Atrial flutter in myotonic dystrophy type 1: Patient characteristics and clinical outcome

Atrial Fibrillation and Flutter in a Contemporary Cohort of Patients With Myotonic Muscular Dystrophy

BACKGROUND

Literature on the prevalence and management of atrial arrhythmias in patients with myotonic muscular dystrophy type 1 (MMD1) or myotonic muscular dystrophy type 2 (MMD2) is limited.

OBJECTIVES

This study sought to describe incidence, prevalence, and predictors of atrial fibrillation (AF) and atrial flutter (AFL) in a contemporary cohort of patients with myotonic muscular dystrophy (MMD).

METHODS

Associations between patient factors and incident AF/AFL were analyzed in patients with MMD referred for routine electrophysiology evaluation between January 2013 and September 2023.

RESULTS

We identified 120 patients (96 MMD1, 24 MMD2) seen for new electrophysiology clinic visits for MMD cardiac evaluation. Median age at MMD diagnosis was 34.6 years (Q1-Q3: 21.8-51.0 years), with a younger age at diagnosis for MMD1 patients (P < 0.001). AF or AFL was diagnosed in 31% of patients (31 of 96 MMD1 patients vs 6 of 24 MMD2 patients; P = 0.656) during the study period. AF occurred in 34 (28%) patients, AFL in 9 (8%), and 6 of 37 had both AF and AFL. Anticoagulation (AC) was prescribed at initial AF/AFL diagnosis in 41% (n = 15 of 37) of patients. The CHA2DS2-VASc score was higher in patients who received AC (P < 0.001). Twelve (32%) patients underwent catheter ablation. One stroke occurred in the AF/AFL group (no AC, CHA2DS2-VASc score 0). Female MMD1 patients were less likely to develop AF/AFL (HR: 0.08). Diagnosis of MMD1 at a younger age (HR: 0.95 per year) and greater CTG nucleotide repeats (HR: 1.09 per 50 repeats) were associated with incident AF/AFL.

CONCLUSIONS

There was a high prevalence of AF/AFL in this single-institution MMD cohort. The CHA2DS2-VASc score may not be an effective tool in this population.

Cardiac involvement in patient-specific induced pluripotent stem cells of myotonic dystrophy type 1: unveiling the impact of voltage-gated sodium channels

Myotonic dystrophy type 1 (DM1) is a genetic disorder that causes muscle weakness and myotonia. In DM1 patients, cardiac electrical manifestations include conduction defects and atrial fibrillation. DM1 results in the expansion of a CTG transcribed into CUG-containing transcripts that accumulate in the nucleus as RNA foci and alter the activity of several splicing regulators. The underlying pathological mechanism involves two key RNA-binding proteins (MBNL and CELF) with expanded CUG repeats that sequester MBNL and alter the activity of CELF resulting in spliceopathy and abnormal electrical activity. In the present study, we identified two DM1 patients with heart conduction abnormalities and characterized their hiPSC lines. Two differentiation protocols were used to investigate both the ventricular and the atrial electrophysiological aspects of DM1 and unveil the impact of the mutation on voltage-gated ion channels, electrical activity, and calcium homeostasis in DM1 cardiomyocytes derived from hiPSCs. Our analysis revealed the presence of molecular hallmarks of DM1, including the accumulation of RNA foci and sequestration of MBNL1 in DM1 hiPSC-CMs. We also observed mis-splicing of SCN5A and haploinsufficiency of DMPK. Furthermore, we conducted separate characterizations of atrial and ventricular electrical activity, conduction properties, and calcium homeostasis. Both DM1 cell lines exhibited reduced density of sodium and calcium currents, prolonged action potential duration, slower conduction velocity, and impaired calcium transient propagation in both ventricular and atrial cardiomyocytes. Notably, arrhythmogenic events were recorded, including both ventricular and atrial arrhythmias were observed in the two DM1 cell lines. These findings enhance our comprehension of the molecular mechanisms underlying DM1 and provide valuable insights into the pathophysiology of ventricular and atrial involvement.

Atrial Flutter in Particular Patient Populations

"Despite being one of the best understood cardiac arrhythmias, the clinical meaning of atrial flutter varies according to the specific context, and its optimal treatment may be limited by both the suboptimal response to rate/rhythm control drugs and by the complexity of the underlying substrate. In this article, we present a state-of-the-art overview of mechanisms, prognostic impact, and medical/interventional management options for atrial flutter in several specific patient populations, including heart failure, cardiomyopathies, muscular dystrophies, posttransplant patients, patients with respiratory disorders, athletes, and subjects with preexcitation, aiming to stimulate further research in this challenging field and facilitate appropriate patient care."

