Objective: To evaluate, whether frequency and duration of atrial tachyarrhythmia (AT) episodes (eps.) in patients (pts.) with a novel DDDRP pacemaker are influenced by the activation of preventive atrial pacing algorithms (alg.) and automatic atrial anti-tachycardia pacing (ATP). Methods: In 23 pts. with conventional pacing indication and documented history of AT, a novel DDDRP device (AT500, model 7253, Medtronic) was implanted. DDDR pacing (60-1201min.) and AT detection (atrial cycle length lmin and classified as atrial flutter (cycle length 220360ms, variability 1min. 0.1, #p=0.1, *p=O.09 Conclusions: Mean AT eps. frequency (per day and patient) and mean AT eps. duration decreased after activation of preventive pacing alg. and automatic atrial ATP, but not significantly. Approximately half of all AT eps. lasted >1 minute. 44% of these eps. were also classified as AFlut and thus treated by ATP delivery. INCIDENCE OF PRIOR UNKNOWN VENTRICULAR TACHYCARDIAS IN PATIENTS WITH ATRIAL TACHYARRHYTHMIAS AND BRADYINDICATED PACEMAKER C. Unterberg 1, C. Israel 2, B. Huegl 3, T. Lawo 4, J. Stevens 1, D. Vollmann 1 ~Department of Cardiology, Georg August Universi~ Goettingen, Germany, 2J.W+ Goethe University Frankfurt, Germany, Heart Center Leipzig, Germany, 4University Hospital Bochum, Germany