Mechanisms of sustained ventricular tachycardia in myotonic dystrophy: implications for catheter ablation

Mechanisms of ventricular tachycardias with a 1:1 His-V relation in patients with heart disease

BACKGROUND

Ventricular tachycardia (VT) with a 1:1 V-His relation can be seen in bundle branch reentry or with passive retrograde activation from scar-related VT or reentry using left ventricular Purkinje fascicles.

OBJECTIVE

This study aimed to review the frequency with which 1:1 V-His relation occurs and to identify differentiating characteristics of these arrhythmias, including new measures obtained during right ventricular (RV) pacing based on orthodromic His-proximal right bundle potential (HisRB) capture and the stimulus to HisRB (S-HisRB) interval approximating RV electrogram to His interval (Egm-HisRBVT).

METHODS

This was a retrospective review of induced VTs that had a HisRB potential recorded while pacing from the distal right ventricle.

RESULTS

From 147 patients, 158 VTs were analyzed. A 1:1 V to HisRB was observed in 86 VTs (54%): 18 bundle branch reentrant VTs (BBR-VTs), 8 LV fascicular/Purkinje-related reentrant VTs (FPVTs), and 60 scar-related reentrant VTs (SRR-VTs). The HisRB-QRSVT was >135 ms, falling within the QRS in 87% of SRR-VTs, and 30-135 ms in all BBR-VTs (P < .001). With RV pacing, the HisRB remained 1:1 in 100% of BBR-VTs and 23 (69.7%) of 33 SRR-VTs. An S-HisRB of >135 ms combined with S-HisRB - Egm-HisRBVT difference <30 ms was specific for BBR-VT. In FPVTs, the HisRB-QRS timing was more variable, and RV pacing was helpful in distinguishing these from BBR-VTs.

CONCLUSION

Retrograde HisRB activation is common in all forms of VT. HisRB timing and new features based on consideration of orthodromic HisRB activation during RV pacing can help distinguish BBR-VT, SRR-VT, and FPVT.

Ventricular stimulation in patients with myotonic dystrophy type 1 may not predict future ventricular arrhythmias

Background

Myotonic dystrophy type 1 (DM1) is associated with progressive conduction disease. Furthermore, DM1 patients are at risk ventricular arrhythmias (VAs), although prediction remains difficult. The 2022 Heart Rhythm Expert Consensus Statement gives a IIb recommendation to the use of electrophysiology study (EPS) to risk-stratify patients for VAs. The utility of EPS in predicting the development of VAs, however, has not been explored in this patient population.

Objective

The study sought to examine the natural history of DM1 patients with positive and negative ventricular stimulation (v-stim) during EPS.

Methods

Patients with a history of DM1 undergoing EPS with associated v-stim from 2008 to present were retrospectively identified.

Results

From 2008 to 2022, 26 consecutive DM1 patients presented for EPS with v-stim. Four v-stim protocols were positive for sustained or hemodynamically significant ventricular tachycardia (VT), one of which was induced with 600 doubles, the others with triple extrastimuli. A total of 22 of 26 subjects received a device implant, with 18 receiving permanent pacemakers and 4 implantable cardioverter-defibrillators. All 4 of the patients with positive v-stims underwent ICD implantation. After a mean of 5.7 years of follow-up, 7 patients had sustained VT, 6 of whom had negative v-stims. Of the 4 patients with positive v-stims, only 1 developed sustained VT in follow-up. Other than baseline QT interval at time of EPS, no baseline characteristics were significantly different between patients with and without subsequent VT.

Conclusion

In this single center, v-stim in DM1 patients did not predict clinical VAs, as a vast majority of DM1 patients who developed VAs had negative v-stims.

Comprehensive pathological and genetic investigation of three young adult myotonic dystrophy type 1 patients with sudden unexpected death

OBJECTIVES

The mechanism and pathological substrate of arrhythmogenic events in dystrophic myopathy type 1 (DM1) have not been fully established, especially for patients without progression of motor and/or cardiac disability. Therefore, we aimed to clarify the pathological appearance and genetic factors, other than CTG repeats in DMPK, associated with sudden cardiac death in patients with DM1.

METHODS

A pathological investigation including the cardiac conduction system in the heart and whole-exome sequencing was conducted for three young adults (Patient 1; 25-year-old female, Patient 2; 35-year-old female, Patient 3; 18-year-old male) with DM1 who suffered sudden death.

