Assessment of left ventricular regional function in affected and carrier dogs with Duchenne muscular dystrophy using speckle tracking echocardiography

Myocardial strain imaging in Duchenne muscular dystrophy

Cardiomyopathy (CM) is the leading cause of death for individuals with Duchenne muscular dystrophy (DMD). While DMD CM progresses rapidly and fatally for some in teenage years, others can live relatively symptom-free into their thirties or forties. Because CM progression is variable, there is a critical need for biomarkers to detect early onset and rapid progression. Despite recent advances in imaging and analysis, there are still no reliable methods to detect the onset or progression rate of DMD CM. Cardiac strain imaging is a promising technique that has proven valuable in DMD CM assessment, though much more work has been done in adult CM patients. In this review, we address the role of strain imaging in DMD, the mechanical and functional parameters used for clinical assessment, and discuss the gaps where emerging imaging techniques could help better characterize CM progression in DMD. Prominent among these emerging techniques are strain assessment from 3D imaging and development of deep learning algorithms for automated strain assessment. Improved techniques in tracking the progression of CM may help to bridge a crucial gap in optimizing clinical treatment for this devastating disease and pave the way for future research and innovation through the definition of robust imaging biomarkers and clinical trial endpoints.

Conventional and advanced echocardiographic assessment of systolic function in dogs sedated with dexmedetomidine or acepromazine

Dexmedetomidine and acepromazine, sedatives commonly used in dogs have opposite vascular effects, resulting in afterload increase and decrease, respectively. This could variably affect systolic myocardial function. Previous echocardiographic studies assessing the cardiovascular effects of these drugs used conventional echocardiography, while advanced techniques such as speckle tracking echocardiography (STE) and tissue Doppler imaging (TDI), which are known to provide a more accurate assessment of systolic function, have been rarely used for this aim. Moreover, in the few studies using advanced techniques, the drugs where combined with opioids. Therefore, the main objective of this prospective study was to assess systolic myocardial function by conventional and advanced echocardiography (STE and TDI), in dogs sedated exclusively with dexmedetomidine or acepromazine not combined with other drugs. Twenty healthy dogs were randomly divided into two groups, Group A (acepromazine, 20 μg/kg IM), and Group D (dexmedetomidine, 5 μg/kg IM), cardiovascular parameters were assessed before sedation (T0), and thirty minutes afterwards (T1). Systolic arterial pressure and heart rate decreased in both groups at T1 as compared to T0. Only one conventional echocardiographic raw variable (left ventricular internal dimension in systole) and three out of five advanced echocardiographic variables (radial TDI systolic velocities at the epicardial region of the left ventricular free wall, longitudinal TDI systolic velocities of the septal mitral valve annulus and the STE-derived left ventricular global strain), were affected in Group D. A systolic impairment was observed in Group D and better estimated by advanced echocardiography. In Group A, only the end diastolic voume index (conventional echocardiography) was decreased. Both protocols seem to induce echocardiographic changes more likely secondary to their vascular action.

Early Myocardial Dysfunction and Benefits of Cardiac Treatment in Young X-Linked Duchenne Muscular Dystrophy Mice

CONTEXT

Duchenne muscular dystrophy (DMD) is associated with a progressive alteration in cardiac function.

OBJECTIVE

The aim of this study was to detect early cardiac dysfunction using the high sensitive two-dimensional speckle-tracking echocardiography (2D strain) in mdx mouse model and to investigate the potential preventive effects of the S107 ryanodine receptor (RyR2) stabilizer on early onset of DMD-related cardiomyopathy.

METHODS AND RESULTS

Conventional echocardiography and global and segmental left ventricle (LV) 2D strains were assessed in male mdx mice and control C57/BL10 mice from 2 to 12 months of age. Up to 12 months of age, mdx mice showed preserved myocardial function as assessed by conventional echocardiography. However, global longitudinal, radial, and circumferential LV 2D strains significantly declined in mdx mice compared to controls from the 9 months of age. Segmental 2D strain analysis found a predominant alteration in posterior, inferior, and lateral LV segments, with a more marked impairment with aging. Then, mdx mice were treated with S107 in the drinking water at a dose of 250 mg/L using two different protocols: earlier therapy from 2 to 6 months of age and later therapy from 6 to 9 months of age. The treatment with S107 was efficient only when administered earlier in very young animals (from 2 to 6 months of age) and prevented the segmental alterations seen in non-treated mdx mice.

