Atrial Fibrillation

Atrial fibrillation (AF) is the most common heart rhythm disorder seen by doctors.

• In the United States, more than 2.2 million people have atrial fibrillation (AF) including 9% of people over the age of 80.
• About 15% to 20% of all strokes result from atrial fibrillation.
• AF can arise from temporary (acute) causes such as alcohol consumption, heart attack, surgery, lung disease, or a metabolic disorder (such as an overactive thyroid gland).
• AF can also be related to long-term (chronic) conditions such as high blood pressure, diabetes, or heart failure.
• Obesity is an important risk factor for the development of AF and weight loss may decrease the risk associated with AF.
• AF can be occasional (paroxysmal, which self terminates) or ongoing (persistent). If it does not respond to an electric current that is used to reset the heart's rhythm back to its regular pattern (called cardioversion), it can progress to permanent AF.
• The most common signs of AF are heart palpitations, chest pain, and shortness of breath.  AF can also be silent.
• There are two approaches to treatment: heart rate control or heart rhythm control, with therapies ideally achieving both goals.. When medication is ineffective, AF treatments can include cardioversion, ablation therapy (that targets specific cells that are causing the AF), and open-heart or minimally-invasive surgery that also targets a specific area of the heart that is causing the problem.
• Heart-healthy lifestyles can help prevent AF or make you better able to live with it.

Background

The heart has an electrical system that controls both the speed and rhythm of each heartbeat. This electrical system is controlled by the autonomic nervous system, which also handles critical functions such as breathing and digestion — all those functions that need to happen automatically rather than under our conscious control. 

An arrhythmia occurs when the heart’s electrical system malfunctions causing a failure in the synchronization that’s required for the heart to work properly. In the specific arrhythmia known as atrial fibrillation, electrical signals no longer start in the sinus node, but rather fire rapidly and haphazardly throughout the heart’s upper chambers. These disorganized electrical impulses cause the atria to contract quickly and irregularly, resulting in rapid quivering of the upper chambers, which is medically known as fibrillation (hence, the name atrial fibrillation). These chaotic and rapid electrical signals also bombard the AV node, usually causing heart rate to rise.  As a result, the organized flow of blood within the heart becomes disrupted and heart rhythm becomes very irregular.  It can also become quite fast, occasionally reaching heart rates as high as 160 beats per minute at rest.

Up to one-third of patients with atrial fibrillation have asymptomatic or "silent" AF, which is more common in the elderly. Other people with AF experience symptoms such as palpitations, fainting, chest pain, or even heart failure.
If the heart’s atria are not contracting properly, blood can pool in the heart’s upper chambers. Such pooled blood can lead to the formation of blood clots within the atria, which in turn can cause strokes if the clots are carried into the blood stream and lodge in the arteries of the brain.

AF is a major risk factor for stroke (increasing stroke risk about 5-fold) with the absolute level of risk somewhat dependent on the number of additional risk factors for stroke in a given individual. Just like there can be silent AF, strokes can be “silent” too, but even these asymptomatic strokes may have significant ramifications. For example, elderly people with silent strokes have greater than double the risk of dementia and a steeper decline in global cognitive function compared to age-matched individuals without evidence of such strokes.

One particular high-risk variable: transient ischemic attacks (TIAs).  These are "warning strokes" that produce stroke-like symptoms but no lasting damage. A person who's had one or more TIAs is almost 10 times more likely to have a stroke than someone of the same age and sex who hasn't.  Therefore a history of TIA and AF is a combination that suggests a strong need for preventive therapy and stroke risk reduction. 
Causes and Risk Factors

There are several well-established risk factors for AF, with coronary artery disease and heart failure being most frequently associated with atrial fibrillation. Rheumatic heart disease, which affects the valves of the heart, and congenital heart abnormalities (inherited heart defects) also increase the chance of AF. Cardiac risk factors such as hypertension and diabetes can also play a role in damaging the atria of the heart, leading to AF. There are a number of acute, temporary causes of AF as well as chronic conditions which lead to this rhythm abnormality.  For the most part, when the temporary condition ceases or is treated, AF usually resolves. In the presence of chronic conditions, treatment should target both the AF and the chronic problem that is contributing to the risk of AF-associated events.

Signs and Symptoms

Probably the most recognizable sign of AF is heart palpitations, where your heart beats so fast that you think it is racing and/or you can feel it thumping or flopping in your chest. It may be accompanied by chest pain; lightheadedness or dizziness, especially if you are exerting yourself; weakness; or shortness of breath, including difficulty breathing when lying down. AF symptoms will vary depending on the degree of pulse irregularity and resultant heart rate, underlying functional status, how long the AF lasts, and individual patient factors.

Remember: one of the effects of AF may be formation of a blood clot in the atria. If this happens and the clot travels up to the brain, you may have a stroke. Sometimes a stroke is the first sign of underlying AF, especially if the symptoms have been light or nonexistent.

There is no set amount of time that marks an episode of AF — it may be very short and stop on its own or it may be prolonged and you find yourself in need of medical intervention. Over time, you may become more accustomed to the pattern of your AF, and what factors contribute to and relieve this arrhythmia. 

Treatment

Atrial fibrillation can be tough to treat. Management of AF is designed to achieve several objectives:
• Prevent blood clots from forming;
• Control the heart rate. Controlling on how many times per minute the heart beats (rate control);
• Restore the heart to a normal rhythm (rhythm control); this helps the heart’s chambers work together more efficiently, which also can improve rate control;
• Treat underlying conditions that may be causing or worsening the AF, such as overactive thyroid function, other metabolic imbalances or various cardiac diseases.
There are different strategies to treat  AF, and the goal may be to achieve some or all of the above objectives.  Which approach is best for you will depend on various factors, including whether you are currently being treated for other heart or medical problems. Sometimes you will need a combination of treatments to effectively treat your AF.

