Watch this short video explaining stroke risk
Although atrial fibrillation can feel weird and frightening, an “attack of AFib” usually doesn’t have harmful consequences by itself. The real danger is the increased risk for stroke. Even when symptoms are not noticeable, AFib can increase a person’s risks for stroke and related heart problems.
What causes atrial fibrillation?
Sometimes the cause of AFib is unknown. Other times, it is the result of damage to the heart's electrical system from other conditions, such as longstanding, uncontrolled high blood pressure or coronary artery disease. AFib is also the most common complication after heart surgery.
View an animation of atrial fibrillation.
Usually, the most serious risk from AFib is that it can lead to other medical problems, including:
atrial fibrillation, high blood pressure and stroke.
How does AFib lead to stroke?
- The heartbeat seems to quiver (or fibrillate) in an erratic way. The upper chambers (the atria) of the heart do not produce an effective, regular contraction, but contract irregularly.
- The contraction fails. Imagine wringing out a sponge. Without a good squeeze, water will still be left in the sponge. In the same way, when a heart contraction is either too fast or too uneven, it doesn’t completely squeeze the blood from the atria into the next chamber.
- Blood pools in the atria. Blood not completely pumped out of the atria can remain and may pool there.
- Risks of clotting go up. When blood has the opportunity to pool, it also has the opportunity to clot.
- Clots can travel and cause blockages. If a blood clot forms in the atria, it can be pumped out of the heart to the brain, blocking off the blood supply to an artery in the brain, causing a stroke. This type of stroke is called an embolic stroke or some doctors call it a cardioembolic stroke.
Heart failure means the heart isn’t pumping enough blood to meet the body's needs. AFib can lead to heart failure because:
- The heart is beating so fast that it never properly fills up with blood to pump out to the body.
- Blood can “back up" in the pulmonary veins (the vessels that return oxygen-rich blood from the lungs to the heart.) which can cause fluid to back up into the lungs.
- When AFib causes heart failure, fluid in the lungs can cause fatigue and shortness of breath. Oxygen-rich blood is not being delivered to the body and brain, causing physical and mental fatigue and reduced stamina. Fluid also can build up in the feet, ankles, and legs, causing heart-failure related weight gain.
Basic answer: The heart’s electrical system stops working properly, and fails to keep the heart chambers in rhythm.
Thorough answer: Every heartbeat is controlled by the heart’s electrical system. To understand why atrial fibrillation is a problem, it is helpful to understand the normal patterns of the heart’s electrical system.
View an animation of a normal heartbeat.
The heart’s normal electrical pattern:
- The current travels from top to bottom. The heartbeat starts at the top of the heart and – like an electrical wave – the current travels to the lower parts of the heart, signaling the tissue to contract.
- The sinoatrial (SA) node starts the contraction in the top of the heart. The right atrium (one of the two types of chambers of the heart) houses a group of cells called the sino-atrial node. In healthy adults, the SA node fires off between 60-100 heartbeats per minute. The electrical wave moves through the atria to “gatekeeper node.”
- The atrioventricular (AV) node regulates the timing for the lower portion of the heart. The AV node serves as a “gatekeeper” for all of the electrical pulses going through the atria (top sections) to the ventricles (bottom sections).The electrical pulses are delayed at the AV node before they are allowed to move into the ventricles. The delay gives the ventricles extra time to finish filling with blood before contracting.
- The ventricles contract and pump blood out to the lungs and the body.
- In AFib, the SA node may not start the contraction. Instead, the contraction might start randomly in other areas of the atria or even in the pulmonary veins.
- In AFib, the electrical current doesn’t flow in an organized top-to-bottom fashion. Instead, contractions are rapid and disorganized.
- In AFib, the AV node often can’t regulate the chaotic current. It does its best to protect the ventricle from extra electrical impulses, but it can’t stop all of them. As a consequence, the ventricle beats more often than it should – giving rise to the noticeable symptoms of breathlessness and fatigue.
- When the beat is off, the blood supply can be unpredictable. So, even though the ventricles may be beating faster than normal, they aren't beating as fast as the atria. Thus, the atria and ventricles no longer beat in a coordinated way. This creates a fast and irregular heart rhythm. In AFib, the ventricles may beat 100 to 175 times a minute, in contrast to the normal rate of 60 to 100 beats a minute.
The body may get rapid, small amounts of blood and occasional larger amounts of blood. The amount will depend on how much blood has flowed from the atria to the ventricles with each beat.
Can AFib simply go away?
Yes, rarely “spontaneous remission” does happen; it simply goes away. However, it is still something you and your healthcare provider will want to monitor for because some people live with AFib and do not feel the symptoms. However, the risks are still present.
Overall, most of the risks, symptoms and consequences of AFib are related to how fast the heart is beating and how often rhythm disturbances occur.
AFib may be brief, with symptoms that come and go. It is possible to have an atrial fibrillation episode that resolves on its own. Or, the condition may be persistent and require treatment. Sometimes AFib is permanent, and medicines or other treatments can't restore a normal heart rhythm.
But for all the reasons listed above, it is important to work with your healthcare provider to determine your treatment needs, and to understand your treatment options. It is also important to maintain a heart-healthy lifestyle and reduce your overall risks as much as possible.
This content was last reviewed July 2016.