Atrial fibrillation (also called “atrial fib” or “A-fib”)

Atrial fibrillation (also called “atrial fib” or “A-fib”) is an irregularity of the heartbeat. It is the most common heart rhythm abnormality among adults. In fact, as people age, atrial fibrillation becomes more common. In people with normal heart rhythm, the electrical impulse that generates the heart beat starts from the upper chamber of the heart, called the atrium, by a specialized group of cells called sinus nodes (SA node) (Figure 1). This impulse travels through a normal connection (called an atrioventricular junction or AV node) between the atria and the lower chambers of the heart, called the ventricles. During atrial fibrillation, the upper chambers have numerous chaotic, small electrical impulses that cannot generate an effective squeeze of the upper chambers. Because of this, blood does not move through the heart in a normal way, which may increase the risk of clots and stroke. Since the atrioventricular junction also works as a gatekeeper, some of these electrical impulses can reach the lower chambers of the heart, generating an irregular and fast pulse. In atrial fibrillation, the heartbeat is irregular and rapid, sometimes beating as often as 300 times a minute in the atria and 100 to 180 times a minute in the ventricles, about four times faster than normal.

Basics of Heart function

Heart’s main function is to pumps blood throughout the body. It is made up of four chambers. The upper chambers are called atria. The atria collect the blood that comes from the rest of the body into the heart. They contract to pump blood to the two lower chambers, called ventricles. The ventricles contract to pump the blood out of the heart. This pumping creates the heartbeat. Although the contraction of the heart chambers is a mechanical action it can only be started by an electrical stimulus from hearts electrical system which is composed of special electrical cells. These cells create and conduct electrical signals that tell the heart when to beat. Some of these cells form groups called nodes. Others form pathways that like electrical cables carry signals through the heart (Figure 1).

The Sinus Node (SA Node) - Normally the SA node starts each heartbeat. A signal from the SA node travels through the atria, telling them to contract.

The Atrioventricular Node (AV Node) – is the electrical connection between the atria and the ventricles. The AV node receives the signal that has traveled through the atria. It is like an electrical terminal box. It slows this signal and transfers it into the ventricles. In a normal heart atrium and ventricles are electrically isolated and the only electrical connection between them is by the AV node.

The Two Bundle Branches are pathways of cells that function as electrical cables and carry the signal through the ventricles. As the signal reaches ventricles through these pathways the ventricles contract.

The heart normally beats at between 60 and 100 beats per minute (bpm). The heart rate varies based on the several factors such as the amount of blood needed by the rest of body, the bloods oxygen level, hemoglobin level, physical and mental stress level, body temperature as well as physical activity level. The heart rate usually slows down at rest and during sleep but increases during awake hours and with activity. The heart usually beats in regular rhythm however in abnormal situation it can beat fast and/or irregular which would cause rhythm disturbances.

Heart rhythm abnormalities

Rhythm abnormalities can arise from the atrium or from the ventricle. If the atria beat quickly, but still evenly, it is called supraventricular tachycardia. Atrial flutter is a type of supraventricular tachycardia. If the atria beat very quickly and irregular, it is called atrial fibrillation. Some patients may have both atrial flutter and atrial fibrillation at different times.

Atrial Flutter

With atrial flutter (Figure 2), electrical signals travel around the atria in an electrical circuit. This will result in the atria to beat quickly (around 250 to 350 bpm). Some of the signals make it through the AV node to the ventricles, which also beat quickly (up to 150 bpm).

Atrial Fibrillation

With atrial fibrillation (Figure 3), there are chaotic and irregular electrical signals wondering in the atria. These signals make the atria beat very quickly (from 400 to 500 BPM) and unevenly. The atrial beat is so fast and uneven that in fact instead of contracting they only quiver without any forceful contraction. Because of lack of real atrial contraction blood doesn’t move enough into the ventricles and in some patient the overall blood output of the heart drops. This may lead to symptoms such as fatigue, dizziness and weakness. Also since blood isn’t moving as well in the atria it can pool and form clots in the atria. These clots can move into other parts of the body and cause serious problems, such as stroke or heart attacks.

Causes of atrial flutter and atrial fibrillation

Although atrial flutter or fibrillation can be caused by things such as a heart attack, long standing high blood pressure, consumption of large amount of alcohol or a thyroid problem they usually have no clear cause. In recent years it has become clear that abnormal electrical impulses made by the veins that drain the blood from the lung to the left side of the heart (called pulmonary veins) have an important role in at least initiating the atrial fibrillation in most patients.

Symptoms of Atrial Fibrillation:

Patients with atrial fibrillation may experience one or more of the following symptoms:

Palpitations (a fluttering, fast heartbeat)
Weakness
Fatigue or lack of energy
Shortness of breath
Chest pain or chest tightness
Dizziness or lightheadedness
Fainting spells
Some people are completely asymptomatic

Atrial flutter can cause symptoms similar to atrial fibrillation.

