Left ventricular diastolic function in congenital myotonic dystrophy

Mice lacking MBNL1 and MBNL2 exhibit sudden cardiac death and molecular signatures recapitulating myotonic dystrophy

Myotonic dystrophy (DM) is caused by expansions of C(C)TG repeats in the non-coding regions of the DMPK and CNBP genes, and DM patients often suffer from sudden cardiac death due to lethal conduction block or arrhythmia. Specific molecular changes that underlie DM cardiac pathology have been linked to repeat-associated depletion of Muscleblind-like (MBNL) 1 and 2 proteins and upregulation of CUGBP, Elav-like family member 1 (CELF1). Hypothesis solely targeting MBNL1 or CELF1 pathways that could address all the consequences of repeat expansion in heart remained inconclusive, particularly when the direct cause of mortality and results of transcriptome analyses remained undetermined in Mbnl compound knockout (KO) mice with cardiac phenotypes. Here, we develop Myh6-Cre double KO (DKO) (Mbnl1^−/−; Mbnl2^cond/cond; Myh6-Cre^+/−) mice to eliminate Mbnl1/2 in cardiomyocytes and observe spontaneous lethal cardiac events under no anesthesia. RNA sequencing recapitulates DM heart spliceopathy and shows gene expression changes that were previously undescribed in DM heart studies. Notably, immunoblotting reveals a nearly 6-fold increase of Calsequestrin 1 and 50% reduction of epidermal growth factor proteins. Our findings demonstrate that complete ablation of MBNL1/2 in cardiomyocytes is essential for generating sudden death due to lethal cardiac rhythms and reveal potential mechanisms for DM heart pathogenesis.

Diastolic heart dysfunction is correlated with CTG repeat length in myotonic dystrophy type 1

The aims of this study were to investigate the correlations of tri-nucleotide (CTG) repeat length with detailed echocardiography (ECHO) parameters that represent myocardial function and to find a relationship between heart function and CTG repeat length in adult-onset myotonic dystrophy type 1 (DM1). In this study, clinical data for patients with DM1, including age, onset age, CTG repeat length, Medical Research Council sum score (MRCSS), and 6-min walking test (6MWT), were recorded. In addition, ECHO parameters and cardiac conduction abnormalities were evaluated. Among the cardiac parameters, the EA ratio and left ventricular end-diastolic dimension (LVEDD) were significantly correlated with the CTG repeat length (p < 0.05). Interventricular septal thickness at end-diastole was also significantly correlated with the 6MWT in a multivariate linear regression model (p < 0.05). In conclusion, motor function (MRCSS and 6MWT) and CTG repeat length significantly correlated with LV diastolic dysfunction in patients with DM1. More emphasis should be given to diastolic dysfunction, which is currently under-recognized, when evaluating patients with DM1 with no abnormalities in routine electrocardiography studies. Lastly, well-designed and longitudinal studies are warranted to characterize and understand the pathophysiology of diastolic dysfunction in DM1.

Heart Disease in Disorders of Muscle, Neuromuscular Transmission, and the Nerves

Little is known regarding cardiac involvement (CI) by neuromuscular disorders (NMDs). The purpose of this review is to summarise and discuss the major findings concerning the types, frequency, and severity of cardiac disorders in NMDs as well as their diagnosis, treatment, and overall outcome. CI in NMDs is characterized by pathologic involvement of the myocardium or cardiac conduction system. Less commonly, additional critical anatomic structures, such as the valves, coronary arteries, endocardium, pericardium, and even the aortic root may be involved. Involvement of the myocardium manifests most frequently as hypertrophic or dilated cardiomyopathy and less frequently as restrictive cardiomyopathy, non-compaction, arrhythmogenic right-ventricular dysplasia, or Takotsubo-syndrome. Cardiac conduction defects and supraventricular and ventricular arrhythmias are common cardiac manifestations of NMDs. Arrhythmias may evolve into life-threatening ventricular tachycardias, asystole, or even sudden cardiac death. CI is common and carries great prognostic significance on the outcome of dystrophinopathies, laminopathies, desminopathies, nemaline myopathy, myotonias, metabolic myopathies, Danon disease, and Barth-syndrome. The diagnosis and treatment of CI in NMDs follows established guidelines for the management of cardiac disease, but cardiotoxic medications should be avoided. CI in NMDs is relatively common and requires complete work-up following the establishment of a neurological diagnosis. Appropriate cardiac treatment significantly improves the overall long-term outcome of NMDs.

