Obesity ups risk of complication after heart surgery

By Anthony J. Brown, MD

NEW YORK (Reuters Health) – Obesity is an important risk
factor for the development of an irregular heart beat called
atrial fibrillation (AF) following cardiac surgery, according
to a report published online Monday.

This is the first study to find a strong and independent
link between excess body weight and the development of AF, a
common and potentially fatal heart rhythm abnormality, study
investigators say.

“We were surprised by the increasing magnitude of AF
incidence as levels of obesity increased,” Dr. Robert H. Habib,
from St. Vincent Mercy Medical Center in Toledo, Ohio, who was
involved in the study, told Reuters Health.

In AF, the heart’s two small upper chambers, called atria,
quiver rather than beat effectively. As a result, blood is not
pumped completely out of the heart. As a result, it may pool
and form clots, raising the risk of stroke.

Obesity is increasingly common among patients having heart
surgery. Obesity has been linked to AF in nonsurgical patient
populations, but whether it increased the odds of “new-onset”
AF after cardiac surgery was not known.

Habib’s team examined the records of 8,051 consecutive
patients — 3,164 of whom were obese — who underwent cardiac
surgery at two hospitals between 1994 and 2004. The subjects
were AF-free before surgery.

Overall, 22.5 percent of the patients developed AF after
surgery. In analyses adjusting for age and the presence of
other factors known to increase the risk of AF, researchers
found that the risk of AF increased as body weight increased.

Relative to normal weight, the elevated risk of AF ranged
from 18 percent for overweight subjects to 139 percent for the
most obese patients (BMI > 40).

Other risk factors for postoperative AF included increasing
age, mitral or aortic valve surgery, chronic obstructive
pulmonary disease, male gender, use of beta-blockers before
surgery, vascular disease, white race, and low ejection
fraction — a measure of the heart’s pumping ability.

Because cardiac surgery is often performed on an acute
basis, there usually is not enough time for obese patients to
lose substantial amounts of weight before surgery, Habib
explained. Therefore, other measures are needed to cut the risk
of postoperative AF in obese patients.

One such measure may be to perform cardiac surgery “off
pump” instead of “on-pump.” In the current study, patients who
had cardiac surgery “off-pump” — in which the heart continues
to beat during surgery — were 39 percent less likely to
develop AF than those who had the standard “on-pump” surgery in
which the heart is stopped and the blood is temporarily pumped
by a machine.

SOURCE: Circulation November 14, 2005.