Monday, July 18, 2011
TOPIC: Advances in A-Fib
Drew Pickett, MD: electrophysiologist (cardiologist)
News notes via www.webmd.com
Atrial Fibrillation and Heart Disease
What Is a Normal Heart Rhythm?
The heart has four chambers, or areas. During each heartbeat, the two uppers chambers (atria) contract, followed by the two lower chambers (ventricles). This action is directed by the heart's electrical system.
The electrical impulse begins in an area called the sinus node, located in the upper part of the right atrium. When the sinus node fires, an impulse of electrical activity spreads through the right and left atria, causing them to contract, forcing blood into the ventricles.
Then the electrical impulses travel in an orderly manner to another area called the atrioventricular (AV) node and HIS-Purkinje network. The AV node is the electrical bridge that allows the impulse to go from the atria to the ventricles. The HIS-Purkinje network carries the impulses throughout the ventricles. The impulse then travels through the walls of the ventricles, causing them to contract. This forces blood out of the heart to the lungs and the body. The pulmonary veins empty oxygenated blood from the lungs to the left atrium. A normal heart beats in a constant rhythm -- about 60 to 100 times per minute at rest.
What Is Atrial Fibrillation?
Atrial fibrillation (also referred to as AF or Afib) is the most common type of irregular heartbeat. It is found in about 2.2 million Americans. It increases with age. If you have AF, the impulse does not travel in an orderly fashion through the atria. Instead, many impulses begin simultaneously and spread through the atria and compete for a chance to travel through the AV node.
The firing of these impulses results in a very rapid and disorganized heartbeat. The rate of impulses through the atria can range from 300 to 600 beats per minute. Luckily, the AV node limits the number of impulses it allows to travel to the ventricles. As a result, the pulse rate is often less than 150 beats per minute, but this is often fast enough to cause symptoms.
What Are the Symptoms of Atrial Fibrillation?
You may have atrial fibrillation without having any symptoms at all. If you have symptoms, they may include:
What Causes Atrial Fibrillation?
Atrial fibrillation is associated with many conditions, including:
Less Common Causes of Atrial Fibrillation
Less common causes of atrial fibrillation include:
In at least 10% of people with AF, no underlying heart disease is found. In many of these people, AF may be related to alcohol or excessive caffeine use, stress, certain drugs, electrolyte or metabolic imbalances, or severe infections. In some people, no identifiable cause can be found.
The risk of AF increases with age, particularly after age 60. According to the CDC, AF affects roughly one in every 10 persons aged 80 years or older.
Why Is Atrial Fibrillation Dangerous?
Many people live for years with atrial fibrillation without problems. However, because the atria are beating rapidly and irregularly, blood does not flow through them as quickly. This makes the blood more likely to clot. If the clot is pumped out of the heart, it can travel to the brain, resulting in a stroke. The likelihood of a stroke in people with AF is five to seven times higher than in the general population. Although about half of all blood clots related to AF result in stroke, clots can travel to other parts of the body -- such as the kidney, heart, or intestines -- also causing problems.
AF can also decrease the heart's pumping ability by as much as 20%-25%. AF combined with a fast heart rate over a period of days to months can result in heart failure. Control of AF can then improve heart failure, also over days to months.
Chronic atrial fibrillation is associated with an increased risk of death.
How Is Atrial Fibrillation Diagnosed?
Four tests are used to diagnose atrial fibrillation, including:
These monitoring devices help your doctor learn if you are having irregular heartbeats, what kind they are, how long they last, and what may be causing them.
How Is Atrial Fibrillation Treated?
Many options are available to treat AF, including medication, lifestyle changes, certain procedures, and surgery. The choice of treatment for you is based on your rhythm and symptoms. The goals of AF treatment are to:
How Are Medications Used to Treat Atrial Fibrillation?
Medications are prescribed in the management of AF depending on the overall treatment goal. If the goal is to restore normal heart rhythm, a type of drug called an antiarrhythmic is prescribed. If it's not possible to achieve this goal, doctors will try to manage your condition by slowing down the heart rate. In both cases, your doctor will give you drugs called anticoagulants to decrease blood clot formation.
Lifestyle Changes for Atrial Fibrillation
In addition to taking medications, there are some changes you can make to improve your heart health and help atrial fibrillation.
