1. INTRODUCTION
Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in the general population.1, 2 The age distribution of AF is predicted to shift with an expected increase in its prevalence among the elderly.1. AF has tremendous socioeconomic implications as it increases the risk of morbidity and mortality due to stroke, congestive heart failure, and impaired quality of life.1-4
AF is associated with significant electrophysiologic and structural remodeling as well as sick sinus syndrome (SSS).5-8 AF develops in up to 50% of patients with tachycardia-bradycardia syndrome.9 Moreover, it is associated with SSS, manifested as sinus bradycardia without the component of tachycardia-bradycardia syndrome. In an animal study, persistent (>2 weeks) rapid atrial pacing and chronic AF resulted in sinoatrial node (SAN) dysfunction.5 In AF, SAN dysfunction is associated with calcium (Ca2+) clock malfunction, characterized by unresponsiveness to isoproterenol and caffeine and down-regulation of ryanodine receptor 2.5, 10 Comparable data in humans have also been reported. SSS patients with tachycardia-bradycardia syndrome showed lesser electrical and structural remodeling and better outcome after radiofrequency ablation of AF than those without it.6, 11
However, the effect of AF on the risk of SSS and pacemaker implantations is not revealed in general population. In this study, the association between incident AF and the risk of SSS was investigated in the cohort of elderly individuals. Additionally, we evaluated whether these associations occurred independent of heart failure or myocardial infarction, and whether they were influenced by medications for cardiac rhythm or rate control.