What is atrial fibrillation?
What are the symptoms of AF?
What causes AF?
How many people have AF?
What are the risks of AF?
Are there different types of AF?
What treatments are offered for AF?
How do I know if I am a candidate for the Cox-Maze procedure?
Atrial fibrillation (AF) is an abnormal heart rhythm defined by an irregular, disorganized heartbeat.
In a person with a normal heart rhythm, the heartbeat is triggered by an electrical impulse that starts in the sinoatrial (SA) node and travels in an organized fashion through the upper and lower chambers of the heart. The SA node is in the right atrium (upper right chamber) and acts as the “pacemaker” of the heart. Electrical signals from the SA node cause the heart’s two atria to contract, and then the impulse travels down the interatrial septum to the atrioventricular (AV) node. At the AV node, the impulse splits off to the left and right bundle branch. This is where the electrical stimulation causes the lower heart chambers – the ventricles – to contract and force blood out of the heart to the lungs and body. This organized, synchronous electrical impulse is called normal sinus rhythm. In normal sinus rhythm, the atria contract between 60-100 beats per minute at rest.
For a person in AF, the atria are activated up to 500 beats per minute. This rapid activation causes the atria to quiver or fibrillate. The AV node stops many of these impulses and prevents the ventricles from contracting too rapidly.
|When the heart is functioning normally (left), it beats in a regular rhythm controlled by electrical discharges regulated by the sinus node (yellow bulb, top left). In atrial fibrillation (right), electrical discharges originate from various locations in the heart. These rapid, irregular pulses cause the chambers of the heart to quiver instead of beating as a unit, reducing the heart’s ability to pump blood.
- Sensation of irregular or fast heartbeat
- Shortness of breath
- Exercise intolerance
- Vague chest discomfort or anxiety
- Some people may not have any symptoms at all.
| Normal heart rhythm
| Irregular atrial fibrillation
What causes AF?
Risk factors for AF include:
- High blood pressure
- Coronary artery disease
- Heart valve disease
- Thyroid condition
- Congestive heart failure
- High levels of caffeine or alcohol use
AF is the most common heart arrhythmia, affecting more than 2 million Americans. The risk of developing AF also increases with age, affecting about 4 percent of the population over 60 years and approximately 10 percent of people older than 80. It is predicted that the number of Americans diagnosed with AF will grow to more than 10 million by the year 2050.
The greatest risk from being in atrial fibrillation is developing a blood clot in the atrium. When the atria are quivering during atrial fibrillation, the inefficiency of blood flow may cause the blood to thicken along the walls of the atria and form a clot. If this clot comes loose, it will be pumped out of the heart and can travel to the brain, the lungs, the arteries feeding the heart muscle or any other part of the body. This moving clot is now called an embolus and can cause a lack of oxygenation in the area where the blood clot lodges. The devastating consequences of an embolus include stroke, heart attack, pulmonary embolus and possibly death.
Another complication of AF is the heart’s inefficiency in circulating oxygen-rich blood. Effective atrial contraction contributes up to 10-20% of normal output (atrial kick). In AF, the atria are unable to contract and this could lead to congestive heart failure in some patients, causing fluid retention in the lower legs, liver and lungs. The symptoms caused by this problem are fatigue, shortness of breath and exercise intolerance. Eventually, the heart may become enlarged (cardiomyopathy), and heart failure may result.
The goal of treating atrial fibrillation is to reduce these symptoms and ultimately reduce the risk of stroke and heart failure.
Yes, there are three types. They are:
- Paroxysmal (intermittent) atrial fibrillation: Atrial fibrillation is not present all the time and goes back to a normal rhythm on its own.
- Persistent (continuous) atrial fibrillation: When this occurs, AF is present all the time, but it can be cardioverted (changed by a cardioverter defibrillator) back to a normal rhythm.
- Permanent (chronic) atrial fibrillation: AF of at least six months’ duration; the heart cannot return to normal rhythm after cardioversion.
Medical therapy: Medical treatments include medications such as rate-control and anti-arrhythmic drugs. For many, AF can be managed with medications alone. You also may require treatment with aspirin or warfarin (Coumadin) to prevent clots from forming and subsequent strokes. Electrical cardioversion to re-establish a normal sinus rhythm also may be prescribed.
Catheter-based ablation: A curative ablation procedure may be appropriate if you have symptoms that cannot be controlled by medication. The current approach is to ablate (destroy) the tissue surrounding the connection of the pulmonary veins to the left atrium using radiofrequency energy. This procedure is curative in 40 to 80 percent of patients, working better in patients with paroxysmal AF than in those with permanent AF. Multiple procedures may be required. Patients who undergo catheter-based ablation may also require antiarrhythmic drugs after procedures to stay in normal sinus rhythm.
For most patients with AF and no other heart disease, catheter ablation is the first line interventional treatment for patients who fail medical therapy.
Surgical treatment: The surgical treatment of atrial fibrillation was pioneered at Washington University School of Medicine by James Cox, M.D. He first performed the Maze procedure for AF in 1987 at Barnes-Jewish Hospital to control the erratic impulses of AF. In this procedure, surgeons make small, strategically placed incisions in the atria. The slits generate scar tissue that serves as barriers, blocking abnormal electric signals in a “maze” of barricades. Only one path remains intact, guiding impulses to their correct destination. Although the Cox-Maze III operation – the final version of the surgical procedure – had excellent long-term results, the cut-and-sew technique was technically challenging, and few surgeons routinely performed the operation. Recent technological advancements in ablation devices have provided surgeons with the option of performing a modified Cox-Maze procedure by replacing some or all of the traditional incisions with lines of ablation.
|In this illustration of the Cox-Maze IV procedure, the white lines demonstrate the lines of ablation using bipolar radiofrequency energy in the left atrium.
|Right atrial lesions of the Cox-Maze IV procedure.
A person suffering from atrial fibrillation should consider the modified Cox-Maze procedure if he or she has the following:
- Symptoms related to AF even with optimal medication therapy.
- Lack of tolerance to medications needed to reduce the symptoms of AF or intolerance to anti-coagulation medication (Coumadin).
- Requires an open-heart procedure for either coronary artery disease or valvular disease.
- Recurrent AF despite catheter-based ablation therapy.