Estimates suggest that pulmonary embolisms cause 1.3% of deaths. This is probably an underestimation of the true number of patients who experience a PE, but the advent of CT angiography has dramatically increased both our ability to detect PE and the number of our patients receiving anticoagulation.
After a diagnosis of pulmonary embolism is established and patients are appropriately treated, we switch to the search for risk factors. Risk factor reversibility and resolution guide the duration of anticoagulation therapy. Most patients with acute PE have an identifiable risk factor at the time of presentation. For those patients who have a first episode of PE with reversed or resolved risk factors – such as immobilization, surgery, and trauma – 3 months of therapy may be warranted.
So, what about those patients who do not have an identified risk factor (that is, "unprovoked") for whom we elect to stop coumadin after 3 months? The risk of recurrence in this group is about 20% within 2 years of discontinuation of vitamin K antagonists (such as coumadin).
Is there anything we can do to reduce this risk for recurrence?
A randomized clinical trial published earlier this year evaluated the efficacy of aspirin 100 mg daily given for 2 years to prevent the recurrence of venous thromboembolism (VTE). Patients were eligible for enrollment if they were at least 18 years of age and were treated for 6-18 months with vitamin K antagonists for a first-ever objectively confirmed unprovoked DVT, PE, or both. Mean patient age was 62 years. Study outcomes were confirmed by a central, independent adjudication committee.
Patients were randomized either to aspirin (205 patients) or placebo (197 patients) (N. Engl. J. Med. 2012;366:1959-67).
The rate of VTE recurrence was significantly lower among patients receiving aspirin than among those receiving placebo: 6.6% vs. 11.2% per year, respectively (hazard ratio 0.58; 95% confidence interval, 0.36-0.93). Subgroup analyses revealed that patients who entered the study because of PE had a significantly lower recurrence rate on aspirin (6.7% per year), compared with placebo (13.5%) (HR 0.38; 95% CI: 0.17-0.88). This was also true of patients who entered the study because of DVT, though the difference wasn’t significant (HR 0.65; 95% CI: 0.65-1.20). No differences were observed in bleeding events between aspirin and placebo.
The aspirin dose used in this study is the dose recommended for the secondary prevention of cardiovascular or cerebrovascular events. These data are extremely compelling and should be incorporated into our practices, if they aren’t already.
Dr. Ebbert is professor of medicine and a primary care clinician at the Mayo Clinic in Rochester, Minn.. The opinions expressed are solely those of the author.