Catheter Ablation Of Atrial Fibrillation

Catheter ablation is rapidly becoming an effective method to cure or palliate selected patients with AF. Two approaches have evolved. The first strategy involves trying to

Fig. 7. Diagram of linear lesions made by intra-operative cryoablation for pulmonary-vein isolation in patients with chronic atrial fibrillation undergoing mitral valvular repair. (Reproduced with permission from ref. 93.)

simulate the surgical maze procedure by trans-catheter placement of multiple left and right atrial linear lesions. The first study using catheter ablation to treat chronic AF was reported by Swartz et al. in 1994 (95). A traditional ablation catheter was used to create a series of long, linear lesions in the right and left atria. AF was terminated and sinus rhythm was maintained in 87% of cases (95,96). Others have subsequently reproduced this work, with success rates ranging from 0-89% (95-100). Several investigators have shown that the left atrial lesion set is critical for curing these patients. In the study by Haissaguerre et al., right atrial-only lesions resulted in cure (no antiarrhythmic drug requirement) in only about 15% of patients; however, palliation (AF controlled with continued antiarrhythmic drugs) was achieved in approx 40% of patients (97,99). Other studies used various other right atrial-only lesion sets, with similar results (96,101,102). In the study by Haissaguerre et al., the addition of left atrial lesions, either with the other right atrial linear lesions or with an atrial flutter ablation only, resulted in cure rates of approx 50%, and 85% cure or palliation rates (97,99). Thus, for catheter-based maze procedures to affect a cure of AF, the left atrium must be ablated in most cases. However, right atrial-only procedures may result in substantial rates of palliation. At the present time, the optimal locations for the lesion sets have not been determined.

Ablating consecutive points with a 4-5 mm tip catheter to create continuous linear lesions is technically difficult, time-consuming, and potentially dangerous. Right and left atrial maze procedures may take over more than 12 h to perform. In addition, the initial linear lesions that are created often have gaps of incompletely ablated tissue, and these gaps may result in recurrent AF or reentrant atrial tachycardias revolving around the linear lesions and through the gaps. Thus, second or even third procedures are often required to fill in these gaps to obtain optimal results. Extensive lesioning may also result in cardiac perforation and tamponade, thrombus formation and thromboembolic complications, pulmonary-vein stenosis, sinus-node dysfunction, and left or right atrial mechanical dysfunction. The rates of major complications in retrospective studies have generally been less than 18% (96). However, ongoing prospective studies have demonstrated considerably higher rates of major complications, and even a small risk of death. Although catheter-based maze procedures were initially greeted with great enthusiasm, the technical difficulty and relatively high risk of major complications have made the procedure rare at the present time. Because of the risks to the patient, catheter-based maze procedures should still be considered investigational. New catheters designed to make transmural and continuous linear lesioning easier and safer are now being evaluated (103).

It has long been known that focal atrial tachycardias could simulate AF in animal models (104), and the AF in humans frequently begins with a regular rapid rhythm (105). In 1994, Haissaguerre et al. localized and ablated focal initiators of AF in 3 patients (106). Since that time, Haissaguerre, Chen, and their colleagues have rapidly expanded this observation to a large number of patients (107-109). Premature atrial contractions (PACs) and rapid atrial tachycardias arising predominantly within the atrial muscular sleeve surrounding the pulmonary veins as they insert into the left atrium may generate AF in susceptible patients (Fig. 8). If the site of origin of these initiating arrhythmias can be localized and ablated, then AF can be cured. However, this approach required frequent spontaneous atrial ectopy to facilitate localization of the AF initiators. Given the observation that most (>70%) of the initiators arise from the pulmonary-vein musculature (107-109) (Fig. 9), approaches to disconnect the atrial myocardium of the pulmonary veins from the left atrium have evolved to provide an empiric anatomic ablation approach in patients without frequent atrial ectopy (110). Both mapping guided (directed) and empiric pulmonary-vein isolation procedures have current success rates exceeding 70% (107-110). Rates of palliation and cure exceed 90% in appropriately selected patients. Patients who are most likely to benefit from the procedure include patients with paroxysmal or persistent (but not chronic) AF with minimal or no structural heart disease. Given the excellent long-term results in these patients, focal AF ablation approaches have become a reasonable therapeutic option when medical approaches have failed. Patients with chronic AF and extensive cardiac disease may still benefit (111)—usually in a palliative rather than curative fashion—from a focal AF ablation procedure, but data are still limited and this approach is probably investigational at this time.

Guided focal AF ablation and pulmonary-vein isolation procedures have success rates considerably less than ablation of other SVTs. This may be a result of the inability to ablate the identified sites of AF initiation, or the failure to identify all the sites responsible for AF initiation. Since up to 30% of triggering sites may occur outside of the pulmonary veins, empirical pulmonary-vein isolation procedures do not affect these individuals. In addition, significant pulmonary-vein stenosis may occur in 1-3% of cases and result in significant dyspnea or hemoptysis (107-110). Lesser degrees of asymptomatic pulmonary-vein stenosis may occur in up to 40% of patients (108). Although these less severe pulmonary-vein stenoses do not result in symptoms, their

Atrial Fibrillation Ablation Procedure

Fig. 8. Intracardiac recordings during the onset of AF from the left upper pulmonary vein. Shown are surface electrocardiographic leads I, aVF, and V1 and multiple intracardiac recordings from the right atrium (RA), His bundle region (HBE), coronary sinus (CS), ablation catheter within the left upper pulmonary vein, and the right ventricular apex (RVA). The first atrial activation is sinus rhythm, followed by ventricular activation. Shortly after the end of the QRS complex, an atrial premature complex (arrow) originates at the site recorded by the distal (d) electrode of the ablation catheter. This premature atrial contraction (PAC) (arrow) initiates AF.

Fig. 8. Intracardiac recordings during the onset of AF from the left upper pulmonary vein. Shown are surface electrocardiographic leads I, aVF, and V1 and multiple intracardiac recordings from the right atrium (RA), His bundle region (HBE), coronary sinus (CS), ablation catheter within the left upper pulmonary vein, and the right ventricular apex (RVA). The first atrial activation is sinus rhythm, followed by ventricular activation. Shortly after the end of the QRS complex, an atrial premature complex (arrow) originates at the site recorded by the distal (d) electrode of the ablation catheter. This premature atrial contraction (PAC) (arrow) initiates AF.

long-term consequences are unknown. In particular, it is not known if these subclinical stenoses may progress and result in occlusion and pulmonary venous hypertension over the years. In cases with symptomatic pulmonary-vein stenosis after ablation, percutaneous stenting may effectively restore pulmonary blood flow (112). Newer ablation energies such as ultrasound (113) or cryoablation may be less likely to cause pulmonary-vein stenosis. Clearly, catheter ablation of AF holds enormous potential for the management of patients with refractory AF. As catheter design, energy technology, mapping technique, and knowledge of the underlying pathophysiology of AF improve, catheter ablation will become safer, more reliable, and faster to perform.

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