Management of Atrial Fibrillation

Atrial fibrillation is a common heart problem, affecting people of all ages and races. It can also lead to other health problems, such as stroke or heart failure. Atrial fibrillation itself is rarely life-threatening. Patients with atrial fibrillation should be able to live an active life. The goal in management of atrial fibrillation is to control the symptoms associated with atrial fibrillation and prevent sequela of atrial fibrillation such as stroke and heart failure. There are two main approaches to managing atrial fibrillation:

Rate-control approach: an attempt to slow down the response of the ventricles to atrial fibrillation. In this approach, the atria may or may not be in atrial fibrillation, but the ventricles are still subdued through medications or a pacemaker.

Rhythm-control approach: This approach tries to keep the patient’s heart rhythm normal to prevent episodes of atrial fibrillation

In both approaches, patients must use a blood thinner, such as coumadin or aspirin, to prevent stroke.

Rate Control Approach

Rate control with medications:

The medications used for this approach are mainly beta-blockers, calcium channel blockers, digitalis, or any combination of these medications. Although these medications have different effects on the heart, they all work to slow down the conduction of the electrical impulses at the atrioventricular junction. These medications prevent most of these electrical impulses generated in the atria from reaching the lower chambers of the heart. This results in lower pulse rates and diminished symptoms.

Rate control with pacemaker:

In some patients, it is not possible to slow down the impulses at the atrioventricular junction, and the patient still experiences fast heart rates despite use of maximum doses of these medications. In these patients, one option is to implant a pacemaker and then destroy the atrioventricular junction (see below) after about a month. This can be done by guiding a catheter from the groin to the heart and using radiofrequency energy to destroy the tissue. Although after this procedure the atria still would be in atrial fibrillation, the pacemaker would drive the ventricles. Since the pulse is generated by the ventricles’ contraction, the pacemaker-guided pulse would be regular. Several studies have shown that a large number of patients who undergo this procedure experience significant symptom relief. Also, some of these patients’ heart function improves.

AV Node Ablation –

The AV node is where the atrial and ventricular electrical systems meet. An AV node ablation is a procedure designed to use radiofrequency energy to disrupt or eliminate the AV node thus preventing the chaotic and irregular electrical impulses from atria to reach the ventricles. This procedure slows and regularizes the heart rhythm and requires placement of a permanent pacemaker. While symptoms improve, atrial fibrillation remains and blood-thinners are required to reduce the risk of stroke.

Rhythm Control

Rhythm control with medications:

Several medications can be used to achieve normal sinus rhythm. Although these medications have different properties, they all work by reducing the possibility of chaotic atrial fibrillation electrical impulses. If the patient is still in atrial fibrillation after starting these medications, an external electrical shock called cardioversion is used to restore normal rhythm.

Electrical cardioversion uses electricity to help normalize the heartbeat. During electrical cardioversion, the doctor gives the heart a brief electric shock. The shock stops all electrical activity in the heart for a brief moment, including the irregular signals that cause atrial fibrillation. A normal heart rhythm can then take over. In some people, more than one procedure may be needed. In others, the procedure may not work at all.

If after some time the medication fails to keep the patient in normal rhythm, then another antiarrhythmic medication can be used, or the patient can undergo catheter-based or surgical-based procedures. Like all medications, the antiarryhthmics have risks and side effects to consider. 2)

Rhythm control with catheter-based procedures (ablation):

Ablation is known by several names, including catheter ablation, radiofrequency ablation, and cardiac catheter ablation. This procedure usually is reserved for patients with symptoms that have not responded to medication or for patient who do not wish to take antiarrhythmics for a long period of time. As the experiences with ablative therapies for atrial fibrillation increases there might be a subset of patients who might benefit from the ablation for atrial fibrillation as a first line of therapy.

An ablation uses energy (usually radiofrequency energy) to disrupt or eliminate the faulty electrical pathways that cause abnormal heart rhythms. Ablation no longer requires open heart surgery and can be done through catheters placed into the heart through the blood vessels. Catheters are inserted into a blood vessel, often through a site in the groin or neck. They are then guided via X-ray through the blood vessels and directed to the heart muscle (Figure 4). Once the catheters are in the heart, radiofrequency energy or another form of energy is directed to areas of the heart that are sending out the abnormal electrical signals that cause atrial fibrillation. Then, a burst of energy destroys the specific problematic tissue and creates an area of tissue that will not conduct electrical activity (Figure 5). Most healthy tissue is left unharmed. In ablation, energy either destroys the troublesome areas that trigger abnormal electrical signals or creates a roadblock that stops such signals from traveling through the heart.

