Definition of Atrial Fibrillation (AF)
Atrial fibrillation (AF) is the most commonly diagnosed arrhythmia, which is characterized by fast and irregular heart rhythms. It is caused frequently by electrical abnormalities located near the pulmonary veins of the left atrium.
What are the symptoms of Atrial Fibrillation?
Individuals experience the symptoms of atrial fibrillation differently. Some who have this condition may not feel any symptoms, and their condition will go unnoticed until it is detected by a physician during a routine examination. Others may experience only minor symptoms, while some are sensitive to the slightest sensation. Symptoms commonly reported include shortness of breath, lightheadedness, palpitations, and/or chest discomfort.
Medical Treatment for AF
The initial treatment for atrial rhythm disorders often includes rate-slowing and antiarrhythmic drug therapy. These drugs can slow the conduction of rapid atrial fibrillation and/or convert atrial fibrillation to a normal sinus rhythm. Drugs, however, do not cure heart rhythm disorders, and they are not effective in all patients. They also require that a patient maintain a very strict schedule of follow-up care with his or her physician. Many patients with atrial fibrillation require a blood thinner, such as Warfarin, to prevent the formation of blood clots, which can cause a stroke.
Many forms of AF are triggered or maintained by a single focus (or few foci) of muscle firing in the heart. In most patients, these sites have been mapped to the pulmonary veins (vessels which empty blood from the lungs to the left side of the heart). These venous structures have "sleeves" of atrial tissue extending from the heart (left atrium) for variable distances into the main branch or its tributaries. This musculature when diseased or damaged is capable of generating ectopic complexes, or repetitive activity at very rapid rates.
In susceptible patients, this may lead to atrial fibrillation as well as perpetuating it. Typically, patients who are candidates for catheter ablation have normal structural heart function and have not had suppression of palpitation with antiarrhythmic drugs.
Elimination of the triggers can lead reduction or elimination of AF. Catheter ablation techniques evolved over the last few years as we further our efforts to treat this common arrhythmia. First, a mapping catheter and an ablation catheter are passed into the left atrium using a trans-septal puncture.
The technique commonly employed by Houston Arrhythmia Associates includes pulmonary vein isolation whereby the ablation catheter is positioned within the left atrium and lesions are delivered to encircle the four pulmonary veins that are often the location of these triggers for atrial fibrillation.
Additionally, we position catheters within the opening of each pulmonary vein to evaluate for pulmonary vein potentials. These potentials represent discrete and limited connections to the atria. Ablation of these connections can also play a role in catheter ablation of atrial fibrillation. The discrete connections of the pulmonary vein to the left atrium are mapped and precisely identified. These connections are then ablated using radiofrequency energy.
The pulmonary vein is then progressively disconnected with the ultimate result of complete electrical isolation of the pulmonary vein musculature from the left atrium. Each pulmonary vein is entered and serially ablated until all pulmonary veins are completely electrically disconnected. This can be achieved in about 99% of targeted veins. The pulmonary veins continue to serve as conduits of oxygenated blood to the left atrium.
The goal of catheter ablation for atrial fibrillation is the elimination of severe symptoms that are affecting a patient's quality of life. Approximately 50-70% of patients are cured of their symptoms and become arrhythmia-free. In these patients, antiarrhythmic drugs are discontinued and anticoagulants such as Coumadin may not be needed.
An additional 20-30% of patients respond to antiarrhythmic drugs that were previously ineffective, or have substantial reduction in AF events. About 10-15% of patients have no response to catheter ablation. Often, these patients benefit from a second procedure to identify areas where the ablation lesions are incomplete.
Some patients remain with atrial fibrillation, presumably due to alternate triggers in the heart. The procedure has a small risk of complications about 1-2%. Fortunately, serious complications are infrequent. The potential complications include pulmonary vein stenosis narrowing of the opening of the pulmonary veins due to aggressive scar tissue formation, small risk of stroke and risk of cardiac perforation requiring catheter drainage or surgery.
Risk of catastrophic complications (heart attack, left atril esophageal perforation and death) is extremely small.
Ideal candidates include patients who have paroxysmal AF without major structural heart disease. Rarely, patients with persistent or chronic AF may be also be candidates for ablation. Catheter ablation is an effective tool offering a curative treatment of atrial fibrillation.
Device Therapy for AF
In a subset of patients with paroxysmal (intermittent) or persistent atrial fibrillation, devices can be used to either prevent atrial fibrillation or convert it to a normal sinus rhythm. These devices include pacemakers and implantable cardioverter defibrillators (CD).