PO27 Cardiac magnetic resonance imaging findings in RASopathy-associated hypertrophic cardiomyopathy

Background Cardiac magnetic resonance (CMR) imaging is an important tool for diagnosis and morphological assessment of the heart in childhood HCM. Up to 20% of patients with childhood onset disease have an underlying RASopathy syndrome but to date no studies have reported the CMR findings in this population. Purpose To characterise CMR findings in RASopathy-associated HCM (RAS-HCM) investigate their role in prediction of major adverse cardiac events (MACE) in this population. Methods CMR findings from a multi-centre, retrospective, observational cohort of 47 children with RAS-HCM were compared with those of 85 children with s-HCM. Results Patients with RAS-HCM had a higher median indexed left ventricular mass (LVMi) (124g/m2 vs 105g/m2, p=0.027) but lower prevalence of left ventricular (LV) late gadolinium enhancement (LGE) (33.3% vs 55.6%, p<0.001). Patients with a RAF1 variant had a higher median maximal LV wall thickness (MLVWT; 23mm vs 12mm, p=0.029) and LVMi (160g/m2 vs 106g/m2, p=0.030), and a higher proportion of patients with hyperdynamic LV function (100% vs 58.3%, p=0.037) compared to PTPN11. Over a median follow up of 7.0 (IQR 3.5-12.0) years, 8 patients (17.0%) reached the MACE end point. On univariate regression analysis, LV end-diastolic volume (LVEDV) (HR 0.6, 95% CI 0.92-1, p=0.04), LV cardiac output (LVCO) (HR 0.43, 95% CI 0.19-0.97, p=0.04) and the presence of RVH (HR 0.09, 95% CI 0.01-0.86, p=0.04) emerged as potential predictors of MACE. Conclusions This multi-centre cohort study is, to our knowledge, the first that describes CMR features of pediatric RAS-HCM. Major findings include a lower prevalence of LV LGE compared to patients with sarcomeric HCM, with a higher LV indexed mass in patients with RAS-HCM, particularly those with RAF1 variants. These findings may have implications for the diagnosis and risk stratification of children with RAS-HCM.