Aspirin better than heparin at VTE prevention after total hip arthroplasty



Aspirin is an effective, safe, convenient, and inexpensive alternative to low-molecular-weight heparin for extended thromboprophylaxis after total hip arthroplasty, according to a report published online June 3 in Annals of Internal Medicine.

In a multicenter randomized trial involving 786 patients undergoing elective total hip replacement in Canada during a 3-year period, 28 days of oral aspirin prophylaxis was noninferior to and as safe as 28 days of subcutaneous dalteparin injections for preventing venous thromboembolism (VTE), according to Dr. David R. Anderson, who is professor of medicine, pathology, and community health and epidemiology of Dalhousie University, Halifax, N.S., and his associates in the EPCAT (Extended Prophylaxis Comparing Low-Molecular-Weight Heparin to Aspirin in Total Hip Arthroplasty) study.

During this trial, the novel oral anticoagulant rivaroxaban was approved for this indication in Canada, which prompted "a major shift" away from using dalteparin and toward using the new drug in clinical practice. In light of this development, it will be important to "evaluate the benefits and risks of aspirin as extended prophylaxis after [total hip replacement], compared with the new oral anticoagulant agents," noted the EPCAT investigators.

Their findings on the benefits of aspirin also indicate that its role for venous thromboprophylaxis in other settings should now be reconsidered as well, Dr. Anderson and his colleagues added.

In the EPCAT study, patients underwent elective unilateral total hip replacement at 12 university-affiliated tertiary medical centers and received thromboprophylaxis in the form of subcutaneous injections of dalteparin for 10 days. They were randomly assigned to continue receiving dalteparin injections and take placebo oral aspirin tablets (400 patients) or to receive placebo injections and begin taking oral aspirin (81 mg) every day for 28 days (386 patients).

The demographic, medical, and surgical characteristics of the two study groups were comparable. Patients, physicians, study coordinators, and members of the health care teams all were blinded to study assignment.

The introduction of rivaroxaban during the course of the study severely affected ongoing recruitment of subjects, because both patients and orthopedic surgeons became increasingly reluctant to participate in a study requiring daily injections for 38 days when a new oral agent was available. The EPCAT study was terminated early when completion of the intended enrollment appeared "unfeasible" and an interim analysis showed that the primary objective – establishing the noninferiority of aspirin – had been reached.

The primary efficacy outcome was the development of symptomatic proximal deep vein thrombosis (DVT) or pulmonary embolism (PE), confirmed by objective testing, during the 90 days after randomization. This outcome occurred in only 0.3% of the aspirin group, compared with 1.3% of the dalteparin group, establishing the noninferiority of aspirin therapy.

There was a single case of proximal DVT in the aspirin group, compared with two cases of proximal DVT and three of PE in the dalteparin group. Another patient in the dalteparin group developed a symptomatic distal DVT in her calf, "but this was not considered an outcome event," the investigators said.

No major bleeding events developed in the aspirin group, but there was one such event in the dalteparin group for an overall rate of 0.3%. Similarly, there were two clinically significant nonmajor bleeding events for aspirin (0.5% rate), compared with four for dalteparin (1.0% rate). And there were eight minor bleeding events for aspirin (2.1% rate), compared with 18 for dalteparin (4.5% rate).

"In a composite analysis of net clinical benefit that combined VTE and clinically relevant major and nonmajor bleeding complications as outcomes," 0.8% of patients receiving aspirin had complications, compared with 2.5% of patients receiving dalteparin.

There were no differences between the two study groups in secondary outcomes such as wound infections, arterial vascular events, MI, stroke, or deaths.

The EPCAT trial was supported by the Canadian Institutes for Health Research. Aspirin was provided by Bayer HealthCare and dalteparin by Pfizer Pharmaceuticals, but neither Bayer nor Pfizer was involved in the design, conduct, or analysis of the study.

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