RESULTS

Only Patient 1 showed abnormal electrocardiogram findings before death. The pathological investigation showed severe fibrosis of the atrioventricular conduction system in Patient 1 and severe fatty infiltration in the right ventricle in Patient 2. Several minimal necrotic/inflammatory foci were found in both patients. Patient 3 showed no significant pathological findings. A genetic investigation showed CORIN_p.W813* and MYH2_p. R793* in Patient 1, KCNH2_p. V794D and PLEC_p. A4147T in Patient 2, and SCN5A_p.E428K and SCN3B_ p.V145L in Patient 3 as highly possible pathogenic variants.

CONCLUSION AND RELEVANCE

The present study showed varied heart morphology in young adults with DM1 and sudden death. Synergistic effects of various genetic factors other than CTG repeats may increase the risk of sudden cardiac death in DM1 patients, even if signs of cardiac and skeletal muscle involvement are mild. Comprehensive genetic investigations, other than CTG repeat assessment, may be useful to estimate the risk of sudden cardiac death in DM1 patients.

Cardiac magnetic resonance findings and prognosis in type 1 myotonic dystrophy

BACKGROUND

Cardiac involvement is a major determinant of prognosis in type 1 myotonic dystrophy (DM1), but limited information is available about myocardial remodeling and tissue changes. The aim of the study was to investigate cardiac magnetic resonance (CMR) findings and their prognostic significance in DM1.

METHODS

We retrospectively identified all DM1 patients referred from a neurology unit to our CMR laboratory from 2009 to 2020.

RESULTS

Thirty-four patients were included (aged 45 ± 12, 62% male individuals) and compared with 68 age-matched and gender-matched healthy volunteers (43 male individuals, age 48 ± 15 years). At CMR, biventricular and biatrial volumes were significantly smaller (all P < 0.05), as was left ventricular mass (P < 0.001); left ventricular ejection fraction (LVEF) and right ventricular ejection fraction (RVEF) were significantly lower (all P < 0.01). Five (15%) patients had a LVEF less than 50% and four (12%) a RVEF less than 50%. Nine patients (26%) showed mid-wall late gadolinium enhancement (LGE; 5 ± 2% of LVM), and 14 (41%) fatty infiltration. Native T1 in the interventricular septum (1041 ± 53 ms) was higher than for healthy controls (1017 ± 28 ms) and approached the upper reference limit (1089 ms); the extracellular volume was slightly increased (33 ± 2%, reference <30%). Over 3.7 years (2.0-5.0), 6 (18%) patients died of extracardiac causes, 5 (15%) underwent device implantation; 5 of 21 (24%) developed repetitive ventricular ectopic beats (VEBs) on Holter monitoring. LGE mass was associated with the occurrence of repetitive VEBs (P = 0.002). Lower LV stroke volume (P = 0.017), lower RVEF (P = 0.016), a higher LVMi/LVEDVI ratio (P = 0.016), fatty infiltration (P = 0.04), and LGE extent (P < 0.001) were associated with death.

CONCLUSION

DM1 patients display structural and functional cardiac abnormalities, with variable degrees of cardiac muscle hypotrophy, fibrosis, and fatty infiltration. Such changes, as evaluated by CMR, seem to be associated with the development of ventricular arrhythmias and a worse outcome.

Progressive outcomes of bundle branch reentrant ventricular tachycardia in patients without structural heart disease

BACKGROUND

Ablation strategies to treat bundle branch reentrant ventricular tachycardia (BBRT) are well described. However, reports of long-term follow-up outcomes in BBRT patients without structural heart disease (SHD) are limited.

OBJECTIVE

The purpose of this study was to investigate the long-term follow-up prognosis of BBRT patients without SHD.

METHODS

Changes in electrocardiographic and echocardiographic parameters were used to evaluate progression during follow-up. Potential pathogenic candidate variants were screened using a specific gene panel.