Diastolic Function in Steinert's Disease

Myotonic dystrophy type 1 (MD) is the most common autosomal dominant muscular dystrophy in adults. Cardiac involvement is mainly characterized by conduction abnormalities and arrhythmias. We sought to assess diastolic function in MD patients. Echocardiography-Doppler was performed in Steinert's patients and in a control group completed by tissue Doppler imaging (TDI). Twenty-six patients with Steinert's disease were included in the study and were compared to a control group. Mean age was similar in the 2 groups (45.1 years ±10.9 in Steinert's patients vs 42.1 years ±11 in control group p 0.4). 6 /26 patients with Steinert's disease disclosed a left ventricular (LV) ejection fraction <50%. Mean left atrial (LA) diameter was statistically different between Steinert's patients and patients in group control (27.8 mm ±8.5 vs 19.7 mm ±4; P=0.0018). Mean peak E/A mitral ratio was 1.29±0.45 in Steinert's patients vs 1.36±0.4 in control group (P=0.6). We found an increase of the mitral E deceleration time in Steinert's patients in comparison with patients in control group (219 ms ±53 vs 176 ms ±29; P=0.013). Mean peak lateral early diastolic velocity Ea was similar in the 2 groups (12.3 cm/s ±3 vs 13.1 cm/s ±3.8; P=0.50). Mean peak septal early diastolic velocity was similar in the 2 groups (11.2 cm/s ±2 vs 10.4±2; P=0.51). We found an increase of the LA diameter and an increase of the mitral deceleration time in Steinert's patients that suggest diastolic abnormalities.

[Heart and Steinert's disease]

Myotonic dystrophy type 1 (Steinert disease) is an autosomal dominant disease characterized by myotonia and multiorgan damage. This latter is the most frequent of the adult-onset muscular dystrophies. Heart involvement is often associated, including cardiomyopathies, atrioventricular block, atrial and ventricular arrhythmias.

Evaluation of biventricular functions with tissue Doppler imaging in patients with myotonic dystrophy

BACKGROUND

Myotonic dystrophy (MD) is characterized by myotonia with dystrophic involvement of the muscles. Cardiac involvement is usually not evident in the early stages of MD.

HYPOTHESIS

We investigated biventricular functions by tissue Doppler imaging (TDI) in MD patients with no overt cardiac involvement to explore the value of TDI in the early detection of myocardial dysfunction.

METHODS

A total of 21 MD patients (15 male, age: 32.2 +/- 12.3 yrs) and 21 healthy controls (13 male, age: 32.2 +/- 7.8 yrs) were included. In addition to conventional echocardiography, pulsed Doppler and TDI were performed including measurement of myocardial performance index (MPI); peak systolic (Sm) and early (Em) and atrial (Am) diastolic myocardial velocities at the basal mitral and tricuspid annulus.

RESULTS

All patients and controls had normal ejection fraction. Transmitral E peak velocity was significantly lower while both deceleration time of E velocity and isovolumic relaxation time were significantly longer in MD patients (P = 0.007, P = 0.001, and P < 0.001, respectively). Sm, Em and Am peak velocities were significantly lower in MD patients in all segments except for Em of the mitral anterior annulus and Am of the tricuspid lateral annulus. Both left and right ventricular MPI were significantly higher in MD patients (P < 0.001 and P = 0.013, respectively).

CONCLUSION

There are changes in myocardial systolic and diastolic functions in MD patients although they have no overt heart failure. Myocardial tissue velocities and MPI are useful in identifying subclinical biventricular involvement in these patients.

Myotonic dystrophy type I in childhood Long-term evolution in patients surviving the neonatal period

In a retrospective study, 32 patients with myotonic dystrophy, including congenital (n=17) and infantile/juvenile forms (n=15) were studied during a long follow-up lasting 7-28 years (median: 17 years). The clinical presentation was extremely variable; however, a continuum did exist between severe and less severe congenital forms, and later-onset forms, without genotype-phenotype correlation. We observed some unusual presentations, such as 3 cases of isolated club-feet during the neonatal period, and 7 patients (23%) with a completely isolated mental deficiency, language delay and school failure, who only completed the clinical picture several years later. Wechsler scale testing was performed in all cases, and repeated with 8 patients. It demonstrated a decrease in intellectual abilities in 5 patients, suggesting the possibility of a degenerative cerebral process occurring in these children. This decrease has also been reported in some adult cases. This study illustrates the extremely heterogeneous clinical presentation of myotonic dystrophy in childhood.

Early detection of biventricular involvement in myotonic dystrophy by tissue Doppler

BACKGROUND

Myotonic dystrophy is associated with arrhythmias and risk of sudden death but also with symptoms of heart failure. Our study aimed to identify early biventricular dysfunction in asymptomatic patients with myotonic dystrophy by tissue Doppler.

METHODS

Thirty-six patients with myotonic dystrophy (M/F=20/16, mean age=36.4 years), asymptomatic for heart failure, and 36 age- and sex-matched healthy controls underwent Doppler echocardiography and pulsed tissue Doppler of lateral mitral annulus and of tricuspid annulus.

