Atrial fibrillation (AF) is an arrhythmia, or abnormal heart rhythm, whose hallmark is an irregular pattern to the beating of the heart. In most patients with untreated AF, the heart also beats too rapidly (termed tachycardia), but many patients have normal heart rates during their AF. "Atrial" refers to the heart's two atria—you may recall that the heart has four chambers that work together to keep the blood coursing through our body: the right atrium receives blood that has been "used" by the various parts of the body (your muscles, brain, liver, etc.) and it ejects this blood into the right ventricle, which then pumps the blood to the lungs so that it can be replenished with oxygen. This oxygenated blood travels from the lungs to the left atrium, which ejects it into the left ventricle, which then pumps this oxygen-rich blood out to the rest of the body and the cycle continues.
It's the squeezing of the left ventricle that we end up feeling as our pulse. "Fibrillation" refers to the uncoordinated contractions of the individual muscle fibers in the atria of the heart that do not allow these chambers to squeeze blood out in their normal fashion. To understand why this occurs, and what problems this can cause, requires a little knowledge about the way the heart's electrical system controls the pumping activity of the heart.
Normally, each heartbeat is initiated by an electrical signal from a small area known as the sinus node. The sinus node resides just outside of the right atrium and it receives messages from the nervous system telling it to speed up or slow down, depending on what is going on with our body. If you're just sitting and relaxing, the signal from the sinus node is fairly regular—like a beacon in the ocean that keeps blinking at regular intervals to alert ships. That signal does two things. First, it travels to the atria to tell them to contract (and help fill the ventricles with blood) and then, a little later, it travels down a specialized pathway to the ventricles to tell them to contract and send blood out to the lungs and rest of the body.
The problem in AF is that instead of having the beacon signal originate from one point, there are multiple beacons going off in different parts of the atria at the same time and this leads to the uncoordinated atrial squeezing. It also results in signals arriving at the ventricle much more often and in a random fashion, and so the heart beats too rapidly and irregularly. One of the worrisome consequences of the uncoordinated squeezing of the atria is that it can lead to blood pooling and remaining stagnant in small areas of the atria. This stagnant blood can lead to the formation of a small blood clot that can get into the left ventricle and get pumped up to the brain where it gets stuck and causes a stroke. Although we know about many conditions that lead to AF, it is still not entirely clear why these conditions cause multiple signals to be sent from the atria.
Diagnosis of AF
The timing of the signal telling the left ventricle to contract is normally very regular and so our pulse is very regular. In AF, the regular timing of this signal is lost and so we generally make the diagnosis when we notice that someone has a very irregular pulse. This is usually confirmed (or sometimes initially diagnosed) by looking at the heart's electrical activity with a simple test done in the office called an electrocardiogram (ECG or EKG). In patients who only occasionally have the arrhythmia—paroxysmal AF—the diagnosis is sometimes more easily obtained by having the patient wear what is essentially a small, portable ECG machine. Two such devices that are commonly used are a Holter monitor, which continually records the heart's electrical activity for a period of 24 or 48 hours, and a patient-triggered event (or loop) recorder, which may be used to record several minutes of the heart's rhythm during symptomatic episodes.
How Common is AF?
AF is the most common sustained arrhythmia and we see it fairly often both in patients whom we see in the office as well as those who are hospitalized for various problems. Although it occurs in people of all ages, it is seen more commonly in older patients. In one of the bigger studies that looked at this question, AF was seen in less than one percent of people aged 50 to 59, but it was seen in nine percent of people aged 80 to 89.
Symptoms of AF
If you have AF, you might notice any combination of the following symptoms: palpitation (a sudden awareness of the heart's beating), fainting or near fainting, shortness of breath, or fatigue. You should be aware, however, that having these symptoms doesn't necessarily mean you have AF since they are commonly seen in people with other disorders. Some people don't have any symptoms and find out about their condition because they, or their doctor, notice that their pulse is irregular or, for some reason or another, an ECG is obtained. Those who don't notice any symptoms tend not to have very high heart rates during their AF and tend to be healthier.
What Causes Symptoms of AF?
Palpitations occur in AF because the left ventricle doesn't contract with the same force with each beat and it is sometimes possible to sense this variation in the force of the heartbeats. Fatigue or fainting tends to result from the heart beating so quickly that it can't pump out enough blood to maintain an adequate blood pressure which, in turn, can starve the brain from its much needed supply of oxygen. Although it turns out that many people do not rely much on the atria for helping pump blood into the ventricles (which will mostly fill on their own, even without an atrial contraction), some people do need every last bit of help getting blood to their ventricles. These people will notice this loss of extra pumping that the atria might otherwise provide, and will easily fatigue or even experience congestive heart failure (fluid backing up into the lungs). Those who have blockages of their coronary arteries may also notice chest pain or pressure (angina).
Why Do People Get AF?
In fairly healthy people, the most common underlying condition is a blood pressure that has been elevated for many years and this is just one of the many reasons why we physicians don't like to see high blood pressure go untreated. Other conditions that can lead to AF include disorders of the mitral valve—the valve that controls the passage of blood from the left atrium to the left ventricle (particularly in people whose valve was damaged from rheumatic heart disease), an overactive thyroid, recent ingestion of large amounts of alcohol, lung disorders in which there is a decreased amount of oxygen in the body, or an inflammation of the sac of tissue immediately surrounding the heart (pericarditis). There are still many people, however, who are otherwise in good health with no obvious cause of AF identified; their AF is sometimes referred to as lone AF.
We see AF fairly often in sicker patients who are hospitalized. Here it tends to occur in patients who have had a heart attack, a blood clot in the lungs (pulmonary embolus), a severe infection, or in patients whose electrolytes are way out of balance. It is also common to see AF develop within days after coronary artery bypass or mitral valve surgery, even in otherwise healthy people who are recovering nicely from their surgery. In this latter group of patients, particularly following bypass surgery, the AF is usually not permanent.
