Abnormalities of Diastolic Function Precede Dilated Cardiomyopathy Associated with Duchenne Muscular Dystrophy

Circumferential strain analysis identifies strata of cardiomyopathy in Duchenne muscular dystrophy: a cardiac magnetic resonance tagging study

OBJECTIVES

This study sought to evaluate the natural history of occult cardiac dysfunction in Duchenne muscular dystrophy (DMD).

BACKGROUND

Duchenne muscular dystrophy is characterized by progressive cardiac dysfunction and myocardial fibrosis late in the disease process. We hypothesized that left ventricular myocardial peak circumferential strain (epsilon(cc)) would decrease in DMD before global systolic functional abnormalities regardless of age or ventricular ejection fraction (EF).

METHODS

We evaluated cardiac magnetic resonance image (MRI) data from 70 DMD patients and 16 aged-matched control subjects. Standard imaging data included steady-state free precession short-axis cine stack images, cine myocardial tagged images, and myocardial delayed enhancement (MDE) (an indicator of myocardial fibrosis) sequences. Analysis was performed with QMASS (Medis Medical Imaging Systems, Leiden, the Netherlands) and HARP (Diagnosoft, Palo Alto, California) software. The DMD patient data were subdivided by age (<10 or >10 years), EF (>55% or <55%), and the presence or absence of MDE.

RESULTS

The DMD patients with normal EF had reduced epsilon(cc) at an early age (<10 years) compared with control subjects (p < 0.01). The DMD patients age >10 years with normal EF had further decline in epsilon(cc) compared with younger DMD patients (p < 0.01). There was further decline in epsilon(cc) with age in patients with reduced EF (p < 0.01) without MDE. The oldest patients, with both reduced EF and positive MDE, exhibited the lowest epsilon(cc). None of the patients had ventricular hypertrophy.

CONCLUSIONS

Myocardial strain abnormalities are prevalent in young DMD patients despite normal EF, and these strain values continue to decline with advancing age. Strain analysis in combination with standard MRI and MDE imaging provides a means to stratify DMD cardiomyopathy.

Early regional myocardial dysfunction in young patients with Duchenne muscular dystrophy

BACKGROUND

In young patients (aged <12 years) with Duchenne muscular dystrophy (DMD), cardiac systolic function is generally described to be within the normal range. Recent studies have suggested the presence of subclinical dysfunction in these young patients using cardiac magnetic resonance imaging, tissue Doppler measurements, and myocardial velocity gradients. The aim of this study was to further assess regional myocardial function in a young group of patients with DMD using myocardial velocity and deformation imaging.

METHODS

Thirty-two patients with DMD (mean age, 7.9 years; range, 3-12 years) and 29 age-matched normal controls were studied with echocardiography. Standard echocardiographic measurements of left ventricular (LV) systolic and diastolic function were performed. Myocardial velocity and deformation data, including peak systolic and early and late diastolic myocardial velocities, peak systolic strain rate (SR), and peak systolic strain (epsilon), were calculated in the radial direction in the inferolateral LV wall and in the longitudinal direction in the interventricular septum, the LV anterolateral wall, and the right ventricular (RV) free wall.

RESULTS

Higher heart rates and increased LV end-systolic dimensions were seen in patients with DMD compared with controls. Significant decreases in radial and longitudinal peak systolic SR, peak systolic epsilon, and peak systolic and early diastolic myocardial velocities were found in the LV inferolateral and anterolateral walls in patients with DMD. No significant differences in longitudinal function could be found in the interventricular septum or in the RV free wall.

CONCLUSION

In young patients with DMD who have global normal systolic function, reductions in systolic deformation parameters as well as reduced early diastolic myocardial velocities can be detected in the anterolateral and inferolateral LV walls. The prognostic significance of these findings warrants further longitudinal follow-up.

Annular and Septal Doppler Tissue Imaging in Children: Normal z-Score Tables and Effects of Age, Heart Rate, and Body Surface Area

The aim of this study was to construct normal z-score tables for longitudinal directed Doppler tissue imaging (DTI) systolic wave (S), DTI early diastolic wave (E'), and DTI late diastolic wave (A') at the mitral valve annulus (MV), superior ventricular septum (VS), and tricuspid valve annulus (TV) in pediatric patients. We analyzed normal echocardiograms from 634 children aged 1 day to 18 years, heart rate (HR) range of 50 to 194/min, and body surface area (BSA) range of 0.1 to 2.8 m2. First we determined the effects of age, HR, and BSA on the S, E', and A' at the MV, VS, and TV sampling sites by univariate analysis. Next we determined which of the 3 factors, age versus HR versus BSA, correlated best with the S, E', and A' at each of the 3 sampling sites by multivariate analysis. Finally, using the specific factor of age versus HR versus BSA that best predicted a particular DTI wave at a particular sampling site, we constructed z-score tables for each of the 3 DTI parameters at each of the 3 sampling sites. The S range was: MV = 2.2 to 23.2 cm/s; VS = 1.6 to 22.3 cm/s; and TV = 1.8 to 31.3 cm/s. By univariate analysis the S correlated negatively with HR and positively with age and BSA with strong correlations at all 3 sites. By multiple regression analysis the S correlated best with age at all 3 sites. The E' range was: MV = 2.4 to 37.1 cm/s; VS = 1.8 to 29.0 cm/s; and TV = 2.4 to 32.4 cm/s. The E' varied negatively with HR and positively with age and BSA with strong correlations by univariate analysis at all 3 sites. By multiple regression, the E' correlated best with age for the VS and TV sites, and correlated best with HR at the MV site. The E' at the MV site also strongly correlated with age by multivariate analysis. The A' range was: MV = 2.9 to 20.7 cm/s; VS = 2.7 to 18.2 cm/s; and TV = 1.1 to 29.3 cm/s. The A' had a strong positive correlation with HR at all 3 sites, a strong negative correlation with BSA and age at the TV site only, with no statistical significant correlation of the MV and VS site A' to BSA or age. Using multiple regression analysis the A' correlated best with HR at all 3 sites. Z-score tables developed from a large sample volume encompassing the entire spectrum of ages, HR, and BSA encountered in pediatric patients and developed using the strongest predicting factor serve as reference data for longitudinal directed DTI annular and septal S, E', and A' normal values in children.

Systemic administration of micro-dystrophin restores cardiac geometry and prevents dobutamine-induced cardiac pump failure

Duchenne muscular dystrophy (DMD) is a fatal disease of striated muscle deterioration resulting from the loss of the cytoskeletal protein dystrophin. Most patients develop significant cardiomyopathy, with heart failure being the second leading cause of death in DMD. Compared with the extensive studies on skeletal muscle defects and potential therapy in DMD, very little attention has been directed at the increasing incidence of heart failure in DMD. Here we show that a single systemic injection of recombinant adeno-associated virus (rAAV2/6) harboring micro-dystrophin leads to extensive cardiac transduction, with micro-dystrophin correctly localized at the periphery of the cardiac myocytes and functionally associated with the sarcolemmal membrane. Significantly, micro-dystrophin gene transfer corrected the baseline end-diastolic volume defect in the mdx mouse heart and prevented cardiac pump failure induced by dobutamine stress testing in vivo, although several parameters of systolic function were not corrected. These results demonstrate that systemic gene delivery of micro-dystrophin can restore ventricular distensibility and protect the mdx myocardium from pump dysfunction during adrenergic stimulation in vivo.