RESULTS

Eleven consecutive BBRT patients without obvious SHD based on echocardiographic and cardiovascular magnetic resonance imaging results were enrolled. Median age was 20 (11-48) years, and median follow-up time was 72 months. During follow-up, PR interval [206 (158-360) ms vs 188 (158-300) ms; P = .018] and QRS duration [187 (155-240) ms vs 164 (130-178) ms; P = .008] each increased significantly compared with postablation. Right- and left-sided chamber dilation and reduced left ventricular ejection fraction (LVEF) also were observed. Clinical deterioration or events occurred in 8 patients: 1 sudden death; 3 both complete heart block and reduced LVEF; 2 significantly reduced LVEF; and 2 prolonged PR interval. Genetic testing results showed that 6 of 10 patients (excluding the patient with sudden death) had ≥1 potential pathogenic candidate variants.

CONCLUSION

Further deterioration of His-Purkinje system conduction was observed in young BBRT patients without SHD after ablation. The His-Purkinje system may be the first target of genetic predisposition.

Evaluation of Index of Cardiac Electrophysiological Balance in Patients With Myotonic Dystrophy Type 1

BACKGROUND

Myotonic dystrophy type 1(MD1), which is characterized by decreased muscle tone, progressive muscle weakness, and cardiac involvement, is an autosomal dominant and progressive congenital muscle disease. Cardiac involvement more often manifests as conduction abnormalities and arrhythmias (such as supraventricular or ventricular). Approximately one-third of MD1-related deaths occur due to cardiac causes. The index of cardiac-electrophysiological balance (ICEB) is a current parameter calculated as QT interval/QRS duration. The increase in this parameter has been associated with malignant ventricular arrhythmias. In this study, our aim was to compare the ICEB values ​​of MD1 patients and the normal population.

MATERIAL AND METHOD

A total of 62 patients were included in our study. They were divided into two groups - 32 MD patients and 30 controls. The demographic, clinical, laboratory, and electrocardiographic parameters of the two groups were compared.

RESULTS

The median age of the study population was 24 (20-36 IQR), and 36 (58%) of these patients were female. Body mass index was higher in the control group (p = 0.037). While in the MD1 group creatinine kinase was significantly higher (p <0.001), In the control group creatinine, aspartate aminotransferase, alanine aminotransferase, calcium, and lymphocyte levels were significantly higher (p=0.031, p= 0.003, p=0.001, p=0.002, p=0.031, respectively). ICEB [3.96 (3.65-4.46) vs 3.74 (3.49-3.85) p=0.015] and corrected ICEB (ICEBc) [4.48 (4.08-4.92) vs 4.20 (4.03-4.51) p = 0.048] were significantly higher in the MD1 group.

CONCLUSION

In our study, ICEB was found to be higher in MD1 patients than in the control group. Increased ICEB and ICEBc values ​​in MD1 patients may precipitate ventricular arrhythmias in the future. Close monitoring of these parameters can be helpful in predicting possible ventricular arrhythmias and in risk stratification.

Catheter Ablation for Ventricular Tachycardia Involving the His-Purkinje System: Fascicular and Bundle Branch Reentrant Ventricular Tachycardia

The Purkinje system has been found to mediate several monomorphic ventricular tachycardias (VTs). These include fascicular VTs and bundle branch reentrant (BBR) VTs. Previous studies have revealed that VTs involving the His-Purkinje system are composed of multiple discrete subtypes that are best differentiated by their mechanism, drug effect, VT morphology, and successful ablation site. Recognition of the heterogeneity of these VTs and their unique characteristics should facilitate the appropriate diagnosis and therapy and help guide catheter ablation therapy. In this article, we focus on the latest updates of the mechanisms underlying left ventricle fascicular VTs and BBR-VTs as well as the latest catheter ablation techniques.

