgery. Patients were included if they had any cardiac surgical procedure, excluding pericardiectomy or device implantation. Patients were excluded if they had a myocardial infarction within 1 day of the surgery or a preoperative cardiac troponin I level of 300ng/L or high within 12 hours of the surgery. The blood troponin I level was measured before surgery, 3-12 hours after surgery, and on postoperative days 1, 2, and 3. The high-sensitivity measurements were performed using the ARTCHITECT STAT assay and the upper reference limit was 26ng/L. Patients, health care providers, and data collectors were blinded from the troponin results. The primary outcome was death within the first 30 postoperative days. Secondary outcomes included postoperative major vascular complications and myocardial infarction within 30 days after surgery. Patients were stratified based on their perioperative complication risk, determined through the European System for Cardiac Operative Risk Evaluation II (EuroSCORE II). By 30 days following surgery, 296 patients (2.1%) had died and 399 (2.9%) had developed a major vascular complication. Among patients who only had a CABG or aortic valve procedure, the lowest troponin I level, measured within 1 day following surgery, that was associated with a EuroSCORE-adjusted hazard ratio of higher than 1.00 for 30-day mortality was 5670ng/L (95% confidence interval [CI], 1045 to 8260). This was 218 times the upper reference limit. On day 2 or 3 following the surgery, the threshold level for increased 30-day mortality was 1522ng/L (95% CI, 1325 to 2433), which was 59 times the upper reference limit. The threshold troponin level, measured within 1 day after surgery, for increased risk of major vascular complications in this group, was 4184ng/L (95% CI 1499 to 7781), which was 161 times the upper reference limit. For patients who underwent other types of cardiac surgery, the lowest troponin I level, measured within 1 day after surgery, that was associated with increased 30-day mortality was 12,981ng/L (95% CI, 2673 to 16,591) and 499 times the upper reference limit. For postoperative day 2 or 3, the threshold level for increased 30-day mortality was 2503ng/L (95% CI, 1228 to 4033)m which was 96 times the upper reference limit. The threshold troponin level, measured within 1 day after surgery, for increased risk of major vascular complications in this group, was 9654ng/L (95% CI, 5227 to 15,107), which was 371 times the upper reference limit. Overall, these results indicated that high-sensitivity troponin I thresholds that were clinically important in heightening mortality risk following cardiac surgery were substantially higher than suggested by consensus recommendations. However, a limitation of the study was that new evidence of myocardial injury which was part of consensus statements, such as imaging data, was not examined.

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