The landscape for stroke prevention in atrial fibrillation (AFib) has changed markedly in recent years, with the availability of non-vitamin K antagonist oral anticoagulants (NOACs, previously referred to as new or novel oral anticoagulants). We are also getting better at understanding how to manage warfarin, recognizing the importance of quality of anticoagulation control, as reflected by the average time in therapeutic range (TTR) kept within an INR range of 2.0 to 3.0. New data are also re-emerging on the poor evidence for the efficacy and safety of aspirin for stroke prevention in AFib.

Guidelines have evolved to reflect these developments. In older guidelines, the focus was to identify AFib patients at "high risk" of stroke to target for warfarin treatment; however, many studies have shown under-use of warfarin amongst such "high-risk" patients. In 2012, the European Society of Cardiology (ESC) guidelines recommended a clinical practice shift, to initially focus on the identification of "truly low-risk" patients who do not need any antithrombotic therapy. These low-risk patients are those age <65 and lone AFib (including females), or a CHA₂DS₂-VASc score of 0 (males) or 1 (females). Subsequent to this step, patients with ≥1 additional stroke risk factors can be offered effective stroke prevention, which is oral anticoagulation.

In 2014, the American College of Cardiology (ACC)/American Heart Association (AHA)/Heart Rhythm Society (HRS) guidelines recommended use of the CHA₂DS₂-VASc score as the stroke risk assessment tool, and recommended oral anticoagulation for those with a score of ≥2, and no treatment for those with a score of 0. For those with a CHA₂DS₂-VASc score=1, the recommendation was no treatment, aspirin or oral anticoagulation. The concern here is that some of the risk factors evident with a CHA₂DS₂-VASc score=1 are in common with those with the older CHADS₂ score=1 (i.e., a single stroke risk factor), and may confer a stroke risk as high as 3.2% per year if left untreated, exposing some AFib patients to a risk of fatal and disabling strokes.

In 2014, the National Institute for Health and Care Excellence (NICE) issued its national clinical guidelines. In contrast to the ESC and ACC/AHA/HRS guidelines, the NICE guidelines are based on systematic reviews and evidence appraisal using Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology, followed by cost effectiveness analyses – only after which are the evidence tables summarized and presented to the Guideline Development Group (GDG) for the discussion and formulation of recommendations. The GDG is also a multidisciplinary writing committee with representation from cardiologists, general practitioners, pharmacy, nursing, internal medicine, elderly care, etc. – plus two patient representatives and technical support from an information specialist, health economist, etc.

What do the NICE guidelines say on stroke prevention in AFib? The section on stroke and bleeding risk recommends that these risks should be assessed in all patients with AFib using the validated CHA₂DS₂-VASc score, consistent with the European and North American guidelines. Risk assessment is also a dynamic process, and regular review and risk re-evaluation is recommended.

Following review of all the bleeding risk scores, the NICE guidelines recommend use of the HAS-BLED score to assess the risk of bleeding in patients "who are starting, or have started, anticoagulation and to highlight, correct, and monitor modifiable risk factors." Stroke risk and bleeding risk do track each other, and while those at high bleeding risk (with a high HAS-BLED score) are also at high risk of stroke, the net clinical benefit balancing stroke reduction against the potential for harm with serious bleeding is still in favor of oral anticoagulation, rather than not.

A high HAS-BLED score is not an excuse to withhold oral anticoagulation, as the benefit of anticoagulation may not always outweigh the bleeding risk, although careful monitoring and/or review of bleeding risk is important. The HAS-BLED score also makes the clinician think about potentially correctable bleeding risk factors: for example, the "H" in HAS-BLED stands for uncontrolled hypertension, while the "L" in HAS-BLED stands for labile INRs (this criterion is only applied if a patient is taking a VKA), and the "D" refers to concomitant use of drugs that increase the risk of bleeding, such as aspirin or a non-steroidal anti-inflammatory drug, or excessive alcohol consumption. The NICE guidelines also recommend that we should not withhold anticoagulation solely because the person is at risk of having a fall, as a history of falls is not an independent risk factor for bleeding while on oral anticoagulation.

The NICE guideline stroke prevention algorithm recommends the first step is to identify AFib patients at very low risk, who should not receive any antithrombotic therapy (i.e., no anticoagulation, or any antiplatelet drug). These low-risk patients are defined as those patients age <65 years with AFib and no risk factors (equating to CHA₂DS₂-VASc score of 0 for men or 1 for females).

