Atrial Fibrillation
Atrial fibrillation is a disorganized heart rhythm leading to an irregular heart beat that is often quite fast. A normal heart beat originates in a collection of cells in the top part of the heart (the right atrium) called the sinus node. These cells are the normal pacemaker of the heart. The electrical impulse that arises in the sinus node causes the top chambers (atria) of the heart to contract, moving the blood to the lower chambers. This electrical impulse is then conducted rapidly to the lower chambers causing contraction of these chambers and thus the pumping of blood to the lungs and to the body. A normal resting heart rate ranges from 60 to 100 beats per minute.
In atrial fibrillation, the electrical activity of the atria becomes very disorganized with multiple waves of electrical activity arising throughout the atria. Instead of the atria contracting in an organized fashion, the atria quiver (fibrillation). This may lead to a decrease in the heart's function by 20 to 25%. Because the lower chambers (ventricles) are seeing multiple electrical signals, the heart rhythm becomes very irregular and often is quite fast. Patients with atrial fibrillation are often aware of the heart beating irregularly and may notice a decrease in their ability to exert themselves. Fatigue and shortness of breath are common complaints.
Causes of Atrial Fibrillation
Many factors may help cause atrial fibrillation. Disease of the heart valves, particularly the mitral valve may lead to atrial fibrillation. A decrease in heart muscle function from previous heart attack or due to a primary problem with the heart muscle (cardiomyopathy) often leads to atrial fibrillation. Certain metabolic disorders, such as an overactive thyroid gland, may cause atrial fibrillation. Approximately 30% of patients undergoing heart surgery will have atrial fibrillation post operatively. Excess caffeine or alcohol can also cause atrial fibrillation as can certain medications such as those used to treat asthma. Patients with lung disease have an increased incidence of atrial fibrillation. In many patients, however, atrial fibrillation occurs for no definable reason. The frequency of atrial fibrillation also increases with age.
Effects of Atrial Fibrillation
Because the ability of the heart to pump blood is reduced by 20 to 25% in atrial fibrillation, many patients will experience fatigue and shortness of breath. Most will sense a rapid and irregular pulse. When the heart rate is excessive, chest pain (angina pectoris) and/or congestive heart failure may result. If the heart remains in atrial fibrillation for more than 48 hours, there is an increased risk that blood clots may form within the atria due to the stagnation of blood due to atrial fibrillation. This increases the risk that a stroke could result if a small blood clot were to break off and travel to a brain blood vessel. This is preventable by promptly restoring normal rhythm or by the use of blood thinners.
Tests Your Doctor Might Order
The diagnosis of atrial fibrillation is made by an electrocardiogram. When the atrial fibrillation is intermittent, recording the heart's electrical activity for a period of time can be helpful. This is done as an outpatient using a recording device known as a Holter Monitor or an Event Monitor. Because it is important to know about the health of your heart when atrial fibrillation occurs, an echocardiogram is frequently done. Using soundwaves, the heart chambers and valves can be visualized. This test also helps determine what patients are likely to stay in atrial fibrillation and which have a high chance of success in maintaining normal rhythm. Blood tests will be done to check your electrolytes and thyroid function. If other medical problems are present (such as coronary artery disease, lung disease, congestive heart failure, anemia and pericarditis) these will also require evaluation and treatment.
Treatment
Because many of the symptoms of atrial fibrillation are due to the rapid heart rate, the first goal of treatment is to slow the heart rate to near normal. Drugs that may be helpful in slowing the heart rate include beta blockers and the calcium channel blockers diltiazem and verapamil. Digitalis (digoxin) might also be used.
Atrial fibrillation may be intermittent and may convert spontaneously. If not, medications or electrical conversion of atrial fibrillation may be necessary. If atrial fibrillation has not converted back to normal rhythm within 48 hours of its onset, there is a increased risk that blood clots may form in the top heart chambers (the atria). To help protect against blood clots breaking off and causing a stroke or other injury, a blood thinner called Coumadin (warfarin) is often started. The dose is regulated through a blood test called an INR (International Normalized Ratio) or prothrombin time. Once you have been on Coumadin for 3 weeks or more, an attempt at restoring normal rhythm may be made.
Medications to help restore and maintain normal rhythm include amiodarone, propafenone, sotalol, flecainide, procainamide, quinidine, diltiazem and beta blockers. If the atrial fibrillation does not convert to regular rhythm on medications, a procedure called cardioversion is generally performed. This is usually a hospital procedure. A brief anesthetic is administered. While you are asleep, an electrical shock is delivered to the chest reorganizing the electrical activity of the heart and restoring normal rhythm. Following successful cardioversion, Coumadin is usually continued for 3 to 4 weeks. Medications may be required long term to maintain normal rhythm. Even with medications, there is a significant chance that atrial fibrillation may return.
The success of conversion to a normal rhythm depends on the length of time atrial fibrillation has been present. If the abnormal rhythm has been present for months or years, successful conversion by any method is less likely. Recurrence of atrial fibrillation is more likely to happen in patients with significant underlying heart disease, in those with significant lung disease and in older patients.
Those patients who fail to convert to normal rhythm or who revert to atrial fibrillation despite medications may be in atrial fibrillation long term. This is referred to as chronic atrial fibrillation. These people should stay on long-term blood thinners to reduce the risk of stroke. In most cases, the heart rate can be controlled with proper medicines. In some patients the heart rate remains excessively fast and a procedure known as AV nodal ablation can be done to control the heart rate in conjunction with a pacemaker.