Aspirin and recurrent venous thromboembolism in patients with symptomatic atherosclerosis: retrospective cohort study

The secondary prevention of venous thromboembolism: Towards an individual therapeutic strategy

After the anticoagulant withdrawal, a substantial proportion of patients with venous thromboembolism will develop recurrent events. Whether to consider an extended treatment depends on the risk of recurrence and bleeding risk. The assessment of the individual risk profile remains a difficult task. Several basal and post-basal factors modulate the risk of recurrence and may help clinicians to select patients who can benefit from the extended therapy. During the year 2017, new evidence regarding the post-basal factors was provided by the Morgagni and Scope studies. Another interesting novelty was the VTE-BLEED score, the first bleeding risk score that obtained the external validation in venous thromboembolism setting. In secondary prevention, the use of direct oral anticoagulants is growing instead of vitamin K antagonist. Even at lower doses, direct oral anticoagulants showed to be effective and safe, to reduce all-cause mortality and seemed to be superior to placebo for the composite outcome of fatal bleeding and fatal recurrence. After the recently published Einstein-Choice trial, the role of aspirin has become truly marginal as rivaroxaban 10 mg showed a bleeding risk similar to aspirin 100 mg but a greater effectiveness reducing the relative risk of recurrence by about 70%. Another option for secondary prevention could be sulodexide, with a lower protective effect than direct oral anticoagulants but an interesting safety profile. In conclusion, in our opinion, an individual strategy taking into account the risk of recurrence, bleeding risk, therapeutic options and patient preferences is the most appropriate approach to secondary prevention of venous thromboembolism.

Optimal duration of anticoagulation

Once anticoagulation is stopped, the risk of recurrent venous thromboembolism (VTE) over years after a first episode is consistently around 30%. This risk is higher in patients with unprovoked than in those with (transient) provoked VTE, and among the latter in patients with medical than in those with surgical risk factors. Baseline parameters that have been found to be related to the risk of recurrent VTE are the proximal location of deep-vein thrombosis, obesity, old age, male sex and non-0 blood group, whereas the role of inherited thrombophilia is controversial. The persistence of residual vein thrombosis at ultrasound assessment has consistently been shown to increase the risk, as do persistently high values of D-dimer and the early development of the post-thrombotic syndrome. Although the latest international guidelines suggest indefinite anticoagulation for most patients with the first episode of unprovoked VTE, strategies that incorporate the assessment of residual vein thrombosis and D-dimer have the potential to identify subjects in whom anticoagulation can be safely discontinued. Moreover, new opportunities are offered by a few emerging anti-Xa and anti-IIa oral compounds, which are likely to induce fewer haemorrhagic complications than vitamin K antagonists while preserving the same effectiveness; and by low-dose aspirin, which has the potential to prevent the occurrence of both venous and arterial thrombotic events.

Why does aspirin decrease the risk of venous thromboembolism? On old and novel antithrombotic effects of acetyl salicylic acid

It is well established that aspirin, an irreversible inhibitor of platelet cyclooxygenase activity, is effective in secondary prevention of arterial thromboembolic events. The pooled results of the recent randomized, multicenter WARFASA and ASPIRE aspirin trials showed a 32% reduction in the rate of recurrence of venous thromboembolism (VTE) in patients receiving aspirin following VTE. These clinical data support evidence that platelets contribute to the initiation and progression of venous thrombosis and aspirin inhibits thrombin formation and thrombin-mediated coagulant reactions. In addition to the known acetylation of serine 529 residue in platelet cyclooxygenase-1, the postulated mechanisms of aspirin-induced antithrombotic actions also involve the acetylation of other proteins in blood coagulation, including fibrinogen, resulting in more efficient fibrinolysis. This review summarizes current knowledge on the aspirin-induced antithrombotic effects that potentially explain clinical studies showing reduced rates of VTE events in aspirin-treated subjects.

The risk of recurrent thromboembolic disorders in patients with unprovoked venous thromboembolism: new scenarios and opportunities

The risk of recurrent thromboembolic disorders in the 10-year period following an episode of unprovoked venous thromboembolism (VTE) ranges between 30 and 50%, the rate being higher in patients with primary deep venous thrombosis (DVT) than in those with primary pulmonary embolism (PE). The clinical presentation with primary PE increases by more than three times the risk of a new PE episode over that with isolated DVT. Baseline parameters that increase this risk are the proximal location of DVT, obesity, old age and male sex, whereas the role of thrombophilia is controversial. An increasing role is played by post-baseline parameters such as the ultrasound assessment of residual vein thrombosis and the determination of D-dimer. While the latest international guidelines suggest indefinite anticoagulation for most patients with the first episode of unprovoked VTE, new scenarios are being offered by the identification of risk stratification models and by strategies that have the potential to help identify patients in whom anticoagulation can be safely discontinued, such as those that incorporate the assessment of D-dimer and residual vein thrombosis. New opportunities are being offered by low-dose aspirin, which has recently been reported to decrease by more than 30% the risk of recurrent events without increasing the bleeding risk; and especially by a few emerging anti-Xa and anti-IIa oral compounds, which are likely to induce fewer haemorrhagic complications than vitamin K antagonists while preserving at least the same effectiveness, do not require laboratory monitoring, and can be used immediately after the thrombotic episode.

Aspirin and recurrent venous thromboembolism

While there is conclusive evidence that aspirin plays a role in reducing the risk of clinically relevant venous thromboembolism (VTE) arising in a number of surgical and non-surgical situations at risk, little is known of the potential of aspirin for the long/term prevention of recurrent VTE. In two recent multicentre, double-blind studies (WARFASA and ASPIRE), the efficacy and safety of a low dose of aspirin (100 mg per day) were assessed in patients with unprovoked VTE who had completed an initial period of conventional treatment with vitamin K antagonists. The two studies used identical aspirin regimens and had similar enrollment criteria and outcome measures. When data from these two trials were pooled, there was a 32% reduction in the rate of recurrence of VTE (hazard ratio [HR], 0.68; 95% confidence interval [CI], 0.51-0.90) and a 34% reduction in the rate of major vascular events (HR, 0.66; 95% CI, 0.51-0.86). Moreover, these benefits were achieved with a low risk of bleeding. As patients with previous symptomatic atherosclerosis were not enrolled in these two studies, whether these results apply also to this category of patients is uncertain. We recently had the opportunity to review the clinical charts of 1919 consecutive patients presented with a first episode of VTE, which was either unprovoked or triggered by transient risk factors, and were followed up for an average period of four years after discontinuing anticoagulation. The rate of recurrent VTE in the 256 patients with a history of symptomatic atherosclerosis who had been given 80-160 mg of aspirin once daily (17.2%) did not differ from that (19.9%) observed in those without atherosclerosis who were left without any antithrombotic treatments. The implication of this observation is that whenever patients with symptomatic atherosclerosis are deemed to require long-term protection against recurrent VTE, they are unlikely to benefit from (resuming) aspirin. Conversely, aspirin in low doses offers an appealing, safe and highly cost-effective option for the long-term prevention of recurrent events in patients with unprovoked VTE who are free from symptomatic atherosclerotic lesions.