Primary Study Objective(s)
1. Determine the effect of warfarin on low-shear blood viscosity levels, as compared with intra-individual baseline levels, in atrial fibrillation patients having CHADS2 score of 2 or greater.

Secondary Study Objective(s)
1. Stratify patients with atrial fibrillation having CHADS2 score of 2 or greater using complete blood viscosity profiles at baseline.  
2. Investigate the variability in blood viscosity responses at shear rates of 5 and 300 s-1 as a function of baseline blood viscosity in atrial fibrillation patients having CHADS2 score of 2 or greater. 

Study Design
Prospective, randomized, open-label, blinded-endpoint study

Treatment

blood viscosity effect with warfarin vs. aspirin:
blood viscosity measurement in the group of warfarin Tx, with International Normalized Ratio (INR) 2-3
blood viscosity measurement in the group of aspirin Tx, with 3 days of medication

Arm Label

Target Number of Participant

Arm Type

Arm Description

Warfarin group; 
blood viscosity measurement at both the initiation of warfarin treatment and when target International Normalized Ratio (INR) reaches 2-3. 
Warfarin 5mg was usually tried at the beginning with INR monitoring, and final dose would be determined accoridng to INR values.

Arm Label

Target Number of Participant

Arm Type

Arm Description

aspirin group; blood viscosity measurement at both the initiation of aspirin and after 5-7 days of medication
Acetylsalicylic acid (Aspirin) dose was 75-100mg/day (fixed).

Gender

Age

Description

• Male or female subjects with treatment-naïve non-valvular atrial fibrillation as evidenced by documented ECG evidence.
o Female subjects of childbearing potential must be abstinent or practicing methods of birth control which are recognized as effective.
o Females of childbearing potential must have a negative serum β-hCG pregnancy test prior to study enrollment.
• Subject has a CHADS2 stroke risk score of 2 or greater and is eligible for warfarin therapy.
o Congestive heart failure, hypertension, age of 75 years or greater, and diabetes each get 1 point towards the risk score.  A previous stroke, transient ischemic attack, or thromboembolism gets 2 points.
• Subject is between 18 and 90 years of age.
• Subject is willing to comply with the requirements of the study protocol.
• Subject has given written informed consent to participate in the study. 

• Subject is pregnant or breast-feeding.
• Subject has transient atrial fibrillation caused by a reversible condition (i.e. thyrotoxicosis, post-surgery)
• Subject has an active infection such as endocarditis.
• Subject has active internal bleeding or history of a condition associated with increased bleeding risk.
• Subject has an anemia.
• Subject has given blood or received a blood transfusion at any point during the study.
• Subject has concurrent hyperthyroidism.
• Patient has polycythemia vera or any hyperviscosity syndrome.
• Platelet count <90,000/µL at initial screening.
• Subject has poor diabetes or hypertension control (sustained systolic blood pressure ≥ 180 mmHg or diastolic blood pressure ≥ 100 mmHg).
• Subject has mitral stenosis or mechanical heart valves.
• Subject is taking steroids.
• Subject has a history of severe liver disease or end-stage renal disease receiving dialysis (HD or PD) or KT.
• Family members or employees of the investigator or study centers involved in the study.

Blood viscosity levels of high (300/sec) and low (5/sec) shear rates

when INR reaches 5-7 or 7th day of acetylsalicylic acid treatment

Blood viscosity distribution according to CHADS2 scores in patients with atrial fibrillation 

initial screening and follow up