Arrhythmia-related workup in hereditary myopathies

Subclinical cardiac involvement present as electrocardiographic abnormalities in various neuromuscular diseases

Background

Cardiac involvement is commonly present in various neuromuscular diseases which may develop life-threatening consequences. The early manifestation is often asymptomatic which however has been insufficiently studied.

Objectives

We aim to characterize electrocardiographic (ECG) changes in neuromuscular diseases without cardiac symptoms.

Methods

Adults having genetically and/or pathologically confirmed type 1 myotonic dystrophy (DM1), Becker muscular dystrophy (BMD), limb girdle muscular dystrophies (LGMDs) and mitochondrial diseases (MtDs) but without history of heart diseases and cardiovascular symptoms were enrolled. The 12-lead ECG characteristics and other test results at diagnosis were retrieved and analyzed.

Results

196 patients with neuromuscular diseases (44 DM1, 25 BMD, 82 LGMDs, 45 MtDs) were consecutively enrolled. ECG abnormalities were identified in 107 (54.6%) patients with a prevalence of 59.1% in DM1, 76.0% in BMD, 40.2% in LGMDs and 64.4% in MtDs. Conduction block was more commonly present in DM1 than the other groups (P < 0.01), which had a longest PR interval and QRS duration of 186.1 ± 38.3 ms and 104.2 [90.0-108.0]ms, respectively. QT prolongation was most frequently seen in DM1 (P < 0.001). Left ventricular hypertrophy features were found in BMD, LGMDs and MtDs (P < 0.05) without intergroup difference, while a significantly higher right ventricular amplitude is observed in BMD than in other groups (P < 0.001).

Conclusions

Subclinical cardiac involvement is commonly present as ECG abnormalities in multiple adult neuromuscular diseases before associated symptoms occur and show diversity in different groups.

Proarrhythmic Manifestations of Neuromuscular Dystrophinopathies

Muscular dystrophy has been an elusive term ever since it was first described in the 19th century. Introduced in 1891 by Wilhelm Heinrich Erb, muscular dystrophy has been classified as part of a larger group of genetically determined, progressive degenerative neuromuscular disorders termed "dystrophinopathies." Cardiac arrhythmias may occur during the neurologic course of the disease. Although descriptions of the dystrophinopathies have been reported in the literature, few articles address the use of antiarrhythmic pharmacotherapy in patients with muscular dystrophy. We discuss the pathophysiology of the most common dystrophinopathies, their proarrhythmic sequelae, and the therapeutic use of antiarrhythmic agents in the clinical setting.

Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a rare muscular dystrophy, but is particularly important to diagnose due to frequent life-threatening cardiac complications. EDMD classically presents with muscle weakness, early contractures, cardiac conduction abnormalities and cardiomyopathy, although the presence and severity of these manifestations vary by subtype and individual. Associated genes include EMD, LMNA, SYNE1, SYNE2, FHL1, TMEM43, SUN1, SUN2, and TTN, encoding emerin, lamin A/C, nesprin-1, nesprin-2, FHL1, LUMA, SUN1, SUN2, and titin, respectively. The Online Mendelian Inheritance in Man database recognizes subtypes 1 through 7, which captures most but not all of the associated genes. Genetic diagnosis is essential whenever available, but traditional diagnostic tools can help steer the evaluation toward EDMD and assist with interpretation of equivocal genetic test results. Management is primarily supportive, but it is important to monitor patients closely, especially for potential cardiac complications. There is a high potential for progress in the treatment of EDMD in the coming years.

Severe congenital RYR1-associated myopathy complicated with atrial tachycardia and sinus node dysfunction: a case report

Background

Cardiac arrhythmias are sometimes encountered in patients with hereditary myopathies and muscular dystrophies. Description of arrhythmias in myopathies and muscular dystrophies is very important, because arrhythmias have a strong impact on the outcomes for these patients and are potentially treatable.

Case presentation

A girl with severe congenital RYR1-related myopathy exhibited atrial tachycardia and sinus node dysfunction during infancy. She was born after uncomplicated caesarian delivery. She showed no breathing, complete ophthalmoplegia, complete bulbar paralysis, complete facial muscle paralysis, and extreme floppiness. At 5 months old, she developed persistent tachycardia around 200–210 beats per minutes. Holter monitoring revealed ectopic atrial tachycardia during tachyarrhythmia and occasional sinus pauses with junctional escape beats. Propranolol effectively alleviated tachyarrhythmia but was discontinued due to increased frequency and duration of the sinus pauses that led to bradyarrhythmia. There was no evidence of structural heart diseases or heart failure. The arrhythmia gradually resolved spontaneously and at 11 months old, she showed complete sinus rhythm.

