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.