Abstract Body (Do not enter title and authors here): Background. Dilated cardiomyopathy (DCM) is the most common cause of pediatric heart failure (HF), but there is limited literature on its long-term prognosis and treatment outcomes. We examined risk factors for long-term morbidity and mortality and outcomes of care in childhood-onset DCM.

Methods. Electronic medical records from a tertiary care pediatric hospital (SickKids, Toronto, Canada) were used to retrospectively follow children ages 0–18 years with DCM from January 1, 2001 to July 1, 2017. Provincial healthcare administrative data was used to monitor outcomes recorded outside of SickKids, following patients during the same time period and into adulthood (age >18 years) until August 31, 2023. We compared DCM cases, with or without echocardiographic recovery (LVEDD z score < 2 and LVEF ≥ 55%), and controls matched on sex, age, and urban/rural residence on a range of health and health service outcomes. Primary outcomes included all-cause mortality, heart transplant (HT), and inpatient admission for HF. Among cases, Cox proportional hazards regression with backwards selection was used to identify demographic, disease, and treatment characteristics associated with each primary outcome, with candidate variables selected based on univariate analysis and clinical judgment.

Results. We studied 156 patients with DCM and 780 controls for a median of 14.8 years. Median age at the end of follow-up was 16.2 years. Compared with controls, DCM cases had higher rates of all-cause death, HT, and HF admission (all P<0.001), as well as chronic kidney disease (P<0.001) and diabetes (P=0.002). Compared to cases with recovered DCM (n=53), non-recovered cases had higher rates of death, HT, and HF admission (all P<0.001). On multivariable analysis, beta blockers were associated with reduced mortality risk (HR 0.343, 95% CI 0.162–0.727). Using any HF medication (HR 0.205, 95% CI 0.102–0.412) and living in an urban versus a rural area (HR 0.166, 95% CI 0.048–0.573) decreased HT risk. Idiopathic (HR 4.16, 95% CI 1.42–12.2) or sarcomeric mutation-related (HR 9.86, 95% CI 2.30–42.3) DCM were associated with higher HT risk than myocarditis-related DCM.

Conclusions. While childhood DCM is associated with long-term adverse health and increased health care utilization, patients who recover have improved morbidity and mortality. Treatment (e.g. medication or access to urban specialist care) was associated with lower mortality and HT risk in DCM.