BackgroundPatients with Barth syndrome (BTHS) can present with cardiomyopathy. BTHS subjects are at risk for cardiac adverse outcomes throughout life, including malignant arrhythmias and death. Electrocardiogram (ECG) parameters have never been assessed as a tool to predict adverse outcomes in individuals with BTHS. ObjectivesThe purpose of this study was to identify any ECG parameters, including QRS fragmentation, presence of arrhythmia, or abnormal intervals, that could predict adverse outcomes and cardiac death among the BTHS population. MethodsWe performed a retrospective case referent study on subjects with BTHS (n = 43) and compared them with our reference group, subjects with idiopathic dilated cardiomyopathy (DCM) from a single institution (n = 53) from 2007 to 2021. BTHS data was obtained from subjects attending the biennial Barth Syndrome Foundation International Scientific, Medical, and Family Conferences (BSFISMFC) from 2002 to 2018. ECG data from the first and last available ECGs prior to an adverse event or cardiac death was analyzed. Then, multivariable regression was performed to determine odd ratios between ECG characteristics and adverse events/cardiac death. ResultsNo ECG variables were statistically significant predictors of adverse events or cardiac death in the BTHS group. Last ECG QRS fragmentation trended to statistically significance (OR 13.3, p = 0.12) in predicting adverse events in the DCM group. ConclusionNo ECG parameters, including QRS fragmentation, presence of arrhythmia, or abnormal interval values, predict adverse events or cardiac death among BTHS patients. QRS fragmentation may be a predictor of adverse events in the DCM population.