Higher BMI Linked to Lower Mortality, More Metabolic Disorders After PCI

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Once again, the obesity paradox appears to be evident, with results of a large cohort of patients undergoing percutaneous coronary intervention (PCI) suggesting that high body mass index (BMI) is associated with lower all-cause mortality. However, the study, published online March 21, 2011, ahead of print in the American Journal of Cardiology, also found that higher BMI was associated with a greater clustering of metabolic abnormalities. Patients with these disorders saw increased mortality risk irrespective of their BMI.

Researchers led by Michael E. Farkouh, MD, MSc, of Mount Sinai Medical Center (New York, NY), examined the prevalence of metabolic abnormality clustering and its relation to mortality in 9,673 obese and normal-weight patients undergoing elective PCI from October 2003 through December 2006. Patients were categorized based on their calculated BMI into the following groups: 18.5 to 24.9, 25.0 to 29.9, 30.0 to 34.9, and at least 35 kg/m².

Patients with higher BMI were younger, more likely to be African-American or Hispanic, and tended to be women. In addition, patients with higher BMI were more likely to be current smokers, use statins, and have higher levels of LDL cholesterol, triglycerides, glucose, C-reactive protein (CRP), and LVEF.

Low BMI, High Death

Patients in the lowest BMI category, between 18.5 and 24.9 kg/m², had the highest mortality rates regardless of their number of metabolic abnormalities. All-cause mortality for that subgroup amounted to 55.5 per 1,000 person-years compared with 33.7, 28.3, and 33.8 per 1,000 person-years in patients with BMI levels of 25 to 29.9, 30 to 34.9, and at least 35 kg/ m², respectively.

Among the 5 metabolic abnormalities measured (hypertension, impaired fasting glucose/diabetes, triglycerides > 150 mg/dL, HDL cholesterol < 40 mg/dL, and CRP > 2.0 mg/L), all were more prevalent at higher BMI categories. The likelihood of having 4 or 5 metabolic abnormalities at once rose in conjunction with increasing BMI (table 1).

Table 1. BMI and Incidence of Multiple Metabolic Abnormalities

 
Compared with patients who had either no abnormalities or only 1, those with 2, 3, or 4 to 5 metabolic disorders each had statistically significant increased hazard ratios for mortality (table 2).

Table 2. Mortality: HR (95% CI)

Results Seem ‘Counterintuitive’

Although the fact that fewer deaths were observed in obese patients who, on average, have more metabolic abnormalities seems counterintuitive, the study authors say, there may be a number of explanations.

For example, because higher BMI is considered a risk factor for developing metabolic abnormalities, obese patients are likely to be more aggressively screened than their normal-weight counterparts, which may lead to earlier recognition of disease states in these patients, Dr. Farkouh and colleagues suggest. In addition, patients with lower BMI—particularly the elderly—may have more debilitating underlying comorbidities such as hemodynamic instability, renal pathology, or chronic obstructive pulmonary disease that may result in a poorer long-term mortality rate irrespective of cardiovascular risk.

“Consequently, patients with lower BMI may not be as robust as those with higher BMI in possessing the metabolic reserve required to effectively deal with the stress of revascularization,” they write.

Another hypothesis is that in some patients higher BMI may indicate greater lean body mass, rather than excess fat. Thus, other measurement tools of adiposity such as waist circumference or waist-to-hip ratio should be considered “if not [to] replace BMI, as a weight risk-stratification tool,” the study authors write.

The results also raise the question of whether patients benefit from being medically optimized, possibly with statin therapy, before undergoing elective PCI, they note.

BMI Not the Best Gauge of Risk

In a telephone interview with TCTMD, Ajay J. Kirtane, MD, SM, of Columbia University Medical Center (New York, NY), said the study casts doubt upon the usefulness of BMI as a clinical tool.

“BMI alone may not be the best reflector of the obesity that is bad for you,” he said. “This study reinforces the ‘obesity paradox’ and revalidates it, but the fact that some of these components of metabolic syndrome are additively important in terms of influencing outcomes is the real message.”

Dr. Kirtane added that multiple factors, including ethnicity, weigh heavily in influencing an individual’s BMI number. “Especially when you are talking about an ethnically diverse population that is undergoing PCI, some have argued that BMI cutoffs should be different,” he said. “Other markers may be more representative of their risk.”

 

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Source:
Bashey S, Muntner P, Kini AS, et al. Clustering of metabolic abnormalities among obese patients and mortality after percutaneous coronary intervention. Am J Cardiol. 2011;Epub ahead of print.

 

 

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