Conclusions

Although supraventricular arrhythmia is sometimes encountered in congenital myopathies, this is the first report of cardiac arrhythmia requiring drug intervention in RYR1-associated myopathy.

Myocardial fibrosis by late gadolinium enhancement cardiovascular magnetic resonance in myotonic muscular dystrophy type 1: highly prevalent but not associated with surface conduction abnormality

BACKGROUND

Conduction disease and arrhythmias represent a major cause of mortality in myotonic muscular dystrophy type 1 (MMD1). Permanent pacemaker (PPM) implantation is the cornerstone of therapy to reduce cardiovascular mortality in MMD1. Cardiovascular magnetic resonance (CMR) studies demonstrate a high prevalence of myocardial fibrosis in MMD1, however the association between CMR myocardial fibrosis with late gadolinium enhancement (CMR-LGE) and surface conduction abnormality is not well established in MMD1. We investigated whether myocardial fibrosis by CMR-LGE is associated with surface conduction abnormalities meeting criteria for PPM implantation according to current guidelines in a cohort of patients with genetically confirmed MMD1.

METHODS

Patients with genetically confirmed MMD1 were retrospectively evaluated. 12-lead electrocardiography (ECG) performed within 6 months of CMR was necessary for inclusion. The severity and extent of MMD1 was quantified using a validated Muscular Impairment Rating Scale (MIRS). Based on current guidelines for device-based therapy of cardiac rhythm abnormalities, we defined surface conduction abnormality as the presence of ECG alterations meeting criteria for PPM implant (class I or II indications): PR interval > 200 ms (type I atrioventricular (AV) block) and/or mono or bifascicular block (QRS > 120 ms), or evidence of advanced AV block. Balanced steady-state free precession sequences (bSSFP) were used for assessment of left ventricular (LV) volumes and ejection fraction. MOdified Look-Locker Inversion Recovery (MOLLI) acquisition schemes were used to acquire T1 maps. Patients' charts were reviewed up to 12 months post-CMR for occurrence of PPM implantation.

RESULTS

Fifty-two patients (38% male, 41 ± 14 years) were included. Overall, 31 (60%) patients had a surface conduction abnormality and 22 (42%) demonstrated midwall myocardial fibrosis by CMR-LGE. After a median of 57 days from CMR exam, 15 patients (29%) underwent PPM implantation. Subjects with vs. without surface conduction abnormality had significantly longer disease length (15.5 vs. 7.8 years, p = 0.015) and higher disease severity on the MIRS scale (p = 0.041). High prevalence of myocardial fibrosis by CMR-LGE was detected in subjects with and without surface conduction abnormality with no significant difference between the two cohorts (42% vs. 43%, p = 0.999). By multivariate logistic regression analysis, disease length was the only independent variable associated with surface conduction abnormality (OR 1.071, 95%CI 1.003-1.144, p = 0.040); while CMR-LGE was not associated with conduction abnormality (ρ = - 0.009, p = 0.949).

CONCLUSIONS

Myocardial fibrosis by CMR-LGE is highly prevalent in MMD1 but not related to surface conduction abnormality meeting current guideline criteria for PPM implantation .

Cardiac conduction disturbances and aging in patients with Duchenne muscular dystrophy

The majority of patients with Duchenne muscular dystrophy (DMD) have electrocardiographic abnormalities, but the clinical significance of conduction disturbances remains unclear. This study aimed to evaluate age-dependent cardiac conduction disturbances by electrocardiogram (ECG) to identify risks of complete atrioventricular (AV) block in this patient population.In total, 47 patients with DMD (age, ≥20 ys) who recorded ECGs at our hospital from July 2015 to June 2016 were included in this study. The PR interval and QRS duration in their previous ECGs were analyzed retrospectively. Associations between ECG findings and left ventricular (LV) systolic function obtained from the latest echocardiography were examined.The mean age of patients was 27.6 ± 6.0 years, and the mean observation period was 9.8 ± 3.7 years. The PR interval gradually increased with age, but no ECGs showed an abnormally prolonged PR interval. On the other hand, the QRS duration tended to increase progressively with age, and some patients had an abnormally prolonged QRS duration. The QRS duration was not correlated with LV systolic function (P = 0.867). One patient who developed a complete AV block had a drastically prolonged QRS duration before the onset of the disorder.The QRS duration tended to increase progressively with age, irrespective of LV systolic function in patients with DMD. Attention should be paid to the QRS duration as an indicator of risk for complete AV block in older patients.