2022 HRS expert consensus statement on evaluation and management of arrhythmic risk in neuromuscular disorders

This international multidisciplinary document is intended to guide electrophysiologists, cardiologists, other clinicians, and health care professionals in caring for patients with arrhythmic complications of neuromuscular disorders (NMDs). The document presents an overview of arrhythmias in NMDs followed by detailed sections on specific disorders: Duchenne muscular dystrophy, Becker muscular dystrophy, and limb-girdle muscular dystrophy type 2; myotonic dystrophy type 1 and type 2; Emery-Dreifuss muscular dystrophy and limb-girdle muscular dystrophy type 1B; facioscapulohumeral muscular dystrophy; and mitochondrial myopathies, including Friedreich ataxia and Kearns-Sayre syndrome, with an emphasis on managing arrhythmic cardiac manifestations. End-of-life management of arrhythmias in patients with NMDs is also covered. The document sections were drafted by the writing committee members according to their area of expertise. The recommendations represent the consensus opinion of the expert writing group, graded by class of recommendation and level of evidence utilizing defined criteria. The recommendations were made available for public comment; the document underwent review by the Heart Rhythm Society Scientific and Clinical Documents Committee and external review and endorsement by the partner and collaborating societies. Changes were incorporated based on these reviews. By using a breadth of accumulated available evidence, the document is designed to provide practical and actionable clinical information and recommendations for the diagnosis and management of arrhythmias and thus improve the care of patients with NMDs.

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.

Bundle Branch Reentrant Ventricular Tachycardia Treated with Catheter Ablation in a Patient with Myotonic Dystrophy

BACKGROUND Bundle branch reentrant ventricular tachycardia (BBRVT) is a rarely encountered ventricular tachycardia (VT) and is classically associated with advanced heart diseases. Importantly, the tachycardia is readily curable with catheter ablation. Without suspicion of BBRVT and recording of the His-Purkinje system, it is hard to diagnose accurately. Myotonic dystrophy (MD) is the most common neuromuscular disease in adults and is known to have a risk of development of BBRVT. Here, we report a case of BBRVT in an MD patient with normal cardiac configuration with typical clinical and electrophysiological features. CASE REPORT A 40-year-old man presented with chest discomfort and weakness at the Emergency Department with unstable vital conditions. Electrocardiography showed wide QRS tachycardia with right bundle branch block pattern. The patient had been diagnosed with MD (type I) 3 years ago and had typical clinical features of MD. Transthoracic echocardiography showed normal left ventricular systolic function and no significant structural abnormalities. In the electrophysiologic study, VTs with left and right bundle branch block pattern were induced and diagnosed with BBRVT. Considering the risk of sudden death, implantation of an implantable cardioverter-defibrillator (ICD) was performed. One month later, VT had recurred and was successfully treated with ablation of the right bundle branch. CONCLUSIONS We present a case of 2 different morphologies of BBRVT in a patient with MD and normal ventricular function. Catheter ablation is a curative method for BBRVT and can be a tool for reducing ICD shock.

The Optimal Timing of Primary Prevention Implantable Cardioverter-Defibrillator Referral in the Rapidly Changing Medical Landscape

The use of implantable cardioverter-defibrillators (ICDs) significantly reduces the risk of mortality in patients with heart failure with reduced ejection fraction (HFrEF). Current guidelines, which are based on seminal clinical trials published nearly 2 decades ago, recommend that patients be on optimal medical therapy for HF for a minimum of 3 months before referral for prophylactic ICD. This waiting period allows for left ventricular reverse remodelling and improvement in HF symptoms, which may render primary prevention ICD implantation unnecessary. However, medical therapy for HFrEF has significantly evolved since the publication of these landmark trials. Given the plethora of medical therapy options now available for HFrEF, it is appropriate to reassess the duration of this waiting period. In the present review, we examine the landmark randomised trials in primary prevention of sudden cardiac death in patients with HFrEF, summarise the novel medical therapies (sacubitril-valsartan, sodium-glucose cotransporter 2 inhibitors, ivabradine, vericiguat, and omecamtiv mecarbil) that have emerged since the publication of those trials, discuss the optimal timing of ICD referral, and review subtypes of nonischemic cardiomyopathy where timing of ICD insertion is guided by alternative criteria. With the steps now needed to optimise medical therapy for HFrEF, in terms of both classes of drugs and doses of each agent, it can easily take up to 6 months to achieve optimisation. Following that, waiting periods of 3 months for ischemic cardiomyopathy and 6 months for nonischemic cardiomyopathy may be required to allow adequate reverse remodelling before reevaluating for ICD implantation.

