Atrial fibrillation (AF) is prevalent in patients with sick sinus syndrome (SSS) and associated with an increased risk of stroke and death. Within the first two years after pacemaker implantation almost half of the patients are diagnosed with AF. Studies have indicated that an increased amount of stimulation from the pacemaker in the atria is associated with an increased amount of AF.

The aim of the present study is to test the hypothesis that a reduction of stimulation from the pacemaker in the atria, and reducing the minimal heart rate, increases the time to AF.

Inclusion Criteria:

• Sick sinus syndrome with and without AV block and indication for first-time implantation of a DDD pacemaker: symptomatic sinus pauses (>2 sec) or bradycardia with or without paroxysmal AF.
• Age ≥18 years.
• Patient informed consent.

Exclusion Criteria:

• Permanent or persisting (>7 days) AF prior to implantation.
• Persisting symptomatic sinus bradycardia and/or chronotropic incompetence where DDD-pacing at a frequency of >40 bpm is indicated (verified with long term ECG monitoring).
• Life expectancy <2 years.
• Participation in another interventional research study.
• Indication for implantable cardioverter defibrillator (ICD) or cardiac resynchronization therapy (CRT).
• Pregnancy.