Arterial Fibrillation (AF) is the most common type of cardiac arrhythmia, which increases the incident rate of stroke by 5 times due to systemic embolism. Also, it is known that 5% of the AF patient population shows the incidence of stroke every year. Especially in case of thromboembolic stroke caused by AF, the extent of brain damage and neurological impairment are more severe than those caused by other factors and has high risk of death or severe disability. Therefore, preventing the thromboembolism with anticoagulant treatment is very important. The safety and efficacy of Non-vitamin K Oral Anticoagulant (NOAC) have been demonstrated to prevent stoke in patients with AF and shown favorable clinical outcomes compared with Warfarin by large scale randomized controlled trials. According to the 2012 ESC(European Society of Cardiology) guideline and 2014 AHA/ACC/HRS (American Heart Association/American College of Cardiology/Heart Rhythm Society) guideline for  the management of AF, the CHA2DS2-VASc score is recommended to evaluate the risk of stroke. The guidelines indicate that patients who have a CHA2DS2-VASc score of ≥2 should receive an anti-coagulant in preference to Warfarin. According to the recent study by ARISTOTLE and ARISTOPHANES, NOACs decrease the incidence rate of bleeding when compared with Warfarin. There are several studies reporting that the patients with single risk factor other than sex ( High risk group: men with CHA2DS2-VASc scores of 1 and women with scores of 2) have a high risk of stroke and the use of anti-coagulants can help mitigate such risk (European Society of Cardiology guideline, class IIa, level of evidence B). All studies that ground for this guideline are based on registry or retrospective cohort study, thus the reduced risk of stroke and bleeding, and patient’s preference shall be taken into consideration before administering anti-coagulants to a patient, rather than to put all patients on anticoagulants therapy. In Korea’s National Health Insurance Service(NHIS), with accordance to this guideline, the criterion for the insurance coverage of NOAC is CHA2DS2-VASc Score of 2 or higher. If a patient has CHA2DS2-VASc sore of 1, they cannot be covered for NOAC. The 2014 ACC/AHA/HRS guideline describes that in case of patients with a CHA2DS2-VASc score of 1, administration of aspirin, anticoagulant, or no anticoagulant can be considered depending individual patients. In case of patients with CHA2DS2-VASc score 1, the risk of cerebral infarction is not considered to be low, and even for patients with the score 0-1, the anti-coagulation treatment is recommended before and after radiofrequency catheter ablation or cardiac defibrillation. Depending on clinical circumstances, it could be inevitable to prescribe uninsured NOAC or Warfarin to the patients which results increase in patient discomfort, treatment duration and cost as well as the complications associated with Warfarin etc. However, currently no prospective study of administrating NOAC to AF patients has been performed. The aim of this prospective registry study is to assess the safety and efficacy of NOAC on high risk patient group (CHA2DS2-VASc score 1(2 for females) with AF.

Cohort/Group Label

Pathients with Nonvalvular  Atrial Fibrillation(NVAF)

Cohort/Group Description

Patients with non-valvular atrial fibrillation (NVAF) who have a CHA2DS2-VASc score of 1 (2 for females) and require administration of Apixaban to prevent stroke and systemic embolism under the medical judgment of the investigator.

Not collect nor Archive

Patients with non-valvular atrial fibrillation (NVAF) who have a CHA2DS2-VASc score of 1 (2 for females) and require administration of Apixaban to prevent stroke and systemic embolism under the medical judgment of the investigator.