Subsequent to that step, oral anticoagulation should be considered or offered to the remainder with ≥1 additional stroke risk factors, taking bleeding risk into account. Oral anticoagulation should be considered for men with a CHA₂DS₂-VASc score=1, while oral anticoagulation should be offered to all patients with a CHA₂DS₂-VASc score ≥2.

Anticoagulation may be with a NOAC (apixaban, dabigatran etexilate, or rivaroxaban, in accordance with individual NICE appraisals for these agents) or a well-controlled VKA (e.g., warfarin), defined as a TTR ≥65%.

The NICE guidelines strongly recommend that we do not offer aspirin monotherapy solely for stroke prevention to patients with AFib. This is based on limited evidence for efficacy, but reasonable evidence for harm (with serious bleeding) and lack of cost effectiveness.

For people receiving warfarin, there is emphasis on adequacy of anticoagulant control, with focus on the TTR. The use of warfarin should be reconsidered for a person with poor anticoagulation control as demonstrated by any of the following: (i) two INR values >5 or one INR value >8 within the past six months; (ii) two INR values <1.5 within the past six months, and (iii) TTR <65%. Left atrial appendage occlusion is only a consideration if oral anticoagulation is contraindicated or not tolerated.

Areas for further research are also discussed in the full version of the NICE guidelines, that includes topics on prospective evaluation of stroke risk assessment, as well as being able to identify the newly diagnosed patients who on the basis of the SAMe-TT₂R₂ score would be able to do well on warfarin with a high TTR (SAMe-TT₂R₂ score 0-2) or those patients who are less likely to achieve good quality INR control (SAMe-TT₂R₂ score >2) where a NOAC may be a better treatment option upfront.

Finally, the NICE guidelines are accompanied by a patient decision aid, as well as a web-based management pathway (see Further Reading list). Also, to aid implementation of NOAC use, there is a NICE NOAC Implementation Collaborative consensus statement, which provides practical aspects on the implementation of NOACs.

References

1. National Institute for Health and Care Excellence (NICE). Atrial fibrillation: the management of atrial fibrillation. Clinical guideline 180. (National Institutes for Health and Care Excellence website). 2014. Available at: http://guidance.nice.org.uk/CG180. Accessed 6/25/2014.
2. Camm AJ, Lip GY, De Caterina R, et al. 2012 focused update of the ESC Guidelines for the management of atrial fibrillation: an update of the 2010 ESC Guidelines for the management of atrial fibrillation--developed with the special contribution of the European Heart Rhythm Association. Europace 2012;14:1385-413.
3. January CT, Wann LS, Alpert JS, et al. 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2014 Mar 28; [Epub ahead of print].
4. Apostolakis S, Sullivan RM, Olshansky B, Lip GY. Factors affecting quality of anticoagulation control among patients with atrial fibrillation on warfarin: the SAMe-TT₂R₂ score. Chest 2013;144:1555-63.

Related Resources:

1. ACC AFib Toolkit: http://www.cardiosource.org/Science-And-Quality/Clinical-Tools/Atrial-Fibrillation-Toolkit.aspx
2. Factors Affecting Quality of Anticoagulation Control Among Patients With Atrial Fibrillation on Warfarin: The SAMe-TT2R2 Score: http://www.cardiosource.org/Science-And-Quality/Journal-Scan/2013/12/Factors-Affecting-Quality-of-Anticoagulation-Control-Among-Patients.aspx

Further Reading:

1. NICE version of guideline: http://guidance.nice.org.uk/CG180/NICEGuidance/pdf/English
2. Full guideline: http://guidance.nice.org.uk/CG180/Guidance
3. The guideline has been published alongside a Patient Decision Aid: http://guidance.nice.org.uk/CG180/PatientDecisionAid/pdf/English
4. The guideline has been published alongside a: http://pathways.nice.org.uk/pathways/atrial-fibrillation
5. There is also a NOAC implementation document to complement the NICE guidelines: http://guidance.nice.org.uk/CG180/NICConsensusStatement/pdf/English

Keywords: Anticoagulants, Aspirin, Atrial Fibrillation, Blood Coagulation, Cytarabine, International Normalized Ratio, Stroke, Vitamin K, Warfarin

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