CONCLUSIONS

This is the first animal study to evaluate the therapeutic effect of a drug targeting early onset of DMD-related cardiomyopathy, using 2D strain echocardiography. Speckle-tracking analyses revealed early alterations of LV posterior segments that could be prevented by 4 months of RyR2 stabilization.

Development of outcome measures according to dystrophic phenotypes in canine X-linked muscular dystrophy in Japan

Duchenne muscular dystrophy (DMD) is an X-linked lethal muscle disorder characterized by primary muscle degeneration. Therapeutic strategies for DMD have been extensively explored, and some are in the stage of human clinical trials. Along with the development of new therapies, sensitive outcome measures are needed to monitor the effects of new treatments. Therefore, we investigated outcome measures such as biomarkers and motor function evaluation in a dystrophic model of beagle dogs, canine X-linked muscular dystrophy in Japan (CXMD_J). Osteopontin (OPN), a myogenic inflammatory cytokine, was explored as a potential biomarker in dystrophic dogs over the disease course. The serum OPN levels of CXMD_J dystrophic dogs were elevated, even in the early disease phase, and this could be related to the presence of regenerating muscle fibers; as such, OPN would be a promising biomarker for muscle regeneration. Next, accelerometry, which is an efficient method to quantify performance in validated tasks, was used to evaluate motor function longitudinally in dystrophic dogs. We measured three-axis acceleration and angular velocity with wireless hybrid sensors during gait evaluations. Multiple parameters of acceleration and angular velocity showed notedly lower values in dystrophic dogs compared with wild-type dogs, even at the onset of muscle weakness. These parameters accordingly decreased with exacerbation of clinical manifestations along with the disease course. Multiple parameters also indicated gait abnormalities in dystrophic dogs, such as a waddling gait. These outcome measures could be applicable in clinical trials of patients with DMD or other muscle disorders.

Widespread severe myodegeneration in a compound heterozygote female dog with dystrophin deficiency

The University of Missouri (MU) has established a colony of dystrophin‐deficient dogs with a mixed breed background to mirror the variable pathologic effects of dystrophinopathies between persons of a given kindred to further the understanding of the genetic and molecular basis of the variable phenotype; thus to facilitate discovery of an effective therapeutic strategy. Herein we report the phenotype and genotype of a normal‐appearing 10‐month‐old colony female that died suddenly. At necropsy examination, there were reduced skeletal and laryngeal muscle volume and mild dilatation of the oesophagus. Microscopic findings consisted of extensive degeneration and regeneration of the axial skeletal, tongue, oesophageal, and laryngeal muscles that were characterized by considerable central nucleation, individual fibre mineralization and interstitial fibrosis. The myocardial findings were limited to infiltration of adipose cells in the interstitium. The female dog was a compound heterozygote with one X chromosome carrying a point mutation in intron 6 of the dystrophin gene and the other X chromosome carrying a repetitive element insertion in intron 13 of the dystrophin gene. Although the direct cause of death was uncertain, it might likely be due to sudden cardiac death as has been seen in Duchenne muscular dystrophy patients. This case demonstrated dystrophinopathy in female dogs that have no ameliorating normal X chromosome.

Dental pulp stem cells can improve muscle dysfunction in animal models of Duchenne muscular dystrophy

Background

Duchenne muscular dystrophy (DMD) is an inherited progressive disorder that causes skeletal and cardiac muscle deterioration with chronic inflammation. Dental pulp stem cells (DPSCs) are attractive candidates for cell-based strategies for DMD because of their immunosuppressive properties. Therefore, we hypothesized that systemic treatment with DPSCs might show therapeutic benefits as an anti-inflammatory therapy.

Methods

To investigate the potential benefits of DPSC transplantation for DMD, we examined disease progression in a DMD animal model, mdx mice, by comparing them with different systemic treatment conditions. The DPSC-treated model, a canine X-linked muscular dystrophy model in Japan (CXMD_J), which has a severe phenotype similar to that of DMD patients, also underwent comprehensive analysis, including histopathological findings, muscle function, and locomotor activity.

