The relationship between the genotype variation and phenotype expression in paediatric hypertrophic cardiomyopathy (HCM) has not been fully elucidated. In HCM, fibrosis and hypertrophy contribute to left ventricular (LV) mechanics with a decreased global longitudinal and radial strains (GLS, GRS). The epicardial thickening leads to preserved global circumferential strain (GCS) and LV twist. Feature tracking – cardiac magnetic resonance (FT-CMR) has enhanced the non-invasive assessment of myocardial deformation in HCM. The aim of our study was to assess differences of LV and LA mechanics features on CMR between patients harbouring multiple pathogenic or likely pathogenic variants (MGv, n=16) or single genetic variations (SGv, n=35).

Our retrospective CMR study included 51 patients (1.7–18.8 years ago). CMR data were: LV and LA's morphological values, late gadolinium enhancement (LGE) of LA and LV walls, LV feature tracking (FT) derived strain and LV twist (LVT). LV twist was calculated as the difference between basal and apical rotation. The LA feature FT derived strain and function's parameters were computed.

In MGv group, the indexed LV mass 108.8–53.0 vs. 74.3 ± 22.2 in SGv (P=0.03). LGE was present in 51% patients of the whole cohort, with LGE in 64% of MGv group. LV FT derived strain values were not statistically significant different between groups (MGv vs. SGv: GLS −15.8 ± 5.3 vs. −18.7 ± 4.8, GCS −27.8 ± 8 vs. −31.1 ± 8.6, GRS 44.7 ± 24.6 vs. 62.3 ± 32). LVT was reduced in MGv group (0.04 ± 7.6) vs. (7.4 ± 7.4) in SGv (P=0.003). LA contractile function did not differ between the groups.

Patients with multiple genetic variants have a greater LV mass and altered LV mechanics with reduced LV twist. This study gives insights in phenotype-genotype correlation in paediatric HCM and warrants larger longitudinal studies to assess its clinical significance (Fig. 1).