Untangling the obesity paradox in patients with acute myocardial infarction after primary percutaneous coronary intervention (detail analysis by age).

Background: Obesity is associated with increased morbidity and mortality. However, obesity paradox has been discussed in some patients with cardiovascular disease.

Objectives: We investigated the mechanisms of the obesity paradox in acute myocardial infarction (AMI) patients.

Methods: We evaluated 1634 AMI patients with primary percutaneous coronary intervention (PCI). Patients were divided into 6 subgroups according to baseline body mass index (BMI) (low BMI: <20 kg/m, normal BMI: 20-24.9 kg/m, high BMI: ≥25 kg/m) and age (the younger and elderly groups consisting of patients <70 and ≥70 years old). The primary outcome was defined as all-cause mortality.

Results: During the follow-up periods (median, 620 days; range, 344 to 730 days), 8.7% of patients experienced all-cause death. According to the Kaplan-Meier survival analysis, the patients in the younger age group with high BMI demonstrated significantly higher all-cause mortality compared to the other patients in the same age group (P = 0.012). In contrast, patients in the elderly age group with low BMI demonstrated significantly higher all-cause mortality compared to the others in the same age group (P < 0.001). Multivariate cox regression analyses showed that low BMI in the elderly age group (HR 1.69, 95% CI 1.12 to 2.55, P = 0.012) and high BMI in the younger age group (HR 2.77, 95% CI 1.19 to 6.45, P = 0.018) were independent predictors of all-cause mortality.

Conclusions: The obesity paradox was recognized only in patients in the elderly age group and not in the younger age group. The prognostic impact of BMI may differ by age in AMI patients.