Risks of AF
Perhaps the most worrisome risk of AF is that if left untreated, it can significantly increase the chance of a stroke occurring. The rapid heart rate and loss of adequate pumping can lead to fainting or even congestive heart failure. In some cases it may exacerbate existing coronary artery disease and cause chest pain or even a heart attack. A very rapid rate that is sustained for weeks to months can also lead to weakening of the heart muscle, which may ultimately lead to congestive heart failure.
Treatment of AF
This is a difficult question. In formulating a response, I'm reminded how complex this arrhythmia can be and how, after over a decade of experience with it, I'm still continually amazed at the number of different clinical scenarios and treatment options that are available. At one end of the spectrum are those people who end up needing no treatment at all, and at the extreme (and fortunately uncommon) end are those who undergo open heart surgery to terminate their arrhythmia. One reason I point this out is to reassure those of you with AF who may wonder why a friend or colleague is being treated differently from you.
If you have AF, there are essentially three main goals in treating you:
- controlling your heart rate
- preventing a stroke
- getting you out of AF and back into a normal heart rhythm
It may be, however, for a variety of reasons beyond the scope of this article, that your physician feels that getting you out of AF and keeping you in a normal rhythm is unrealistic and we'll consider that option shortly—for now we'll assume that we will be able to get you back to a normal rhythm.
The first goal, controlling your heart rate, is usually accomplished by administering one or more medications that can slow the heart down (examples include the drug digoxin, and medications called beta-blockers or calcium channel-blockers). The most common way to accomplish the goal of preventing a stroke is to have you take Coumadin (also called warfarin), a medicine that will thin your blood, for several weeks before converting you back to a normal rhythm.
You will continue that medication for several weeks even after you are back in a normal rhythm. Depending on your situation, your physician may decide to use an ultrasound examination of you heart (an echocardiogram) to see if there is a clot in the left atrium. If there isn't one, he or she may then opt to avoid the initial several weeks of blood thinning and try to get you out of AF much sooner.
Converting you out of AF back to sinus rhythm is usually accomplished by giving you an antiarrhythmic medication (frequently this is done under observation in the hospital) and this is called chemical cardioversion. If it works, great. If not, your physician may decide to use an electrical device to administer a brief electrical shock to your heart. This is called electrical cardioversion and it is sometimes the method that is chosen initially. Following successful cardioversion, your physician may decide that you will need to continue taking an antiarrhythmic medicine—some people only need to take them for brief periods (days to months) but others end up taking medication forever to keep their heart in a normal rhythm.
If your physician has tried both chemical and electrical cardioversion, but has not succeeded in converting your rhythm to a normal one, there is a good chance that he or she will recommend no further attempts at cardioversion. In that case you will probably end up staying in AF and will likely need to take Coumadin to help prevent a stroke. There is a small subset of people with AF who have absolutely nothing else wrong with them (lone AF) and some experts feel that these people do not need a strong blood thinner (like Coumadin) and will be fine taking only aspirin. If your heart beats too rapidly when you are in AF you may also need to take medication to control your heart rate. If you are one of the rare people who either don't respond to or cannot tolerate these rate-controlling medications, you may need to have a procedure in which a physician inserts a catheter temporarily into your heart (via a blood vessel in your leg) to create a small scar that will permanently block the signals from reaching your ventricles. After such a procedure, you will still be in AF and you will need to have a pacemaker implanted to control your heart rate.
AF Surgery
There is a special heart operation that can terminate AF, but I should emphasize that it is highly invasive and so is generally reserved for that rare individual who, for some reason or another, simply cannot tolerate staying in AF (or has AF refractory to treatment and will be undergoing heart surgery for some other problem). In this operation, called the Maze procedure, the surgeon eliminates AF by making a number of small cuts inside the atria. There is an experimental version of this procedure being developed that does not require a major heart operation and involves a cardiologist making the cuts in the atria using a special catheter that has been inserted into the heart.
What if I am Only Occasionally in AF and for Only Short Periods of Time?
The treatment of people with paroxysmal AF depends on how fast their heart beats during AF and low long the episodes last. If the episodes are often enough or of long enough duration your physician may recommend taking an antiarrhythmic medication to prevent them (or lessen their number and decrease their duration). If your heart goes too fast during the episodes of AF, you may also need to take a medication that slows it down (some antiarrhythmic medications used to prevent AF also slow the heart so you might not need another medication). We now know that a substantial portion of patients with paroxysmal AF have their abnormal rhythm triggered by a small amount of atrial tissue present in one (or more) of the veins leading to the left atrium. There is a procedure being developed that involves removing that focus using the catheter approach described above. It is still in the earlier phases of development but it does hold promise for future treatment of AF.
Do I Need to See a Cardiologist for My AF?
That depends on how complicated your case is and how comfortable your primary care physician is at managing this type of problem. Many internists end up referring patients with AF to a general cardiologist. Both our knowledge about AF and the number of treatment options for it have grown over the past several years, and it is now becoming increasingly common for general cardiologists to refer their more complicated cases to a special type of cardiologist (sometimes called an electrophysiologist) who specializes in patients with abnormal heart rhythms.
Conclusion
AF is a common arrhythmia that is generally easy to diagnose. It is usually characterized by a rapid irregular rhythm and it may cause symptoms ranging from minor palpitations to fainting. Although the treatment of AF is straightforward for some patients, others may require more specialized treatment that is best administered by a cardiologist specializing in arrhythmias. As always, if you still have questions or concerns about AF or about your health in general, you should feel free to consult your physician.
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