Cardiac Biomarker May Provide New Tool for Diagnosing Post-Surgical MI

Researchers from the Heart Center at Massachusetts General Hospital have discovered that, in patients who are recovering from coronary-artery bypass grafting (CABG), high levels of a particular biomarker may be a new prognostic tool for diagnosing heart attacks.

James Januzzi, MD, director of the MGH Cardiac Intensive Care Unit and lead author of the study, and his team of researchers found that, out of the study participants, almost all of them had elevated cardiac troponin T (cTnT) levels, though only 2% of those patients “actually met postoperative myocardial infarction criteria.”

According to the researchers, current standards for the diagnosis of a post-operative myocardial infarction include “consideration of symptoms such as chest pain, electrocardiogram changes and the results of biomarker tests.” They add, however, that because patients who are recovering from CABG often experience chest pain, and because the results of post-operative electrocardiograms “are often unclear,” biomarkers such as cTnT are often more heavily relied upon for diagnostic purposes. This served as the basis for the study, according to the researchers, the primary aim of which was to determine “the usefulness of cTnT in the diagnosis of post-CABG heart attack and to examine factors associated with postoperative cTnT elevation and how well cTnT levels predicted postoperative complications in general.”

For the study, the researchers took measurements of cTnT levels from 850 patients immediately after the CABG procedure and then again at 6, 8, 18 and 24 hours after surgery. Analysis of cTnT levels was based on “several factors” that were correlated to the patient’s original illness, surgery, and short- and long-term outcomes.

According to the researchers, though “the near-universality of cTnT elevation made it a less useful indicator of heart attack,” cTnT levels in patients that are 10 times higher than current guidelines suggest are able to “powerfully and independently predicted the risk of death and other postoperative complications.” In addition, the researchers state that this new finding may suggest that the current guidelines for using cTnT levels to diagnose post CABG heart attacks should be revised.

"These findings imply that the diagnosis of regional post-CABG myocardial infarction should continue to be based largely on clinical judgment and angiographic demonstration of postoperative closure of a bypass graft, which is fortunately a rare situation," said Januzzi, who is also an associate professor of medicine at Harvard Medical School. "On the other hand, excessive diffuse myocardial injury - as reflected by significant cTnT elevation - may be more common than suspected; and cTnT does an excellent job of identifying those patients destined for complication in the postoperative period. This makes a strong case that troponin testing should be incorporated into overall post-CABG risk assessment, independent of its use for MI diagnosis."