Impact of Obesity on the Prognostic Value of the N-Terminal Pro-B-Type Natriuretic Peptide (NT-proBNP) in Patients With Acute Myocardial Infarction

Study Questions:

Does body mass index (BMI) impact the predictive value of pro-B-type natriuretic peptide (NT-proBNP) in patients with acute myocardial infarction (AMI)?

Methods:

This was a subanalysis of prospectively collected data from the Observatoire des Infarctus de Cote d’Or (RICO) study, a multicenter, observational study of patients admitted to intensive care units in France with the diagnosis of AMI (defined as typical ischemic symptoms with either electrocardiogram changes or positive cardiac markers). Patients were matched according to age, Killip class, gender, and renal function, and were then categorized by BMI as obese, overweight, or normal. The correlation between NT-proBNP and BMI was assessed. Multivariable predictors of 1-year cardiovascular mortality were then evaluated with logistic regression.

Results:

There were 739 patients in each BMI category (n = 2,217 total). In all categories, the median age, was 70 years, 80% were males, and median left ventricular ejection fraction (LVEF) was 55%. BMI was inversely correlated with NT-proBNP (r = -0.20, p < 0.001). One-year mortality did not differ between normal (8.2%), overweight (6.3%), and obese patients (7.5%, p = 0.69). Correlates of cardiovascular mortality at 1 year included log NT-proBNP (odds ratio [OR], 2.4; 95% confidence interval [CI], 1.7-3.3), LVEF (OR, 0.95; 95% CI, 0.93-0.96 per %), Grace score decile (OR, 1.09; 95% CI, 1.02-1.18), and angiotensin-converting enzyme inhibitor use (OR, 0.56; 95% CI, 0.36-0.85). When stratified by BMI category, NT-proBNP was predictive of mortality in normal (adjusted OR, 3.6; 95% CI, 1.9-6.7) and overweight patients (adjusted OR, 3.7; 95% CI, 1.8-7.8), but not in obese patients (adjust OR, 1.3; 95% CI, 0.83-2.1).

Conclusions:

The authors concluded that NT-proBNP levels are lower in obese patients presenting with AMI, and the marker’s prognostic discrimination is compromised in obesity.

Perspective:

Elevated natriuretic peptide levels have repeatedly been shown to portend poor prognosis in patients with AMI. However, several factors are known to affect natriuretic peptides levels, including obesity, renal dysfunction, and age. While normal and overweight patients in this study had over a threefold higher adjusted risk of death at 1 year per log NT-proBNP increase, obese patients demonstrated a nonsignificant trend for log NT-proBNP risk at a third the magnitude. Similarly, Kaplan-Meier survivals of obese patients in the highest NT-proBNP tertile appeared better than that of nonobese patients with similar NT-proBNP elevations. Thus, while obesity tends to lower NT-proBNP levels, this study also suggests that obesity is ‘protective’ in those with higher natiuretic peptide levels. Clearly, much remains to be elucidated about natriuretic peptides, their metabolism, and prognostication. Regardless of peptide level, all patients should get aggressive secondary prevention according to current guidelines.

Keywords: Myocardial Infarction, France, Body Mass Index, Biological Markers, Overweight, Obesity, Electrocardiography, Natriuretic Peptide, Brain


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