By Kerry Grens
NEW YORK (Reuters Health) - People in better shape heading into bypass surgery are less likely to die shortly following the procedure than those who are less fit, according to a new study.
"We were not surprised because it makes intuitive sense that those patients who are not fit are going to do poorly with a large operation," said Dr. James Smith, the lead author of the study and an interventional cardiology fellow at Beaumont Health System in Royal Oak, Michigan.
The findings echo results from earlier studies showing that patients with a greater exercise capacity tend to do better after transplant, weight loss and other surgeries.
Smith said none of those studies looked at heart surgery, however, so he and his colleagues collected data from 596 patients who had undergone coronary artery bypass grafting at their hospitals.
The operation involves transplanting a healthy artery from another part of the body to the heart as a detour around a coronary artery that is blocked by plaque.
According to the National Institutes of Health, it is the most common type of heart surgery among adults.
In the three months before their surgery, all of the patients in the study - who were in their 60s, on average - had gone through a treadmill stress test, which involves walking on a treadmill while one's heart rate and breathing are monitored.
Patients' exercise capacity, or cardiorespiratory fitness, was measured in units called metabolic equivalents (METs). A MET of five is about as strenuous as walking up a flight of stairs. Jogging is equal to about seven METs and walking to about three.
There were 78 patients who maxed out at a score below five METs on the stress test and were therefore considered not fit.
Smith's team found that four patients in the unfit group - or five percent - died during their surgery, while five out of 518 patients in the fit group - just one percent - died.
The pattern was similar for people who died within one month of the surgery and after other patient characteristics were taken into account, the researchers reported in The American Journal of Cardiology.
Smith said it's not entirely clear why those who performed worse on the stress test were more likely to die after bypass surgery.
"Those with lower fitness may actually have, for whatever reason, a technically more challenging surgery," he told Reuters Health.
The body's ability to cope with physical stress is also likely to be involved, researchers said.
Michael Trenell, a physiologist at Newcastle University in the UK who was not involved in the study, said "cardiorespiratory fitness is a useful (marker) of the body's ability to deal with stress, whether that be exercise or surgical stress. The same physiological systems in the body are involved in both."
Trenell said in an email to Reuters Health that studies from his research group and others are beginning to look at whether improving cardiac fitness before surgery can increase patients' chances of survival.
The challenge for some surgeries, including heart bypass, is that there is not much time to intervene between diagnosis and operation.
Smith said exercise capacity could perhaps inform doctors and patients about the risks tied to an operation and whether alternative treatments such as inserting a stent should be explored.
Oftentimes exercise capacity is incorporated into discussions for each individual patient, but is not part of a standardized risk assessment, he said.
Smith's study couldn't go so far as to determine whether some patients would have done better with an alternative treatment.
He added that the study was small, and "further investigation is warranted to underscore the findings here to make sure they are valid."
SOURCE: http://bit.ly/13XZBRl The American Journal of Cardiology, July 15, 2013.