A short discussion of atrial fibrillation, or AF, and its mechanisms is useful in understanding the complexity of the problem and how the method and apparatus of the present invention will help treat this arrhythmia more effectively.
Atrial fibrillation, which is an arrhythmia in which the atria (upper chambers of the heart) stop contracting as they fibrillate, is the most common of the heart rhythm problems. Present data suggests that AF is the most common arrhythmia-related cause of hospital admissions. Patients with AF have a high incidence of medically significant complications such as stroke and congestive heart failure. Premature atrial contractions can act as triggers and initiate paroxysms of AF. These premature atrial contractions have been shown to predominantly originate in the pulmonary veins from the left atrium. Since infrequent and nonreproduceable premature atrial contractions limit the utility of ablating trigger sites, a variety of surgical and catheter techniques have been used to isolate the pulmonary veins from the left atrium.
One of the surgical techniques used to treat AF involves the use of radio-frequency waves (modified electrical energy) to create small scars on the heart's surface near the connection between the pulmonary veins and the left atrium. The small scars created by the radio-frequency waves stop the erratic impulses of atrial fibrillation by directing the impulses to follow a normal electrical pathway through the heart. Typically, this type of surgical procedure is performed through a chest incision. Surgeons use specially designed instruments to deliver radio-frequency waves to the abnormal tissue, typically during open heart surgery performed for other reasons, such as a mitral valve repair. Although this type of surgical technique is effective when the patient is undergoing open heart surgery for another reason, catheter-related treatment methods are more practical when the patient does not require the invasive open heart surgery for other reasons.
One of the catheter techniques involves the application of radio-frequency energy at areas showing double potentials suggestive of sites capable of conducting between the left atrium and the pulmonary veins. The currently crude three-dimensional reconstruction of the left atrium, the inability of the physician to visualize the pulmonary vein ostia from inside, the varying size of the pulmonary veins and thus the pulmonary vein ostia, the difficulty in keeping the mapping catheter stable at the pulmonary vein ostia sites, all make current approaches to mapping using fluoroscopically-guided imaging techniques cumbersome, lengthy and inadequate.
Because of these limitations, radio-frequency ablation is much less successful than surgery, especially in patients with persistent atrial fibrillation. In fact, less than 20 percent of patients undergoing radio-frequency catheter ablation for AF benefit from this approach.
A number of modalities presently exist for medical diagnostic imaging. One such approach utilizes computed tomographic imaging to delineate the precise anatomy of an organ. Once the left atrium and pulmonary veins are visualized, a catheter design which will conform to the anatomy of the different pulmonary veins will help isolate the pulmonary veins more precisely and easily and assure the same success rate for the radio-frequency approach as for surgery.