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.