Wern Yew Ding, MBChB
Thromboembolism is a major cause of global mortality. The risk of thromboembolism with atrial fibrillation (AF) is well established. However, most studies on this topic have focused on the risk of stroke and systemic arterial embolism. The risk of venous thromboembolism (VTE) in association with AF is less studied or even recognized in clinical practice.
In this study, Hornestam and colleagues investigated the relationship between AF and total VTE, including pulmonary embolism (PE) and deep venous thrombosis (DVT). The authors utilized the Swedish National Inpatient Register to identify patients with a first diagnosis of AF and no prior history of stroke, PE, DVT, or pulmonary hypertension along with matched controls by sex, age, and county from 1987 to 2013. The final cohort consisted of 463,244 patients with AF and 887,336 controls without AF. The main findings of the study were that patients with AF had a significantly greater risk of PE, DVT, and VTE compared to matched controls, particularly in younger patients and females, after accounting for other risk factors. Moreover, patients were at greatest risk of VTE (and DVT and PE) during the initial 1 month (male: HR 6.64 [95% CI, 5.74 – 7.69]; female: HR 7.56 [95% CI, 6.47 – 8.83]), but this risk declined over time and did not persist beyond the first year.
The findings from this study were consistent with other observational studies and highlighted a higher risk of VTE among younger patients and females with AF. It is also supported by our understanding of shared mechanisms between AF and thromboembolism. The excess risk during the initial period may be contributed by other conditions that led to hospitalization, immobilization, and the paradoxical prothrombotic risk associated with warfarin initiation (the predominant choice of anticoagulation agent in this cohort). Nonetheless, if AF is to be considered an independent risk factor for VTE, it is puzzling that this risk did not persist beyond 1 year, given the suboptimal rates of oral anticoagulation (57% in males and 53% in females at 1 year). Moreover, it would be interesting for future studies to evaluate whether a similar trend is observed with non-vitamin K antagonist oral anticoagulation.