The purpose of this study is to monitor heart rate regularization in patients with permanent atrial fibrillation and standard indication for single chamber rate adaptive pacing VVI(R).

The RARE PEARL is a multicenter prospective, randomized, double-blinded, crossover study.

Prior entering the study the patient should be informed and should give his written consent. Besides he/she should meet all selection criteria. The Investigator has to check that all selection criteria are satisfied. Then the patient undergoes pacemaker implantation, receiving a pacemaker model C20 SSIR or T20 SSIR (or later). The ventricular lead must be bipolar independently of the manufacturer.

After pacemaker implantation, a 45 days Stabilization Period is necessary to stabilize leads and drug therapy.

At the end of the stabilization period the patient is randomized to have VRS algorithm switched either ON or OFF. The 1° Study Phase ends after 2 months. Then a cross-over takes place: VRS algorithm is switched respectively OFF or ON and the 2° Study Phase is started. Also the 2° Study Phase ends after 2 months.

The randomization will be centralized: randomization lists will be generated and managed by the sponsor. Because the patients will undergo a QoL questionnaire at each crossover phase, they will have to be blinded about the status of their VRS setting. Similarly, also the co-investigators administering the QoL questionnaires have to be blinded about the status of VRS setting. Only the principal investigator knows if the VRS algorithm is ON or OFF. The principal investigator will be instructed not to inform the patient and the co-investigators administering QoL questionnaire about the setting until after the end of the study.

The co-investigator(s) responsible for QoL questionnaire should not perform the patient follow-up at 1° and 2° Study Phase, otherwise the patient is automatically excluded from the study.

After the cross-over period (2 + 2 months) a Free Therapy Phase (3° Phase) starts. Device settings and drug therapy are left to the physician's discretion.

One year after implantation a final follow-up is scheduled. The study ends and the pacemaker can be programmed according to the physician's discretion.

Inclusion Criteria:

• Patient has signed informed consent form
• Patient with permanent atrial fibrillation, standard indication for VVI(R) pacing, and at least 1 episode of rate irregularity in the last month
• New York Heart Association (NYHA) Class I, II, III
• Patient is able to comply with follow-up times and will comply with the protocol
• > 18 years of age

Exclusion Criteria:

• Paroxysmal atrial fibrillation
• NYHA Class IV
• Left ventricular ejection fraction (LVEF) < 35
• Patients with unstable angina
• Patients who have experienced an acute myocardial infarction or received coronary artery revascularization (CABG), or coronary angioplasty (PTCA) within 3 months prior to enrolment
• Patient candidate for cardiac surgery, or coronary angioplasty (PTCA)
• Patients who experienced a cardiovascular accident (CVA) or transient ischemic attack (TIA) with permanent disability
• Life expectancy < 12 months due to other medical conditions
• Pregnancy
• The patient is enrolled in any concurrent (drug and/or device) study