OBJECTIVE: To define the risks and consequences of cardiac abnormalities in ATP1A3-related syndromes.
METHODS: Patients meeting clinical diagnostic criteria for Rapid-onset Dystonia-Parkinsonism (RDP), Alternating Hemiplegia of Childhood (AHC), and Cerebellar ataxia, Areflexia, Pes cavus, Optic atrophy, and Sensorineural hearing loss (CAPOS), with ATP1A3 genetic analysis, and had at least one cardiac assessment, were included. We evaluated the cardiac phenotype in an Atp1a3 knock-in mouse (Mashl+/-) to determine the sequence of events in seizure-related cardiac death.
RESULTS: 98 AHC, nine RDP, and three CAPOS patients (63 females, mean age 17 years) were included. Resting EKG abnormalities were found in 52/87 (60%) AHC, 2/3 (67%) CAPOS, and 6/9 (67%) RDP patients. Serial EKGs showed dynamic changes in 10/18 AHC patients. The first Holter EKG was abnormal in 24/65 (37%) AHC and RDP cases, with either repolarization or conduction abnormalities. Echocardiography was normal. Cardiac intervention was required in 3/98 (∼3%) AHC patients. In the mouse model, resting EKGs showed intra-cardiac conduction delay; during induced seizures, heart block or complete sinus arrest led to death.
CONCLUSIONS: We found increased prevalence of EKG dynamic abnormalities in all ATP1A3-related syndromes, with a risk of life-threatening cardiac rhythm abnormalities equivalent to that in established cardiac channelopathies (∼3%). Sudden cardiac death due to conduction abnormality emerged as a seizure-related outcome in murine Atp1a3-related disease. ATP1A3-related syndromes are cardiac diseases as well as neurological diseases. We provide guidance to identify patients potentially at higher risk of sudden cardiac death who may benefit from insertion of a pacemaker or implantable cardioverter-defibrillator.