Neurological complications of cardiomyopathies

There is a multifaceted relationship between the cardiomyopathies and a wide spectrum of neurological disorders. Severe acute neurological events, such as a status epilepticus and aneurysmal subarachnoid hemorrhage, may result in an acute cardiomyopathy the likes of Takotsubo cardiomyopathy. Conversely, the cardiomyopathies may result in a wide array of neurological disorders. Diagnosis of a cardiomyopathy may have already been established at the time of the index neurological event, or the neurological event may have prompted subsequent cardiac investigations, which ultimately lead to the diagnosis of a cardiomyopathy. The cardiomyopathies belong to one of the many phenotypes of complex genetic diseases or syndromes, which may also involve the central or peripheral nervous systems. A number of exogenous agents or risk factors such as diphtheria, alcohol, and several viruses may result in secondary cardiomyopathies accompanied by several neurological manifestations. A variety of neuromuscular disorders, such as myotonic dystrophy or amyloidosis, may demonstrate cardiac involvement during their clinical course. Furthermore, a number of genetic cardiomyopathies phenotypically incorporate during their clinical evolution, a gamut of neurological manifestations, usually neuromuscular in nature. Likewise, neurological complications may be the result of diagnostic procedures or medications for the cardiomyopathies and vice versa. Neurological manifestations of the cardiomyopathies are broad and include, among others, transient ischemic attacks, ischemic strokes, intracranial hemorrhages, syncope, muscle weakness and atrophy, myotonia, cramps, ataxia, seizures, intellectual developmental disorder, cognitive impairment, dementia, oculomotor palsies, deafness, retinal involvement, and headaches.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Prevalence of Left Ventricular Systolic Dysfunction in Myotonic Dystrophy Type 1: A Systematic Review

Cardiac involvement is recorded in about 80% of patients affected by myotonic dystrophy type 1 (DM1). The prevalence of cardiac conduction abnormalities and arrhythmias has been well described. Data regarding the prevalence of left ventricle systolic dysfunction (LVSD) and heart failure (HF) are still conflicting. The primary objective of this review was to assess the prevalence of LVSD and HF in DM1. The secondary aim was to examine the association of clinical features with LVSD and to detect predisposing and influencing prognosis factors. A systematic search was developed in MEDLINE, EMBASE, Cochrane Register of Controlled Trials, and Web of Science databases to identify original reports between January 1, 2009, and September 30, 2017, assessing the prevalence of LVSD and HF in populations with DM1. Retrospective and prospective cohort studies and case series describing the prevalence of LVSD, as evaluated by echocardiography, and HF in patients with DM1 were included. Case reports, simple reviews, commentaries and editorials were excluded. Seven studies were identified as eligible, of which 1 was a retrospective population-based cohort study, and 6 were retrospective single-center-based cohort studies. Echocardiographic data concerning LV function were available for 647 of the 876 patients with DM1 who were included in the analysis. The prevalence of LVSD in patients with DM1, defined as LVEF < 55%, was 13.8%, 4.5-fold higher than in general population. Patients with DM1 and LVSD were older, were more likely to be male, had longer baseline atrioventricular and intraventricular conduction-time durations, had higher incidences of atrial arrhythmias, and were more likely to have undergone device implantation. Also, symptomatic HF is more prevalent in patients with DM1 despite their limited levels of physical activity. Further studies are needed to evaluate the prevalence of LVSD and HF in patients with DM1 and to investigate electrocardiographic abnormalities and other clinical features associated with this condition.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Cardiac Conduction Disorders as Markers of Cardiac Events in Myotonic Dystrophy Type 1

Background Myotonic dystrophy type 1 involves cardiac conduction disorders. Cardiac conduction disease can cause fatal arrhythmias or sudden death in patients with myotonic dystrophy type 1. Methods and Results This study enrolled 506 patients with myotonic dystrophy type 1 (aged ≥15 years; >50 cytosine-thymine-guanine repeats) and was treated in 9 Japanese hospitals for neuromuscular diseases from January 2006 to August 2016. We investigated genetic and clinical backgrounds including health care, activities of daily living, dietary intake, cardiac involvement, and respiratory involvement during follow-up. The cause of death or the occurrence of composite cardiac events (ie, ventricular arrhythmias, advanced atrioventricular blocks, and device implantations) were evaluated as significant outcomes. During a median follow-up period of 87 months (Q1-Q3, 37-138 months), 71 patients expired. In the univariate analysis, pacemaker implantations (hazard ratio [HR], 4.35; 95% CI, 1.22-15.50) were associated with sudden death. In contrast, PQ interval ≥240 ms, QRS duration ≥120 ms, nutrition, or respiratory failure were not associated with the incidence of sudden death. The multivariable analysis revealed that a PQ interval ≥240 ms (HR, 2.79; 95% CI, 1.9-7.19, P<0.05) or QRS duration ≥120 ms (HR, 9.41; 95% CI, 2.62-33.77, P < 0.01) were independent factors associated with a higher occurrence of cardiac events than those observed with a PQ interval <240 ms or QRS duration <120 ms; these cardiac conduction parameters were not related to sudden death. Conclusions Cardiac conduction disorders are independent markers associated with cardiac events. Further investigation on the prediction of occurrence of sudden death is warranted.