Procedures for Atrial Fibrillation
When drugs do not work to correct or control atrial fibrillation, or when medications are not tolerated, a procedure may be necessary, such as: electrical cardioversion, pulmonary vein isolation, catheter ablation of the AV node, or device therapy.
What Is Electrical Cardioversion?
Electrical cardioversion frequently restores a normal rhythm, although its effect may not be permanent. After a short-acting anesthesia is given, a machine (defibrillator/cardioverter/pacemaker) is used to deliver specific amounts of energy (an electric shock) through electrode patches placed on the chest to synchronize the heartbeat and restore a normal rhythm. Although this procedure only takes a few seconds, several attempts may be needed to restore a normal rhythm. In general, a patient will need to be on Coumadin for at least three weeks before this procedure is performed. This decreases the risk of a stroke that can occur with the cardioversion.
What Is Ablation Therapy?
Catheter ablation therapy is an option for people who cannot tolerate medications or when drugs fail to maintain the normal heart rhythm.
Pulmonary vein antrum isolation: Research has shown that most atrial fibrillation signals come from the four pulmonary veins. During this procedure, special catheters are inserted into the heart. Two catheters are inserted into the right atrium and two into the left atrium.
A specialized viewing device called intracardiac echocardiography is used to visualize the left atrium during the procedure. One catheter in the left atrium is used to map or locate the abnormal impulses coming from the pulmonary veins. The other catheter is used to deliver the radiofrequency energy to create lesions outside the pulmonary veins. The procedure is repeated for all four pulmonary veins.
The lesions heal and within four to eight weeks and form a circular scar around the pulmonary veins. The scar blocks any impulses firing from within the pulmonary veins, thereby "disconnecting" the pathway of the abnormal rhythm and curing atrial fibrillation.
Ablation of the AV node: During this procedure, the doctor applies radiofrequency energy to injure the AV node. The end result is a permanent, very slow heart rate, since the electrical impulses from the top chamber of the heart cannot travel down to the lower chamber. Therefore, the patient needs a permanent pacemaker to maintain an adequate heart rate.
What Is Device Therapy?
Implantable atrial defibrillator is a device used to treat AF symptoms. When the symptoms of AF occur, the person can turn on the device and treat the AF when appropriate and convenient. Or, the device can be set to operate automatically. The atrial defibrillator can be programmed to identify when a person is having an episode of atrial fibrillation. When it occurs, the device delivers low-dose energy to convert AF to a normal heart rhythm. This procedure improves atrial fibrillation symptoms, but does not cure the condition. This device is still being tested to determine who would benefit the most from this type of therapy.
What Is a Permanent Pacemaker?
Permanent Pacemaker: A pacemaker is a device that sends small electrical impulses to the heart muscle to maintain a suitable heart rate. Pacemakers are implanted in people with AF who have a slow heart rate. The pacemaker has a pulse generator (which houses the battery and a tiny computer) and leads (wires) that send impulses from the pulse generator to the heart muscle, as well as sense the heart's electrical activity.
Newer pacemakers have many sophisticated features designed to help with the management of arrhythmias and to optimize heart rate-related function as much as possible.
What Is Surgical Therapy?
Patients with chronic atrial fibrillation not relieved by medication or procedures, or patients who have other conditions requiring heart surgery, may be candidates for surgical treatment of AF. These procedures are types of open-heart surgery that require general anesthesia (you are put to sleep) and a hospital stay.
During the Maze procedure, a series of precise incisions are made in the right and left atria to confine the electrical impulses to defined pathways to reach the AV node.
Surgical pulmonary vein isolation is a modification of the Maze procedure in which the surgeon uses alternative energy sources instead of incisions to create lesions. The alternative energy sources used during surgical pulmonary vein isolation include: radiofrequency, cryothermy, microwave, and laser. The goal of all four energy sources is to produce lesions and ultimately scar tissue to block the abnormal electrical impulses from being conducted through the heart and to promote the normal conduction of impulses through the proper pathway.
Many of these approaches can be performed with minimally invasive (endoscopic or "keyhole") surgical techniques.
Some patients may have atrial fibrillation in addition to other heart problems (such as valve or coronary artery disease) which require surgery. In these cases, the surgeon may combine the surgeries to correct the atrial fibrillation and the coexisting heart condition at the same time.