Philadelphia, PA, October 15, 2015 - Patients with atrial fibrillation (AF) have an increased risk for stroke and are often prescribed oral anticoagulation (OAC) therapy. OAC therapy can prevent disastrous strokes, but at the expense of increased bleeding risks. There are now well-established guidelines to assess the risk of stroke and bleeding in AF patients to determine whether OAC is needed. However, in new a study in the Canadian Journal of Cardiology, researchers found that primary care physicians were often under- or over-estimating stroke and/or bleeding risk, in part because they failed to utilize guideline-recommended risk scoring approaches in one-half and three-quarters of their patients, respectively. This, in turn led to under- and over-prescription of OACs, misdosing, and other problems that could result in an unnecessarily increased risk of stroke and bleeding events.
"Anticoagulation in patients at risk for stroke is an important intervention to reduce the risk of this potentially devastating complication," explained lead investigator Shaun G. Goodman, MD, MSc, of the Canadian Heart Research Centre, a cardiologist at St Michael's Hospital, and the Heart & Stroke Foundation of Ontario Polo Chair at the University of Toronto. "The Canadian Cardiovascular Society (CCS) AF Guidelines recommend that all patients with AF should be stratified using a predictive index for the risk of stroke and for the risk of bleeding, and that most patients should receive antithrombotic therapy. However, despite these recommendations, the uptake of these evidence-based therapies was suboptimal. Among those who did receive anticoagulation with warfarin, as many as four in 10 patients spent less time in the therapeutic range we know is optimal to reduce the risk of stroke."
A multi-institutional team of researchers collected data on 4,670 patients from the primary care practices of 474 physicians in Canada. As part of the Canadian Facilitating Review and Education to OptiMize stroke prevention in Atrial Fibrillation (FREEDOM AF) knowledge translation program (February-September 2011), primary care physicians were asked to classify patients for both stroke and bleeding risk as low, intermediate, or high in each category. They also noted whether a specific stroke or bleeding predictive index had been used to evaluate risk. Data included demographics as well as details about current stroke prevention therapies in use and other cardiovascular-related details. The researchers then calculated risk estimates using established systems called CHADS2 for stroke and HAS-BLED for bleeding, two well-known scoring methods that have been validated in many studies.
The investigators found that physicians did not provide any estimates of stroke risk for 15% of their patients and bleeding risk for 25% of patients. When risks were provided, they were based on a predictive stroke and bleeding risk index for only 50% and 26% of patients, respectively. The physicians provided both over- and under-estimation of stroke and bleeding risk in a large proportion of patients. Although antithrombotic therapy with warfarin was prescribed for 90% of the patients, 44% of patients were not receiving a proper dosage for over 70% of the time.
In an accompanying editorial, Laurent Macle, MD, Montreal Heart Institute, University of Montreal, and Jason G. Andrade, MD, Montreal Heart Institute and Vancouver General Hospital, discuss the implications of these results. "This study suggests that the decision to initiate OAC is complex and considers many factors beyond simple risk prediction tools, likely relating to the inherent subjectivity within the risk prediction scores. Specifically, previous studies indicate physicians selectively emphasize components of the risk prediction models, attributing greater weight to certain factors such as previous stroke and age, in preference to others such as hypertension and diabetes. As a result, for the same empiric CHADS2 score, a physician may subjectively categorize a patient as being at higher or lower risk. Given this complexity, the need exists for future knowledge translation activities with respect to the management of AF and stroke prevention, as well as for follow-up studies to ensure these knowledge translation activities are effecting appropriate changes in practice."
Dr. Macle and Dr. Andrade caution that patients in this study were already being treated with OAC at a significantly greater rate than would be expected in a general AF population, so that the results might not be generalizable. Moreover, these data predate the release of newer OAC drugs such as apixaban, dabigatran, and rivaroxaban, which have different risk-benefit profiles and are now prescribed more frequently than warfarin.