PVI+?

The efficacy of catheter ablation for paroxysmal atrial fibrillation (AF) is improving as the technologies used to perform durable pulmonary vein isolation (PVI), such as the second-generation cryoballoon and contact force sensing radiofrequency ablation catheters, have evolved. Additional tools are also being developed to safely and reliably electrically isolate the PVs, including electrode- and balloon-based, “single-shot” technologies. However, while limiting the ablation strategy for paroxysmal AF to PVI alone is gaining acceptance, the best non-pharmacologic approach for the treatment of persistent and long-standing persistent AF appears to be getting more controversial and was the topic of many conversations last month at Heart Rhythm 2015, the Heart Rhythm Society’s 36th Annual Scientific Sessions.

The approach to ablation of persistent AF is highly variable among centers. For several years, it has been recognized that PVI is important, but even wide-area PV antral isolation has been shown to be insufficient as a sole strategy in many patients. The two most commonly employed supplemental ablative approaches have been ablation of complex fractionated atrial electrograms (CFAEs) and linear atrial ablation. When done in a stepwise fashion, with the goal of AF termination, outcomes have appeared to be better than PVI alone. However, a recent study called the Substrate and Trigger Ablation for Reduction of Atrial Fibrillation Part 2 (STAR AF 2) trial¹ found no benefit to supplemental ablation of CFAEs or attempts to create lines of block in the LA. Furthermore, a separate publication recently demonstrated that the five-year, single-procedure success rate of the stepwise approach is only 20%.² There are limitations to these studies and the definitions of ablation failure, but these two publications argue for better methods to treat AF beyond current ablation practices. 

Nonpharmacological strategies for the treatment of persistent AF can be categorized into three groups: extensive ablation, selective ablation, and non-ablative approaches (Figure 1). The Focal Impulse and Rotor Modulation (FIRM) mapping system (Abbott) is an example of an invasive technique to identify rotors that could be responsible for AF perpetuation, and the combination of panoramic body surface electrical data with anatomical data obtained from imaging scans (CardioInsight Technologies) is an example of a noninvasive technique. These approaches continue to be refined. More extensive approaches that have been developed and are under further investigation include both catheter and surgical ablation of the posterior left atrium, extensive biatrial CFAE ablation, and the use of a set of catheters and duty-cycled RF energy delivery to isolate the PV, ablate the left atrial septum, and ablate sites associated with high frequency activity. Non-ablative approaches to the treatment of persistent AF are also being pursued. These include gene delivery to the posterior left atrium to reduce autonomic input and fibrosis, low-level transcutaneous electrical tragus stimulation (LLTS), and renal artery denervation.

The STAR AF 2 trial should be interpreted with caution since the findings are inconsistent with many prior trials, but it has forced us to acknowledge that PVI alone for persistent AF is associated with an unacceptable success rate, and that the strategies that many centers are currently employing as supplemental to PVI do not appear to help much, if at all. It is time to move forward. The question now for the treatment of persistent AF is “PVI+?"

References

1. Verma A, Jiang C, Betts, TR, et al. Approaches to catheter ablation for persistent atrial fibrillation. N Engl J Med. 2015;372:1812-1822.
2. Schreiber D, Rostock T, Frohlich M, et al. Five-year follow-up after catheter ablation of persistent atrial fibrillation using the “stepwise approach” and prognostic factors for success. Circ Arrhythm Electrophysiol. 2015;8:308-317.