The incidence of Atrial Fibrillation (AF) in Sick Sinus Syndrome patients treated with pacing is quite high. As AF can cause dizziness, fatigue, thromboembolism and ischemic stroke it is clinically relevant. Due to earlier publications pacing modes and lead placement seem to influence the incidence of AF. In this study the incidence of AF will be compared between 4 different atrial lead positions: