Obese Patients Have Survival Edge After Revascularization for Unstable Angina or MI

KROZINGEN, Germany, June 20 -- Obese patients given early revascularization after unstable angina or an acute myocardial infarction are less than half as likely to die within three years than normal-weight patients, researchers here reported.

This finding emerged from a three-year prospective cohort study of 1,676 consecutive patients designed to assess the impact of obesity on outcomes following early revascularization for unstable angina or a non-ST-segment elevation MI.

Whenever possible, coronary stenting or a coronary artery bypass graft were done immediately afterward, Heinz J. Buettner, M.D., of Herz-Zentrum here, and colleagues, reported online in the June issue of the European Heart Journal.

Although patients who are overweight, obese, or very obese have a higher risk of developing diabetes, hypertension, and coronary artery disease, this study found that once a coronary event has occurred and has been optimally treated, obese patients "switch to a more favorable prognosis" compared with normal-weight patients, the researchers said.

This is not the first time that overweight and obesity have been associated with survival in acute coronary syndromes. In 2005, Duke researchers reported that in more than 15,000 acute coronary syndrome patients, 30-day survival was better in overweight and obese patients than in normal-weight and thin patients.

The current findings contrast with primary prevention studies that implicate BMI as a strong risk factor for mortality, Dr. Buettner said. Instead, the results suggest that the prognostic impact of obesity is confounded by a cardiovascular event.

Patients came from a single center from 1996 to 1999 and were divided into four groups according to BMI.

A third of the patients (551) had a normal BMI (18.5-24.9). Half (824) were overweight (BMI 25-29.9), 18% (244) were obese (BMI 30-34.9) and 48 were very obese (BMI above 35).

Obese and very obese patients were younger and had higher rates of hypertension, diabetes, elevated cardiac troponin T, and C-reactive protein levels. The angiographic extent of coronary artery disease was similar in all the BMI groups.

Although discharge medications included a greater use of statins, ACE-inhibitors, and beta-blockers in the obese and very obese patients, analysis ruled out the survival effect of these factors.

Cumulative three-year mortality rates were 9.9% for normal BMI patients, 7.7% for overweight patients, 3.6% for obese patients, and no deaths for very obese individuals (log-rank P =0.043).

Obese and very obese patients had less than half the long-term mortality when compared with normal BMI patients (hazard ratio [HR] 0.38, 95% confidence interval 0.18-0.81, P = 0.012), the researchers said.

These results remained significant even after adjusting for confounding prognostic factors including coronary status and left ventricular function (adjusted HR 0.27, CI 0.08-0.92, P = 0.036).

Given the observational nature of this study, the researchers said further studies are needed to explain the underlying pathophysiology responsible for the more favorable outcomes among obese patients.

Possible explanations could be that obese patients have more detectable and potentially modifiable risk factors for hypercholesterolemia, diabetes, and hypertension. Combined with increased exercise, diet change, and intentional weight loss, these factors might eventually have a stronger impact in obese patients compared with normal-weight patients.

Although the researchers did not have information on whether obese patients embarked on a more vigorous or improved lifestyle and weight loss, Dr. Buettner thought it probably did not affect the results.

Other potential mediators include protective endogenous cannabinoids (higher in obese patients), lower platelet counts, excess triglyceride content in heart tissue, including areas of healed MI, and younger age (obese patients were less likely to have had an earlier MI).

Endogenous cannabinoids, which are increased in obese patients, might have important protective cardiovascular effects, as they are potent vasodilators in the coronary and cerebrovascular beds, the researchers said.

Study limitations included the inability to account for recent weight loss and shifts in body weight and a low absolute number of very obese patients, indicating that the study findings should not be extrapolated to patients with a BMI over 40.

Also, they said, BMI may reflect muscle mass, so that other factors, such as waist-to-hip ratio, might be a better measure of body fat content and distribution.