TUESDAY, Feb. 8 (HealthDay News) -- High levels of certain blood enzymes following coronary-artery bypass surgery can signal an increased risk of death, a new study suggests.

For those with the highest enzyme levels, the risk of dying within 30 days was double that of those with the lowest levels.

Elevated levels of creatine kinase or troponin are common after bypass surgery, and small increases were not considered significant until now, the researchers noted.

"When people have a bypass operation done sometimes there is some damage to the heart muscle, and chemicals are released that mark that," said study author Dr. Michael J. Domanski, from the Mount Sinai Cardiovascular Institute in New York City.

"What our study shows is that there is a strong graded association of enzyme elevation with mortality," he said. "More is worse, but even small amounts have an impact on mortality."

Domanski doesn't think that measuring these enzymes after surgery would have any impact on treatment. However, he said that since most of the heart damage occurs during surgery, these enzymes could be measures of the quality of heart operations in different hospitals.

"I'd rather have my bypass operation with somebody who has less enzyme elevation," he said. "The larger their enzyme elevations, the less I'd like to go to them."

The report is published in the Feb. 9 issue of the Journal of the American Medical Association.

Domanski and his colleagues set out to study the effect of elevated enzymes on short- and long-term patient outcome after coronary-artery bypass surgery to replace blocked heart arteries. To do this, they conducted a meta-analysis, which consists of reviewing published studies to look for patterns.

They identified seven studies that included 18,908 patients who underwent CABG and were followed for three months to five years.

Patients with even moderately increased levels of creatine kinase or troponin after surgery were at greater risk of dying both one month and five years after surgery, the researchers found.

While age, history of kidney disease and an earlier heart attack were also associated with the risk of death, enzyme levels were still the strongest predictor.

According to the authors, the findings need confirmation in large clinical trials, but levels of these enzymes might one day be used as markers for bypass surgery outcomes. Doctors often test for elevated creatine kinase or troponin levels to confirm a heart attack, but testing is not routinely done after bypass since these patients usually get aggressive treatment with statins and other medications.

Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles, said the findings could influence patient treatment.

"It is well-established that large increases in cardiac enzymes are associated with higher risk of subsequent mortality," Fonarow said. "However, the data as to whether smaller increases in cardiac enzymes are associated with increased risk have been mixed."

This new analysis suggests that elevations of these enzymes in the first 24 hours after coronary artery bypass grafting (CABG) surgery were associated with increased 30-day and one-year mortality even in patients with modest elevations, compared with patients who had no increase in enzyme levels, he said.

"Patients undergoing CABG who are found to have early elevations in cardiac enzymes should be recognized as being at higher risk for mortality and potentially treated more aggressively with cardiovascular protective medications," Fonarow said.

More information

For more information on coronary artery bypass surgery, visit the American Heart Association.