March 14, 2015 – Past performance on warfarin may not be predictive of future performance, according to a new study.
Atrial fibrillation (AF) is the most common arrhythmia in clinical practice; there are more than 20 million patients with the disorder worldwide. The prevalence of AF will continue to rise due to an aging patient population and increasing cardiovascular comorbidities that are associated with the disorder.
Compared to individuals without AF, patients with AF are as much as seven times more likely to have a stroke. Oral anticoagulants reduce the risk of stroke by more than two-thirds, but they also increase the risk of bleeding, including intracranial hemorrhage.
Vitamin K antagonists, such as warfarin, have been the mainstay of anticoagulation therapy for many years. Non-vitamin K antagonist oral anticoagulants (NOACs) have been approved in recent years for stroke prevention in AF patients, but warfarin remains a commonly used anticoagulant.
The clinical benefit of warfarin is associated with maintaining the patient’s international normalized ratio (INR) values between 2.0 and 3.0. The risk of thromboembolic events increases when the INR value goes below 2.0, and the risk of bleeding increases when the INR value goes above 3.0. NOACs do not require INR monitoring and have similar efficacy and less intracranial bleeding relative to warfarin.
Given the potential advantages to use of NOACs, many clinicians are now considering which of their patients should be switched from warfarin to an NOAC. According to the DCRI’s Sean Pokorney, MD (pictured), many providers believe that patients who are stable on warfarin and doing well should not be switched, but there are little available data characterizing the stability of INR values and indicating whether stability predicts future INR values.
“There have been several studies that have described the characteristics of patients on warfarin,” Pokorney said, “but there have been few studies that have looked at the stability of INR values over time, and the question of evaluating the association between historical and future INR values is a unique perspective.”
To address this, Pokorney and several colleagues studied data from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF), and they presented their findings Saturday at the Scientific Sessions of the American College of Cardiology in San Diego.
“Based on the available data about anticoagulation prescriptions, the majority of patients who are being initiated on oral anticoagulants are being prescribed NOACs, but many patients who have historically been on warfarin are not being changed to NOACs,” Pokorney said. “It is important to try to identify patients who may do better on NOACs, as providers face the question of which patients to switch.”
When asked what he found most surprising about his team’s findings, Pokorney indicated that while it wasn’t a surprise that the vast majority of patients (98 percent) had at least one INR value outside of the therapeutic range (2.0 to 3.0) during the study, it was noteworthy that 65 percent of patients had at least one INR value meaningfullyoutside of the therapeutic range (< 1.5 or > 4.0).
“It was surprising to see that even among patients with all INR values in the 2.0 to 3.0 range over a 6-month period, 85 percent went on to have at least one INR value outside of the therapeutic range over the subsequent year, and more than 1 in 5 of these patients went on to have at least one INR value well outside the therapeutic range (1.5 to 4.0) over the subsequent year,” he said. “Furthermore, approximately one-third of patients had 30 to 50 percent of their INR values out of the 2.0 to 3.0 range in a 1-year period regardless of the number of INR values in range over the preceding 6 months.”
Currently, when seeing a patient on warfarin, many providers will look at the last several months of INR values to get a sense of whether the patient has been doing well and been stable on warfarin. But this might not be the best practice.
“It is important for patients and providers to realize that past performance on warfarin may not be predictive of future performance as people have thought,” Pokorney said. “The decision to switch a patient from warfarin to an NOAC needs to be individualized to every patient scenario, but this study raises the question about whether or not all eligible patients should be considered for NOAC regardless of how well they have been doing on warfarin.”
When asked what the next steps are following this research, Pokorney said, “This study is descriptive, but there are no outcomes data. The next step will be to evaluate the association between INR stability or instability and outcomes.”
To see Dr. Pokorney discussing this topic, watch this video.