The objective of this study is to intra-individually compare the performances of two pacemaker algorithms designed to reduce unnecessary right ventricular pacing: Intrinsic Rhythm Support Plus (IRSplus) and Ventricular Pace Suppression (VpS). The study will compare ventricular pacing percentage, long-term atrio-ventricular conduction time, occurrences of atrial tachyarrhythmic events and atrial fibrillation burden percentage in patients implanted with a pacemaker for Sick Sinus Syndrome.

Inclusion Criteria:

• Patients over 18 years of age;
• Patient has proven informed consent;
• Subject with indication of dual chamber pacemaker due to Sinus Node Dysfunction;
• Subjects with a dual chamber pacemaker already implanted within six months from enrollment, provided that ventricular pacing percentage ≤ 40% and with the right ventricular lead in the apical position;
• Stable medical situation;
• Stable geographical situation;

Exclusion Criteria:

• Permanent or paroxysmal AV block ≥ II;
• Permanent Atrial fibrillation/Atrial flutter;
• Device Replacement;
• Patient with a poor echocardiographic window;
• Patient already implanted with the right ventricular lead not in the apical position;
• Subjects with a dual chamber pacemaker, implanted later than six months;
• Subjects with a dual chamber pacemaker with ventricular pacing percentage ≥ 40%;
• Contraindication for DDD(R)-ADI(R) or DDD(R) pacing modes;
• VpS or IRSplus algorithm contraindications;
• Age < 18 years;
• Life expectancy < 12 months;
• Cardiac surgery planned within the FU period;
• Participation to another clinical investigation;