Long term risk of recurrence among survivors of sudden cardiac arrest: A systematic review and meta-analysis

Aims: With a growing number of survivors of sudden cardiac arrest globally, their natural disease progression is of interest. This systematic review and meta-analysis aimed to determine the risk of recurrence after sudden cardiac arrest and its associated risk factors. Methods: Medline, Embase, Cochrane Library and Scopus were searched from inception to October 2021. Studies involving survivors of an out-of-hospital sudden cardiac arrest event of any non-traumatic aetiology were included. Meta-analyses of proportions using the random-effects model estimated the primary outcome of first recurrent sudden cardiac arrest incidence as well as secondary outcomes including cumulative incidence of recurrence at 1-year and incidence of second recurrence among survivors of first recurrence. A recurrent episode was defined as a sudden cardiac arrest that occurs 28 or more days after the index event. Subgroup and meta-regression analyses were conducted for predetermined variables. The Newcastle-Ottawa Scale was used to assess risk of bias for most studies. Results: 35 studies of moderate to high quality comprising a total of 7186 survivors were analysed. The pooled incidence of first recurrence was 15.24% (32 studies; 95%CI, 11.01-19.95; mean follow-up time, 41.3 +/- 29.3 months) and second recurrence was 35.03% (3 studies; 95%CI, 19.65-51.93; mean follow-up time, 161.1 +/- 54.3 months). At 1-year, incidence of recurrence was 10.62% (3 studies; 95%CI, 0.25-30.42). Subgroup analyses found no significant difference (p= 0.204) between incidence of first recurrence published from 1975-1992 and 1993-2021, and between studies with mean follow-up time of <24 months, 24-48 months, and >48 months. On meta-regression, initial shockable rhythm increased incidence of first recurrence (p = 0.01). Conclusion: 15.24% of sudden cardiac arrest survivors experienced a recurrence, and of these, 35.03% experienced a second recurrence. Most recurrences occurred in the first year. Initial shockable rhythm increased this risk. Despite the limitations of inter-study heterogeneity, these findings can still guide intervention and follow-up of sudden cardiac arrest survivors.