To guide clinicians in the selection of antithrombotic therapy for the prevention of ischemic stroke and arterial thromboembolism in patients with atrial fibrillation.# BACKGROUND:
Atrial fibrillation (AF) is the most common pathologic arrhythmia and increases in prevalence with increasing age (prevalence of 10-15% in patients who are 80 years). The most devastating complication of AF is arterial embolism of a left atrial thrombus resulting in ischemic stroke, peripheral limb ischemia, or other end organ damage. AF is associated with a 3-to 6-fold increased risk of stroke or non-central nervous system (CNS) systemic embolism. Furthermore, ischemic strokes in patients with AF are larger and more frequently associated with death and disability than strokes that occur in the absence of AF. Therefore, stroke prevention is a critical part of AF treatment.
The risk of arterial thromboembolism can be significantly reduced with anticoagulant therapy (warfarin, apixaban, dabigatran, edoxaban or rivaroxaban) and, to a much lesser extent, with antiplatelet therapy. Selection of antithrombotic therapy should be guided by assessment of presumed thrombotic risk, assessment of presumed bleeding risk on antithrombotic therapy and patient preference.
Thrombotic Risk: Prognostic models incorporating patient age and co-morbidities provide validated estimates of the annual risk for thromboembolism without anticoagulant therapy. These models were developed for patients with non-valvular AF, which refers to AF occurring in the absence of a mechanical heart valve or rheumatic heart disease with severe mitral stenosis or regurgitation. The most frequently used score is the CHADS2 score (see Table 1). 

# TOTAL score
The Canadian Cardiovascular Society and this guide use a modified "CHADS-65"scoring system as the basis for recommendations (see Recommendations and Figure 1).
Risk calculators for the CHADS2 score and, another modification, CHA2DS2-VASc score are available on the Thrombosis Canada website . In general, in patients with a CHADS2 score or a CHA2DS2-VASc score 1, the risk of arterial thromboembolism (and resulting morbidity/mortality) without anticoagulation outweighs the risk of bleeding from anticoagulants.
Bleeding Risk: Bleeding risk should also be assessed in all patients. However, in most cases, bleeding risk should not preclude the use of anticoagulant therapy. The risk-benefit ratio almost always favours anticoagulation unless the risks for bleeding are very high and the risk of thromboembolism is very low. Patients at increased risk for bleeding, typically, are also those who will benefit the most from anticoagulation to prevent stroke, and attempts should be made to modify bleeding risk factors (i.e. NSAID or alcohol use, frequent falls). There are prognostic models for the estimation of bleeding risk in patients with AF on warfarin therapy (e.g. HAS-BLED, available on Thrombosis Canada website ), which can help to identify potentially reversible risk factors for bleeding.

# AGENTS AND DOSING:
Anticoagulants: Warfarin (with target INR of 2-3) was the anticoagulant of choice for the prevention of stroke in patients with AF for many years.  Antiplatelet agents: In patients with AF at low risk of stroke, who decline oral anticoagulation, or in whom oral anticoagulation is considered contraindicated due to bleeding risk, low dose aspirin (80-100 mg/day) may be considered. However, aspirin provides less protection than an anticoagulant and increases bleeding risk.

# RECOMMENDATIONS:
See Figure 1  Patients with AF and valvular heart disease (severe mitral stenosis, mechanical heart valves) are at significantly increased risk for ischemic stroke, and warfarin is recommended for this indication.
Treatment with a DOAC is not recommended in these patients with AF and these drugs are not approved for this use.
In patients with coronary artery disease, antithrombotic management should be individualized and based on an assessment of risk of atrial fibrillation-related stroke, ischemic coronary event, and clinically relevant bleeding associated with the use of antithrombotic agents.
OTHER RELEVANT THROMBOSIS CANADA CLINICAL GUIDES:
- Apixaban (Eliquis) 

# Date of Version: 14Jan2020
Please note that the information contained herein is not to be interpreted as an alternative to medical advice from your doctor or other professional healthcare provider. If you have any specific questions about any medical matter, you should consult your doctor or other professional healthcare providers, and as such you should never delay seeking medical advice, disregard medical advice or discontinue medical treatment because of the information contained herein.