Background Danon disease is a rare X‐linked storage disorder characterized by hypertrophic cardiomyopathy leading to arrhythmias and heart failure. A preexcitation pattern on electrocardiogram (ECG) has been described in these patients, however, invasive studies to distinguish between Wolff‐Parkinson‐White syndrome syndrome and fasciculoventricular pathways (FVP) are limited. Objectives The purpose of this study was to delineate the electrophysiological cardiac abnormalities in patients with Danon disease and to describe the presence of FVP in this population. Methods We performed a retrospective study of all patients with a confirmed diagnosis of Danon disease presenting to a single center from May 2005 to May 2018. Baseline demographics, clinical characteristics, ECG findings, and electrophysiology study (EPS) results were collected. Results Ten patients with Danon disease (30% male, average age 17.4 years) were identified. Seven patients (70%) had tachyarrhythmias including five with atrial arrhythmias and six with nonsustained ventricular tachycardia. Preexcitation pattern on ECG was found in four (40%) patients. Of these, two underwent an EPS which confirmed the presence of an FVP. One patient underwent an adenosine challenge which supported a FVP. Implantable cardioverter defibrillator was placed in five patients for primary prevention with no patients receiving an appropriate discharge. Over a follow‐up of 5.3 years, five underwent heart transplantation. Conclusions This study reports a high incidence of FVP in patients with Danon disease and preexcitation. It underscores an alternate etiology of preexcitation in this population which can potentially be diagnosed without invasive EPS testing. Future multicenter studies are needed to expand this experience.

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Background: There is little known about the spectrum of cardiac injury in acute COVID-19 infection in children. Methods: A single-centre, retrospective chart analysis was performed. The protocol was deemed IRB exempt. All patients under the age of 21 years admitted from 20 March, 2020 to 22 June, 2021 for acute symptomatic COVID-19 infection or clinical suspicion of multisystem inflammatory syndrome in children (MIS-C) associated with COVID-19 were included. Past medical history, lab findings, echocardiogram and electrocardiogram/telemetry findings, and clinical outcomes were reviewed. Results: Sixty-six patients with MIS-C and 178 with acute COVID-19 were reviewed. Patients with MIS-C had more cardiac testing than those with acute COVID-19. Inflammatory markers were more likely elevated, and function was more likely abnormal on echocardiogram in those with MIS-C with testing performed. Among patients with MIS-C, 17% had evidence of coronary dilation versus 0% in the acute COVID-19 group. One (0.6%) patient with acute COVID-19 had clinically significant electrocardiogram or telemetry findings, and this was in the setting of prior arrhythmias and CHD. Four (6%) patients with MIS-C had clinically significant findings on electrocardiogram or telemetry. Among patients with acute COVID-19, extracorporeal membrane oxygenation support was required in 0.6% of patients with acute COVID-19, and there was a 2.8% mortality. There were no deaths in the setting of MIS-C. Conclusions: Patients with acute COVID-19 and clinical suspicion of cardiac injury had a lower incidence of abnormal laboratory findings, ventricular dysfunction, or significant arrhythmia than those with MIS-C.