Results

We demonstrated a therapeutic strategy for long-term functional recovery in DMD using repeated DPSC administration. DPSC-treated mdx mice and CXMD_J showed no serious adverse events. MRI findings and muscle histology suggested that DPSC treatment downregulated severe inflammation in DMD muscles and demonstrated a milder phenotype after DPSC treatment. DPSC-treated models showed increased recovery in grip-hand strength and improved tetanic force and home cage activity. Interestingly, maintenance of long-term running capability and stabilized cardiac function was also observed in 1-year-old DPSC-treated CXMD_J.

Conclusions

We developed a novel strategy for the safe and effective transplantation of DPSCs for DMD recovery, which included repeated systemic injection to regulate inflammation at a young age. This is the first report on the efficacy of a systemic DPSC treatment, from which we can propose that DPSCs may play an important role in delaying the DMD disease phenotype.

The Dog Model in the Spotlight: Legacy of a Trustful Cooperation

Dogs have long been used as a biomedical model system and in particular as a preclinical proof of concept for innovative therapies before translation to humans. A recent example of the utility of this animal model is the promising myotubularin gene delivery in boys affected by X-linked centronuclear myopathy after successful systemic, long-term efficient gene therapy in Labrador retrievers. Mostly, this is due to unique features that make dogs an optimal system. The continuous emergence of spontaneous inherited disorders enables the identification of reliable complementary molecular models for human neuromuscular disorders (NMDs). Dogs’ characteristics including size, lifespan and unprecedented medical care level allow a comprehensive longitudinal description of diseases. Moreover, the highly similar pathogenic mechanisms with human patients yield to translational robustness. Finally, interindividual phenotypic heterogeneity between dogs helps identifying modifiers and anticipates precision medicine issues.

This review article summarizes the present list of molecularly characterized dog models for NMDs and provides an exhaustive list of the clinical and paraclinical assays that have been developed. This toolbox offers scientists a sensitive and reliable system to thoroughly evaluate neuromuscular function, as well as efficiency and safety of innovative therapies targeting these NMDs. This review also contextualizes the model by highlighting its unique genetic value, shaped by the long-term coevolution of humans and domesticated dogs. Because the dog is one of the most protected research animal models, there is considerable opposition to include it in preclinical projects, posing a threat to the use of this model. We thus discuss ethical issues, emphasizing that unlike many other models, the dog also benefits from its contribution to comparative biomedical research with a drastic reduction in the prevalence of morbid alleles in the breeding stock and an improvement in medical care.

Variability among strain variables derived from two-dimensional speckle tracking echocardiography in dogs by use of various software

OBJECTIVE

To determine variability of global longitudinal strain (GLS) and strain rate (SR) measurements in dogs with and without cardiac disease derived from 2-D speckle tracking echocardiography (STE) by use of various software.

ANIMALS

2 cohorts comprising 44 dogs (23 cardiovascularly healthy and 21 with cardiac disease) and 40 dogs (18 cardiovascularly healthy and 22 with cardiac disease).

PROCEDURES

Transthoracic echocardiographic images in each cohort were analyzed with vendor-independent software and vendor-specific 2-D STE software for each of 2 vendors. Values for GLS and SR obtained from the same left parasternal apical views with various software were compared. Intraobserver and interobserver variability was determined, and agreement among results for the various software was assessed.

RESULTS

Strain analysis was not feasible with vendor-independent software for 20% of images obtained with the ultrasonography system of vendor 1. Intraobserver and interobserver coefficient of variation was < 10% for GLS values, whereas SR measurements had higher variance. There was a significant difference in GLS and SR obtained for each cohort with different software. Evaluation of Bland-Altman plots revealed wide limits of agreement, with variance for GLS of up to 6.3 units in a single dog.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of longitudinal strain analysis were not uniform among software, and GLS was the most reproducible measurement. Significant variability in results among software warrants caution when referring to reference ranges or comparing serial measurements in the same patient because changes of < 6.5% in GLS might be within measurement error for different postprocessing software.

Use of 2-dimensional speckle-tracking echocardiography to assess left ventricular systolic function in dogs with systemic inflammatory response syndrome

Background

Early identification of systolic dysfunction in dogs with systemic inflammatory response syndrome (SIRS) potentially could improve the outcome and decrease mortality.

