Atrial fibrillation (AF) is the most common sustained arrhythmia seen in clinical practice, affecting approximately 1% of the population. AF is frequently associated with reductions in functional status and health-related quality of life, as well as an increased risk of mortality and stroke.
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Despite advances in treatment strategies, AF-related mortality has remained relatively static. Tellingly, only oral anticoagulation (OAC) therapy has been shown to improve survival.- Rietbrock S.
- Heeley E.
- Plumb J.
- van Staa T.
Chronic atrial fibrillation: Incidence, prevalence, and prediction of stroke using the Congestive heart failure, Hypertension, Age >75, Diabetes mellitus, and prior Stroke or transient ischemic attack (CHADS2) risk stratification scheme.
Am Heart J. 2008; 156: 57-64
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As such, the appropriate use of OAC in the prevention of AF-associated thromboembolism is paramount in the management of AF.Unfortunately, despite strong evidence of clinical benefit, OAC use is limited by nonprescription (∼ 50% patients with an indication for treatment do not receive an OAC),
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nonadherence (∼ 30% 1-year OAC discontinuation rate),9
or subtherapeutic drug levels (∼ 25%-40% of patients taking warfarin have an international normalized ratio outside the therapeutic range).10
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This combination portends an unnecessarily increased risk of stroke, an event that entails high social and economic costs.12
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This is especially true in the case of AF-associated strokes, because they are often recurrent and relatively more severe compared with strokes from other causes, resulting in a significantly greater use of resources as well as long-term disability and mortality.13
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However, despite the presence of major national and international society guidelines advocating the importance of objectively assessing stroke and bleeding risk through the use of well-validated risk prediction scores, the decision to initiate OAC therapy remains a relatively personal and subjective assessment of individual risks vs benefits.
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, - Steinberg B.A.
- Kim S.
- Thomas L.
- et al.
Lack of concordance between empirical scores and physician assessments of stroke and bleeding risk in atrial fibrillation: results from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry.
Circulation. 2014; 129: 2005-2012
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As a result, the real-world implementation of OAC therapy is often skewed by subjective physician interpretation, leading to the risk/treatment paradox, whereby proven efficacious therapy (in this case OAC) is not necessarily more likely to be prescribed to higher-risk patients.16
, - Steinberg B.A.
- Kim S.
- Thomas L.
- et al.
Lack of concordance between empirical scores and physician assessments of stroke and bleeding risk in atrial fibrillation: results from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry.
Circulation. 2014; 129: 2005-2012
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It is within this context that Angaran et al. present the results of a practice audit of more than 470 Canadian primary care providers in this issue of the Canadian Journal of Cardiology.
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This large real-world contemporary study of primary care specialists offers an important insight into current practice patterns for patients with AF. Despite a familiarity with the management of AF, these primary care physicians do not seem to use existing stroke and bleeding prediction schemes and do only a modest job at assessing risk.Specifically, the authors observed a significant disconnect between the physicians' categorized assessments of stroke and bleeding risk (lower [< 3%/y], intermediate [3%-6%/y], and higher [> 6%/y]) and the subsequently derived empirical stroke risk estimate using the CHADS2 (Congestive Heart Failure, Hypertension, Age, Diabetes, Stroke/Transient Ischemic Attack) and CHA2DS2VASc CHA2DS2-VASc (Congestive Heart Failure, Hypertension, Age [≥ 75 years], Diabetes, Stroke/Transient Ischemic Attack, Vascular Disease, Age [65-74 years], Sex [Female] score) schema and bleeding risk using the HAS-BLED (Hypertension, Abnormal Renal/Liver Function, Stroke, Bleeding History or Predisposition, Labile INR, Elderly [> 65 Years], Drugs/Alcohol Concomitantly) score (calculated from the data collection forms of each patient). In the case of stroke risk, there was only a 54% agreement between physician-estimated and CHADS2-calculated stroke risk. In 13% of cases, the physician-estimated risk would have resulted in delivery of potentially unnecessary anticoagulation (estimated high risk but low calculated risk), and in 35% the physician-estimated risk would have led to undertreatment (estimated low risk but high calculated risk). More dramatic disparity was observed for bleeding risk in which agreement between the physician estimate and the empirically calculated score was only 31%. In this case, the physicians underestimated the risk of bleeding in 61% of patients and overestimated the risk in 8.0% of patients. However, despite apparent suboptimal stroke risk stratification and concerns about bleeding, the majority of patients were receiving OAC.
