Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia encountered by clinicians in the United States,1 occurring in approximately 0.4% to 1.0% of the general population. Since incidence of AF risk increases with age, prevalence is anticipated to rise as the population grows older.2
Pulmonary vein (PV) isolation is an effective treatment and standard approach for patients with drug-refractory symptomatic paroxysmal atrial fibrillation (PAF).3 This is accomplished through ablation, which uses 1 of 2 energy sources and modes of application.4
Radiofrequency (RF) ablation utilizes a RF current that is applied in a point-by-point mode, heating the tissue and leading to cellular necrosis.4 Cryogenic ablation induces necrosis by pumping refrigerant (N2O) through a balloon in a single-step mode, thereby freezing the tissue.4,5 Both methods are approved by the US Food and Drug Administration (FDA) for treatment of paroxysmal AF.
Several small studies have compared these 2 methods of ablation.5-9 A larger-scale, multinational study, FIRE and ICE, was conducted by Kuck et al, and included 762 symptomatic patients with drug-refractory paroxysmal AF, who were randomized to receive either cryoablation (n=378) or RF ablation (n=384).10
The mean duration of follow-up was 1.5 years, and the primary efficacy end point was the first documented clinical failure (recurrence of AF, occurrence of atrial flutter or atrial tachycardia, use of antiarrhythmic drugs, or repeat ablation), following a 90-day period after the index ablation. The noninferiority margin was defined as a hazard ratio (HR) of 1.43, and the primary safety end point was a composite of death, cerebrovascular events, or serious treatment-related adverse events.10
The primary efficacy end point occurred in 138 patients in the cryoablation group, vs 143 in the RF group (1-year Kaplan-Meier event rate estimates, 34.6% and 35.9% respectively; HR: 0.96; 95% confidence interval [CI]: 0.76-1.22; P<.001 for noninferiority). The primary safety end point occurred in 40 patients in the cryoablation group, vs 51 in the RF group (1-year Kaplan-Meier event rate estimates 10.2% and 12.8% respectively; HR: 0.78%; 95% CI, 0.52-1.18; P=.24).
These findings demonstrated that cryoablation is noninferior to RF in efficacy, and that there was no significant difference between the 2 methods with regard to overall safety.10
“This was an impressive study,” commented Hugh Calkins, MD, professor of medicine and director of the Cardiac Arrhythmia Service at Johns Hopkins, Baltimore, Maryland. “This was the largest prospective multicenter comparison of catheter ablation of AF using either RF energy or the cryoballoon,” he told The Cardiology Advisor.