What Troponin Level Indicates Injury After Cardiac Surgery?

March 03, 2022

High-sensitivity cardiac troponin thresholds used to diagnose myocardial infarction (MI) and injury after cardiac surgery may need to be considerably higher than those currently recommended, a new study suggests.

"We observed that the lowest troponin thresholds associated with an increased risk of death at 30 days after cardiac surgery were substantially higher than the levels that are currently recommended in consensus statements as the basis for diagnosis of perioperative myocardial infarction or clinically important perioperative myocardial injury," the authors report.

Results of the Vascular Events in Surgery Patients Cohort Evaluation (VISION) study are published in the March 3 issue of the New England Journal of Medicine.

The investigators, led by Philip J. Devereaux, a cardiologist at Hamilton Health Sciences in Hamilton, Ontario, Canada, explain that although cardiac surgery has the potential to improve the quality and prolong the duration of a patient's life, it is associated with complications. Prognostically important myocardial injury, detected by an elevated concentration of cardiac troponin, is one of the most common complications after cardiac surgery and is associated with increased mortality.

Based on expert opinion, the Fourth Universal Definition of Myocardial Infarction suggested that in patients who have normal concentrations of cardiac troponin at baseline, a concentration more than 10 times the upper reference limit should be the threshold used in the diagnosis of MI.

Although there is no evidence-based threshold for cardiac troponin levels after cardiac surgery, a level of 35 times the upper reference limit has been suggested for the diagnosis of MI, along with new evidence of ischemia, and a threshold of 70 times the upper reference limit as a stand-alone criterion for clinically important periprocedural myocardial injury, the researchers note.

Globally, many hospitals now use high-sensitivity cardiac troponin assays, but limited data are available to define a prognostically important degree of myocardial injury after cardiac surgery based on those assays.

The current study was therefore performed to try to determine the relationship between postoperative high-sensitivity cardiac troponin I levels and the risk of death within 30 days after cardiac surgery.

The international prospective cohort study included 13,862 patients undergoing cardiac surgery. High-sensitivity cardiac troponin I measurements were obtained 3 to 12 hours after surgery and on days 1, 2, and 3 after surgery.

Results showed that 296 patients (2.1%) died within 30 days of the surgery. Among patients who underwent isolated coronary-artery bypass grafting (CABG) or aortic-valve replacement or repair, the threshold troponin level, measured within 1 day after surgery, that was associated with an increased risk of death within 30 days (adjusted hazard ratio of more than 1.00) was 5670 ng/L, a level 218 times the upper reference limit.

The threshold level at day 2 or 3 after surgery associated with increased risk of death at 30 days was 1522 ng/L (59 times the upper reference limit).

Among patients who underwent other cardiac surgeries, the results showed the threshold troponin value that was associated with an increased risk of death by 30 days to be 12,981 ng/L (499 times the upper reference limit) within 1 day after surgery and 2503 ng/L (96 times the upper reference limit) on day 2 or 3 after surgery.

The troponin thresholds currently recommended in consensus statements (> 10, ≥ 35, and ≥ 70 times the upper reference limit) were exceeded in 97.5%, 89.4%, and 74.7% of patients, respectively, within the first day after surgery.

Myocardial Injury "Ubiquitous After Cardiac Surgery"

In an accompanying editorial, James de Lemos, MD, and Michael Jessen, MD, University of Texas Southwestern Medical Center, Dallas, point out that the key finding of the study is that myocardial injury is ubiquitous after cardiac surgery and only extremely large troponin elevations are associated with the 30-day risk of death.

"The high-sensitivity cardiac troponin I ratios that were identified as associated with excess risk ranged from approximately 40 to approximately 500, generally well above ratios in the Universal Definition of Myocardial Infarction or Academic Research Consortium-2 consensus recommendations, with thresholds varying according to the type of cardiac surgery, the timing of the high-sensitivity cardiac troponin I assessment, and the outcome that was modeled," the editorialists note.

"These findings suggest that high-sensitivity cardiac troponin thresholds used to diagnose perioperative myocardial infarction and injury may need to be considerably higher than those currently recommended," they add.

But the editorialists suggest that the current findings have limited applicability to clinical practice at present, because many different troponin assays are used.

"For centers that use the same assay as the VISION investigators, the present study does suggest that currently recommended high-sensitivity cardiac troponin I thresholds for diagnosing perioperative myocardial infarction and significant myocardial injury are too low. Sites using other assays will need to await additional assay-specific data before drawing any conclusions," they say.

De Lemos and Jessen also point out that the present study does not provide any insight into the mechanisms of perioperative cardiac injury or attempt to distinguish perioperative MI from injury.

"Such a distinction is critical, since evaluation and treatment approaches would differ notably," they state.

"Until more is understood about underlying mechanisms and strategies for prevention or treatment, the diagnosis of perioperative injury (without infarction) arguably has limited value, other than perhaps suggesting careful review of the surgical and postoperative course for unrecognized complications and closer follow-up with consideration of echocardiography," they write.

"Thus, for many cardiac surgeons and clinical cardiologists, this study will confirm the impression that large troponin elevations are expected after routine cardiac surgery, correlate poorly with clinically evident complications, and remain difficult to interpret and use in determining patient care," the editorialists conclude.

This study was supported by Abbott Laboratories and various international academic and government bodies. Devereaux reported grants and nonfinancial support from Abbott Laboratories and support from CloudDX, Philips Healthcare, Roche Diagnostics, and Siemens outside the submitted work. De Lemos reported grants from Abbott Diagnostics and Roche Diagnostics and personal fees from Ortho Clinical Diagnostics and Quidel Corporation, outside the submitted work.

N Engl J Med. Published online March 3. Abstract, Editorial

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