Objective

To compare 2‐dimensional speckle tracking (2D‐STE) with 2‐dimensional (2D) and M‐mode echocardiography in the evaluation of systolic function in SIRS dogs.

Animals

Seventeen SIRS and 17 healthy dogs.

Methods

Prospective observational case‐control study. Each dog underwent physical examination, conventional echocardiography, 2D‐STE, and C‐reactive protein measurement.

Results

Dogs with SIRS had lower 2D‐STE ejection fraction (X4D‐EF; 44 ± 8 versus 53 ± 8; P = .003), endocardial global longitudinal strain (ENDO‐G‐Long‐St; −14.6 ± 3.2 versus −18.5 ± 4.1; P = .003), and normalized left ventricular diameter in diastole (1.38 ± 0.25 versus 1.54 ± 0.17; P = .04) and systole (0.85 ± 0.18 versus 0.97 ± 0.11; P = .03) as compared to healthy dogs. Simpson method of disks (SMOD) right parasternal EF (55 ± 9 versus 60 ± 6; P = .07) and end systolic volume index (ESVI; 23 ± 10 versus 21 ± 6; P = .61), SMOD left apical EF (59 ± 9 versus 59 ± 6; P = .87) and ESVI (20 ± 8 versus 22 ± 6; P = .25), fractional shortening (FS; 34 ± 5 versus 33 ± 4; P = .39), M‐mode EF (64 ± 7 versus 62 ± 5; P = .35), and ESVI (23 ± 11 versus 30 ± 9; P = .06) were not significantly different between SIRS and control group, respectively.

Conclusion and Clinical Importance

Speckle tracking X4D‐EF and ENDO‐G‐Long‐St are more sensitive than 2D and M‐Mode FS, EF, and ESVI in detecting systolic impairment in dogs with SIRS.

Speckle-Tracking Echocardiography in Children With Duchenne Muscular Dystrophy: A Prospective Multicenter Controlled Cross-Sectional Study

BACKGROUND

Prognosis of Duchenne muscular dystrophy (DMD) is related to cardiac dysfunction. Speckle-tracking echocardiographic (STE) imaging is emerging as a noninvasive functional biomarker to consider in the early detection of DMD-related cardiomyopathy. However, STE analysis has not been assessed in a prospectively controlled study, especially in presymptomatic children with DMD, and no study has used STE analysis in all three displacements (longitudinal, radial, and circumferential) and for both ventricles.

METHODS

This prospective controlled study enrolled 108 boys, 36 of whom had DMD (mean age, 11 ± 3.8 years) and 72 of whom were age-matched control subjects in a 1:2 case-control design. Conventional echocardiographic variables were collected for the left and right ventricles. STE analyses were performed in the longitudinal, radial, and circumferential displacements for the left ventricle and in the free wall longitudinal displacement for the right ventricle. The effect of age on the evolution of two-dimensional strain in children with DMD was studied by adding an interaction term, DMD × age, in the models.

RESULTS

Conventional echocardiographic measures were normal in both groups. Left ventricular (LV) ejection fraction ranged from 45% to 76% (mean, 63 ± 6%) in the DMD group and from 55% to 76% (mean, 64 ± 5%) in the control group. Global LV strain mean measures were significantly worse in the DMD group for the longitudinal (-16.8 ± 3.9% vs -20.6 ± 2.6%, P < .0001), radial (22.7 ± 11.3% vs 31.7 ± 14%, P = .002), and circumferential (-16.5 ± 3.8% vs -20.3 ± 3.1%, P < .0001) displacements. The decrease of global LV longitudinal strain with age in children with DMD was 0.34% per year more marked than that in control subjects. The LV inferolateral and anterolateral segments were specifically impaired, especially in the basal area. Right ventricular function evaluated using conventional echocardiography and STE analysis was normal and not different between children with DMD and control subjects.

CONCLUSIONS

The existence of altered LV strain despite normal LV function in children with DMD represents an important perspective for future pediatric drug trials in DMD-related cardiomyopathy prevention.

