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Aims: To explore the prevalence and incidence of paediatric implantable cardioverter-defibrillator (ICD) patients in Sweden and identify risk factors associated with appropriate shocks and adverse events.

Methods and results: We performed a nationwide, retrospective cohort study of ICD use in paediatric patients (<19 years) between 1995 and 2017; 120 patients underwent ICD implantation at median age 14.7 (range 1.1–18.9) years and were followed for 7.1 (0.3–20.4) years. Fifty-four patients (45%) received a primary preventive ICD; 46% had cardiomyopathy, and 41% had primary electrical disease. The estimated 5-year survival without appropriate shocks was 68% (confidence interval 59–78). Secondary preventive ICDs and lower weight (<30 kg) at implantation were associated with a higher rate of appropriate shocks, respectively. Lower weight at implantation was not a risk factor for adverse events. Inadequate medication and insufficient compliance were common in patients who experienced shocks. Less than half (46%) of the cases with inappropriate shocks were adequately medicated with good compliance. Secondly, an incidence and prevalence study of all paediatric and adult patients who had an ICD implanted in Sweden was analysed in 4-year periods between 2002 and 2021. The incidence of paediatric ICD implantations in Sweden peaked at 0.56 per 100 000 person-years in 2010–13, decreasing to 0.45 per 100 000 person-years in the last study period (2018–21).

Conclusion: Appropriate shocks were more than twice as common in the youngest patient group, whereas adverse events were not more frequent than in the older patient group. Inadequate medication and lack of compliance were common in connection with ICD shocks.