RESULTS

The two groups had similar body mass index, blood pressure, heart rate, cardiac mass and endocardial shortening. Standard Doppler showed significantly lower transmitral early (E) diastolic peak velocity, longer transmitral deceleration and isovolumic relaxation times and higher tricuspid inflow atrial peak velocity in myotonic dystrophy than in controls. Tissue Doppler of mitral annulus showed lower myocardial systolic velocity (p<0.02), lower early diastolic velocity (E(m)) (p<0.05) and atrial velocity (A(m)) (p<0.005), but no difference of E(m)/A(m) ratio. At tricuspid annulus, E(m) and E(m)/A(m) ratio were lower (p<0.02 and p<0.005, respectively). The ratio between tricuspid inflow E velocity and E(m), index of the degree of right ventricular filling pressure, was higher (p<0.001) than in controls. Tissue Doppler derived left ventricular and right ventricular measurements were all associated with the disease condition, independent of age and heart rate.

CONCLUSIONS

Tissue Doppler identifies subclinical biventricular involvement in myotonic dystrophy. Early left ventricular myocardial systolic and diastolic changes are evident. Right ventricular dysfunction, involving myocardial relaxation and right ventricular filling pressure, might be the arrhythmogenic substratum of these patients.

Subclinical cardiac involvement in myotonic dystrophy manifesting as decreased myocardial Doppler velocities

To assess subendocardial (long-axis) and mid-wall (short-axis) left ventricular (LV) function in patients with type 1 myotonic dystrophy (MD1), with no symptoms or clinical signs of heart disease, to investigate if they have subclinical cardiac involvement, 28 subjects (14 with MD1, and 14 age- and sex-matched normals) had conventional and tissue Doppler echocardiography. Myocardial velocities and timings to peak systolic contractions were measured. LV wall thickness, diameters, and ejection fraction were not different between the groups. 4/14 of the MD1 patients (29%) had global diastolic dysfunction. Both long-axis and short-axis systolic and early diastolic myocardial velocities were lower in patients with MD1, whereas time-to-peak myocardial contraction was longer; mean longitudinal systolic velocity was 5.5+/-1.7 cm/s in patients with MD1, compared with 7.8+/-1.3 cm/s in normal subjects (P<0.001) 10/14 of the patients (71%) had reduced longitudinal systolic function. Longitudinal systolic and diastolic velocities were inversely related to the duration of the QRS complex ( r=-0.86 and r=-0.63 respectively, both P<0.01), but they did not correlate with the CTG-repeat size. Patients with MD1 have subclinical cardiac impairment revealed by measurement of myocardial velocities using tissue Doppler echocardiography.

Myotonic dystrophy and paediatric anaesthesia

Myotonic dystrophy is a neuromuscular condition inherited in an autosomal dominant fashion, and is most commonly diagnosed in the neonatal period. With improving levels of care, these patients are now presenting more commonly for anaesthesia. We review the clinical features of the condition, and then discuss the steps in the anaesthetic process, outlining the anaesthetic implications of myotonic dystrophy at each stage.

Characterization of cardiac conduction system abnormalities in mice with targeted disruption of Six5 gene

Myotonic dystrophy (DM) is an autosomal dominant multisystem disorder, caused by expansion of a CTG trinucleotide repeat in the 3' untranslated region of the myotonic dystrophy protein kinase gene (DMPK) on chromosome 19q13. Cardiac involvement in DM includes conduction abnormalities and functional deficits. Three hypotheses of molecular mechanisms for DM pathophysiology are; first, partial loss of myotonic dystrophy protein kinase (DMPK); second, decreased transcription of a neighboring homeodomain-encoding gene, Six5 (or DMAHP), and third, transdominant effects of the RNA and regulation of splicing associated with expression of expanded CUG repeats. However, the precise pathogenetic mechanism remains unresolved. We previously reported that dosage of Dm15, the mouse homologue of DMPK, strongly associates with the cardiac conduction abnormalities. For further distinction of the molecular mechanisms underlying the cardiac phenotype of DM, in the present study, we characterized the cardiac conduction findings of mice with targeted disruption of Six5 gene. Six5 heterozygous mice (adult and young) and their age matched wild type littermates were studied using in vivo electrophysiologic techniques, echocardiography, heart rate variability and exercise tolerance testing. No PR prolongation was detected, however, prolonged QRS duration and delayed infraHisian conduction were significant in adult Six5 heterozygous mice. By echocardiography, left ventricular (LV) end-diastolic dimension was enlarged in adult Six5 heterozygous mice, although neither fractioning shortening nor LV wall thickness showed significant differences. Six5 loss may partly contribute to conduction abnormalities in myotonic dystrophy, particularly infraHisian conduction delay, one of the initial phenotypes of adult-onset cardiac conduction abnormalities in DM patients.