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.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Myotonic Dystrophies: Targeting Therapies for Multisystem Disease

Myotonic dystrophy is an autosomal dominant muscular dystrophy not only associated with muscle weakness, atrophy, and myotonia but also prominent multisystem involvement. There are 2 similar, but distinct, forms of myotonic dystrophy; type 1 is caused by a CTG repeat expansion in the DMPK gene, and type 2 is caused by a CCTG repeat expansion in the CNBP gene. Type 1 is associated with distal limb, neck flexor, and bulbar weakness and results in different phenotypic subtypes with variable onset from congenital to very late-onset as well as variable signs and symptoms. The classically described adult-onset form is the most common. In contrast, myotonic dystrophy type 2 is adult-onset or late-onset, has proximal predominant muscle weakness, and generally has less severe multisystem involvement. In both forms of myotonic dystrophy, the best characterized disease mechanism is a RNA toxic gain-of-function during which RNA repeats form nuclear foci resulting in sequestration of RNA-binding proteins and, therefore, dysregulated splicing of premessenger RNA. There are currently no disease-modifying therapies, but clinical surveillance, preventative measures, and supportive treatments are used to reduce the impact of muscular impairment and other systemic involvement including cataracts, cardiac conduction abnormalities, fatigue, central nervous system dysfunction, respiratory weakness, dysphagia, and endocrine dysfunction. Exciting preclinical progress has been made in identifying a number of potential strategies including genome editing, small molecule therapeutics, and antisense oligonucleotide-based therapies to target the pathogenesis of type 1 and type 2 myotonic dystrophies at the DNA, RNA, or downstream target level.

Ventricular Tachycardia Ablation in Nonischemic Cardiomyopathy

Catheter ablation is being increasingly performed as adjunctive treatment to prevent recurrent implantable cardioverter-defibrillator therapies in patients with nonischemic cardiomyopathy and ventricular tachycardia (VT). In the context of VT ablation, nonischemic cardiomyopathy usually refers to dilated cardiomyopathy (DCM) as one morphological phenotype. Over the past decades, progress has been made to better characterize distinct subtypes and to differentiate between causes of DCM, which has important practical and prognostic implications. The goal of this review is to summarize available data on VT ablation in patients with DCM and, more specifically, review procedural and outcome data in specific etiologies and substrate location. It will focus on our current understanding of nonischemic scars, as well as the value of multimodal imaging, image integration, and electroanatomic mapping for substrate identification, procedural planning, and ablation. In addition, recent findings from whole human heart histology of patients with DCM and VT and their potential implications for imaging and mapping will be discussed.

[Bundle branch reentry VT : Diagnosis, mapping, and ablation]

Macroreentry in the His-Purkinje system can result in sustained ventricular tachycardia (VT) termed bundle branch reentry VT. Bundle branch reentry is usually associated with His-Purkinje disease and depressed left ventricular function. In the case of typical bundle branch reentry, the right bundle is activated in the anterograde direction and ventricular depolarization begins at the distal end of the right bundle on the ventricular septum generating a typical left bundle branch block QRS morphology. However, atypical surface ECGs can also be found in patients with severe left ventricular dysfunction and involvement of the right ventricle complicating the diagnosis of bundle branch reentry VT. It is important to diagnose bundle branch reentry VT because patients with bundle branch reentry VT may suffer from a high rate of serial implantable cardioverter defibrillator (ICD) interventions based on VT recurrences due to immediate reinitiation of the arrhythmia. Ablation of the right bundle branch easily cures bundle branch reentry VT and can prevent frequent ICD interventions. After ablation of bundle branch reentry VT, mortality remains high due to the severe left ventricular dysfunction in many patients, and the patients are candidates for cardiac resynchronization therapy (CRT-D).

