Hypertrophic cardiomyopathy (HCM) is the presence of a hypertrophied, non-dilated ventricle in the absence of a hemodynamic cause, and it is the most common genetic heart disease with an estimated prevalence of 1 in every 500 individuals and annual mortality rate of 1-8%. HCM is diagnosed by echocardiogram (ECHO) when the interventricular septum thickness in diastole (IVSd) measurement is > 15 mm or represents a Z score value that is > 2 for the age and body surface area of the individual. Children and adolescents with HCM have IVSd, left ventricular posterior wall thickness in diastole (LVPWd), left ventricular end diastolic diameter (LVEDd), and mass of the left ventricle measurements that are above the upper range of normal values. As the child grows and/or their condition progresses, it is important to understand the trajectory of their ECHO measurement values to stratify their risks and determine appropriate treatments to mitigate adverse outcomes when possible. 

Our study separated subjects diagnosed with HCM with ECHO records available in the CHOP HCM study RedCap database into two cohorts, one with HCM subjects <12 years and the other ≥12 years. Stata 17 software was utilized to obtain descriptive statistics and perform a t-test analysis of IVSd, LVPWd, LV mass, LVIDd, LVIDs, ejection fraction mean and Z score differences between cohorts in addition to patient characteristics marking HCM progression. ECHO measurements were stratified by subject demographics. The study had two objectives. The first objective was to develop a more complete understanding associated with the age of presentation of HCM and to determine the effects of age, sex, race, and ethnicity on clinical course and outcomes between the two cohorts. The second objective of the study was to determine the progression of HCM in pediatric subjects by age of presentation. 

A majority of HCM subjects presented in their first year of life for the <12 years cohort while in the ≥12 years cohort most presented at 18 years. Differences in family history between the cohorts were found however determined to be nonsignificant. As a result of the t-test analysis multiple statistically significant findings were obtained. Specifically, there were statistically significant differences in patient characteristics in clinical presentation attributed to symptoms/events (Pr=0.03), abnormal ECG (Pr=0.02), and myomectomy (Pr=0.002) and heart failure (Pr=0.009) outcomes. There were no significant differences between the two cohorts for the absolute measured values of all of the ECHO measurements observed, however there were statistically significant differences in the Z scores of IVSd (0.0056), LVPWd (0.0041), and LV mass (0.0015) supporting the observation of younger HCM subjects having more extreme echocardiographic signs and further poorer outcomes compared to older HCM subjects. 

The findings of this study contribute to the existing literature of HCM progression in pediatric subjects, especially as seen on ECHO which will hopefully aid in the earlier diagnosis and the modification of treatment plans in consideration of the variation of HCM progression within the pediatric population with age.