Although previous studies have helped define the natural history of Duchenne Muscular Dystrophy (DMD)-associated cardiomyopathy, the myocardial pathobiology associated with functional impairment in DMD is not yet known.
The objective of this study was to assess the distribution of transverse relaxation time (T2) in the left ventricle (LV) of DMD patients, and to determine the association of myocardial T2 heterogeneity to the severity of cardiac dysfunction. DMD patients (n = 26) and normal control subjects (n = 13) were studied by Cardiovascular Magnetic Resonance (CMR). DMD subject data was stratified based on subject age and LV Ejection Fraction (EF) into the following groups: A (<12 years old, n = 12); B (≥12 years old, EF ≤ 55%, n = 8) and C (≥12 years old, EF = 55%, n = 6). Controls were also stratified by age into Groups N1 (<12 years, n = 6) and N2 (>12 years, n = 5). LV mid-slice circumferential myocardial strain (εcc) was calculated using tagged CMR imaging. T2 maps of the LV were generated for all subjects using a black blood dual spin echo method at two echo times. The Full Width at Half Maximum (FWHM) was calculated from a histogram of LV T2 distribution constructed for each subject.
In DMD subject groups, FWHM of the T2 histogram rose progressively with age and decreasing EF (Group A FWHM= 25.3 ± 3.8 ms; Group B FWHM= 30.9 ± 5.3 ms; Group C FWHM= 33.0 ± 6.4 ms). Further, FWHM was significantly higher in those with reduced circumferential strain (|εcc| ≤ 12%) (Group B, and C) than those with |εcc| > 12% (Group A). Group A FWHM was not different from the two normal groups (N1 FWHM = 25.3 ± 3.5 ms; N2 FWHM= 24.0 ± 7.3 ms).
Reduced EF and εcc correlates well with increased T2 heterogeneity quantified by FWHM, indicating that subclinical functional impairments could be associated with pre-existing abnormalities in tissue structure in young DMD patients.