• Primary objective is to assess how the pacing mode affects the incidence of atrial fibrillation (AF) in patients with sick sinus syndrome. Since there are no data on the safety of AAI pacing in patients with Wenckebach points < 120 bpm and accor
  

• Number of patients with atrial fibrillation or heart failure > NYHA II
  
• AF burden
  
• Symptomatic atrial fibrillation
  
• Time period to first recurrence of AF
  
• Number of patients without recurrence of AF
  
• Mean duration of sinus rhythm
  
• Course of Wenckebach point
  
• Second- and third-degree AV block
  
• Reprogramming from AAI to DDD
  
• Fraction of atrial versus ventricular pacing
  
• Safety of treatment, complications
  
• Number of cardioversions
  
• Patients with persistent atrial fibrillation (AF >48h)
  
• Patients with permanent atrial fibrillation (AF throughout the follow-up period)
  
• Hospital admissions for cardiac reasons
  

Background: Dual-chamber pacemaker therapy has become the mainstay for treating symptomatic sick sinus syndrome (SSS). This approach aims to results in a physiologic conduction pattern, while protecting against atrioventricular conduction anomalies. Smaller studies and subgroup analyses of larger trials suggest that ventricular stimulation associated with this treatment has adverse effects, especially an increased incidence of atrial fibrillation and heart failure.

Methods: In MODEST, a study on patients with sick sinus syndrome who have an indication for pacing therapy, atrial pacing (AAI) is compared with dual-chamber pacing (DDD) combined with a novel algorithm developed to lower the number of ventricularly paced beats. The study aims to assess the impact of ventricular pacing on the development of atrial arrhythmias and to test the hypothesis that DDD pacing using the algorithm is associated with a higher rate of atrial arrhythmias as atrial pacing. Included will be patients with SSS and no high degree AV node disease except for patients with first-degree AV block ≤300ms. Patients will be followed stratified by their Wenckebach point (≥ 120 bpm versus < 120 bpm).

Conclusion: MODEST is a large, prospective, randomized, multicenter trial aiming to compare a novel type of dual-chamber pacing approach (that includes an algorithm designed to lower the number of ventricularly paced beats) with pure atrial pacing, assessing the impact on the incidence of atrial arrhythmias in patients with sick sinus syndrome.