Catheter-Based Ablation of Atrial Fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia.^1,2 It can be classified into 4 types: first detected episode; paroxysmal AF (PAF), which is self-terminating; persistent AF, in which an episode lasts more than 7 days and requires cardioversion to terminate; and permanent AF, which is continuous AF for which cardioversion has failed or has not been attempted.³ There are various options for the treatment of AF, including pharmacologic therapy and invasive electrophysiologic interventions.⁴ Catheter-based radiofrequency ablation is an effective treatment for AF, and it can be used instead of or in combination with antiarrhythmic medications.⁵

Ectopic focal activity and reentry is the predominant model of the pathogenesis of AF.⁶ According to this model, AF originates from a rapidly firing focus in one of the atria, which maintains the AF through short reentrant circuits and causes spiraling (fibrillatory) conduction. Most triggers for AF are located in the pulmonary veins (PVs).⁷ Less commonly, triggers arise in other areas, such as the posterior wall of the left atrium, the musculature of the coronary sinus, the crista terminalis, the ligaments of Marshal, and the superior and inferior venae cavae.⁶ Lee and colleagues⁸ showed that, of 293 patients with ectopic beats that initiated PAF, 199 (68%) had pure PV ectopic beats, 36 (12%) had pure non-PV ectopic beats, and 58 (20%) had both PV and non-PV ectopic beats that caused PAF.

Maintenance of sinus rhythm is the main goal of AF treatment. Antiarrhythmic drug therapy is the first-line treatment in patients with PAF and persistent AF. Because drugs have limited efficacy and are not free of adverse cardiac and systemic side effects, there is a persistent need to develop and improve drugs, devices, and ablative approaches for the treatment of AF.

Recent findings in regard to the mechanisms of AF have resulted in extraordinary progress in various nonpharmacologic methods for eliminating AF triggers. In 1991, Cox and colleagues⁹ opened a new door in the management of AF by introducing a surgical technique—the creation of an electrical maze in the atrium that was feasible as a surgical cure for human AF. Subsequently, other surgical techniques were developed to treat AF. All of these necessitated a thoracotomy and cardiopulmonary bypass, both of which increase the risk of sequelae. A desire to avoid these risks led to the development of alternative procedures, including catheter ablation.

Since the first description of PVs as triggers of AF was published in 1998 by Haïssaguerre and colleagues,¹⁰ the technique of using catheter ablation to eliminate these triggers has undergone multiple modifications. Approaches to catheter ablation include PV isolation (PVI), complex fractionated atrial electrogram ablation, autonomic ganglionated plexi ablation, atrial compartmentalization via linear lesions, and sequential ablation.

In 2003, Pappone and coworkers¹¹ compared 589 patients who underwent PVI with 582 patients who received antiarrhythmic medication for sinus-rhythm control. The investigators found that PVI reduced death and morbidity and improved quality of life, compared with medication. Then, in 2004, Chen and colleagues¹² released the results of their study of PVI in 377 patients, 94 of whom had impaired LV function, and proposed that PVI might be a feasible therapeutic option in AF patients with impaired ejection fraction. That same year, Ouyang and coworkers¹³ reported their experience, in 41 patients, in creating continuous circular lesions with the double-Lasso technique, guided by 3D mapping. This technique had 95% efficacy at 6-month follow-up.

In 2010, Wilber and colleagues¹⁴ performed a randomized controlled trial involving 167 patients at 19 hospitals, in order to compare the success rates of antiarrhythmic drug therapy and radiofrequency catheter ablation in patients with PAF. The success rate was 66% in the ablation group, compared with 16% in the antiarrhythmic group. That trial was the basis of the United States Food and Drug Administration's (FDA's) first approval of a catheter for the treatment of PAF.

Isolation of the PVs is the cornerstone of any ablation approach, and, in most trials of catheter ablation for AF, PVI has been used as an endpoint for the ablation procedure. Regardless of the technique used (Lasso, double Lasso, intracardiac echocardiogram-guided, or wide-area circumferential ablation), the goal should be the ablation of a large area of the atrium to eliminate all PV potentials. Ablation procedures are usually guided by 3D electroanatomic mapping systems, which facilitate the procedure by providing accurate visualization of the atrial anatomy and shortening the fluoroscopic time required.

Studies have examined the adverse sequelae of catheter PV ablation. Bertaglia and coworkers¹⁵ prospectively evaluated the incidence of early complication at 10 Italian centers at which 1,011 patients underwent radiofrequency ablation for every type of AF. Complications occurred in 40 patients (3.9%), including 4 (0.4%) who had PV stenosis of more than 50%. In 2011, Baman and colleagues¹⁶ published a retrospective review of data obtained from 1,295 patients who had undergone radiofrequency ablation for PAF (53%) or persistent AF (47%). The rate of complications was 3.5% (50/1,295), and PV stenosis occurred in only 1 patient (< 0.01%).

In the years since PVI was introduced, PV stenosis has decreased in frequency, primarily because ablation techniques are now precise enough to avoid the PV ostium. One of the new tools used to increase the precision of ablation procedures is the irrigated-tip magnetic catheter. This catheter is steerable by a magnetic field, which enables the operator to move the catheter in different directions with an external remote control. In addition, the irrigated tip reduces procedure time and prevents charring, enabling this catheter to induce larger, deeper, and more effective lesions than a nonirrigated magnetic catheter.^17,18 Pappone and colleagues,¹⁹ who monitored 130 patients (81 with PAF and 49 with persistent AF) for 15.3 ± 4.9 months after PVI with the irrigated-tip magnetic catheter, found success rates of 81.4% in patients with PAF and 67.3% in patients with persistent AF. No PV stenosis, tamponade, or stroke was observed.

Another ablation catheter, which was recently approved by the FDA, is the Arctic Front® Cardiac CryoAblation Catheter (Medtronic, Inc.; Minneapolis, Minn). Numerous studies of the device have been performed in Europe. Neumann,²⁰ Van Belle,²¹ Kojodjojo,²² and their colleagues conducted prospective studies that enrolled 293, 141, and 90 AF patients, respectively, all of whom underwent PV cryoablation with the Arctic Front catheter. The studies showed respective short-term success rates of 97%, 98.5%, and 83% of patients. After 1 year, 74%, 73%, and 77% of enrolled patients, respectively, were free of AF.

The STOP-AF trial²³ was the basis for the approval of the Arctic Front catheter in the United States. This trial, which was the first randomized study of cryoablation versus antiarrhythmic drugs to be conducted in the United States, involved 245 patients with PAF. Effectiveness was defined for cryoablation patients as both short-term procedural success and freedom from long-term treatment failure, which meant no detectable AF after the blanking period, no use of non-study drugs to treat AF, and no additional intervention for AF. One year after treatment, 69.9% of patients treated with cryoablation had achieved the primary endpoint of freedom from AF, compared with only 7.3% of patients treated with AF drugs.

The approach to ablative therapy for AF should be tailored to each case. Multiple variables should be considered, including the type of AF (paroxysmal, persistent, or chronic), the duration of chronic AF, the presence of concomitant valvular heart disease, and the size of the left atrium. In patients with PAF or persistent AF, catheter-based ablation therapy has produced promising results, including shorter length of stay, decreased morbidity, and success rates similar to those of surgical approaches.