We Have Come Full Circle for Venous Thromboembolism Prevention: Commentary on an article by Emanuele Chisari, MD, et al.: "Aspirin Is an Effective Prophylaxis for Venous Thromboembolism in Ambulatory Patients with Femoral Neck Fracture Undergoing Hip Arthroplasty".

Abstract

Commentary In their study, Chisari et al. add to the recent literature that has shown that aspirin is as effective as other anticoagulants at preventing symptomatic venous thromboembolism (VTE) for surgical lower-extremity conditions. This evidence may be practice-changing for surgeons treating patients with hip fractures and once again elevates aspirin to a preferred prophylactic option. After decades of opinion and evidence that aspirin was not the best prophylaxis for preventing VTE, the pendulum is now strongly swinging back toward aspirin. Studies on elective hip and knee arthroplasty provide the highest-quality evidence to answer important questions about preventing VTE. In patients undergoing elective procedures, tight study control is more feasible than in other conditions in which VTE is a high risk, such as trauma. Previous guidelines for these elective surgical procedures indicated that aspirin was less effective than more powerful anticoagulants. However, more recent studies have suggested otherwise. For instance, a systematic review and meta-analysis of randomized clinical trials found that aspirin for VTE prevention was as safe and effective as other anticoagulants1. Aspirin is now routine for standard-risk patients undergoing hip or knee arthroplasty, but patients with other risk factors for VTE are still considered for more powerful anticoagulation. One such risk factor is trauma. Patients with hip fractures are at extremely high risk for VTE, for reasons including that trauma is a procoagulant, there could be endothelial damage, there could be relative immobility, and hip fractures tend to occur in elderly patients with other comorbid risk factors. Because of these increased risks, patients with hip fracture have not commonly been treated with aspirin and other anticoagulants have been recommended. For instance, in a 2019 update on current practice, the authors noted that, for patients with hip fracture, other chemoprophylaxis has been found to be more effective than aspirin2. In the current study, Chisari et al. show that aspirin prophylaxis for patients with femoral neck fracture treated with arthroplasty is equivalent to prophylaxis with other anticoagulants. The patients in the aspirin group actually had lower rates of VTE, but, when statistical balancing through propensity matching was employed, there was no difference in the VTE rates between the 2 groups. This suggests that aspirin could be used routinely for VTE prophylaxis in these patients. Surgeons should consider a few other factors before broadly accepting the results of this study. First, this was a retrospective study, and it is clear that aspirin was chosen for patients with a lower risk of VTE. However, the propensity matching employed, utilizing an accepted VTE risk score, increases confidence that similar groups of patients were compared. Second, all patients were mobilized on the same day as or the day after the surgical procedure, and all had mechanical compression devices as part of the treatment protocol. The absence of these best practices could have changed the results. Finally, even among the trauma group, there were patients who were higher-risk than others. Exactly which categories of these high-risk patients benefit from more powerful anticoagulation remains unknown. In 1 study of hip and knee arthroplasty, aspirin was equivalent to other anticoagulants even in high-risk patients3. It is interesting to speculate why there is new evidence about a drug that has been studied for decades. After all, aspirin is not new for VTE prophylaxis, so why is it making this data-driven resurgence? Here are a few speculative answers. Perhaps we now have better research or perhaps the disease process has changed in some way. These seem unlikely. Maybe there was bias against the simpler option of aspirin in earlier studies. There clearly has been a shift in studies toward relying on only clinically important outcome measures. For instance, in the current study, only clinically apparent deep vein thrombosis or pulmonary embolism was included as outcomes, compared with surrogates based on imaging studies or ultrasound frequently used in the past. This might be an important difference. Finally, as in this study, aspirin is now combined with early mobilization and mechanical compression devices, things that were not routine in earlier studies. Although it is hard to know what has driven the strong trend toward literature that demonstrates aspirin equivalence to other anticoagulants, this change does give me the feeling of having gone full circle and now we are back to where we started with aspirin.