Although the association between obesity and CV risk in the general population is clear, whether it's a risk factor following surgical intervention or percutaneous coronary intervention (PCI) is less certain than you might think. Logically, it would make sense that obesity would be linked to worse outcomes given that it predisposes to chronic coronary artery disease, postprocedural wound complications, higher 30-day readmissions, and increased hospital length of stay.

However, studies have described an obesity paradox in patients undergoing PCI or coronary artery bypass grafting (CABG), with evidence of similar or lower postoperative mortality rates in obese patients compared to individuals of normal weight. Indeed, it has been 10 years since the first paper was published using the term "obesity paradox," and there are now a total of 185 papers catalogued in PubMed.

Obesity Paradox

For example, a meta-analysis of 10 post-PCI and 12 post-CABG populations found no evidence of a detrimental association between overweight or obesity and short- or long-term mortality following coronary revascularization.¹ Indeed, the evidence suggested a beneficial effect of elevated BMI levels on both short- and long-term post-procedural mortality. The protective effect diminished during long-term follow-up as obesity progressed into the moderate or severe range.

About half of all patients with chronic HF have a normal or near-normal (i.e., "preserved") left ventricular ejection fraction (LVEF). Like many studies in the last few years, when the I-PRESERVE trial data were analyzed to determine the effect of obesity on death or hospitalization, the best results were seen among patients who were obese; the worst outcomes were seen in the thinnest and the fattest groups of individuals. The stylishly thin Markus Haass, MD, of Theresien Hospital Mannheim, Germany, finished his presentation in November 2009 at the American Heart Association's Scientific Sessions by saying, "If I ever develop heart failure, I had better gain some weight."

Lavie et al., one of the best-known teams researching the obesity paradox, conducted a study of 209 patients with advanced chronic systolic HF, and found that both body mass index (BMI) and percent body fat (BF) were independent predictors of better event-free survival. For every 1 percent increase in BF, clinical events were independently reduced by 13 percent.² In preliminary data in 875 patients with advanced HF, the same team again found a paradoxical independent prognostic impact of BF and all-cause mortality.³

Back in 2001, Tamara Horwich, MD, and colleagues first reported that elevated BMI was an independent predictor of improved survival.⁴ Promotion of weight loss in patients with HF did not seem to lower the mortality risk, and was potentially harmful. A few years later, they reported that B-type natriuretic peptide (BNP) levels are relatively lower in obese than non-obese subjects.⁵ This finding has important implications given that BNP has become widely used both to assay for the presence or absence of HF and its severity. Horwich et al. compared BNP levels in more than 300 patients with systolic HF (LVEF <40 percent) stratified by BMI, and found:

• First, for unknown reasons, BNP levels are lower in obese patients compared to non-obese patients with similar hemodynamics.
• Second, even in obese patients, elevated BNP remains a significant predictor of adverse outcomes, but different cut-off values should be used.

More recently, Dr. Horwich and her team evaluated waist circumference, an alternative anthropometric index of obesity that is more specific to abdominal adiposity.⁶ Again, the obesity paradox was apparent: bigger waist circumference, high BMI, and the combination of both were each associated with improved outcomes in an advanced HF cohort and the effect was seen in both men and women.⁷

One result of such studies is a need to perfect methods that provide information beyond just static measures (weight, height and BMI) to kinetic measures that yield information on metabolic and biological functions. Body composition measurement methods in use or under study today include dilution techniques, air displacement plethysmography, dual-energy X-ray absorptiometry, and magnetic resonance spectroscopy. Recent developments include three-dimensional photonic scanning and quantitative magnetic resonance.

However, Dr. Horwich herself says the most broadly clinically applicable approach is bioelectrical impedance analysis. Since the advent of the first commercially available devices in the mid-1980s, the method has become popular owing to its ease of use, portability of the equipment, and relatively low cost compared to some of the other methods of body composition. Also, in recent years, more accurate methods of bioelectrical impedance analysis have been developed.

References

1. Oreopoulos A, et al. Obesity (Silver Spring). 2008;16:442-50.
2. Lavie CJ, et al. Am J Cardiol. 2003;91:891-4.
3. Lavie CJ, et al. Circulation. 2007;116:II360.
4. Horwich TB, et al. J Am Coll Cardiol. 2001;38:789-95. http://content.onlinejacc.org/article.aspx?articleid=1127418
5. Horwich TB, et al. J Am Coll Cardiol. 2006;47:85-90. http://content.onlinejacc.org/article.aspx?articleid=1137150
6. Clark AL, et al. J Card Fail. 2011;17: 374-80.
7. Clark AL, et al. Am J Cardiol. 2012;110:77-82.

To listen to an interview with Tamara Horwich, MD, about the obesity paradox, visit youtube.cswnews.org. The interview was conducted by Sidney C. Smith, Jr., MD.

 

Keywords: Plethysmography, Waist Circumference, Coronary Artery Disease, Absorptiometry, Photon, Body Mass Index, Weight Loss, Risk Factors, Obesity, Magnetic Resonance Spectroscopy, Percutaneous Coronary Intervention, Length of Stay, Natriuretic Peptide, Brain

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