Abstract Body (Do not enter title and authors here): Background: Mitochondrial disease has an estimated incidence of 1.6 per 5,000 live births and can affect nearly any organ system; however, the cardiac presentations and clinical implications of mitochondrial disease remain poorly understood. The purpose of this study was to describe the prevalence of cardiac disease in a cohort of patients with known mitochondrial disease and compare outcomes between patients with and without cardiac disease.

Methods: This retrospective study performed at a single pediatric tertiary-care hospital included patients with a clinical and genetic diagnosis of mitochondrial disease that had at least one encounter with our hospital system between 2019 and 2024. Available echo and ECG data and cardiology documentation was reviewed. Clinical characteristics including hospital admissions and number of subspecialties involved in care were retrieved from the electronic medical record from 2007-2024. Analysis of clinical findings was performed using chi-squared analysis, and comparison of hospitalized days, ICU days, and number of subspecialties involved in care was performed using Student’s T test analysis. Cardiac abnormalities that were identified at the time of death or arrest unrelated to a primary cardiac etiology were not included as cardiac disease.

Results: Cardiac disease was present in 31/94 patients. More than one cardiac diagnosis was present in 5 patients thus 37 unique cardiac diagnoses were made. Cardiomyopathy was most common (17/95), with hypertrophic cardiomyopathy in 9/17. Electrophysiology disease was present in 9/94 patients with 5/9 having antegrade ventricular pre-excitation. Two patients recieved heart transplant. Patients with cardiac disease were more likely to be hospitalized than those without disease (83% vs 59%, p=0.02), and more likely to require admission to an ICU (61% vs 37%, p=0.02). Hospital and ICU days varied widely within groups and there was no significant difference between those with vs those without cardiac disease. There was no statistical difference in mortality.

Conclusions: Cardiac disease is present in a third of children with genotype positive, phenotype positive mitochondrial disease. No current guidelines exist to determine cardiac screening in most forms of mitochondrial disease, despite a higher prevalence of severe cardiac abnormalities than in many other populations where screening is vocally advocated, such as athletes and patients with a positive family history of cardiac disease.