Impact of ischemic stroke on the risk of venous thromboembolism in the general population: The Tromsø Study and The Trøndelag Health Study

Background: Data on venous thromboembolism (VTE) after ischemic stroke in the general population is limited. We aimed to explore the impact of ischemic stroke on overall VTE and VTE subtypes and by sex at the population level, and to evaluate whether the risk of stroke-related VTE changed between 1994-2007 and 2008-2019

Methods: Participants (n=107,321) were recruited from three surveys of the Tromsø Study (enrolment:1994-2008) and two surveys of the Trøndelag Health Study (enrolment:1995-2008), and followed through 2014 and 2019, respectively. Hazard ratios (HRs) of VTE were calculated using Cox models with stroke as time-varying exposure. Cumulative incidences of VTE were estimated with death as a competing event.

Results: Ischemic stroke was diagnosed in 5,974 individuals, of whom 199 developed VTE during follow-up. Within three months post-stroke, the cumulative incidence and HR of VTE was 1.13% and 13.47 (95%CI:9.41-19.27) in women, and 0.76% and 9.50 (95%CI: 6.38-14.14) in men, respectively. Stroke conferred a 19-fold increased risk of provoked VTE (HR 18.67; 95% CI:14.01-24.88) and a 3-fold increased risk of unprovoked VTE (HR 3.05; 95% CI:1.45-6.45) within three months. The risk estimates of VTE after stroke did not change between the two time-periods.

Conclusion: Sex-specific risk estimates for VTE were only marginally higher in women than in men. Ischemic stroke was associated with particularly high risk of provoked VTE, emphasizing the potentiating effect of additional risk factors. The risk of VTE after ischemic stroke has not declined over the past decades.