A Phase III Study of Apixaban in Patients With Atrial Fibrillation

The purpose of this clinical research study is to determine whether apixaban is more effective than acetylsalicylic acid in the prevention of strokes associated with patients with atrial fibrillation. The safety of this treatment will also be studied.

An optional Long-term Open-label Extension Phase of treatment with apixaban will be provided for qualifying participants following the conclusion of the double-blind phase

Eligibility Criteria:
Key Inclusion Criteria:

* Male and female
* Age of 50 years or older
* Permanent, paroxysmal, or persistent atrial fibrillation (at screening or within 6 months prior to enrollment) documented by 12-lead electrocardiogram)
* At least 1 of the following risk factors for stroke:

  * Prior stroke or transient ischemic attack
  * Age of 75 years or older
  * Arterial hypertension on treatment
  * Diabetes mellitus
  * Heart failure (New York Health Authority Class 2 or greater at time of enrollment)
  * Left ventricular ejection fraction of 35% or less, documented within 6 months of enrollment
  * Peripheral arterial disease (previous arterial revascularization, limb or foot amputation, or current intermittent claudication with ankle-arm systolic blood pressure ratio \<0.9)
* Not currently receiving vitamin K antagonist therapy for 1 of the following reasons:

  * Previous vitamin K antagonist therapy demonstrated as unsuitable and discontinued
  * Vitamin K antagonist therapy not previously used but expected unsuitable

Key Exclusion Criteria:

* Women who are pregnant or breast feeding
* Women of child bearing potential who are unwilling to meet the study requirements for pregnancy testing or are unwilling or unable to use an acceptable method to avoid pregnancy
* Atrial fibrillation due to reversible causes, such as thyrotoxicosis or pericarditis
* Valvular disease requiring surgery
* Planned ablation procedure for atrial fibrillation to be performed within 3 months
* Conditions other than atrial fibrillation that require chronic anticoagulation (such as, prosthetic mechanical heart valve, venous thromboembolism)
* Patients with serious bleeding in the last 6 months or at high risk for bleeding, including but not limited to those with:

  * Active peptic ulcer disease
  * Platelet count \<100,000/mm\^3 or hemoglobin \<10g/dL
  * Recent stroke (within 10 days)
  * Documented hemorrhagic tendencies or blood dyscrasias
* Current alcohol or drug abuse or psychosocial reasons that make study participation impractical
* Severe comorbid condition with life expectancy \<1 year
* Severe renal insufficiency; any patient with a serum creatinine level \>2.5 mg/dL or a calculated creatinine clearance \<25 mL/min is excluded
* Alanine transaminase or aspartate aminotransferase levels \>2 times upper limit of normal (ULN) or a total bilirubin level \>1.5 times ULN (unless an alternative causative factor \[such as Gilbert's syndrome\] is identified)
* Allergy or adverse reaction to acetylsalicylic acid
* Required treatment with a thienopyridine (clopidogrel or ticlopidine)
* Prisoners or participants who are compulsory detained (involuntarily incarcerated)
* Use of an investigational drug or device within the past 30 days or prior randomization into an apixaban clinical study
* Patients who are compulsorily detained for treatment for a psychiatric or physical illness