Predicting Mortality Risk in CABG Patients

A large-scale study of 19,000 coronary artery bypass graft (CABG) patients whose biomarker levels were checked within 24 hours of surgery suggests that the mortality risk is higher in patients with elevated creatine kinase (CK-MB), troponin, or both.

Although several small studies have indicated that cardiac enzyme elevation in the 24 hours following CABG surgery is associated with worse prognosis, definitive data has never been presented, and the long-term prognostic impact of small increases of perioperative enzyme has not been reported.

In a study published in the Journal of the American Medical Association, Michael J. Domanski, MD, of Mount Sinai Cardiovascular Institute in New York, and colleagues sought to “quantify the relationship between peak post-CABG elevation of biomarkers of myocardial damage and early, intermediate-, and long-term mortality, including determining whether there is a threshold below which elevations lack prognostic significance.”

The authors performed a PubMed search in July 2008 using the search terms “coronary artery bypass,” “troponin”, “CK-MB”, and “mortality.” Studies evaluating mortality and CK-MB, troponin, or both were included, and data were examined to ensure that cardiac markers had been measured within 24 hours after CABG surgery, and key baseline covariates, and mortality were available.

The researchers looked at a total of 18,908 subjects from seven studies who were followed for between three months and five years. Mortality was found to be a monotonically increasing function of the CK-MB ratio, according to Domanski and colleagues, who found that the 30-day mortality rates by categories of CK-MB ratio were 0.63% for 0 to <1, 0.86% for 1 to <2, 0.95% for 2 to <5, 2.09% for 5 to <10, 2.78% for 10 to <20, and 7.06% for 20 to ≥40. Of the variables considered, the CK-MB ratio was the strongest independent predictor of death to 30 days and remained significant even after adjusting for a wide range of baseline risk factors. This result was strongest at 30 days; however, the adjusted association persisted from 30 days to one year, and a trend was present from one year to five years. Similar analyses using troponin as the marker of necrosis led to the same conclusions.

The investigators concluded that “among patients who had undergone CABG surgery, elevation of CK-MB or troponin levels within the first 24 hours was independently associated with increased intermediate- and long-term risk of mortality.”

To access the study, click here.

For more information, check out these CAGB resources from the American Heart Association.