The purpose of the study is to demonstrate the efficiency on AT / AF prevention and termination of a new algorithm contained in the Medtronic AT500 Antitachycardia device in patients with conventional pacemaker indications.

Aim. More than 30% of patients (pts) implanted with a pacemaker are known to have atrial tachyarrhythmias (AT) despite medical treatment and about 20% of pts experience AT prior to implant. The Medtronic AT500TM is a new DDDRP pacemaker with extended memory and features designed for preventing and terminating AT. The objective of this European multi-center prospective crossover and randomized study is to evaluate efficacy of this device for decreasing AT burden, improving QOL and reducing symptoms and costs. Method. 243 pts are implanted with the AT500TM and followed at 1, 7 and 13 months after implant. All patients are selected for a dual chamber pacemaker indication plus at least two episodes of AT in the last 12 months. One month after implantation patients are randomized either to a six month therapy phase (activation of preventive and ATP pacing) or a six month observation phase (No AT prevention nor Therapy). Crossover (CO) takes place at seven months after implant and the endpoint is reached at 13 months. Symptom checklist and QOL questionnaires are completed by pts at enrollment and after the two randomization periods. At each follow-up, a Save to Disk (STD) of device-stored AT episodes is performed and hospitalization, visits and/or other examinations are reported for future cost evaluation.

Inclusion Criteria:

• ACC/AHA Class I or II indication for dual chamber pacing and two symptomatic atrial fibrillation or flutter episodes in the three months prior to implant as well as ECG documentation of at least one episode in the prior year.

Exclusion Criteria:

• Patients with permanent/persistent AF, an indication for an implantable cardioverter defibrillator or class IV heart failure.