By Aaron P Kithcart, MD PhD

This past fall, at the annual meeting of the American Heart Association, the results of an exciting clinical trial called COMPASS were announced. The study looked at the benefit of adding a low dose of rivaroxaban, an oral blood thinner frequently used for patients with blood clots, to a low dose of aspirin in patients with atherosclerosis. Also known as hardening of the arteries, atherosclerosis can lead to many serious complications, including heart attacks and strokes. More than 90 million Americans are thought to have some form of cardiovascular disease. Let’s take a closer look at the study.

How was the study designed?

COMPASS is a double blinded, randomized clinical trial, meaning that neither the doctors nor the patients knew which drugs enrollees were receiving. Researchers tested three different combinations: rivaroxaban plus aspirin, rivaroxaban alone, or aspirin alone. The dose of rivaroxaban for this trial, 2.5 mg twice a day, was lower than what is commonly used today. The primary question was whether or not a low dose of a blood thinner added additional benefit to aspirin. Currently, patients who have had a heart attack or stroke, or have risk factors for atherosclerosis including high blood pressure, high cholesterol, diabetes, or a family history, are started on a low dose of aspirin to prevent complications from blockages in arteries. In this study, enrollees were followed for nearly two years and regularly evaluated for events including heart attacks, strokes, or death.

What were the results of COMPASS?

The study created a lot of excitement because the addition of rivaroxaban resulted in a significant reduction in heart attacks, strokes, and death. Importantly, this was not associated with an increased risk for bleeding, which is unfortunately a complication of patients taking blood thinners. The low risk of bleeding may have been due to the lower dose of rivaroxaban used in this study. There was also a benefit for patients with peripheral artery disease, another form of atherosclerosis in the arms and legs. Those patients taking both rivaroxaban and aspirin had fewer limb complications, including amputations and surgeries. Across the board, patients seemed to benefit from the combination of blood thinner and aspirin without any significant additional risk.

What does this mean for me?

Patients with heart disease are often at risk for future complications, and after the first sign of problems are almost always started on a baby dose of aspirin. The results of COMPASS tell us that someday we may add a low dose of blood thinner as well. Right now, we don’t know if these benefits extend to other blood thinners in the same class, including apixaban, dabigatran, betrixaban, or edoxaban. We also don’t know if patients already on one of these drugs would benefit from the addition of a baby aspirin. Patients with a history of blood clots, including deep vein thromboses or pulmonary emboli, are usually on higher doses of these oral blood thinners. More studies will need to be done to know if there is a benefit for this group of patients.

What happens now?

The dose of rivaroxaban used in this trial was much lower than what is commercially available now. The Food and Drug Administration will look at the results of this trial and determine if this is safe to be used in the appropriate patient population. At the same time, experts from around the world who write international guidelines will take a hard look at whether or not our recommendations for patients should change. The results of big trials like this one often take several years before becoming fully incorporated into patient care. Perhaps most importantly, the people who run clinical studies will now ask if there are other combinations of blood thinners and aspirin that should be tested for the same benefits. Stay tuned!




Dr. Aaron Kithcart is a vascular medicine fellow at Brigham and Women’s Hospital in Boston.