An overview of heart rhythm disorders and management in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is the most common adult form of muscular dystrophy, presenting with a constellation of systemic findings secondary to a CTG triplet expansion of the noncoding region of the DMPK gene. Cardiac involvement is frequent, with conduction disease and supraventricular and ventricular arrhythmias being the most prevalent cardiac manifestations, often developing from a young age. The development of cardiac arrhythmias has been linked to increased morbidity and mortality, with sudden cardiac death well described. Strategies to mitigate risk of arrhythmic death have been developed. In this review, we outline the current knowledge on the pathophysiology of rhythm abnormalities in patients with myotonic dystrophy and summarize available knowledge on arrhythmic risk stratification. We also review management strategies from an electrophysiological perspective, attempting to underline the substantial unmet need to address residual arrhythmic risks for this population.

Clinical Care Recommendations for Cardiologists Treating Adults With Myotonic Dystrophy

Myotonic dystrophy is an inherited systemic disorder affecting skeletal muscle and the heart. Genetic testing for myotonic dystrophy is diagnostic and identifies those at risk for cardiac complications. The 2 major genetic forms of myotonic dystrophy, type 1 and type 2, differ in genetic etiology yet share clinical features. The cardiac management of myotonic dystrophy should include surveillance for arrhythmias and left ventricular dysfunction, both of which occur in progressive manner and contribute to morbidity and mortality. To promote the development of care guidelines for myotonic dystrophy, the Myotonic Foundation solicited the input of care experts and organized the drafting of these recommendations. As a rare disorder, large scale clinical trial data to guide the management of myotonic dystrophy are largely lacking. The following recommendations represent expert consensus opinion from those with experience in the management of myotonic dystrophy, in part supported by literature-based evidence where available.

Cardiovascular manifestations of myotonic dystrophy

Patients with myotonic dystrophy, the most common neuromuscular dystrophy in adults, have a high prevalence of arrhythmic complications with increased cardiovascular mortality and high risk for sudden death. Sudden death prevention is central and relies on annual follow-up and prophylactic permanent pacing in patients with conduction defects on electrocardiogram and/or infrahisian blocks on electrophysiological study. Implantable cardiac defibrillator therapy may be indicated in patients with ventricular tachyarrhythmia.

The Frequency and Risk Factors for Ischemic Stroke in Myotonic Dystrophy Type 1 Patients

INTRODUCTION

Patients with myotonic dystrophy type 1 have several cardiac abnormalities, especially myocardial conduction disorders. Few studies have investigated cerebral infarction. We investigated the frequency of both symptomatic and asymptomatic ischemic strokes in patients with myotonic dystrophy type 1.

METHODS

Patients who were diagnosed with myotonic dystrophy type 1 using genetic testing or clinical examinations at Asahikawa Medical Center were included. We retrospectively reviewed their medical history, neuroradiological imaging, electrocardiograms, and treatment. Their CHADS2 and CHA2DS2-VASc scores were calculated.

RESULT

A total of 108 patients were diagnosed with myotonic dystrophy type 1. Magnetic resonance imaging was performed in 72 and 1 patient whose results were not available was excluded. Among these, 2 patients had atrial flutter and 3 had atrial fibrillation. Regarding the CHADS2 score, 11 patients scored more than 2. Regarding the CHA2DS2-VASc score, 22 patients scored more than 2. Ischemic strokes were found in 9 patients with 1 having an atrial flutter and 4 having atrial fibrillation. All patients with stroke had CHADS2 and CHA2DS2-VASc scores higher than 2. There were significant differences between the 2 groups in atrial fibrillation (P < .001), CHADS2 score (P < .001), and CHA2DS2-VASc score (P < .001).

CONCLUSIONS

Ischemic stroke in patients with myotonic dystrophy type 1 is associated with atrial fibrillation. The CHADS2 score seems to be useful for the management of patients with myotonic dystrophy type 1. Repeated electrocardiograms are necessary for managing these patients.

Neuromuscular Disease: Cardiac Manifestations and Sudden Death Risk

Cardiovascular complications of neuromuscular diseases disproportionately affect the cardiac conduction system. Cardiomyopathy and cardiac arrhythmias produce significant morbidity and mortality. Patients with neuromuscular diseases should be carefully and frequently evaluated for the presence of bradycardia, heart block, and tachyarrhythmias. Preemptive treatment with permanent pacemakers or implanted defibrillators is appropriate in patients with conduction system disease or who are at risk for ventricular arrhythmias.