Nocturnal Atrioventricular Block: Natural History and Clinical Implications.

BACKGROUND

Atrioventricular block (AVB) occurring exclusively at night has traditionally been considered a result of increased vagal tone and thought to have a favorable prognosis. While nocturnal AVB is generally not an indication for pacemaker implantation, supporting evidence remains limited. This study aimed to assess the natural history of nocturnal AVB.

METHODS

Patients with 2:1, high-degree, or complete AVB (CAVB) detected exclusively during nighttime (21:00-07:00) on 24-hour electrocardiogram (ECG) monitoring were classified as having nocturnal AVB. The primary outcome was pacemaker implantation during the follow-up period.

RESULTS

A total of 10,977 individuals underwent 24-hour ECG monitoring in Seoul St. Mary's Hospital between January 2000 and June 2020. Among them, 342 patients were diagnosed with CAVB, high-degree AVB, or 2:1 AVB, and 92 of these 342 patients had nocturnal AVB. Excluding 11 patients lost to follow-up, 81 patients were enrolled. Fourteen patients underwent immediate pacemaker implantation due to daytime bradycardia symptoms, while the remaining 67 patients underwent watchful waiting. During a median follow-up period of 2.4 years, 14 of these 67 patients received pacemaker implantation (n: CAVB 5/14, high-degree AVB 4/14, 2:1 AVB 5/14). The indications for pacemaker insertion included the development of bradycardia symptoms or signs (n = 13) and sick sinus syndrome (n = 1) during the daytime.

CONCLUSION

Despite being asymptomatic during the daytime, 21% (14/67) of patients with nocturnal AVB required pacemaker implantation during a median follow-up period of 2.4 years. These findings suggest that active surveillance is needed even in patients with nocturnal AVB.