Atrial fibrillation (AF) increases risks of stroke, heart failure and sudden death. Single catheter ablation only has a low success rate due to inadequate transmurality and continuity of the lesion lines. Unilateral thoracoscopic epicardial ablation by radiofrequency energy from left side (Mei Mini Maze procedure, 3M procedure) was applied in our institution in the last 10 years, and gained reasonable results. A more attractive hybrid strategy of epicardial and endocardial ablation was tested to improve the treatment of persistent AF in the investigator's hospital (NCT02968056). Preliminary data from this trial found that insufficient ablation around right upper pulmonary vein area was the key point leading to failure or recurrence. In order to overcome this weakness of the current Mei Mini Maze procedure, concomitant focal epicardial cryoablation performed during the operation may reinforce the lesion lines. The hypothesis of the present study is that additional epicardial cryoablation will improve the success rate compared to Mei Mini Maze procedure alone in the treatment of AF.

This study is a prospective randomized controlled trial within a single institution. Lone AF patients admitted to the cardiovascular surgery department of Shanghai Xinhua Hospital will be screened for enrollment of this study. The study will recruit 150 patients in total. The patients will be randomized allocated into Mei Mini Maze procedure group (3M group) and Concomitant epicardial cryoablation group (3M + Cryoablation group). The 3M group patients only have surgical ablation surgery from left thoracoscope as previously reported, while the 3M + Cryoablation group patients will have additional focal epicardial cryoablation around right upper pulmonary vein area after the Mei Mini Maze procedure is done. The ratio of 3M to 3M + cryoablation group is 1:1, so that each group contains 75 patients. The perioperative data is collected, and the patients will be followed for 6 months. The primary outcome is the maintenance of sinus rhythm at 6 months post operation. The secondary outcomes include off antiarrhythmic drug rate, perioperative complications, major cardiovascular events, stroke, left ventricular systolic function, medical expense, serum brain natriuretic peptide level and quality of life. The aim of this study is to evaluate the efficacy and safety of this novel combined procedure of epicardial radiofrequency and cryoablation.

Inclusion Criteria:

1. Isolated atrial fibrillation, without structural heart disease.
2. Failed medical treatment
3. Patient admitted with intent to be treated by surgical ablation

Exclusion Criteria:

1. Previous surgical ablation of atrial fibrillation
2. Concomitant other cardiac diseases which require surgery at the same procedure, such as heart valve disease, congenital heart disease, coronary disease, dilated cardiomyopathy etc.
3. With other forms of severe arrhythmia
4. Ejection fraction of left ventricle less than 30%
5. Anteroposterior diameter of left atrial over 60mm
6. Tumor, active infection, pregnancy.
7. Previous surgeries with left thoracotomy, or expected left pleural adhesion, such as history of tuberculosis infection, pleural effusion, pneumothorax etc.
8. Hyperthyroidism
9. Thrombosis within left atrial appendage
10. General conditions too weak to tolerate the surgeries
11. Patient's circumstance that precludes completion of follow-up and/or obtaining information from the 6 months follow-up
12. Other conditions not appropriate for this study based on the investigators' judgments