Primary Endpoint Safety and tolerability of ablation using the AFreeze Cryoablation System consisting of the ablation CoolLoop® catheter, its steerable sheath and the cryoconsole Cryo-Caddy will be assessed and expressed in number of participants with Adverse Events (AEs).

Therefore, the primary endpoint will be a measurement of the following parameters and expressed in number of participants with AE:

• deformation of the catheter loop resulting in entrapment of the catheter in the heart and difficulties removing the catheter during visit 3 (treatment)
• phrenic nerve palsy during visit 3 (treatment)- onset and time course between visit 3 (treatment) and visit 5 (discharge) of death, pericardial tamponade, valve damage requiring surgery and hemorrhage requiring transfusion.
• onset and time course between visit 3 (treatment) and visit 9 (final visit) of atrioesophageal fistula, sepsis, abscesses, endocarditis, stroke, transient ischemic attack, and pulmonary vein (PV) stenosis requiring intervention.

Secondary Endpoint

The following parameters will be assessed and expressed in number of participants with AE/duration time:

• feasibility, defined by the ability to position the catheter in the proximal part in each of the PVs using an over-the-wire technique, forming the cryo-applicator of the catheter to a loop by operating the catheter handle, position-ing the loop at the wall of the PV antrum and delivering cryothermia.
• acute efficacy of catheter ablation is defined as the percentage of electrodes within the PV without measureable signals.
• clinical efficacy of catheter ablation defined by freedom of Atrial Fibrillation (AF) four, eight and twelve weeks after ablation.
• procedure time defined from introduction of the CoolLoop® catheter into the left atrium until removal of the CoolLoop® catheter from the left atrium after termination of the last cryoapplication.
• fluoroscopy time defined from introduction of the CoolLoop® catheter into the left atrium until removal of the CoolLoop® catheter from the left atrium after termination of the last cryoapplication.
• cumulative cryoablation time.
• onset and time course between visit 3 (treatment) and visit 5 (discharge) of pneumothorax, hemothorax, femoral pseudoaneurysm, arteriovenous fistulae, hemorrhage not requiring transfusion.

Inclusion Criteria:

• age 18 - 70 years
• symptomatic paroxysmal AF, according to the actual guidelines of the Eu-ropean Society of Cardiology, despite treatment with at least one antiarr- hythmic drug
• at least one episode of AF within the last 3 months documented by ECG
• signed and dated informed consent documented by the patient, indicating that the patient has been informed of all the pertinent aspects of the trial prior to study enrollment
• female subjects of childbearing potential can be included, if they: agree to use, and be able to comply with, effective contraception without in-terruption, from study enrollment, throughout hospitalization and until 12 weeks after catheter ablation (day 0, visit 3). This applies unless the subject commits to absolute and continued abstinence. The following are effective methods of contraception:
• Implant,
• Levonorgestrel-releasing intrauterine system (IUS),
• Medroxyprogesterone acetate depot,
• Tubal sterilization,
• Sexual intercourse with a vasectomized male partner only; vasectomy must be confirmed by two negative semen ana-lyses,
• Ovulation inhibitory progesterone-only pills (i.e., desoge-strel). (Combined oral contraceptive pills are not recommended. If a subject was using combined oral contraception, she must switch to one of the methods above. The increased risk of venous thromboembolism (VTE) continues for 4 to 6 weeks after stopping combined oral contraception.

Exclusion Criteria:

• left atrial diameter > 50 mm as assessed by transthoracic echocardiogra-phy,
• electrical cardioversion performed later than seven days after onset of AF,
• advanced structural heart disease including
• moderate-to-severe valvular stenosis or regurgitation,
• previous myocardial infarction with impaired left ventricular systolic function,
• congenital heart disease,
• left ventricular ejection fraction < 45% during sinus rhythm,
• coronary artery bypass graft surgery within the last 3 months.
• chronic obstructive pulmonary disease treated with beta-sympathomimetic drugs,
• severe respiratory insufficiency,
• known bleeding diathesis or intolerance of heparin or oral anticoagulation,
• previous AF ablation,
• left atrial thrombus,
• severe comorbidity,
• hyperthyreosis,
• any condition, including the presence of laboratory abnormalities, which would place the subject at unacceptable risk if he / she were to participate in the study or confound the ability to interpret data from the study,
• any serious medical condition, laboratory abnormality, or psychiatric illness, that would prevent the subject from signing the Informed Consent Form,
• pregnant or lactating females,
• other severe conditions, which makes the patient unsuitable to participate in the study, as judged by the Investigator,
• the patient is active in another clinical trial.

First patient - first visit: September 11, 2012; Last patient - last visit: March 26, 2013 (6 months and 15 days)

Patients were closely followed for adverse events during treatment and within the defined follow up period according to the study protocol. All Adverse Events including intercurrent disease had to be documented in the patient's medical file and subsequently in the case report form.