The aim of this study is to assess the benefits from the AAISafeR/SafeR algorithm of Symphony 2550 or REPLY DR in a wide range of pacemaker patients.

The expected benefits will be a result of the reduction of the percentage of ventricular pacing.

It contributes to the longevity of the cardiac pacemaker and has an effect on the incidence of sustained (or persistent) Atrial Fibrillation and Heart Failure. These clinical benefits are a result of spontaneous ventricular activation which ensures a more physiological ventricular activation.

The benefits will be assessed by comparing the incidence of atrial arrhythmias and the evolution of the haemodynamic status of the patients (QOL, echo and BNP)

Inclusion Criteria:

• Patient primo-implanted with a Symphony 2550 or Reply DR for less than 1 month according to the official guidelines.
• Patient implanted for sinus node dysfunction (including bradycardia-tachycardia syndrome) or 2nd, advanced or 3rd degree intermittent or allegedly permanent AV block.
• Patient implanted with a bipolar right atrial lead and a right ventricular lead
• Patient has signed a consent form after having received the appropriate information

Exclusion Criteria:

• Patient with permanent AF
• Patient suffering from sustained ventricular arrhythmias
• Patient with congenital complete heart block
• Patient with vasovagal syncope, carotid sinus syndrome
• Patient with AV node ablation
• Patient having suffered from a myocardial infarction within the last month
• Patient suffering from severe aortic stenosis
• Patient suffering from unstable angina pectoris
• Patient is not able to understand the study objectives and protocol or refuses to co-operate
• Patient is not available for scheduled follow-up
• Patient has a life expectancy less than one year
• Patient is included into another clinical study
• Patient is minor, this is < 18 years
• Patient is a pregnant woman
• Any patient with a contra-indication for the device labeling