The atria (singular = 1 atrium) are chambers of the heart (4 chambers: 2 Atria and 2 Ventricles — see Diagram — Anatomy of the Heart). Our heart pumps blood at about 60-80 beats per second. It can do this because it has its own electrical circuit that starts up at around 4-6 weeks of fetal life in pregnancy, and keeps going until we die. The circuit begins in the muscle of the right atrium, travels to the left atrium, then down to both ventricles. The electricity makes the heart muscle contract, and thus pump.
The pumping is supposed to follow a normal rhythm. The atria contract at the same time, sending blood down to the ventricles. Then the ventricles contract, pumping the blood out to the body (left ventricle) or to the lungs (right ventricle), while the atria fill up for the next beat.
With Atrial Fibrillation (“A. Fib” for short), the atria lose the ability to send a real beat. Their electricity just fires constant weak impulses, and the atrial muscle simply squiggles in place (fibrillates) like a “bag of worms”. So the ventricles have to pump on their own, and do so randomly. Blood still flows from atria down to ventricles to get pumped, but the rhythm becomes totally irregular. A. Fib is one kind of heart Arrhythmia (abnormal rhythm), see the link for others
There are 2 main dangers with this. First, the ventricles may happen to pump way too slowly, or way too fast. That makes circulation inefficient, causes symptoms like palpitations or shortness of breath (Heart Failure), and is bad for the body. Secondly, since the atria can’t pump, blood may pool around there, allowing clots to form. If a blood clot gets loose, trickles down to the ventricles & gets pumped out, it can cause a Stroke, or cut off circulation to another body part.
A. Fib usually happens all on its own. Sometimes it’s due to other heart diseases that damage heart muscle. A. Fib might just occur on and off (“paroxysmal”), sometimes it’s continuous. It’s more dangerous in older persons with other conditions like diabetes, hypertension, or heart failure. It’s especially dangerous if a person also has disease of certain heart valves. Risks are less among younger healthy people, especially if the arrhythmia only occurs rarely.
We diagnose Atrial Fibrillation by detecting an irregularly irregular rhythm when we listen to the heart (or count a pulse rate). We confirm it with an Electrocardiogram (EKG). The diagnosis is easy. If we suspect a patient may have had A. Fib because of past symptoms, but the rhythm is normal now, we order ambulatory EKG monitoring (portable) for varying periods of time; see EKG, also Arrhythmias.
Sometimes there are ways of bringing back normal rhythm, usually by shocking the heart (in a very controlled manner). But that often doesn’t work well. So the main goals are 1) prevent very fast heart rates; and 2) prevent clots from forming. Various medicines are used to accomplish these. Sometimes a procedure called ablation can wipe out the electrical short circuit; this works better in younger people with recent A. Fib that isn’t persistent.
Anytime you have to make a decision about any kind of treatment of anything, you always want to ask:
- What is the probability of success?
- What are the possible risks?
- What is the probability of each risk (especially the really dangerous ones)?
See also Interpreting Risks / Benefits of Medical Treatment.