Evaluation of the right parasternal four-chamber view for the assessment of left ventricular longitudinal strain and strain rate by two-dimensional speckle tracking echocardiography in dogs

Two-dimensional (2-D) speckle tracking echocardiography (STE) is a relatively new imaging technique, introduced in veterinary medicine to aid the assessment of left ventricular (LV) myocardial function. Among other indices, LV longitudinal strain and strain rate (SR) can be measured with this modality, and in dogs they are usually obtained from the left apical four-chamber (LAp4Ch) view. However, in this species, a good quality right parasternal four-chamber (RP4Ch) view can generally be attained, and the aim of this study was therefore to determine its feasibility and reliability for longitudinal strain and SR assessment, and to establish whether the two projections can be used interchangeably. Fifty-one healthy dogs and twenty-five dogs with various cardiac diseases were examined. Longitudinal global and segmental strains and global SR of the LV were obtained with 2-D STE by use of RP4Ch and LAp4Ch views. Intra-observer (within-day and between-day) and inter-observer variabilities were established, and strain and SR values obtained from the two views were compared. The RP4Ch view demonstrated to be feasible for the assessment of longitudinal strain and SR by use of 2-D STE in healthy and diseased dogs. However, out of sector motion of the apical segments could occur and induce tracking errors. The deformation parameters obtained from this view and the LAp4Ch view were often significantly different, and therefore they should not be used interchangeably. Further, the software employed in the present study performed better global than segmental strain analysis for both views.

Comparison of left ventricular function assessment between echocardiography and MRI in Duchenne muscular dystrophy

BACKGROUND

Cardiomyopathy in Duchenne muscular dystrophy (DMD) is associated with death in approximately 40% of patients. Echocardiography is routinely used to assess left ventricular (LV) function; however, it has limitations in these patients.

OBJECTIVE

We compared echocardiographic measures of cardiac function assessment to cardiac MRI.

MATERIALS AND METHODS

We included children and young adults with DMD who had MRI performed between January 2010 and July 2015. We measured echocardiographic and MRI parameters of function assessment, including strain. Presence of late gadolinium enhancement (LGE) was assessed by MRI. Subjects were divided into two groups based on MRI left ventricular ejection fraction (LVEF): group I, LVEF ≥55% and group II, LVEF <55%.

RESULTS

We included 41 studies in 33 subjects, with 25 in group I and 16 in group II. Mean age of subjects was 13.6 ± 2.8 years and mean duration between echocardiogram and MRI was 7.6 ± 4.1 months. Only 8 of 16 (50%) patients in group II had diminished function on echocardiogram. Echocardiographic images were suboptimal in 16 subjects (39%). Overall, echocardiographic parameters had weak correlation with MRI-derived ejection fraction percentage. MRI-derived myocardial strain assessment has better correlation with MRI ejection fraction as compared to echocardiography-derived strain parameters.

CONCLUSION

Echocardiography-based ventricular functional assessment has weak correlation with MRI parameters in children and young adults with Duchenne muscular dystrophy. While this correlation improves in the subset of subjects with adequate echocardiographic image quality, it remains modest and potentially suboptimal for clinical management. Accordingly, we conclude that MRI should be performed routinely and early in children with DMD, not only for LGE imaging but also for functional assessment.

Intra-amniotic rAAV-mediated microdystrophin gene transfer improves canine X-linked muscular dystrophy and may induce immune tolerance

Duchenne muscular dystrophy (DMD) is a severe congenital disease due to mutations in the dystrophin gene. Supplementation of dystrophin using recombinant adenoassociated virus vector has promise as a treatment of DMD, although therapeutic benefit of the truncated dystrophin still remains to be elucidated. Besides, host immune responses against the vector as well as transgene products have been denoted in the clinical gene therapy studies. Here, we transduced dystrophic dogs fetuses to investigate the therapeutic effects of an AAV vector expressing microdystrophin under conditions of immune tolerance. rAAV-CMV-microdystrophin and a rAAV-CAG-luciferase were injected into the amniotic fluid surrounding fetuses. We also reinjected rAAV9-CMV-microdystrophin into the jugular vein of an infant dystrophic dog to induce systemic expression of microdystrophin. Gait and cardiac function significantly improved in the rAAV-microdystrophin-injected dystrophic dog, suggesting that an adequate treatment of rAAV-microdystrophin with immune modulation induces successful long-term transgene expression to analyze improved dystrophic phenotype.

