weight an AF risk factor

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By 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. H. Habib, from St. 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.