Optical Mapping Approaches on Muscleblind-Like Compound Knockout Mice for Understanding Mechanistic Insights Into Ventricular Arrhythmias in Myotonic Dystrophy

Background

Cardiac arrhythmias are common causes of death in patients with myotonic dystrophy (dystrophia myotonica [DM]). Evidence shows that atrial tachyarrhythmia is an independent risk factor for sudden death; however, the relationship is unclear.

Methods and Results

Control wild‐type (Mbnl1^+/+; Mbnl2^+/+) and DM mutant (Mbnl1^−/−; Mbnl2^+/−) mice were generated by crossing double heterozygous knockout (Mbnl1^+/−; Mbnl2^+/−) mice. In vivo electrophysiological study and optical mapping technique were performed to investigate mechanisms of ventricular tachyarrhythmias. Transmission electron microscopy scanning was performed for myocardium ultrastructural analysis. DM mutant mice were more vulnerable to anesthesia medications and program electrical pacing: 2 of 12 mice had sudden apnea and cardiac arrest during premedication of general anesthesia; 9 of the remaining 10 had atrial tachycardia and/or atrioventricular block, but none of the wild‐type mice had spontaneous arrhythmias; and 9 of 10 mice had pacing‐induced ventricular tachyarrhythmias, but only 1 of 14 of the wild‐type mice. Optical mapping studies revealed prolonged action potential duration, slower conduction velocity, and steeper conduction velocity restitution curves in the DM mutant mice than in the wild‐type group. Spatially discordant alternans was more easily inducible in DM mutant than wild‐type mice. Transmission electron microscopy showed disarranged myofibrils with enlarged vacuole‐occupying mitochondria in the DM mutant group.

Conclusions

This DM mutant mouse model presented with clinical myofibril ultrastructural abnormality and cardiac arrhythmias, including atrial tachyarrhythmias, atrioventricular block, and ventricular tachyarrhythmias. Optical mapping studies revealed prolonged action potential duration and slow conduction velocity in the DM mice, leading to vulnerability of spatially discordant alternans and ventricular arrhythmia induction to pacing.

Incidence and predictors of sudden death, major conduction defects and sustained ventricular tachyarrhythmias in 1388 patients with myotonic dystrophy type 1

AIMS

To describe the incidence and identify predictors of sudden death (SD), major conduction defects and sustained ventricular tachyarrhythmias (VTA) in myotonic dystrophy type 1 (DM1).

METHODS AND RESULTS

We retrospectively enrolled 1388 adults with DM1 referred to six French medical centres between January 2000 and October 2013. We confirmed their vital status, classified all deaths, and determined the incidence of major conduction defects requiring permanent pacing and sustained VTA. We searched for predictors of overall survival, SD, major conduction defects, and sustained VTA by Cox regression analysis. Over a median 10-year follow-up, 253 (18.2%) patients died, 39 (3.6%) suddenly. Analysis of the cardiac rhythm at the time of the 39 SD revealed sustained VTA in 9, asystole in 5, complete atrioventricular block in 1 and electromechanical dissociation in two patients. Non-cardiac causes were identified in the five patients with SD who underwent autopsies. Major conduction defects developed in 143 (19.3%) and sustained VTA in 26 (2.3%) patients. By Cox regression analysis, age, family history of SD and left bundle branch block were independent predictors of SD, while age, male sex, electrocardiographic conduction abnormalities, syncope, and atrial fibrillation were independent predictors of major conduction defects; non-sustained VTA was the only predictor of sustained VTA.

CONCLUSIONS

SD was a frequent mode of death in DM1, with multiple mechanisms involved. Major conduction defects were by far more frequent than sustained VTA, whose only independent predictor was a personal history of non-sustained VTA. ClinicalTrials.gov no: NCT01136330.

Human His-Purkinje System: Abnormalities of Conduction, Rhythm Disorders and Case Studies

This review covers many of the arrhythmias and conduction abnormalities related to His-Purkinje System. These include junctional premature complexes, junctional and fascicular tachycardias, bundle branch reentry (BBR), and the role of apparent conduction in various forms of supraventricular tachycardias (SVT) with or without involvement of accessory pathways (AP).