Atrial fibrillation often originates from the four pulmonary veins that carry blood from the lungs to the left atrium (Figure 6). With this procedure, catheters are placed in the heart and are guided to the left atrium, where energy is delivered to destroy or isolate the areas that trigger the atrial fibrillation (Figure 7). In some patients, a second procedure may be needed if the atrial fibrillation is not cured by the initial ablation. The initial catheter ablation cures about two-thirds of patients. With a second procedure, up to 75 percent of patients can be cured.

Atrial fibrillation ablation is one of the most complex cardiac procedures and is mainly performed by electrophysiologists, cardiologists who have undergone additional years of training to specialize in management of cardiac rhythm problems. Like any other cardiac procedures, catheter ablation for atrial fibrillation carries risks that the electrophysiologist would discuss with the patient.

Typically, patients have a follow-up exam and electrocardiogram within a month or two of the procedure. The first three months after the procedure the patients need to be on blood thinner (coumadin) as well as an antiarrhythmic (usually amiodarone) to prevent recurrence of atrial fibrillation during the first few months after the procedure. The doctor and patient usually decide whether to discontinue medication after three months. After that, the follow-up evaluations may be as infrequent as once every six to 12 months.

Risks

Complications in catheter ablation are uncommon, although like most heart procedures risks do exist and should be discussed and understood before the procedure. Risks include:

Bruising
Bleeding
Puncture of the heart
Damage to the heart’s conduction system
Blood clot formation, which could lead to stroke or other damage (that is the reason that patients need to stay on blood thinner for few months after this procedure)
Rarely, the pulmonary veins that carry blood from the lungs to the heart may narrow

The Procedure

Catheter ablations are performed in a hospital while the patient is sedated. The procedure usually takes between three and six hours.

During the procedure, patient will be connected to a number of monitors.

All patients have sedation for the procedure to help them relax, and many sleep through the entire procedure and will not remember the procedure afterward. Other patients may be awake for parts of the procedure. Some patients rarely report pain during the procedure. However, most patients have very little or no pain and do not recall of the procedure.

After the procedure, the doctor removes the catheters. Pressure is applied to the puncture points to prevent bleeding and ensure that the entry point begins to heal properly. The patient must lie fairly flat for several hours.

Patients usually recover quickly. Most patients are monitored in the hospital overnight and go home the next day.

Before going home, a patient reviews with the doctor and the nurse how to care for the puncture sites, the medication list and what activities are appropriate. A follow-up visit with the doctor also will be scheduled.

Rhythm control with surgical approach

Several surgical approaches can restore normal rhythm in patients with atrial fibrillation. Based on the current guidelines these procedures are usually reserved for patients who are undergoing cardiac surgery for other reasons (like bypass or valvular surgeries) or those with at least two failed catheter ablations. The surgical approaches range from modified Maze procedure which is an open heart surgery to the less invasive approaches such as mini Maze. However, in general the surgical approaches are more invasive than the catheter based approaches.

Preventing Clots

Blood does not circulate properly in patients with atrial fibrillation, which could increase the risk of clot formation. If a blood clot forms in the atria, part of the clot can break off and travel from the heart to the brain or other organ. This can cause a stroke. In order to prevent this sequel of atrial fibrillation, aspirin or coumadin (Warfarin) is used to thin the blood. The choice between aspirin or coumadin is based on several different factors, including the patient’s age and risk of stroke.

Stroke Risk

Patients with atrial fibrillation, even lone atrial fibrillation without other evidence of heart disease, are at increased risk of stroke during long-term follow up. A systematic review of risk factors for stroke in patients with nonvalvular atrial fibrillation concluded hat a prior history of stroke or transient ischemic attack is the most powerful risk factor for future stroke, followed by advancing age, hypertension, and diabetes.

The risk of stroke increases whether the lone atrial fibrillation was an isolated episode, recurrent, or chronic. The risk of systemic embolization (atrial clots migrating to other organs) depends strongly on whether there is an underlying structural problem with the heart and the presence of other risk factors, such as diabetes and high blood pressure. Patients under 65 are much less likely to develop embolization compared with patients over 75. In young patients with few risk factors and no structural heart defect, the benefits of anticoagulation may be outweighed by the risks of hemorrhage (bleeding). Those at a low risk may benefit from mild anticoagulation with aspirin (or clopidogrel in those who are allergic to aspirin). In contrast, those with a high risk of stroke derive most benefit from anticoagulant treatment with warfarin or similar drugs.

Conclusion:

Although it is frightening to learn you have a heart problem, patients with atrial fibrillation have a number of treatment options. With a good, long-term relationship between the patient and rhythm specialist, it is often possible to bring regularity to a chaotic heart and prevent symptoms and sequela of atrial fibrillation. This should give those with atrial fibrillation an opportunity to experience a normal, active life.