Atrial Fibrillation and Stroke: Understanding the Connections

With atrial fibrillation present in approximately 20% of strokes, the potentially life-threatening connections between these two conditions cannot be ignored.

Atrial fibrillation (AF or AFib) is an irregular heartbeat. It is the most common heart arrhythmia, affecting roughly 2.7 million Americans, according to the American Heart Association. Stroke, a condition that occurs when blood supply is cut off from the brain, is the number four cause of death in America, according to the American Stroke Association.

To understand the connections between atrial fibrillation and stroke, it is important to first have a working knowledge of the heart's basic functions.

Heart Anatomy

Your heart, the organ responsible for pumping oxygen-rich blood throughout your body, has four chambers. Although the shape of the heart isn’t a perfect circle, you could imagine it looking like a slightly misshapen pie chart that is divided into four sections.  You have two smaller, upper chambers: the left and right atria. You also have two lower chambers: the left and right ventricles. The atria pump blood into the ventricles. The ventricles, bigger and stronger than the atria, pump blood to the rest of the body.

The beating of your heart is orchestrated by electrical impulses. Each heartbeat starts in your right atria with a group of cells called the sinus node (SA node). The SA node signals the atria to contract or squeeze blood, sending it into the ventricles. The electrical impulse that originated in your SA node then travels to another node in the middle of your heart, the atrioventricular node (AV node). The AV node tells your ventricles to contract, sending blood out from the heart and to the rest of the body. A normal heart rate is 60-100 beats per minute.

Atrial Fibrillation Explained

Imagine being introduced to someone. You extend your hand, smile, and greet him with your name. He reaches out his hand to meet yours. But rather than giving your hand a nice, solid clutch, his hand only lightly squeezes with a weak, quivering grip.

Like the handshake described above,  AFib occurs when the atria receive erratic signals from the SA node. Rather than a solid "squeeze," they quiver instead. This quivering, also called fibrillation, is much faster than a normal contraction but it doesn’t pump blood as effectively. The AV node passes on the erratic signals to the ventricles, ordering them to also pump faster too. With atrial fibrillation, your heart rate can range from 100-175 beats per minute instead of the normal rate of 60-100 beats per minute.

As a result, blood that should have been pumped into the ventricles can lag and pool in the atria. When blood pools, it can form a clot known by medical professionals as an embolus. The danger with clots is that they can become lodged in your blood vessels and block the flow of blood and oxygen needed by organs. Atrial fibrillation increases your chances of forming these dangerous blood clots.

Stroke Explained

Strokes occur when your arteries, the blood vessels that carry oxygen-rich blood to your brain, become blocked or burst. Causes may vary, but they are commonly due to damaged arteries or a blood clot.

The Connection Between Atrial Fibrillation and Stroke

Atrial fibrillation is present in about one in five strokes. AFib causes a rapid heartbeat, leading to pooling blood in the heart and an increased chance of clotting that can result in a stroke. The type of stroke caused by AFib is called an embolic stroke.

According to the National Stroke Association, when a stroke is caused by AFib, the outcome is worse than when caused by other problems. AFib-related strokes result in a higher mortality rate as well as greater functional impairment and dependency.

The National Stroke Association states that up to 80% of strokes in people with atrial fibrillation can be prevented, but many people do not know they have AFib. AFib is often treated with blood-thinning medication, which helps to prevent clots. This condition can also be treated with catheter ablation, a noninvasive procedure which involves eliminating the source of the erratic electrical signals by disconnecting it from the rest of the heart.