Hip and knee arthroplasty, thromboembolic prophylaxis: New oral anticoagulants or Aspirin?

The prophylaxis of venous thromboembolism is recommended in all patients undergoing total hip or knee arthroplasty. The choice of an appropriate prophylaxis regimen, however, requires a correct assessment of the patient’s risk profile, for a treatment that is balanced in terms of efficacy and safety.
The fact is that the use of these periprocedural therapies has helped to drastically reduce not only the complications related to thromboembolic phenomena, but also the mortality rates.
In recent times, two major changes have been proposed in relation to the use of the usual antithrombotic drugs. The first is the replacement of Warfarin with the most recent direct anticoagulants. The second, and in some ways more revolutionary change, has proposed replacing the usual “venous” antithrombotic drugs with Acetylsalicylic acid (ASA).
So far, however, no adequate clinical trials have been available to clarify the real effectiveness of antiplatelet treatment.
To fill this gap, an experiment that compares the efficacy of Rivaroxaban and ASA in the prevention of venous thromboembolism in patients undergoing hip or knee arthroplasty is now reported in the pages of the New England Journal of Medicine.
Intra-hospital prophylaxis was performed with Rivaroxaban (10 mg/day) on all patients, starting on the day surgery was perfpormed or on the first post-operative day, up to the fifth post-operative day.
Patients who underwent total knee arthroplasty were later randomized for further treatment with Rivaroxaban (10 mg /day) or ASA (81 mg/day) for an additional nine days.
Patients who had undergone total hip arthroplasty were randomized in regard to the same two treatments, but for thirty days.
The primary efficacy outcome considered in the study was symptomatic venous thromboembolism, defined as deep vein thrombosis with involvement of the popliteal vein, or multiple proximal veins of the legs, or a pulmonary embolism.
The final analysis of the study included 3,427 patients, with an average age of 63 years.
During the 90-day follow-up period, the main endpoint was recorded in 0.64% of patients assigned to the treatment with ASA and 0.70% of patients treated with Rivaroxaban.
Regarding the safety profile of these two drugs, major hemorrhagic events occurred in 0.47% of patients treated with ASA and in 0.29% of those treated with Rivaroxaban (P = 0.42). By analyzing combined major and minor hemorrhagic events, these occurred in 1.29% of patients in the ASA group and in 0.99% of those in the Rivaroxaban group (P = 0.43).
These results therefore seem to indicate that aspirin provides substantially similar protection to that of a direct anticoagulant such as Rivaroxaban, in the prevention of thromboembolic events in patients undergoing arthroplasty operations considered in the study, while at the same time highlighting a similar risk profile for hemorrhagic events.
It is surprising that in the discussion, the authors do not take into consideration the principal doubt that arises from the results concerning this and other similar studies. Is this the reason why a drug like ASA, known for its mechanism of action aimed at acting prevalently on the prevention of arterial thromboembolism, provides results comparable to those of an anticoagulant even in the prevention of venous thromboembolism?
Evidently the study is not designed to provide an answer to this question, but it is obviously a crucial point, in that the two pathophysiological pathways leading to the formation of arterial and venous thrombus are clearly distinct, and clarifying this aspect could help to understand not only how the platelet anti-aggregation can exert a protective effect also in regard to venous circulation, but above all to hypothesize on any new and wider prospects for the use of ASA.
What emerges from this experimentation should also be considered in the field of pharmacoeconomics. Given the huge difference in the costs of the two drugs compared, it is clear that the use of ASA would bring substantial savings in terms of the cost of treatment, and a containment of health expenses related to adverse events of hemorrhagic type.

 

 

D.R. Anderson, et al. Aspirin or Rivaroxaban for VTE Prophylaxis after Hip or Knee Arthroplasty. N Engl J Med 2018;378:699-707.

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