AF Ablation: Inside or Out?

Dear Readers,

A 68-year-old woman with hypertension and medically refractory, highly symptomatic recurrent persistent atrial fibrillation (AF) underwent a radiofrequency catheter ablation procedure involving wide area circumferential ablation with electrical isolation of the pulmonary veins (PVs). She recovered well, but had three more episodes of persistent AF requiring cardioversion at 3, 4, and 5 months after the procedure. What next? Although it is common for patients with persistent AF to require more than one catheter ablation procedure to significantly reduce their AF burden, minimally invasive surgical techniques are available as well. Should this patient have cardiac surgery instead of another catheter ablation procedure?

At the 2011 American Heart Association Scientific Sessions in Orlando, the results of the Atrial Fibrillation Catheter Ablation Versus Surgical Ablation Treatment (FAST) trial were presented by Dr. Boersma from the Netherlands.¹ In this study, also published in Circulation on the same day, 144 patients with either paroxysmal and/or persistent AF were enrolled. Patients were required to have either left atrial dilatation and hypertension (42 patients), or have had a prior catheter ablation procedure that was ineffective (82 patients). Key exclusion criteria were age over 70 years, ejection fraction < 45%, and prior surgery — all common characteristics of patients with AF. Patients were randomized to either catheter ablation or surgery. The catheter ablation procedure involved PV antral isolation with additional linear left ablation at the discretion of the electrophysiologist. Patients assigned to surgery had video-assisted epicardial surgical ablation, which consisted of ablation of bilateral PVs using an AtriCure^™ bipolar radiofrequency ablation clamp, ablation of ganglionated plexi, left atrial appendage stapling and excision, and additional linear ablation at the discretion of the surgeon. Follow-up monitoring included a 7-day Holter at 6 and 12 months. Any atrial arrhythmia lasting more than 30 seconds in the absence of antiarrhythmic drugs after a three-month blanking period was considered a failure. At 1 year, 66% of patients assigned to surgery had no atrial arrhythmias compared to only 37% of patients who underwent catheter ablation (P=0.0022). However, the acute procedural complication rate was much higher for surgery compared to catheter ablation (23% vs. 3%; p=0.043).

Head-to-head comparative studies of this type are critical as our non-pharmacologic options for patients with problematic AF increase. This study is reminiscent of the early comparisons between bypass surgery and angioplasty, which interestingly have usually shown similar findings, with surgery being more effective, but probably riskier. It is likely that this study will lead many cardiologists to consider surgical options for their patients with refractory AF.

The observations from this study are important. Why was surgery more effective? Is ablation of ganglionated plexi key? Does removal of the left atrial appendage prevent recurrent AF? Are surgical ablation lesions using a bipolar clamp more antrally located or more durable? However, there are several issues to consider. First, the success rate for catheter ablation was relatively low. One explanation could be that only a standard 4-mm ablation electrode catheter was used at one of the two ablation centers. Irrigated electrodes are more commonly used nowadays, and are thought to provide more durable ablation lesions and better outcomes. Subgroup analysis did not indicate this was a factor, though. Another explanation is that at one of the catheter ablation centers, the mitral isthmus was ablated without proving conduction block. Incomplete linear ablation is a recipe for creating reentrant atrial flutter. It is also notable that 56% of the patients in the surgical group had no AF detected on the pre-procedural Holter monitor compared to only 40% of patients in the ablation group. This is important considering that this was the type of monitoring used to determine efficacy during follow up.

A second issue is extrapolation of the study results to most patients with AF. It is important to recognize that many patients with AF would have been excluded from this trial on the basis of age, ventricular dysfunction, or prior cardiac surgery, and that two thirds of the patients in this study had failed a prior catheter ablation procedure.

The most critical issue is the balance of safety and efficacy. The success rates for surgery were significantly better, but is sinus rhythm really worth a complication rate of 26%? In fact, we need to do better on both the surgical and catheter sides. It is interesting to note that recent panel meetings at the U.S. Food and Drug Administration (FDA) during November 2011 recommended against approval of the duty-cycled radiofrequency catheters (Medtronic Ablation Frontiers) for the treatment of persistent AF, not based on lack of efficacy, but based mostly on a 2.8% stroke rate; yet a similar FDA panel the day before recommended approval of the AtriCure surgical ablation device that, at least in this study, is associated with a very high acute complication rate. The main point of this study might actually be that we need better tools to improve the success and safety of both catheter and surgical ablation of AF.

Reference

1. Boersma LV, Castella M, van Boven W, et al. Atrial Fibrillation Catheter Ablation Versus Surgical Ablation Treatment (FAST): A 2-Center Randomized Clinical Trial. Circulation. 2011;125:1-8.