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Elevated Levels of Cardiac Biomarkers Post-coronary Artery Bypass Surgery Associated with Increased Risk of Death

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According to a recent JAMA study, patients who underwent coronary artery bypass graft surgery and had elevated levels of the cardiac enzymes creatine kinase or troponin in the 24 hours following surgery had an associated intermediate and long-term increased risk of death.

Approximately 400,000 coronary artery bypass grafting (CABG) procedures are done in the U.S. every year. Several small studies have suggested that elevated levels of cardiac enzyme in the 24 hours following CABG surgery is associated with worse prognosis. To examine the relationship between post-CABG elevation of enzyme markers of myocardial damage and early, intermediate- and long-term mortality, Michael J. Domanski, M.D., of the Mount Sinai Cardiovascular Institute, New York, and colleagues analyzed data from randomized clinical trials or registries in which patients underwent CABG surgery and had postprocedure biomarker measurements (CK-MB, troponin, or both). Researchers identified 7 studies that included a total of 18,908 patients. Follow-up varied from 3 months to 5 years.

For each patient, the CK-MB ratio was calculated as the ratio between the peak CK-MB and the upper limit of normal for the participating laboratory of each study. The researchers found that higher ratios were associated with greater risk of death. The 30-day mortality rates by categories of CK-MB ratio were:

  • 0.63 percent for 0 to less than 1
  • 0.86 percent for 1 to less than 2
  • 0.95 percent for 2 to less than 5
  • 2.09 percent for 5 to less than 10
  • 2.78 percent for 10 to less than 20
  • 7.06 percent for 20 to 40 or greater

In the study, the researchers write:

This is the largest study of the relationship between post-CABG surgery enzyme elevation and mortality and shows a strong, graded, independent association of elevation of markers of myocardial necrosis — CK-MB and troponin levels — and mortality following CABG surgery for all CK-MB and troponin ratios greater than 1.

The researchers also found that of the variables in the model, including CK-MB ratio, age, history of kidney dysfunction and prior heart attack, the CK-MB ratio was the strongest predictor of death and remained significant even after adjusting for baseline risk factors. This result was strongest at 30 days, but the adjusted association persisted from 30 days to one year and a trend was present from one year to five years. The findings were similar when the troponin ratio, rather than CK-MB ratio, was examined.

The researchers conclude that elevated levels of CK-MB post-CABG surgery is associated with a poorer long-term prognosis:

Although enzyme elevations are common following CABG surgery, our data make clear that the long-term prognosis is worse for patients who experience even a small elevation of CK-MB than those who do not experience such a increase. These findings may inform the design of future clinical trials with respect to using cardiac markers as an outcome measure following CABG surgery. Although these findings require confirmation in large prospective studies, they suggest that there are clinical implications in terms of long-term prognosis for cardiac enzyme elevations following CABG surgery, particularly among those with very high levels.

Study: Association of Myocardial Enzyme Elevation and Survival Following Coronary Artery Bypass Graft Surgery

Source: JAMA News Releases