Rare Cause of Wide QRS Tachycardia

Cardiac involvement is a well-known feature of neuromuscular diseases. Most commonly cardiac manifestations occur later in the course of the disease. Occasionally severe cardiac disease, including conduction disturbances, life-threatening arrhythmias, and cardiomyopathy, with its impact on prognosis, may be dissociated from peripheral myopathy. We report a case of bundle branch reentrant ventricular tachycardia as primary manifestation of myotonic dystrophy and discuss associated diagnostic and treatment challenges.

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.

Prevalence of type 1 Brugada ECG pattern after administration of Class 1C drugs in patients with type 1 myotonic dystrophy: Myotonic dystrophy as a part of the Brugada syndrome

BACKGROUND

Both type 1 myotonic dystrophy (MD1) and Brugada syndrome (BrS) may be complicated by conduction disturbances and sudden death. Spontaneous BrS has been observed in MD1 patients, but the prevalence of drug-induced BrS in MD1 is unknown.

OBJECTIVE

The purpose of this study was to prospectively assess the prevalence of type 1 ST elevation as elicited during pharmacologic challenge with Class 1C drugs in a subgroup of MD1 patients and to further establish correlations with ECG and electrophysiologic variables and prognosis.

METHODS

From a group of unselected 270 MD1 patients, ajmaline or flecainide drug challenge was performed in a subgroup of 44 patients (27 men, median age 43 years) with minor depolarization/repolarization abnormalities suggestive of possible BrS. The presence of type 1 ST elevation after drug challenge was correlated to clinical, ECG, and electrophysiologic variables.

RESULTS

Eight of 44 patients (18%) presented with BrS after drug challenge. BrS was seen more often in men (26% vs 6%, P = .09) and was related to younger age (35 vs 48 years, P = .07). BrS was not correlated to symptoms, baseline ECG, HV interval, results of signal-averaged ECG, or abnormalities on ambulatory recordings. MD1 patients with BrS had longer corrected QT intervals, greater increase in PR interval after drug challenge, and higher rate of inducible ventricular arrhythmias (62% vs 21%, P = .03). Twelve patients were implanted with a pacemaker and 5 with an implantable cardioverter-defibrillator. Significant bradycardia did not occur in any patients, and malignant ventricular arrhythmia never occurred during median 7-year follow-up (except 1 hypokalemia-related ventricular fibrillation).

CONCLUSION

BrS is elicited by a Class 1 drug in 18% of MD1 patients presenting with minor depolarization/repolarization abnormalities at baseline, but the finding seems to be devoid of a prognostic role.

Myotonic dystrophy type 1 mimics and exacerbates Brugada phenotype induced by Nav1.5 sodium channel loss-of-function mutation

BACKGROUND

Myotonic dystrophy type 1 (DM1), a muscular dystrophy due to CTG expansion in the DMPK gene, can cause cardiac conduction disorders and sudden death. These cardiac manifestations are similar to those observed in loss-of-function SCN5A mutations, which are also responsible for Brugada syndrome (BrS).

OBJECTIVE

The purpose of this study was to investigate DM1 effects on clinical expression of a loss-of-function SCN5A mutation causing BrS.

METHODS

We performed complete clinical evaluation, including ajmaline test, in 1 family combining DM1 and BrS. We screened the known BrS susceptibility genes. We characterized an SCN5A mutation using whole-cell patch-clamp experiments associated with cell surface biotinylation.

RESULTS

The proband, a 15-year-old female, was a survivor of out-of-hospital cardiac arrest with ventricular fibrillation. She combined a DMPK CTG expansion from the father's side and an SCN5A mutation (S910L) from the mother's side. S910L is a trafficking defective mutant inducing a dominant negative effect when transfected with wild-type Nav1.5. This loss-of-function SCN5A mutation caused a Brugada phenotype during the mother's ajmaline test. Surprisingly, in the father, a DM1 patient without SCN5A mutation, ajmaline also unmasked a Brugada phenotype. Furthermore, association of both genetic abnormalities in the proband exacerbated the response to ajmaline with a massive conduction defect.

CONCLUSION

Our study is the first to describe the deleterious effect of DM1 on clinical expression of a loss-of-function SCN5A mutation and to show a provoked BrS phenotype in a DM1 patient. The modification of the ECG pattern by ajmaline supports the hypothesis of a link between DM1 and Nav1.5 loss of -function.