Feasibility of radial and circumferential strain analysis using 2D speckle tracking echocardiography in cats

The purpose of the present study is to investigate the feasibility of strain analysis using speckle tracking echocardiography (STE) in cats and to evaluate STE variables in cats with hypertrophic cardiomyopathy (HCM). Sixteen clinically healthy cats and 17 cats with HCM were used. Radial and circumferential strain and strain rate variables in healthy cats were measured using STE to assess the feasibility. Comparisons of global strain and strain variables between healthy cats and cats with HCM were performed. Segmental assessments of left ventricle (LV) wall for strain and strain rate variables in cats with HCM were also performed. As a result, technically adequate images were obtained in 97.6% of the segments for STE analysis. Sedation using buprenorphine and acepromazine did not affect any global strain nor strain rate variable. In LV segments of cats with HCM, reduced segmental radial strain and strain rate variables had significantly related with segmental LV hypertrophy. It is concluded that STE analysis using short axis images of LV appeared to be clinically feasible in cats, having the possibility to be useful for detecting myocardial dysfunctions in cats with diseased heart.

Inflammation and cardiac dysfunction during sepsis, muscular dystrophy, and myocarditis

Inflammation plays an important role in cardiac dysfunction under different situations. Acute systemic inflammation occurring in patients with severe burns, trauma, and inflammatory diseases causes cardiac dysfunction, which is one of the leading causes of mortality in these patients. Acute sepsis decreases cardiac contractility and impairs myocardial compliance. Chronic inflammation such as that occurring in Duchenne muscular dystropshy and myocarditis may cause adverse cardiac remodeling including myocyte hypertrophy and death, fibrosis, and altered myocyte function. However, the underlying cellular and molecular mechanisms for inflammatory cardiomyopathy are still controversial probably due to multiple factors involved. Potential mechanisms include the change in circulating blood volume; a direct inhibition of myocyte contractility by cytokines (tumor necrosis factor (TNF)-α, interleukin (IL)-1β); abnormal nitric oxide and reactive oxygen species (ROS) signaling; mitochondrial dysfunction; abnormal excitation-contraction coupling; and reduced calcium sensitivity at the myofibrillar level and blunted β-adrenergic signaling. This review will summarize recent advances in diagnostic technology, mechanisms, and potential therapeutic strategies for inflammation-induced cardiac dysfunction.

Left ventricular strain distribution in healthy dogs and in dogs with tachycardia-induced dilated cardiomyopathy

Background

Recently, left ventricular (LV) strain distribution pattern has been assessed in several cardiac disease states. Tachycardia-induced cardiomyopathy (TIC) is an animal model of non-ischemic cardiomyopathy well characterized in terms of global LV dysfunction but with poor understanding of regional variability in LV function. We hypothesized that TIC induces specific changes in LV strain distribution pattern.

Methods

Twenty five adult mongrel conscious dogs were trained to lie down calmly for echocardiography. In seven selected dogs, we implanted pacing system for TIC induction under general anesthesia. We measured LV geometry and function, strains, and torsion before and after the development of TIC in awake non-sedated state.

Results

In 25 healthy dogs, all three types of normal strain significantly increased from base to apex (p <0.05), while a definite and recognizable twist could be measured due to presence of shear strain. In 7 dogs with TIC, marked changes in LV mechanics occurred throughout the cardiac cycle, resulting in decrease of strain (p <0.001), twist (p <0.05), and negative peak twist rate (p <0.05). Interestingly, the relative decrease of strain due to TIC was more pronounced in the apex (p < 0.001), with the radial strain decreasing the most (p < 0.05).

Conclusion

TIC is accompanied by decreased systolic LV strain and twist deformation, as well as loss of early diastolic recoil. In addition, the decrease of strain was more profound in the apex. This “reverse” distribution of LV strain may help us understand LV dysfunction in the presence of nonischemic etiology.

