Sex differences in paediatric onset hypertrophic cardiomyopathy

Abstract Background Hypertrophic Cardiomyopathy (HCM) is a heterogeneous disease characterised by age related incomplete penetrance and variable long term outcomes. Sex differences have been described in both the clinical phenotype and natural history of adults with the disease, which have been attributed to both biological (eg sex hormone effect) and non-biological (eg societal and cultural effects) factors. It is unknown if similar sex differences exist in childhood-onset HCM. Purpose This study aimed to investigate the influence of biological sex on the clinical characteristics and outcomes of children with HCM. Methods Retrospective cohort study from an international registry of patients diagnosed under the age of 18 years with HCM. Patients with syndromic disease (RASopathy syndromes, inborn errors of metabolism, neuromuscular disease) were excluded. Sex differences in baseline characteristics and clinical outcomes were described. Primary outcomes were all-cause mortality or cardiac transplantation, Major Arrhythmic Cardiac Event (MACE) and heart failure event (defined as heart failure death or cardiac transplantation) Results Of 1262 patients, 851 (67.4%) were male (median age 11 yrs (IQR 7.4, 14.4) vs 11.1 (IQR 6.9, 14.0) in females, p=0.0312). Female patients were more likely to have a sarcomeric variant identified (n=208, 85.6% vs 388 (79.4%), p=0.041) despite equivalent genetic testing utilisation between sexes. Female patients were more likely to have severe heart failure symptoms (NYHA 3 or 4) (n=19, 6.1% vs n=20, 2.5% p value 0.030) but there was no difference in the proportion on medical therapy (male n=328, 39.7%, female n=167, 41.8, p value 0.476). The clinical phenotype in terms of degree of hypertrophy, left atrial size and left ventricular outflow tract gradient did not differ by sex. Over a median follow up of 5.2 years (IQR 2.4, 9.9) all-cause mortality or cardiac transplantation did not vary by sex but females were more likely to experience a heart failure event (females 0.6/100,000 pt years (95% CI 0.39-0.92) vs males 0.32/100,000 pt years (95% CI 0.21 – 0.50), hazard ratio 1.89, p value 0.0467). The incidence of MACE did not differ by sex but there was a trend towards higher implantable cardioverter defibrillator implantation in females (n=123, 30.7% vs n=210, 25.4%, p value 0.051). Conclusions For the first time, this study has shown sex differences in paediatric-onset hypertrophic cardiomyopathy. Despite no difference in baseline clinical phenotype, young female patients are more likely to experience heart failure symptoms and heart failure events over follow up. Further studies are required to explore the underlying mechanisms for these observed differences.Table summarising outcomes by sexSurvival free from heart failure