Clinical Features and Course of Preadolescent Hypertrophic Cardiomyopathy

Quick Takes

  • Analysis of a multicenter, international cohort of children with HCM shows similar symptom burden and HCM phenotype in children <12 years of age at presentation when compared to older children.
  • Incidences of mortality, cardiac transplant, and SCD were similar in children <12 years of age as compared to children ≥12 years of age.
  • Children presenting under 12 years of age were more likely to have a myectomy but less likely to receive a primary prevention ICD at follow-up.

Study Questions:

What are the clinical characteristics and outcomes of a multicenter cohort of children with nonsyndromic hypertrophic cardiomyopathy (HCM) presenting before 12 years of age?


This was a study of children with HCM between 1 and <12 years old identified from a large, multicenter, international cohort between 1970–2019 compared to children ≥12 years. Clinical data collected included echocardiograms at baseline and follow-up, ambulatory electrocardiogram, and interventions such as implantable cardioverter-defibrillator (ICD) implantation/myectomy. Genetic testing was performed at the discretion of the treating clinician. The primary outcome was all-cause mortality or cardiac transplant. The secondary outcome was first life-threatening cardiac arrhythmia.


A total of 639 children were diagnosed with HCM between 1 to <12 years of age. This included 65% males with a median age of diagnosis of 7 years. Genetic testing information was available on 55% of patients with negative or benign variants on testing for 22%. Most commonly affected genes included MYH7 and MYBPC3. There were no significant differences in HCM phenotype between children presenting at <12 years versus ≥12 years. Median follow-up duration was 5.6 years. Overall, 10% underwent septal myectomy, 3% needed a pacemaker, and 23% had an ICD implanted. During follow-up, approximately 7% died, 3% had a cardiac transplant, and median age at death or transplant was 12.9 years. Predictors of mortality included presence of heart failure, increasing left atrial diameter, and absence of a disease-causing variant on genetic testing. Life-threatening arrhythmic event was noted in 11% of patients with a median age at event of 12.6 years with all children being >5 years of age. When compared with children presenting at >12 years of age, incidence of transplant or death and life-threatening arrhythmia did not differ in children <12 years of age. More children presenting under 12 years had a myectomy, but a lower proportion received a primary prevention ICD when compared to children presenting after 12 years of age.


In this multicenter cohort study, early-onset HCM before age of 12 years had similar burden of symptoms and HCM phenotype compared to children ≥12 years of age. Mortality and incidence of sudden cardiac death (SCD) did not differ either. However, children presenting at age <12 years were more likely to have a myectomy but less likely to have a primary prevention ICD.


Traditionally, sarcomeric HCM has been considered to be a disease manifesting in adolescence or adulthood. However, more recent data suggests that the disease can present during childhood as well. This cohort study is the first exploring characteristics of children under the age of 12, presenting with HCM. It shows that these children had similar symptom burden and phenotype compared to older children presenting with HCM. Yield of genetic testing was high. Incidences of mortality, transplant, and SCD were similar as well. Notably, incidence of ICD implant for primary prevention was lower in children <12 years of age despite a greater incidence of myectomy and a similar symptom burden with no difference in phenotype either. These findings suggest that even young children presenting with HCM likely benefit from similar management strategies as older children, challenging the age-old notion that preadolescent children with HCM should not be considered at risk.

Clinical Topics: Arrhythmias and Clinical EP, Cardiac Surgery, Congenital Heart Disease and Pediatric Cardiology, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Prevention, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Aortic Surgery, Cardiac Surgery and Arrhythmias, Cardiac Surgery and CHD and Pediatrics, Cardiac Surgery and Heart Failure, CHD and Pediatrics and Arrhythmias, CHD and Pediatrics and Imaging, CHD and Pediatrics and Interventions, Acute Heart Failure, Heart Transplant, Interventions and Imaging, Interventions and Structural Heart Disease, Echocardiography/Ultrasound

Keywords: Adolescent, Arrhythmias, Cardiac, Cardiomyopathy, Hypertrophic, Cardiomyopathies, Child, Death, Sudden, Cardiac, Defibrillators, Implantable, Echocardiography, Electrocardiography, Genetic Testing, Heart Failure, Heart Transplantation, Pacemaker, Artificial, Pediatrics, Phenotype, Primary Prevention

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