The purpose of this study is to determine the incidence rate of stroke or systemic embolism and all major bleeding events associated with NVFA patients who receiving apixaban for 12 months. The sample size was estimated by referring to the findings of previous studies on apixaban.
A randomized study comparing the incidence of stroke or systemic embolism and major bleeding events between apixaban and warfarin has been conducted by Granger et al in 2011. The incidence rate of stroke or systemic embolism were 1.27% /year and the major bleeding events was 3.52%/year.
Other retrospective observational study of 434,046 patients has been performed by Gregory et al in 2018. The incidence rate of stroke or systemic embolism and the major bleeding events were observed in the 6 cohorts: apixaban-warfarin, dabigatran-warfarin, rivaroxaban-warfarin, apixaban-dabigatran, apixaban-rivaroxaban, and dabigatran-rivaroxaban patient pairs. The unadjusted incidence rate of stroke or systemic embolism and the major bleeding events in patients with apixaban were 1.3%/year and 3.6 %year, respectively.
Based on the previous study findings, the incidence rate of stroke or systemic embolism and all major bleeding events in this observational study are expected to be 1.27-1.3%/year and 3.52-3.6%/year, respectively.
However, since this study will be conducted on patients with a CHA2DS2-VASc score of 1 point (2 points for women), the incidence of stroke or systemic embolism is set to 1%/year for a more conservative approach. Also, the incidence rate of stoke or systemic embolism, which is the purpose of this study is expected to occur with a low probability of 1%, thus the number of subject is estimated to identify at least 10 events based on the Poisson distribution. 
This study required at least 1,571 patients to confirm the incidence of stroke or systemic embolism and the all major bleeding events of at least 10 at a 95% confidence level. Therefore, 2,000 subjects will be recruited by applying 10% of dropout rate.

Gender

Age

Description

1)	Males and females over 19 years old
2)	Patients diagnosed with NVAF
3)	Patients with CHA2DS2-VASc score of 1 (2 for females)
* CHA2DS2-VASc score: Assess the risk of stroke up to 9 points by considering the following factors: Congestive heart failure (+1 point), Hypertension (+1 point), Age 75 or over (+2 points), Diabetes mellitus (+1 point), Stroke (+2 points), Transient Ischemic Attack (TIA)/Thromboembolism (TE), Vascular disease (+1 point each), Age 65-74 (+1 point), and Sex (+1 point for females).[6]
4)	When the investigator determines that the use of an anticoagulant is necessary to prevent stroke or systemic embolism
5)	Patients who have no history of taking medications containing Apixaban within 6 months of screening
6)	When the patients who understand the description of this study, agree to participate in the study, and completed/submitted the informed consent form

1)	Patients who are contraindicated according to the precautions for using Apixaban
2)	Pregnant and lactating women

Incident rate of stroke or systemic embolism

At baseline(Visit 2) and at 3 month, 6 month, 9 month, 12 month after the baseline visit, or at 1~3 month interval with regard to the subject's therapy.

Incident rate of major bleeding events

At baseline(Visit 2) and at 3 month, 6 month, 9 month, 12 month after the baseline visit, or at 1~3 month interval with regard to the subject's therapy.

Incidence rate of all major bleeding events by each organ

At baseline(Visit 2) and at 3 month, 6 month, 9 month, 12 month after the baseline visit, or at 1~3 month interval with regard to the subject's therapy.

Overall incidence rate and incidence rate by each organ of all bleeding events excluding major bleeding events according to ISTH criteria

At baseline(Visit 2) and at 3 month, 6 month, 9 month, 12 month after the baseline visit, or at 1~3 month interval with regard to the subject's therapy.

All bleeding events according to the HAS-BLED risk score and the number of subjects and incidence rate of major bleeding events

At baseline(Visit 2) and at 3 month, 6 month, 9 month, 12 month after the baseline visit, or at 1~3 month interval with regard to the subject's therapy.

Assessment of Apixaban use pattern (Totoal prescription period and compliance of Apixaban, Change rates of Apixaban dosage and its reasons, Discontinuation rates of Apixaban and its reasons)

At baseline(Visit 2) and at 3 month, 6 month, 9 month, 12 month after the baseline visit, or at 1~3 month interval with regard to the subject's therapy.

Incidence rate of final clinical events (Mortality, Transient Ischaemic Attack, Myocardial Infarction, Exacerbation of heart failure)

At baseline(Visit 2) and at 3 month, 6 month, 9 month, 12 month after the baseline visit, or at 1~3 month interval with regard to the subject's therapy.

Other adverse events

At baseline(Visit 2) and at 3 month, 6 month, 9 month, 12 month after the baseline visit, or at 1~3 month interval with regard to the subject's therapy.