Purpose and design

The STOP AF First Trial1,2 (NCT03118518) is a prospective, multicenter randomized study evaluating whether cryoballoon catheter ablation  is superior to antiarrhythmic drug (AAD) therapy as a first-line rhythm control treatment in patients with symptomatic paroxysmal atrial fibrillation (PAF). A total of 225 drug-naïve patients (AAD for < 7 days) with symptomatic PAF aged 18–80 were enrolled at 24 centers in the United States. The Arctic Front Advance™ cryoballoon was used to establish pulmonary vein isolation (PVI) and the drug therapy arm received a class I or III AAD therapy.

Key findings

Primary Safety Endpoint Met 1.9%

Low Complication Rate

Primary safety events occurred in two subjects (estimated 12-month rate: 1.9%, 95% CI: 0.5–7.5%) in the cryoballoon arm. Since the upper bound of the 95% confidence interval was below the prespecified performance goal, the primary safety endpoint was met.

Primary safety endpoint result for the STOP AF First clinical trial for first-line cryoablation therapy

< 2% Serious Complication Rate

Primary Effectiveness Endpoint Met 74.6%

Freedom from Acute Procedural Failure or Atrial Arrhythmia Recurrence 12 Months Post-ablation

By modified intention-to-treat analysis (which included all randomized patients who initiated therapy), freedom from primary efficacy failure was: 

  • 74.6% in the cryoballoon arm 
  • 45.0% in the AAD arm (p < 0.001)

Primary efficacy endpoint result for the STOP AF First clinical trial for first-line cryoablation therapy

Quality-of-life Outcomes

A significant improvement (p < 0.01) in subjects’ quality of life was observed at 12 months for those in the ablation group as assessed with the AFEQT and EQ-5D questionnaires. Improvements in AF-specific quality of life at 12 months assessed using the AFEQT were larger with cryoballoon ablation versus AAD therapy.


Primary efficacy endpoint

Treatment success at 12 months

Treatment failure is defined as:

  • Acute procedural failure*
  • Any subsequent AF surgery or ablation in the left atrium (including those performed during the blanking period)
  • Any of the following after the 90-day blanking period:
    • Documented AF/AT/AFL
    • Cardioversion
    • Class I or III AAD use*

Primary safety endpoint

Composite of prespecified procedure- and system-related serious adverse events evaluated in the cryoballoon catheter ablation arm (prespecified performance goal: failure rate < 12%).

Primary safety events include:

  • Within 7 days:
    • Transient ischemic attack
    • Stroke
    • Major bleeding
    • Myocardial infarction
    • Vascular complication
  • Within 30 days:
    • Significant pericardial effusion
  • Within 12 months:
    • Symptomatic pulmonary vein stenosis
    • Atrial-esophageal fistula
    • Unresolved phrenic nerve injury at 12 months

Patient inclusion criteria 

Key inclusion criteria

  • A diagnosis of symptomatic PAF with the following documentation: 
    • Physician’s note indicating recurrent self-terminating AF or PAF; and 
    • Any ECG-documented AF within 6 months prior to enrollment
  • Age 18–80

Key exclusion criteria

  • History of AF treatment with class I or III AAD, including sotalol, with the intention to prevent an AF recurrence. However, patients pretreated with above AAD for less than 7 days with the intention to convert an AF episode were allowed.
  • Prior left atrial ablation or left atrial surgical procedure
  • Prior persistent AF (continuous AF > 7 days)
  • Left atrial diameter > 5.0 cm
  • NYHA class III or IV congestive heart failure and/or known left ventricular ejection fraction (LVEF) less than 45%

Recurrence monitoring

  • Patient-activated Ambulatory ECG (TTM; weekly and when symptomatic)
    3 months and beyond
  • 12-lead ECG
    Baseline, 1, 3, 6, and 12 months
  • 24-hour Continuous Ambulatory ECG
    6 and 12 months 
Table highlighting recurrence monitoring duration for STOP AF First clinical trial data

Treatment arm only.



Wazni OM, Dandamudi G, Sood N, et al. Cryoballoon Ablation as Initial Therapy for Atrial Fibrillation. N Engl J Med. January 28, 2021;384(4):316-324.


Wazni OM, Dandamudi G, Sood N, et al. Cryoablation versus antiarrhythmic drug therapy as initial treatment for atrial fibrillation: impact on quality of life. J Am Coll Cardiol. 2021;77(18_Supplement_1):225-225.