A Better Technique for Ablation of Persistent Atrial Fibrillation?

Abstract & Commentary

By John P. DiMarco, MD, PhD

Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville

Source: Narayan SM, et al. Treatment of atrial fibrillation by the ablation of localized sources: CONFIRM (Conventional Ablation for Atrial Fibrillation With or Without Focal Impulse and Rotor Modulation) trial. J Am Coll Cardiol 2012;60:628-636.

This paper discusses the clinical utility of impulse and rotor mapping to guide atrial fibrillation (AF) ablation and is a follow-up to the acute observations discussed in Clinical Cardiology Alert several months ago.1 The authors hypothesized that AF is sustained by localized sources that may be targeted during AF ablation procedures. They then developed a computational mapping approach that allows real-time detection of localized sources of AF during ablation procedures that could then be targeted during the procedure. Focal impulse and rotor modulation (FIRM) mapping was performed using 64-pole basket catheters placed in the left and right atria. Mapping was performed during stable, spontaneous, or induced AF using a proprietary computational methodology. This technique allows identification of both electrical rotors, defined by sequential clockwise or counterclockwise isochronal contours around a center of rotation and focal impulse sources, defined by centrifugal activation patterns from a single point of origin. Rotors and focal impulses were considered AF sources if they showed consistent patterns in recordings over at least 10 minutes. Mapping results were not used to guide ablation (FIRM-blinded group) in 71 patients and were used (FIRM-guided group) in 36 patients. In FIRM-guided patients, the catheter was maneuvered to the basket electrodes overlying each identified source and radiofrequency bursts were applied for 15 to 30 seconds within that region. The endpoint was either termination or slowing of AF. FIRM-guided ablation was permitted at up to three sources for up to 10 minutes at each source. A conventional ablation set of lesions was performed after FIRM-guided ablation in the FIRM-guided group and as the sole therapy in the FIRM-blinded group. Wide areas, circumferential pulmonary vein isolation with the possible addition of left atrial roof lines, or flutter lines were employed. After follow-up, monitoring was performed at regular intervals. Implanted AF monitors or cardiac rhythm devices with atrial electrogram storage were used in the majority of FIRM-guided patients and in a smaller proportion of the FIRM-blinded group. The prespecified primary long-term efficacy endpoint was defined as an AF burden less than 1% using a continuously implanted monitor or freedom from AF of longer than 30 seconds during intermittent monitoring. Freedom from any AF was a secondary endpoint.

Persistent AF was present in 81% of the FIRM-guided group and in 66% of the FIRM-blinded group. Electrical rotors and focal impulses were present in 98 of 101 patients with sustained AF during their procedure. The mean number of rotors or focal impulse sources was 2.1 ± 1 with 70% rotors and 30% focal sources. These sources were observed virtually any place in the left or right atrium. Right atrial sites were identified in 24% of patients. Sources were more numerous in patients with persistent AF than paroxysmal AF. FIRM-guided ablation alone achieved the acute endpoint of AF termination or AF slowing in 31 of 36 (86%) patients. In four patients, FIRM-guided ablation could not be completed since an identified source was adjacent to either the phrenic nerve, atrial pacing lead, compact AV node, or esophagus. Total FIRM-guided ablation time for targeted sources was 16.1 ± 9.8 minutes. In contrast, among the 71 FIRM-blinded patients, the acute endpoint was achieved in only 13 of 65 patients with sustained AF after 43.4 ± 28 minutes of ablation. Total ablation times were similar in the two groups. During follow-up, single procedure freedom from AF was 82.4% for FIRM-guided cases compared to 44.9% for FIRM-blinded cases over a median duration of 273 days. For the endpoint of freedom from any atrial tachyarrhythmia after a single procedure, the results were 70.6% in the FIRM-guided group compared to 39.1% in the FIRM-blinded group.

Commentary

The results of AF ablation procedures in patients with persistent AF have been disappointing. The procedures themselves are complicated and tedious with uncertain acute endpoints. Multiple procedures are often required and late recurrences are common. Although pulmonary vein isolation alone may be adequate in patients with paroxysmal AF and no or limited heart disease, the long-term success rate of this in patients with persistent AF is limited. Many investigators have felt that an approach that targets both potential triggers, often in the pulmonary veins, and the areas that allow AF to continue is necessary to improve outcomes.

The details of the computational mapping system are still proprietary and the system hasn’t been evaluated yet in a large number of labs. However, the results presented here look very promising and this technique might represent the conceptual breakthrough needed to advance the field.

Reference

1. DiMarco JP. New insights into atrial fibrillation ablation. Clin Cardiol Alert 2012;31:53-54.