Neuromuscular Disorders and the Role of the Clinical Electrophysiologist

Cardiac involvement is common and may be the presenting or predominant manifestation in a variety of neuromuscular disorders, most notably the inherited muscle disorders, or muscular dystrophies. Cardiac manifestations of the neuromuscular disorders result from pathological involvement of the myocardium and the cardiac conduction system, with resulting cardiomyopathy or rhythm disturbances including supraventricular arrhythmias, life-threatening ventricular arrhythmias, and sudden cardiac death. Many of these neuromuscular disorders are rare and may be unrecognized by even experienced specialists in internal and cardiovascular medicine. Furthermore, the initial cardiac manifestations in these patients are often asymptomatic. The goal of this investigation is to review the scope of cardiac conduction defects and rhythm disturbances in these disorders and to propose some practical recommendations for arrhythmia monitoring and management of these patients.

Management of Bradyarrhythmias in Heart Failure: A Tailored Approach

Patients with heart failure (HF) may develop a range of bradyarrhythmias including sinus node dysfunction, various degrees of atrioventricular block, and ventricular conduction delay. Device implantation has been recommended in these patients, but the specific etiology should be sought as it may influence the choice of the type of device required (pacemaker vs. implantable cardiac defibrillator). Also, pacing mode must be carefully set in patients with heart failure (HF) and left ventricular systolic dysfunction.In this chapter, we summarize the knowledge required for a tailored approach to bradyarrhythmias in patients with heart failure.

[Indications for implantable loop recorders in patients with channelopathies and ventricular tachycardias]

Implantable loop recorders (ILR) do not play a pivotal role in the current guidelines on ventricular arrhythmias except in identifying rhythm-symptom correlations if ventricular arrhythmias are assumed. Before a decision for a pure diagnostic implantable device is made, a thorough arrhythmic risk assessment is of major importance due to the potential lethal outcome of ventricular arrhythmias. Nevertheless, some clinical circumstances exist where long-term monitoring by an ILR may add significant information in electrical heart diseases, in patients with ventricular arrhythmias, or structural heart diseases and a potential risk of ventricular arrhythmias. As medical therapy (β-blocker therapy) plays an important role in long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardias (cpVT), the ILR can be used to control therapy in patients at risk. In electrical diseases without pharmacologic therapeutic options (e. g., Brugada syndrome), the ILR may be used in low-risk patients with atypical syncope as benign faints may occur without association to the underlying disease. Evidence on cardiomyopathies with preserved left ventricular function and nonsustained VT or premature ventricular complexes is scarce. The ILR may also add long-term information on the individual risk in these circumstances. In very rare diseases like infiltrative disease or muscular dystrophies, the ILR may also provide evidence on risk stratification. In summary, ILR in electrical heart diseases and in patients with ventricular tachycardia remains a very individual decision taking into account various clinical, electrocardiographic, and genetic parameters. The following review aims at highlighting possible indications and clinical scenarios for ILR in ventricular tachycardias and electrical heart diseases with-probably debatable-case presentations.

Deficiency of cyclase-associated protein 2 promotes arrhythmias associated with connexin43 maldistribution and fibrosis

INTRODUCTION

Cyclase-associated protein 2 (CAP2) plays a major role in regulating the actin cytoskeleton. Since inactivation of CAP2 in a mouse model by a gene trap approach (Cap2 (gt/gt) ) results in cardiomyopathy and increased mortality, we hypothesized that CAP2 has a major impact on arrhythmias and electrophysiological parameters.

MATERIAL AND METHODS

We performed long-term-ECG recordings in transgenic CAP2 deficient mice (C57BL/6) to detect spontaneous arrhythmias. In vivo electrophysiological studies by right heart catheterization and ex vivo epicardial mapping were used to analyze electrophysiological parameters, the inducibility of arrhythmias, and conduction velocities. Expression and distribution of cardiac connexins and the amount of cardiac fibrosis were evaluated.

