Obese patients with atrial fibrillation are more efficiently protected from thrombosis under warfarin or xabans compared to non-obese patients; a systematic review and Meta-analysis of six randomized controlled trials.

INTRODUCTION: Recommendations about proper anticoagulation in obese patients, body mass index (BMI) > 30 kg/m2, are not yet clearly defined. Obese patients were included in randomized controlled trials comparing new anticoagulants (NOACs) with warfarin in patients with atrial fibrillation or thromboembolism.

METHODS: We performed a medline search entering proper criteria and finally 6 post-hoc analysis of RCTs, reporting outcome according to BMI, were included in this meta-analysis. Two major outcomes were considered end points in our meta-analysis; thrombosis, including ischemic cerebral events (transient or not) and venous thrombosis (DVD) /pulmonary embolism (PE) and bleeding, including major bleeding and clinically relevant non-major bleeding.

RESULTS: In the NOACs treated group, thrombosis occurred less frequently in obese vs non-obese patients; RR and 95 % CI 0,75 (0,58-0,97), p = 0,03, while low heterogeneity was observed (I2= 40 %). In the warfarin treated subgroup there was statistically significant difference with less thrombotic events occurring in the obese vs non-obese patients; RR and (95 % CI) 0,80 (0,66-0,98), p = 0,03, and heterogeneity was low (I2  = 24 %). This protective effect called the obesity paradox is limited to obese patients anticoagulated for non-valvular atrial fibrillation (NVAF); RR (95 % CI) was 0,70 (0,58-0,85) p = 0,03 and I2  = 24 %. Bleeding events were similar under both NOACs and warfarin in obese vs non-obese analysis.

CONCLUSIONS: Obese patients anticoagulated for NVAF with either standard dose of xabans or INR guided warfarin are more efficiently protected against thrombosis compared to non-obese patients.