According to the National Institute of Health, atrial fibrillation occurs if rapid, disorganized electrical signals causing the heart's two upper chambers, called the atria, to fibrillate. The term "fibrillate" means to contract very fast and irregularly. In atrial fibrilation, blood pools in the atria. It isn't pumped completely into the heart's two lower chambers, called the ventricles. As a result, the heart's upper and lower chambers don't work together as they should. Based on the passage above, how will atrial fibrillation affect blood pressure?

It will lower blood pressure because less blood is pumped per beat.
It will increase blood pressure because the heart is contracting faster.
It will increase blood pressure because the atria fill fully with blood.
It will lower blood pressure because blood volume drops in the atria.