RESULTS

Spontaneous ventricular arrhythmias could be detected in Cap2 (gt/gt) during the long-term-ECG recording. Cap2 (gt/gt) showed marked conduction delays at atrial and ventricular levels, including a reduced heart rate (421.0 ±40.6 bpm vs. 450.8 ±27.9 bpm; p < 0.01), and prolongations of PQ (46.3 ±4.1 ms vs. 38.6 ±6.5 ms; p < 0.01), QRS (16.2 ±2.6 ms vs. 12.6 ±1.4 ms; p < 0.01), and QTc interval (55.8 ±6.0 ms vs. 45.2 ±3.3 ms; p = 0.02) in comparison to wild type mice. The PQ prolongation was due to an infra-Hisian conduction delay (HV: 9.7 ±2.1 ms vs. 6.5 ±3.1 ms; p = 0.02). The inducibility of ventricular tachycardias during the electrophysiological studies was significantly elevated in the mutant mice (inducible animals: 88% vs. 33%; p = 0.04). Cap2 (gt/gt) showed more abnormal distribution of connexin43 compared to WT (23.0 ±4.7% vs. 2.9 ±0.8%; p < 0.01). Myocardial fibrosis was elevated in Cap2 (gt/gt) hearts (9.1 ±6.7% vs. 5.5 ±3.3%; p < 0.01).

CONCLUSIONS

Loss of CAP2 results in marked electrophysiological disturbances including impaired sinus node function, conduction delays, and susceptibility to malignant arrhythmias. Structural changes in Cap2 (gt/gt) are associated with alterations in myocardial connexins and fibrosis.

Phenotype-Genotype Analysis of Chinese Patients with Early-Onset LMNA-Related Muscular Dystrophy

This study aimed to analyze the correlation between the phenotype and genotype of Chinese patients with early-onset lamin A (LMNA)-related muscular dystrophy (MD). The clinical and myopathological data of 21 Chinese pediatric patients with early-onset LMNA-related MD were collected and analyzed. LMNA gene mutation analysis was performed by direct sequencing of genomic DNA. Sublocalization of wild-type and mutant proteins were observed by immunofluorescence using cultured fibroblasts and human embryonic kidney 293 (HEK 293) cell. Seven patients were diagnosed with Emery-Dreifuss muscular dystrophy (EDMD) and 14 were diagnosed with LMNA-associated congenital muscular dystrophy (L-CMD). Four biopsy specimens from the L-CMD cases exhibited inflammatory changes. Abnormal nuclear morphology was observed with both transmission electron microscopy and lamin A/C staining. We identified 10 novel and nine known LMNA gene mutations in the 21 patients. Some mutations (c.91G>A, c.94_96delAAG, c.116A>G, c.745C>T, c.746G>A, and c.1580G>C) were well correlated with EDMD or L-CMD. LMNA-related MD has a common symptom triad of muscle weakness, joint contractures, and cardiac involvement, but the severity of symptoms and disease progression differ greatly. Inflammatory change in biopsied muscle is a characteristic of early-stage L-CMD. Phenotype-genotype analysis determines that some mutations are well correlated with LMNA-related MD.

Myotonic dystrophy and the heart: A systematic review of evaluation and management

Myotonic dystrophy (MD) is a multisystem, autosomal dominant disorder best known for its skeletal muscle manifestations. Cardiac manifestations arise as a result of myocardial fatty infiltration, degeneration and fibrosis and present most commonly as arrhythmias or conduction disturbances. Guidelines regarding the optimal cardiac management of patients with MD are lacking. The present article provides a summary of the pathophysiology of cardiac problems in patients with MD and provides a practical approach to contemporary cardiac monitoring and management of these patients with a focus on the prevention of complications related to conduction disturbances and arrhythmias.

METHODS

A literature search was performed using PubMed and Medline. The keywords used in the search included "myotonic dystrophy", "cardiac manifestations", "heart", "arrhythmia", "pacemaker" and "defibrillator", all terms were used in combination. In addition, "myotonic dystrophy" was searched in conjunction with "electrophysiology", "electrocardiogram", "echocardiograph", "signal averaged electrocardiograph", "magnetic resonance imaging" and "exercise stress testing". The titles of all the articles revealed by the search were screened for relevance. The abstracts of relevant titles were read and those articles which concerned the cardiac manifestations of myotonic dystrophy or the investigation and management of cardiac manifestations underwent a full manuscript review.

Heart failure and atrial fibrillation: from basic science to clinical practice

Heart failure (HF) and atrial fibrillation (AF) are two growing epidemics associated with significant morbidity and mortality. They often coexist due to common risk factors and shared pathophysiological mechanisms. Patients presenting with both HF and AF have a worse prognosis and present a particular therapeutic challenge to clinicians. This review aims to appraise the common pathophysiological background, as well as the prognostic and therapeutic implications of coexistent HF and AF.