Signal-averaged electrocardiography in myotonic dystrophy

The value of the 12-lead electrocardiogram in the prediction of sudden cardiac death

Sudden cardiac death (SCD) can be caused by several clinical conditions, overt or misconceived, which recognize different pathophysiologies determining the development of fatal arrhythmic events. In the various forms of structural heart disease such as ischaemic heart disease, cardiomyopathies (e.g. hypertrophic cardiomyopathy, dilated cardiomyopathy, and arrhythmogenic cardiomyopathy), channelopathies (e.g. long-QT syndrome, congenital short QT, Brugada syndrome, early repolarization (ER) syndrome, and idiopathic ventricular fibrillation) but also in the apparently healthy subject, the 12-lead electrocardiogram (ECG) has proved, over the years, to be a reliable and readily available method for stratifying the risk of adverse arrhythmic events and consequently SCD. Several electrocardiographic markers have been shown to be associated with adverse outcomes in different types of patients. Although with different sensitivity and specificity in each clinical condition, depolarization abnormalities, such as QRS fragmentation, Q waves, QRS duration, left posterior fascicular block, low QRS voltage, and left ventricular hypertrophy and similarly repolarization abnormalities as ER pattern, T wave alternans, QT interval, and QT dispersion, have shown significant efficacy in predicting SCD. Despite the advancement of techniques especially in the field of imaging, the correct interpretation of the 12-lead ECG remains, therefore, an effective tool for assessing the possible prognostic outcome in terms of arrhythmic risk and SCD in different types of patients.

Signal-averaged electrocardiography: Past, present, and future

Signal-averaged electrocardiography records delayed depolarization of myocardial areas with slow conduction that can form the substrate for monomorphic ventricular tachycardia. This technique has been examined mostly in patients with coronary artery disease, but its use has been declined over the years. However, several lines of evidence, derived from hitherto clinical data in patients with healed myocardial infarction, indicate that signal-averaged electrocardiography remains a valuable tool in risk stratification, especially when incorporated into algorithms encompassing invasive and noninvasive indices. Such an approach can aid the more precise identification of candidates for device therapy, in the context of primary prevention of sudden cardiac death. This article reappraises the value of signal-averaged electrocardiography as a predictor of arrhythmic outcome in patients with ischemic heart disease and discusses potential future indications.

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.

Risk of arrhythmias in myotonic dystrophy: trial design of the RAMYD study

OBJECTIVE

Myotonic dystrophy type 1 (DM1) is the most frequent muscular dystrophy in adults. DM1 is a multisystem disorder also affecting the heart with an increased incidence of sudden death, which has been explained with the common impairment of the conduction system often requiring pacemaker implantation; however, the occurrence of sudden death despite pacemaker implantation and the observation of major ventricular arrhythmias generated the hypothesis that ventricular arrhythmias may play a causal role as well. The aim of the study was to assess the 2-year cumulative incidence and the value of noninvasive and invasive findings as predictive factors for sudden death, resuscitated cardiac arrest, ventricular fibrillation, sustained ventricular tachycardia and severe sinus dysfunction or high-degree atrioventricular block.

METHODS/DESIGN

More than 500 DM1 patients will be evaluated at baseline with a clinical interview, 12-lead ECG, 24-h ECG and echocardiogram. Conventional and nonconventional indications to electrophysiological study, pacemaker, implantable cardioverter defibrillator or loop recorder implantation have been developed. In the case of an indication to electrophysiological study, pacemaker, implantable cardioverter defibrillator or loop recorder implant at baseline or at follow-up, the patient will be referred for the procedure. At the end of 2-year follow-up, all candidate prognostic factors will be tested for their association with the endpoints.

TRIAL REGISTRATION

ClinicalTrials.gov ID NCT00127582.

CONCLUSION

The available evidence supports the hypothesis that both bradyarrhythmias and tachyarrhythmias may cause sudden death in DM1, but the course of cardiac disease in DM1 is still unclear. We expect that this large, prospective, multicenter study will provide evidence to improve diagnostic and therapeutic strategies in DM1.

Anomalies cardiaques au cours de la dystrophie myotonique de Steinert

INTRODUCTION

Cardiac involvement is described as one of the most frequent multisystemic manifestations of Steinert myotonic dystrophy (DM1). This study was performed to determine the frequency of cardiac abnormalities in Steinert myotonic dystrophy and to decipher the correlation between the severity of cardiac involvement and the degree of neurologic deficit.

