This clinical investigation is a prospective, single-blinded, randomized trial. The primary objective concerns the safety and effectiveness of the AAIsafeR mode with the preventive algorithms.

In this study, patients are randomized to DDD mode, AAIsafeR mode, or AAIsafeR mode plus atrial arrhythmia preventive algorithms. The atrial arrhythmia (AA) burden serves as the primary measure of effectiveness.

Inclusion Criteria:

• A pacemaker indication for sinus node dysfunction and/or brady-tachy syndrome OR already implanted for less than three months for the mentioned reasons and supplied with a symphony 2550 DR at time of inclusion AND
• A PR interval <250ms AND
• Documented atrial arrhythmia in the past year
• Medication for anti-arrhythmic must be stable for at least one month (2 months for amiodarone) prior to enrollment
• Patients must have less than two known cardioversions within the last year
• Patient has signed a consent form after having received the appropriate information

Exclusion Criteria:

• Need a replacement pacemaker device
• Have an unknown PR interval
• Known AV block ≥ 250 ms PR interval
• Minor and/or pregnant woman
• Patients enrolled in other clinical trials
• Patients with sustained ventricular arrhythmia
• Patients with severe coronary artery disease (at the discretion of the investigator)
• Patients with advanced cardiomyopathy (at the discretion of the investigator)
• Patients who have sustained a myocardial infarction or undergone cardiac surgery within the past 30 days
• Patients with unstable angina pectoris
• Patients whose life expectancy is less than 1 year
• Patients who are unlikely to return for required follow-up visits
• Patients who present with permanent atrial arrhythmia or those who usually require cardioversion to terminate such arrhythmia and/or
• Patients whose physician plans to add or change medical treatment because of AA episodes during the follow-up period.
• Patient unable to understand the purpose of the study or refusing to cooperate