The purpose of this study is to determine the incidence of atrial fibrillation and heart failure in patients with pacemaker therapy with different pacing modes (AAI, DDD, and a novel algorithm to minimize ventricular pacing).

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.

Inclusion Criteria:

• Symptomatic sinus bradycardia, Sinusarrest
• Symptomatic SA block
• Bradycardia-Tachycardia-Syndrome
• Binodal diseases

Exclusion Criteria:

• 1st degree AV Block
• 2nd degree AV block
• 3rd degree AV block
• Total right bundle branch block
• Indication for biventricular stimulation
• Inter atrial conduction delays (P-wave > 150MS)
• Permanent or therapy refractory Atrial Fibrillation
• Heart Failure acc. NYHA III or IV
• Myocardial Infarction less than 6 months before pacemaker implant
• Hypertrophic obstructive cardiomyopathy
• Symptomatic hypo- or hyperthyreosis
• Cardiogenic shock
• Pregnancy
• Lactation period
• Unstable angina pectoris
• Poorly controlled Diabetes mellitus
• Neuromuscular diseases
• Patients under 18 years of age
• Patients involved in other studies
• Reduced expectancy of life due to other diseases
• Patients who cannot attend follow-up visits regularly