PATIENTS AND RESULTS

Thirty-four DM1 patients 23 men and 11 women, aged 13-61 years (mean 37.3+/-13.2 years) underwent neurological and cardiac evaluations. According to the MDRS scale, 32.5 percent were classified in the second stage, 23 percent in stage 3; 32.5 percent in stage 4 and 12 percent in stage 5. There was a positive correlation between neurological symptoms duration and the MRDS scale. Cardiac involvement was detected in 77.4 percent of patients. Electrocardiographic conduction abnormalities were the most frequent, represented by first-degree atrioventicular block in 64 percent of patients and bundle-branch block in 32 percent. From 5 patients having an invasive electrophysiology testing, subhisien block was observed in 3 patients. We respectively found alterations in systolic and diastolic left ventricular function in 22 percent and 30 percent of patients and a cardiac pacemaker was implanted in 3 patients. The frequency of cardiac manifestations was correlated to the degree of the neurological involvement assisted by MDRS scale, but it seam that the severity of cardiac abnormalities is not correlated to the degree of neurological deficit.

CONCLUSION

We recommend that patients with DM1 undergo 24-h electrocardiogram monitoring and echocardiography at least yearly. Long-term prospective follow-up is required to determine the prognostic value of the observed abnormalities.

Tumor necrosis factor-alpha and myocardial function in patients with myotonic dystrophy type 1

An imbalance of TNF system activity has been reported in patients with myotonic dystrophy type 1 (DM1). Nevertheless, the question whether TNF-alpha action is directly implicated in the pathogenesis of DM1 or is a simple marker of disease activity is still open. Therefore, the present study was aimed to investigate serum tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 levels in association with the disease stage, cytosine-thymine-guanine (CTG) expansion and cardiac function of 56 patients with DM1 (40+/-14 years) and 28 healthy controls (42+/-12 years). All subjects were submitted to resting electrocardiogram (EKG), Signal-averaged EKG (SA-EKG), and M-mode/2-D echocardiography. TNF-alpha levels were higher in patients compared to controls (p<0.0003) and were associated to disease stage (p<0.02). Significant correlation were observed between TNF and CTG expansion (p<0.005) or PQ intervals (p<0.0005). Ventricular late potentials (VLPs) occurred in 54% of cases. In these patients, TNF-alpha levels were higher compared to those without VLPs (p<0.05). We may conclude that TNF-alpha levels might represent and adjunctive criterion for disease staging in patients with myotonic dystrophy type 1, and that elevated TNF levels in DM1 may lead to cardiac fibrosis affecting diastolic function, conduction, and automaticity.

Natural history of cardiac involvement in myotonic dystrophy (Steinert's disease): a 13-year follow-up study

Myotonic dystrophy (MD) is associated with a wide spectrum of cardiac abnormalities, but only a few longitudinal studies have investigated the natural course of heart disease in MD. To assess whether neuromuscular involvement significantly predicts cardiac disorders in MD, 83 patients with various grades of disease severity were enrolled in a 13-year follow-up study (mean, 60.6 +/- 37.8 months) that included periodic physical and instrumental cardiac examinations (standard and Holter electrocardiography, echocardiography). During follow-up, muscular disease worsened clinically in 9 patients (11%) whose baseline severity grade changed accordingly; only 3 of them demonstrated parallel worsening of cardiac disturbance, however, compared with a large number of patients who showed additional cardiac abnormalities. These included further worsening of pre-existing pathologic features (19/83) and the appearance de novo of serious arrhythmias and/or conduction defects (23/83). Pacemaker implantation was necessary in 11 of 83 patients (13.2%) who had symptomatic bradyarrhythmias, bifascicular block, and P-R prolongation with a His-to-ventricle interval exceeding 55 ms, as documented by electrophysiologic study. Eight (9.6%) patients died: 2 from noncardiac and 1 from unknown causes, 1 from heart failure, and 4 from sudden death closely related to documented ventricular tachycardia. The incidence and seriousness of arrhythmic and conduction disturbances correlated with the severity of the muscular involvement. Nevertheless, cardiac and muscular disease did not show a linear progression. Cardiac involvement generally worsened more rapidly than did skeletal muscle disease.

[Cardiac involvement in neuromuscular diseases]

Many neuromuscular disorders involve the heart, occasionally with overt clinical disease. Muscular dystrophies (dystrophinopathies, limb girdle muscular dystrophy, Emery-Dreifuss muscular dystrophy, Steinert's myotonic dystrophy), congenital myopathies, inflammatory myopathies and metabolic diseases (glycogenosis, periodic paralysis, mitochondrial diseases) may produce dilated or hypertrophic cardiomyopathy and heart rhythm or conduction disturbances. Furthermore the heart is commonly involved in some hereditary and degenerative diseases (Friedreich's ataxia and Kugelberg-Welander syndrome) and acquired (Guillain-Barré syndrome) or inherited (Refsum's disease and Charcot-Marie-Tooth syndrome) polyneuropathies. A cardiologist's high clinical suspicion and a simple but systematic skeletal muscle and peripheral nerve investigation, including muscle enzymes quantification, neurophysiological study and muscle biopsy, are necessary for an accurate diagnosis. In selected patients, more sophisticated biochemical and genetic analysis will be necessary. In most cases, endomyocardial biopsy is not essential for the diagnosis.