Cardiac structure and function in female carriers of a canine model of Duchenne muscular dystrophy

This investigation tested the hypothesis that carriers of golden retriever muscular dystrophy (GRMD), a genetically homologous condition of Duchenne muscular dystrophy (DMD), have quantifiable abnormalities in myocardial function, structure, or cardiac rhythm. Eleven GRMD carriers and four matched controls had cardiac evaluations and postmortem examinations. 24-h ECG Holter monitoring disclosed ventricular ectopy in 10 of 11 carriers and 2 of 4 controls. Conventional echocardiography failed to demonstrate significant differences between carriers and controls in systolic function. All carriers had multifocal, minimal to marked myofiber necrosis, fibrosis, mineralization, inflammation, and/or fatty change in their hearts. Immunohistochemistry revealed a mosaic dystrophin deficiency in scattered cardiac myofibers in all carriers. No controls had cardiac histologic lesions; all had uniform dystrophin staining. Despite cardiac mosaic dystrophin expression and degenerative cardiac lesions, GRMD carriers at up to 3 years of age could not be distinguished statistically from normal controls by echocardiography or 24-h Holter monitoring.

Left ventricular function quantified by myocardial strain imaging in small-breed dogs with chronic mitral regurgitation

BACKGROUND

The presence of left ventricular (LV) systolic dysfunction may influence prognosis or therapy in dogs with chronic mitral regurgitation (MR). Assessment of LV function in MR by conventional echocardiography is confounded by altered ventricular loading. Myocardial deformation (strain) imaging might offer more sensitive estimates of LV function in this disease.

OBJECTIVE

Prospectively measure myocardial strain in dogs with asymptomatic MR compared to a control group.

ANIMALS, MATERIALS AND METHODS

Forty healthy dogs (3.5-11.5 kg): 20 Controls; 20 dogs with MR and LV remodeling (Stage B2), were evaluated in this study. LV size and function were assessed in a short-axis plane. Segmental radial strain and strain rate and global circumferential strain were measured using a 2D echocardiographic speckle-tracking algorithm (GE EchoPAC). Groups were compared using Bonferroni t-tests. Influences of heart rate and body weight were explored with linear regression.

RESULTS

The MR group had significantly greater mean values for heart rate, LV size, and LV systolic function. Specifically, LV diastolic diameter, diastole area, shortening fraction, averaged peak systolic and early diastolic radial strain, global circumferential strain, and averaged radial strain rate were significantly greater in the MR group (p < 0.015 to p < 0.001). Strain was unrelated to weight, but weakly correlated with heart rate.

CONCLUSIONS

Similar to conventional indices, Stage B2 dogs with MR demonstrate hyperdynamic deformation in the short-axis plane. Short-axis strain variables measured by 2D speckle tracking are greater than for controls of similar age and weight. These results imply either preserved LV systolic function or that LV dysfunction is masked by altered ventricular loading.

Speckle tracking analysis of the left ventricular anterior wall shows significantly decreased relative radial strain patterns in dystrophin deficient mice after 9 months of age

Background: Duchenne muscular dystrophy (DMD) is an inherited X-linked disorder with an incidence of 1 in 3,500 male births. Early treatment of DMD cardiomyopathy is under investigation and echocardiographic analysis of strain patterns may provide measures to better quantify early treatment outcomes.

Methods: We compared cardiac function in 3, 9 and 12 month old dystrophin deficient mdx mice to wild type (C57BL10/J) using in vivo high frequency echocardiography (Vevo 770, VisualSonics, Inc., Toronto, CA) and 2D speckle tracking [Velocity Vector Imaging (VVI), Siemens Medical Solutions, Inc., Malvern, PA]. Mice were anesthetized with 1-2% inhaled isoflurane and images were obtained using a 30 MHz transducer in modified parasternal long and short axis views obtained at the level of the papillary muscles. Myocardial motion was analyzed using VVI in single-beat reconstructed images.

Results: M-mode imaging showed significantly decreased shortening fraction in mdx mice compared to wild type at 12 months of age (SF% 26.6±3 vs. 32.2±2; p=0.002). Mdx mice showed significantly increased cardiac fibrosis at 12 months of age compared to controls (p<0.0001). Speckle tracking analysis of the left anterior mid ventricular wall segment showed significantly decreased relative radial strain in mdx mice at 9 and 12 months (4.5±1.3% vs. 8.4±0.7%; p=0.001). There were no significant differences in circumferential or longitudinal strain.

Conclusion: Mdx mice show significantly decreased LV anterior mid wall radial strain with mild cardiomyopathy after 9 months of age compared to wild type. Speckle tracking analysis may provide novel outcome measures for preclinical cardiac drug treatment studies in DMD.