Bariatric Surgery Reduces MI, Stroke, and Death

Abstract & Commentary

By Andrew J. Boyle, MBBS, PhD, Assistant Professor of Medicine, Interventional Cardiology, University of California, San Francisco. Dr. Boyle reports no financial relationships relevant to this field of study.

Source: Sjostrom L, et al. Bariatric surgery and long-term cardiovascular events. JAMA 2012;307:56-65.

The prevalence of obesity is increasing throughout the western world at an alarming rate. Obesity has been associated with higher rates of cardiovascular events, although the converse association (between weight loss and reduction in cardiovascular events) has been harder to prove. In recent years, surgical treatment of obesity has advanced significantly. Compared to medical treatments, bariatric surgery results in greater and more sustained weight loss. To assess the effects of bariatric surgery on cardiovascular outcomes, the Swedish Obese Subjects (SOS) registry has been prospectively collecting data on patients undergoing bariatric surgery since 1987 in Sweden. The authors report the outcomes of 2010 patients undergoing bariatric surgery by choice (not randomization) in comparison to 2037 control subjects who were treated with standard care in 25 surgical departments and 480 primary care centers in Sweden. The inclusion criteria were men and women ages 37 to 60 years with a body mass index (BMI) ≥ 34 for men and ≥ 38 for women. The exclusion criteria of both groups were prior surgery for gastric or duodenal ulcer, prior bariatric surgery, gastric ulcer during the past 6 months, ongoing malignancy, active malignancy during the past 5 years, myocardial infarction (MI) during the past 6 months, bulimic eating pattern, drug or alcohol abuse, psychiatric or cooperative problems contraindicating bariatric surgery, and continuous steroid or anti-inflammatory treatment.

The mean BMI was 42.4 in the bariatric surgery group and 40.1 in the control group. The patients were followed for a median of 14.7 years and the primary endpoint was a combination of fatal or non-fatal MI or stroke. Secondary endpoints were MI and stroke. In the surgery group, 13.2% had gastric bypass, 18.7% had banding and 68.1% had vertical banded gastroplasty. There was significant and sustained weight loss in the surgery group of approximately 20% of body weight, with no change at all in the control group. Gastric bypass appeared to achieve slightly greater weight loss. Surgery resulted in a 17% reduction in the rate of the primary endpoint of fatal plus nonfatal MI and stroke (hazard ratio [HR] 0.67, P < 0.001). Cardiovascular mortality was lower in the bariatric surgery group (HR 0.47, P = 0.002). Bariatric surgery was associated with lower risk of MI (HR 0.71, P = 0.02) and stroke (HR 0.66, P = 0.008).

Interestingly, the beneficial effects of bariatric surgery on cardiovascular events were not related to baseline BMI, or to weight change. Other baseline variables including age, gender, blood pressure, diabetes, weight, lipid levels, blood glucose, and the presence of metabolic syndrome had no interaction on cardiovascular outcomes in the surgery group. Yet, in the control group, these parameters were predictive of outcomes, as one might expect. The only independent predictor of cardiovascular outcomes in patients undergoing bariatric surgery was a high plasma insulin level. The post-operative complication rate was 13%.

Commentary

The SOS study adds to the growing body of literature that bariatric surgery for obese individuals leads to rapid loss of significant amounts of weight that is sustained over many years, and that this is associated with fewer incident cardiovascular events and lower mortality. This is a large dataset and the study was performed at numerous centers, which strengthen these data and suggest it is more widely applicable. However, because this study was not randomized, there may be considerable selection bias in the patients who selected surgical treatment over standard therapies. This means that although there is circumstantial evidence suggesting benefit, this has not yet been unequivocally proven. Future randomized, controlled trials are needed to confirm this. This study is not only limited by a lack of randomization, we are not given detail of the usual care in this cohort, including exercise levels, dietary interventions, or medication use. Thus, we cannot make firm conclusions from the dataset.

One might predict that the higher the BMI, the greater the benefit a patient would achieve from bariatric surgery. It is fascinating that baseline weight and BMI did not predict who would achieve most benefit. Indeed, the amount of weight lost after surgery was also not predictive of reduction in cardiovascular events. Yet, we continue to select patients for bariatric surgery based on weight and/or BMI. The cardiovascular benefits may not be realized through the mechanism that we originally thought i.e., through loss of fat. Perhaps other hormonal changes following surgery are more important than the amount of body fat. Mechanistic translational studies are urgently needed to more fully understand how this treatment works. Understanding the mechanism of action may allow us to better select patients who may benefit from bariatric surgery, while not exposing those who would not derive benefit to the small but real risks of surgery.