Unfortunately these findings are not isolated phenomena. The recently published Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) study observed a similar under- and overestimation of stroke risk, with disagreement in up to 80% of cases.
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In this case, the difference was particularly marked for patients at high risk for stroke and bleeding, for whom physicians tended to underestimate risk in both instances. However, similar to the Facilitating Review and Education to Optimize Stroke Prevention in Atrial Fibrillation (FREEDOM AF) program, a significant majority of physician-estimated “low-risk” patients were receiving OAC (90% in Freedom AF program and 76% in ORBIT-AF). In the Freedom AF program, the use of OAC in this lower-risk group was disproportionately high, with 56% of patients with a CHA2DS2VASc of 0 receiving OAC therapy.- Steinberg B.A.
- Kim S.
- Thomas L.
- et al.
Lack of concordance between empirical scores and physician assessments of stroke and bleeding risk in atrial fibrillation: results from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry.
Circulation. 2014; 129: 2005-2012
What messages should we take away from this study? First, we should view the results with some degree of caution. As alluded to earlier, the overall rate of OAC was significantly greater than would be expected, with community rates of OAC reported to be in the range of 50%-60%.
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Although this may be a function of the inclusion criteria (enrolling primary care patients in whom OAC was felt to be warranted), it suggests that the results may not be generalizable. Second, despite the apparent familiarity of this group, there exist opportunities for future knowledge translation with respect to the management of AF and stroke prevention. The discordance between physician estimated risk and empirical risk suggests that the risk schemes are not understood or used appropriately, leading to inaccurate risk stratification with overestimation of stroke risk and overprescription of OAC therapy. Specifically, previous studies indicate that 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 empirical CHADS2 score, a physician may subjectively categorize a patient as being at higher or lower risk. Third, the data from this series predate the release and uptake of non–vitamin K antagonist OAC (novel OAC) medications such as apixaban, dabigatran, and rivaroxaban. These novel OACs are currently advocated as the first-line option for OAC therapy in AF and are collectively prescribed more frequently than warfarin for stroke prevention in AF.18
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Given the different risk/benefit profiles of these newer medications, it is unknown whether the rate of OAC use would have differed with these agents. Future studies in this area would be enlightening. Finally, the annual rate of stroke to which the current Canadian Cardiovascular Society guidelines attribute a low risk of stroke,22
and thus suggest that OAC is not justified, is < 1.0%-1.5% and not the < 3% used in this study. As such, the use of a higher annual event rate would include a proportion of “high-risk” patients in the subjectively “low risk” category. That being said, when the low-risk group was re-examined using the CHA2DS2VASc, the use of OAC remained unexpectedly high (59% of CHA2DS2VASc of 0 and 76% of CHA2DS2VASc of 1 received OAC). It is important to recall that these patients represent a subgroup in which the use of OAC has been previously associated with apparent harm.6
This study by Angaran et al. highlights the discordance that exists between empirical risk assessment tools and subjective physician assessments, as well as between the assessment itself and subsequent rates of OAC. The study suggests that the decision to initiate OAC is complex and considers many factors beyond simple risk prediction tools. In other words, the assessment of risk involves an educated, informed, and balanced assessment of individualized risk with a weighting of consequences (permanent neurologic incapacity vs major bleeding events). Given this complexity, the need exists for future knowledge translation activities with respect to the management of AF and stroke prevention, as well as follow-up studies to ensure that these knowledge translation activities are effecting appropriate changes in practice.
Funding Sources
J.G.A. is supported by a Michael Smith Foundation Scholar Award.
Disclosures
The authors have no conflicts of interest to disclose.
References
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- Lack of concordance between empirical scores and physician assessments of stroke and bleeding risk in atrial fibrillation: results from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry.Circulation. 2014; 129: 2005-2012
- Physician practices regarding contraindications to oral anticoagulation in atrial fibrillation: findings from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry.Am Heart J. 2014; 167: 601-609.e1
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Article info
Publication history
Published online: October 14, 2015
Accepted:
June 21,
2015
Received:
June 16,
2015
Footnotes
See article by Angaran et al., pages 336-343 of this issue.
See page 279 for disclosure information.
Identification
Copyright
© 2016 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.
