4.1. The development of SSS in patients with AF
The prevalence of SSS is estimated to be 1 in 1000 in adults over 45 years of age,13 with the incidence rate increasing with age, up to 1 in 600 patients over 65 years of age. SSS accounts for significant healthcare use, including hospitalization and pacemaker implantation (about half of implant indications in the United States).13 However, a characteristic feature of SSS is the development of supraventricular arrhythmias, among which, AF is the most common.9, 14, 15 In a large population study, the estimated HR for new-onset AF in patients with SSS was 4.14 At initial diagnosis of SSS, AF can appear simultaneously in 40–70% of patients.9, 14, 15 In patients without clinical AF, incident AF occurs in 4–22% of patients during follow-up.9, 14, 15During long-term follow-up, 68% of patients had AF recorded in their pacemakers.14
AF can change a normal SAN or promote preexisting SSS. However, the incident of SSS in patients with incident AF has not been well elucidated. This study showed that about a third of SSS occurred before or after 30 days of incident AF. After regarding AF as time-varying covariate, the estimated HR for the newly developed SSS in patients with incident AF was 8.2 and 13.4, compared with the overall and PS-matched patients without AF. The concept of a single pacemaker dominating the cardiac rhythm of the atria is effective wherein AF blocks the SAN by long-term overdrive suppression of its activity. Patients with paroxysmal AF and prolonged sinus pauses (>3 s) had improved SAN function after ablation of AF. Sinus pauses were caused by long-term suppression of the SAN activity.16