Prevention of blood clots
The two most common drugs used to prevent blood clot formation (and thus reduce the risk of stroke) are warfarin and aspirin. Warfarin (commonly known as Coumadin) is more effective than aspirin for preventing stroke in this situation. However, warfarin has more side effects — such as potential bleeding problems — than aspirin. Aspirin is the standard treatment for patients without other risk factors for stroke who are also under 75 years of age. If you have only one moderate risk factor for stroke in addition to atrial fibrillation (such as hypertension, diabetes, or heart failure), either aspirin or warfarin may be considered to reduce stroke risk. If you have at least one high-risk factor (e.g., a previous stroke or TIA, age older than 75), you will likely receive warfarin.  Because warfarin is a powerful blood thinner, it requires intense monitoring. Such monitoring involves regular blood tests to measure INR.  INR stands for international normalized ratio and this test allows doctors to determine how thin the blood is.  For patients with atrial fibrillation, goal INR is usually 2.0 to 2.5.  The frequency of INR measurements varies from patient to patient and is driven by how stable the INR measurements are over time.  While aspirin and warfarin can be very effective in reducing the risk of stroke (and heart attack), they are associated with a small risk of serious side effects. Most of the side effects are bleeding related. Patients at higher risk for injury (those with balance issues, patients who abuse alcohol, and those who work in professions where falls are possible, etc.) may not be able to use warfarin, even if they would otherwise qualify for this therapy.. 

Rate control
To slow heart rate, doctors usually rely on beta-blockers (such as metoprolol, propranolol, etc.), calcium channel blockers (verapamil, diltiazem, etc.), or digoxin. Other agents can be prescribed depending on your particular needs. Beta blockers and calcium channel blockers, although relatively safe, can lower blood pressure and slow the heart rate profoundly. That is why your doctor will carefully monitor the effects of whatever medication you are prescribed.

Rhythm control
Ideally, you want to get your heart to regain its normal rhythm, although this becomes more difficult the longer you have AF. To convert the heart to normal sinus rhythm, doctors may use cardioversion, which is defined as the conversion of one cardiac rhythm or electrical pattern to another. This can be accomplished with drug therapy or with medical procedures.

The medications used to treat AF, generally referred to as antiarrhythmics, are designed to suppress arrhythmias or pharmacologically convert an arrhythmia to a normal rhythm. The particular agent used to treat an episode of AF will depend on a number of variables, including the type of AF being treated (paroxysmal or persistent), patient age and other health issues which may be present. These drugs may be given by mouth or intravenously for faster delivery (although the latter is more likely if you have been hospitalized). If the antiarrhythmic medications produce the desired effect on an episode of AF (that is, you return to normal sinus rhythm), you may be given the same or similar medication to prevent repeat episodes of AF.  In some cases, you will need to take the medicine on a regular, ongoing basis; in others, you will take it as needed.  

Alternatives to drug therapy
When medications do not work, there are alternatives. Electrical cardioversion uses a jolt of electricity to your heart either through paddles or wired patches attached to your chest. This is a controlled, usually prescheduled procedure — not the type of emergency “defibrillation” depicted in film or on TV when a character’s heart has stopped. Defibrillation is done under light anesthesia in the hospital, and the patient usually goes home the day of the procedure.

Another option is catheter ablation, which targets and destroys small areas of cells in the heart thought to be the source of electrical malfunction. In this technique, a catheter is threaded into your heart and radio frequency energy in the form of radio waves is emitted to selectively cauterize the errant heart cells. This procedure usually improves heart function, exercise capacity, and quality of life. The aim of catheter ablation is to “cure” AF, although that word may be misleading. Most studies which have looked at the outcome of ablation have followed patients for only 5- to 10-years. It’s unknown whether these “cured” patients may once again develop AF. Not all patients undergoing ablation have their arrhythmia completely eliminated by the procedure.  Nevertheless, many such patients sill experience greatly improved heart rate control. The result of ablation may be that drug therapy that failed to control heart rate in the past may be effective once again. Between those patients experiencing an effective “cure” and those who see great improvement following ablation, the overall success rate of this procedure is about 70% to 80%.

Living With Atrial Fibrillation

Always take antiarrhythmic drugs exactly as directed. These drugs work best when they are at constant levels in the blood. To help keep levels constant, take your medicine as directed; do not miss any doses and never take larger or more frequent doses. Don’t stop taking antiarrhythmic drugs without checking first with your physician, because stopping some of these drugs suddenly could lead to serious side effects. If taking medicine at night interferes with sleep, or if it is difficult to remember to take your medicine during the day, check with a health care professional for suggestions.

When you visit your doctor or an emergency room (whether for an AF-related problem or not), bring a detailed list of all your prescription drugs with you.   Having a complete picture of all your medications is critical in any health care setting, but it is especially important if you are taking antiarrhythmics. Also, keep all medical appointments; don’t assume that because you’re feeling better it is not necessary to visit your doctor. Precise updates on your condition are required to make sure that the treatment strategy is right (and safe) for you. Keeping regular doctor’s appointments is particularly critical if you are taking anticoagulants or blood-thinning medications. If you experience medication side effects or symptoms of AF, be sure to share that with your doctor.

Written by Dr. Mark Steiner, Cardiologist in Orlando