Review
Cardiac manifestations of myotonic dystrophy type 1

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Abstract

Aims

To estimate the degree of cardiac involvement regarding left ventricular ejection fraction, conduction abnormalities, arrhythmia, risk of sudden cardiac death (SCD) and the associations between cardiac involvement and cytosine–thymine–guanine (CTG)-repeat, neuromuscular involvement, age and gender in patients with myotonic dystrophy type 1 (MD1).

Methods and results

A Pub-Med search for the period 1980 to 2010 was performed according to specified criteria. Cardiac parameters including left ventricular ejection fraction (LVEF), conduction abnormalities and arrhythmia were compiled and only studies without ascertainment bias were included.

Eighteen studies, 1828 MD1-patients, were included. The prevalence of atrioventricular block grade 1 (AVB1) was 28.2%, QTc > 440 ms 22%, QRS > 120 ms 19.9%, frequent ventricular premature contractions (VPC) 14.6%, atrial fibrillation/flutter (AF/AFL) 5%, right/left bundle branch block (RBBB/LBBB) 4.4/5.7% and non-sustained ventricular tachycardia (NSVT) 4.1%. Left ventricular systolic dysfunction (LVSD) was reported in 7.2% of the patients.

There was an overall positive association between CTG-repeat size and cardiac involvement and between the degree of neuromuscular and cardiac involvement. Male gender and age were positively associated with arrhythmia and conduction abnormalities.

The prevalence of pacemaker- (PM) and implantable cardioverter defibrillator-(ICD) implantations were 4.1% and 1.1%, respectively.

The risk of SCD in this MD1-population was 0.56% per year.

Conclusion

MD1-patients have a high level of cardiac morbidity and mortality, strongly emphasizing the need of pre-symptomatic screening for arrhythmia and heart failure, as effective and well-documented preventive means are available.

Introduction

Myotonic dystrophy type 1 (MD1) is the most common muscular dystrophy with an incidence of approximately 1:8.000. MD1 is an autosomal dominant disorder with a highly variable phenotypic expression. The genetic basis of MD1 is an abnormal expansion of a CTG trinucleotide repeat on chromosome 19q21.3 [1], [2].

MD1 is a multisystem disorder associated with myotonia, progressive weakness and atrophy of the skeletal muscles, cataract and systemic manifestations. Cardiac involvement may present as asymptomatic electrocardiographic (ECG) abnormalities, e.g. prolongation of the PR-, QRS- and QT-intervals. Arrhythmic events may be due to sinus-node dysfunction, progressive heart block, atrial tachycardia, -flutter or -fibrillation or ventricular tachycardia or -fibrillation [2], [3].

The conduction abnormalities and the arrhythmia are thought to be due to myocardial fibrosis, which may lead to degeneration of the cardiac conduction system and compose a substrate for re-entrant arrhythmia, e.g. the development of atrioventricular block and ventricular arrhythmia. The myocardial fibrosis probably also relates to the observed systolic ventricular function [3], [4], [5], [6]. The symptomatic presentations include palpitations, pre-syncopes and syncopes, heart failure symptoms and sudden cardiac death (SCD), but the cardiac involvement in MD1 is often clinically asymptomatic.

In a 10-years follow-up study, Mathieu et al. report a mean age of death at 53.2 years in MD1-patients and a significantly increased number of observed versus expected deaths for cardiovascular diseases [5]. It has been demonstrated that certain ECG abnormalities, including atrial tachyarrhythmia, are independent predictors of sudden death in patients with MD1 [3].

There are no evidence-based recommendations for the timing of initiation, frequency and extent of cardiovascular screening to prevent or reduce cardiac morbidity and mortality in patients with MD1. We reviewed the literature to get an overview of the degree of cardiac involvement regarding left ventricular ejection fraction, conduction abnormalities, arrhythmia and the relations between cardiac involvement and CTG-repeat, neuromuscular involvement, age and gender in MD1-patients. We aimed to provide cardiologists with a unique and detailed overview of cardiac manifestations in MD1-patients based on the present literature and to provide suggestions for patient management.

Section snippets

Search strategy

A Pub-Med search was performed and included all studies published in English between 1980 and 2010, meeting the search terms myotonic dystrophy in combination with one of the following terms; cardiac abnormalities, cardiac involvement, arrhythmia, echocardiography, ECG, Holter, conduction disturbances, structural abnormalities, heart disease and sudden death, respectively. Studies from both cardiac and non-cardiac journals were included. The primary Pub-Med search resulted in 1617 hits.

Classification

Clinical

Results

Detailed information including the authorship, year of publication, number of included patients, mean age, gender, ECG-/24 hour Holter-parameters and LVEF in each study is shown in Tables 1 and 2.

Discussion

This review demonstrates that a substantial fraction of MD1-patients has major cardiac involvement, mainly conduction abnormalities and arrhythmia.

Our review reveals a high prevalence of AVB1-block (28%). According to a large prospective, community-based cohort including 7575 individuals from the Framingham Study (mean age 47 years; 54% women), 124 patients (1.6%) had PR interval > 200 ms at baseline. AVB1 was found to be associated with increased risk of atrial fibrillation, PM-implantation and

Conclusions

Cardiac involvement such as conduction disturbances, arrhythmia and cardiomyopathy is a common finding in MD1-patients and carries a raised risk of SCD. In the management of MD1-patients it is important to stay attentive to the variety of cardiac manifestations. Without pre-symptomatic cardiac screening, MD1-patients may be diagnosed later than other patients with a cardiac disease, because of the muscular dystrophy-related reduced physical abilities. A delayed diagnosis of cardiac involvement

Acknowledgment

The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [43].

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    Funding: this work was supported by the Research Foundation of Rigshospitalet.

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