The impact of underweight and obesity on outcomes in anticoagulated patients with atrial fibrillation: A systematic review and meta-analysis on the obesity paradox.

Although obesity is associated with the development and progression of atrial fibrillation (AF), an obesity paradox may be present, illustrated by seemingly protective effects of obesity on AF-related outcomes. Body mass index (BMI) has an impact on outcomes in AF patients using oral anticoagulants. After searching Medline and Embase, meta-analysis of results of four randomized and five observational studies demonstrated significantly lower risks of stroke or systemic embolism (RR 0.80, 95%CI [0.73-0.87]; RR 0.63, 95%CI [0.57-0.70]; and RR 0.42, 95%CI [0.31-0.57], respectively) and all-cause mortality (RR 0.73, 95%CI [0.64-0.83]; RR 0.61, 95%CI [0.52-0.71]; and RR 0.56, 95%CI [0.47-0.66], respectively) in overweight, obese and morbidly obese anticoagulated AF patients (BMI 25 to <30, ≥30 and ≥40 kg/m , respectively) compared to normal BMI anticoagulated AF patients (BMI 18.5 to <25 kg/m ). In contrast, thromboembolic (RR 1.92, 95%CI [1.28-2.90]) and mortality (RR 3.57, 95%CI [2.50-5.11]) risks were significantly increased in underweight anticoagulated AF patients (BMI <18.5 kg/m ). In overweight and obese anticoagulated AF patients, the risks of major bleeding (RR 0.86, 95%CI [0.76-0.99]; and RR 0.88, 95%CI [0.79-0.98], respectively) and intracranial bleeding (RR 0.75, 95%CI [0.58-0.97]; and RR 0.57, 95%CI [0.40-0.80], respectively) were also significantly lower compared to normal BMI patients, while similar risks were observed in underweight and morbidly obese patients. This meta-analysis demonstrated lower thromboembolic and mortality risks with increasing BMI. However, as this paradox was driven by results from randomized studies, while observational studies rendered more conflicting results, these seemingly protective effects should still be interpreted with caution.