Cardiomyopathy is the leading cause of death in patients with Duchenne muscular dystrophy. The relationship between cardiac and skeletal muscle progression is unclear. The objective of this study was to evaluate the correlation between muscle activity and cardiomyopathy. We hypothesised that cardiomyopathy and skeletal muscle activity are directly related.

Physical activity was assessed with accelerometers worn for 7 days. Average activity (vector magnitude/min) and percentage of time in different activities were reported. Cardiac MRI was used to assess left ventricular ejection fraction, global circumferential strain (Ecc), late gadolinium enhancement, and cardiac index. Associations were assessed between physical activity and cardiac variables using a Spearman correlation.

Duchenne muscular dystrophy subjects (n = 46) with an average age of 13 ± 4 years had a mean left ventricular ejection fraction of 57 ± 8%. All physical activity measures showed significant correlations with left ventricular ejection fraction (rho = 0.38, p = 0.01) and left ventricular cardiac index (rho = 0.51, p < 0.001). Less active subjects had lower left ventricular ejection fraction (p = 0.10) and left ventricular cardiac index (p < 0.01). Non-ambulatory patients (n = 29) demonstrated a stronger association between physical activity and left ventricular ejection fraction (rho = 0.40, p = 0.03) while ambulatory patients demonstrated a stronger association between physical activity and left ventricular cardiac index (rho = 0.53, p = 0.03). Ecc did not associate with physical activity in either cohort.

Physical activity correlates with left ventricular ejection fraction and left ventricular cardiac index and is modified by ambulation. Future analysis should assess the temporal relationship between physical activity and cardiomyopathy.

Distinguishing between hypertrophic cardiomyopathy and other causes ofleft ventricular hypertrophy can be difficult in children. We hypothesised that cardiac MRI T1 mapping could improve diagnosis of paediatric hypertrophic cardiomyopathy and that measures of myocardial function would correlate with T1 times and extracellular volume fraction.

Thirty patients with hypertrophic cardiomyopathy completed MRI with tissue tagging, T1-mapping, and late gadolinium enhancement. Left ventricular circumferential strain was calculated from tagged images. T1, partition coefficient, and synthetic extracellular volume were measured at base, mid, apex, and thickest area of myocardial hypertrophy. MRI measures compared to cohort of 19 healthy children and young adults. Mann–Whitney U, Spearman’s rho, and multivariable logistic regression were used for statistical analysis.

Hypertrophic cardiomyopathy patients had increased left ventricular ejection fraction and indexed mass. Hypertrophic cardiomyopathy patients had decreased global strain and increased native T1 (−14.3% interquartile range [−16.0, −12.1] versus −17.3% [−19.0, −15.7], p < 0.001 and 1015 ms [991, 1026] versus 990 ms [972, 1001], p = 0.019). Partition coefficient and synthetic extracellular volume were not increased in hypertrophic cardiomyopathy. Global native T1 correlated inversely with ejection fraction (ρ = −0.63, p = 0.002) and directly with global strain (ρ = 0.51, p = 0.019). A logistic regression model using ejection fraction and native T1 distinguished between hypertrophic cardiomyopathy and control with an area under the receiver operating characteristic curve of 0.91.

In this cohort of paediatric hypertrophic cardiomyopathy, strain was decreased and native T1 was increased compared with controls. Native T1 correlated with both ejection fraction and strain, and a model using native T1 and ejection fraction differentiated patients with and without hypertrophic cardiomyopathy.