Cryoballoon Ablation of Pulmonary Veins for Paroxysmal Atrial Fibrillation - STOP AF


Although radiofrequency ablation (RFA) after pulmonary vein isolation (PVI) for atrial fibrillation (AF) has been shown to be associated with a reduction in symptomatic AF, especially paroxsymal AF, it often requires multiple lesions, and may be associated with complications. Further, antiarrhythmic drugs (AAD) can also be associated with significant morbidity and mortality. Accordingly, the investigators sought to assess the safety and effectiveness of a novel cryoballoon ablation technology designed to achieve PVI with a continuous cryolesion.


Cryoballoon ablation would be safe and efficacious in the treatment of symptomatic AF.

Study Design

  • Parallel

Patients Enrolled: 245
NYHA Class: I (94%)
Mean Follow Up: 12 months
Mean Patient Age: 56.6 years
Female: 23
Mean Ejection Fraction: 60%

Patient Populations:

  • ≥2 AF episodes in 2 months with ECG documentation of one
  • Treatment failure of ≥1 AAD

Primary Endpoints:

  • Combined treatment failure (no detectable AF, no use of nonstudy drugs, no AF intervention)

  • Major adverse AF events (composite of disease and treatment safety adverse events)
  • Composite of device and procedure-related adverse events

Drug/Procedures Used:

Patients were randomized in a 2:1 fashion to either PVI with the cryoballoon, or treatment with a nonfailed AAD. Cryoballoons were available in two sizes, 23 mm and 28 mm. This is a double balloon, and is delivered by a steerable balloon through a 14F sheath. PVI was done without any ablation lines.

Principal Findings:

A total of 245 patients were enrolled, 163 to the cryoballoon, and 82 to AAD. Baseline characteristics were fairly similar between the two arms. Most patients were highly symptomatic, with a mean of 23 symptomatic episodes in the 2 months prior to enrollment. About 22% of the patients had early permanent AF, whereas the rest had paroxysmal AF. In addition, 45% had a history of atrial flutter. Subjects had previously failed ≥1 AAD (36% flecainide, 47% propafenone, 29% sotalol). The mean CHADS2 score was 0.6, and mean left atrial diameter was 4.1 cm.

Balloon-only isolation of PVs was achieved in 90.8%, and the overall procedural success (≥3 PVs isolated) was achieved in 98.2% of the patients. The number of deliveries per PV ranged from 2.9 to 3.4. The mean duration of delivery ranged from 196 to 230 seconds, with a mean 62.8 minutes. The cryoballoon temperatures ranged from -49 to -54 degrees Celsius. About 40% of the patients also underwent cavo-tricuspid isthmus ablation. In addition, about 19% of the patients needed a repeat cryoablation procedure within the 90-day blanking period. There was also a high amount of cross-over from the AAD arm to the cryoballoon arm.

The incidence of the primary endpoint of treatment success was significantly better in the cryoablation arm, as compared with the AAD arm (69.9% vs. 7.3%, p < 0.001). A single ablation procedure was associated with success in 60.1% of the patients. In addition, 57.7% of patients in the cryoballoon arm were on no AADs at the end of follow-up, whereas 12.3% were still on one or more AADs. Of the 95% of patients in the cryoballoon arm who were on warfarin at baseline, only 24% were still on it at 12 months. Symptomatic AF was reduced from 100% at baseline to 19.6% in the cryoballoon arm. The incidence of new atrial flutter was higher in the AAD arm (3.7% vs. 15.9%).

The overall rate of procedural complications with cryoballoon ablation was 6.3%, which was lower than the projected rate of 14.8%. The incidence of combined AF events (disease and procedure related) was 3.1% vs. 8.5% in the cryoballoon and AAD arms, respectively (p < 0.001). The incidence of combined procedural events and major adverse AF events was similar between the two arms (6.1% vs. 8.5%, p = 0.60). Procedural complications with cryoballoon included PV stenosis (3.1% vs. 2.4%), and phrenic nerve palsy (13.5% vs. 7.3%). Of the 11.2% of patients who had phrenic nerve palsy post-procedure, only four (13.8%) had persistent phrenic nerve palsy at 12 months.


The results of the STOP-AF trial indicate that cryoballoon ablation is safe and efficacious in the treatment of symptomatic AF, as compared with AAD alone. A significant proportion of patients in the cryoballoon arm were free of AAD and warfarin use at the end of 12 months, as compared with baseline.

While these early results are interesting, they are tempered by a high incidence of procedural complications, especially phrenic nerve palsy with cryoballoon ablation. The mean number of applications per PV was about three, and it is likely that there is a steep learning curve associated with this procedure.

One potential limitation of this study was that about 45% of the patients had a history of atrial flutter, and a significant number of patients in the cryoballoon arm also underwent cavo-tricuspid isthmus ablation. Not surprisingly, new atrial flutter over the duration of follow-up was higher in the AAD arm, and would have contributed to the overall arrhythmia burden. Further studies will need to evaluate the efficacy of cryoballoon ablation versus conventional RFA with PVI.


Packer DL, Kowal RC, Wheelan KR, et al. Cryoballoon Ablation of Pulmonary Veins for Paroxysmal Atrial Fibrillation: First Results of the North American Arctic Front (STOP AF) Pivotal Trial. J Am Coll Cardiol 2013;61:1713-23.

Presented by Dr. Douglas Packer at the ACC.10/i2 Summit, Atlanta, GA, March 2010.

Clinical Topics: Anticoagulation Management, Arrhythmias and Clinical EP, Cardiac Surgery, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Cardiac Surgery and Arrhythmias

Keywords: Treatment Failure, Heart Atria, Follow-Up Studies, Heart Conduction System, Pulmonary Veins, Warfarin, Learning Curve, Constriction, Pathologic, Electrocardiography, Cost of Illness, Temperature, Research Personnel, Phrenic Nerve, Propafenone, Cryosurgery, Sotalol, Flecainide, Catheter Ablation, Atrial Flutter

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