Wern Yew Ding, MBChB
Obesity, as typically defined by body mass index (BMI), is a growing public health problem that is associated with excess cardiovascular disease and all-cause mortality in the general population. Once a condition which was predominantly confined to Western countries, it is now a major challenge in Asia. Yet, the relationship between obesity and atrial fibrillation (AF) remains poorly understood. An increased BMI has been found to be associated with a greater incidence of AF but reduced adverse events during long-term follow-up. However, there is sparse evidence in an Asian-specific cohort which have different BMI distributions compared with a non-Asian population.
In this study of new users of oral anticoagulation in patients diagnosed with AF between January 2015 and December 2017, Lee and colleagues sought to investigate the association between BMI and clinical outcomes in Asian patients using a retrospective observational nationwide cohort database from the Korean National Health Insurance Service (NHIS). The Korean NHIS database is comprised of information for the entire Korean population (~50 million) and has previously been validated. The authors defined BMI categories using the World Health Organisation recommendation for an Asian population: underweight, <18.5 kg/m2 ; normal range, 18.5 to <23 kg/m2; overweight, 23 to <25 kg/m2; obese I, 25 to <30 kg/m2; and obese II, ≥30 kg/m2.
Unsurprisingly, 69.7% (n=30,101/43,173) of the included patients were overweight/obese. These patients had a greater incidence of comorbidities such as hypertension, hyperlipidaemia, diabetes mellitus and peripheral artery disease but were generally younger than patients with lower BMI. The follow-up period for adverse events was 0.6 years. After adjustment for baseline confounders using multivariable cox regression analysis, a higher BMI was associated with a lower risk of ischemic stroke, hospitalization for gastrointestinal bleeding, major bleeding, all-cause death and composite clinical outcome of ischemic stroke, major bleeding and all-cause death. There was no significant relationship observed between BMI and intracranial hemorrhage.
The findings from this study that was conducted using an Asian population are consistent with those reported from predominantly White cohorts. Yet, the counterintuitive results from these observational studies should be interpreted with caution as it is likely subject to a degree of residual bias. Furthermore, as acknowledged by the authors of this study, patients with higher BMI were treated more aggressively than their counterparts, which may have influenced their long-term outcomes. Indeed, AF is a systemic condition for which the treatment should include management of other cardiovascular risk factors, as emphasized by the recent ESC guidelines using the ABC pathway. Moreover, the mechanism by which obesity offers protection in AF remains elusive.
Overall, this study adds to the evidence of an obesity paradox in AF but presents a conundrum for clinicians as it appears that while obese patients are exposed to a greater risk of incident AF, they have better outcomes if they develop the condition.