Left Bundle Pacing for Left Bundle Branch Block and Intermittent Third-Degree Atrioventricular Block in a MYH7 Mutation-Related Hypertrophic Cardiomyopathy With Restrictive Phenotype in a Child

MYH7 in cardiomyopathy and skeletal muscle myopathy

Myosin heavy chain gene 7 (MYH7), a sarcomeric gene encoding the myosin heavy chain (myosin-7), has attracted considerable interest as a result of its fundamental functions in cardiac and skeletal muscle contraction and numerous nucleotide variations of MYH7 are closely related to cardiomyopathy and skeletal muscle myopathy. These disorders display significantly inter- and intra-familial variability, sometimes developing complex phenotypes, including both cardiomyopathy and skeletal myopathy. Here, we review the current understanding on MYH7 with the aim to better clarify how mutations in MYH7 affect the structure and physiologic function of sarcomere, thus resulting in cardiomyopathy and skeletal muscle myopathy. Importantly, the latest advances on diagnosis, research models in vivo and in vitro and therapy for precise clinical application have made great progress and have epoch-making significance. All the great advance is discussed here.

Conduction system pacing for ventricular pacing requirement is feasible and effective on patients with hypertrophic cardiomyopathy and cardiac dysfunction

Objective

We aimed to evaluate the feasibility and safety of his-bundle pacing (HBP) and left bundle branch pacing (LBBP) in patients with hypertrophic cardiomyopathy (HCM) and heart failure (HF).

Methods

Patients with HF and interventricular septal thickness (IVST) ≥ 13 mm resulted from HCM, who accepted conduction system pacing (CSP) with a percentage of ventricular pacing > 40% from May 2018 to April 2022 were consecutively enrolled in our center. LBBP was preferred and HBP was the alternative therapy unless IVST ≥ 16 mm or LBBP failed, whereas LBBP would be the alternative therapy if HBP failed in patients with IVST ≥ 16 mm. All patients were followed up for at least one year. Data including clinical, echocardiographic parameters and electrocardiogram measurements, were collected and evaluated in patients with and without left ventricular ejection fraction (LVEF) < 50%.

Results

A total of 27 patients (65.93 ± 9.09 years old) were enrolled and only 3 patients failed in CSP (11.11%) via LBBP (6/13) and HBP (18/21) procedures. LVEF (P = 0.521), left ventricular end-diastolic diameter (LVEDD) (P = 0.816), and QRS duration (P = 0.928) did not worsen after CSP, and left atrial diameter (LAD) (49.58 ± 8.99 mm vs.47.04 ± 9.82 mm, P = 0.045) tended to improve slightly after 19.19 ± 7.71 months follow-up. Of note, LVEF (39.22%±7.51% vs. 45.22%±9.59%, P = 0.015), LVEDD (52.11 ± 10.10 mm vs. 48.33 ± 9.07 mm, P = 0.037), LAD (50.33 ± 8.93 mm vs. 46.11 ± 5.97 mm, P = 0.013) and New York Heart Association (NYHA) grade (2.67 ± 0.5 vs. 1.38 ± 1.02, P = 0.029) improved in 9 patients with LVEF < 50%, whereas LVEF (P = 0.372), LVEDD (P = 0.665), LAD (P = 0.093) and NYHA grade (P = 0.452) did not deteriorate in patients with preserved ejection fraction.

Conclusion

CSP was safe and feasible in patients with HCM and cardiac dysfunction, and did not worsen cardiac performance especially in patients with LVEF < 50%. HBP might be an effective alternative to LBBP in patients with significantly thickened interventricular septum.

Case Report: Hypertrophic cardiomyopathy with recurrent episodes of ventricular fibrillation and concurrent sinus arrest

Background

Hypertrophic cardiomyopathy (HCM) is a serious hereditary cardiomyopathy. It is characterized morphologically by an increased left ventricular wall thickness and mass and functionally by enhanced global chamber function and myocellular contractility, diastolic dysfunction, and myocardial fibrosis development. Typically, patients with HCM experience atrial fibrillation (AF), syncope, and ventricular fibrillation (VF), causing severe symptoms and cardiac arrest. In contrast, sinoatrial node (SAN) arrest in the setting of HCM is uncommon. In particular, during VF, it has not been described so far.

Case summary

In this study, we report an 18-year-old woman patient with sudden cardiac arrest due to VF and successful cardiopulmonary resuscitation as the first clinical manifestation of non-obstructive HCM. Subsequently, a subcutaneous implantable cardioverter-defibrillator (ICD) was implanted for secondary VF prophylaxis. However, additional episodes of VF occurred. During these, device interrogation revealed a combined occurrence of VF, bradycardia, and SAN arrest, requiring a device exchange into a dual-chamber ICD. A heterozygous, pathogenic variant of the MYH7 gene (c.2155C>T; p.Arg719Trp) was identified as causative for HCM.

Discussion

First published in 1994, the particular MYH7 variant (p.Arg719Trp) was described in HCM patients with a high incidence of premature cardiac death and a reduced life expectancy. Electrophysiological studies on HCM patients are mainly performed to treat AF and ventricular tachycardia. Further extraordinary arrhythmic phenotypes were reported only in a few HCM patients. Taken together, the present case with documented co-existing VF and SAN arrest is rare and also emphasizes addressing the presence of SAN arrest (in particular, during VF episodes) in HCM patients when a distinct ICD device is considered for implantation.

Conduction System Pacing versus Conventional Biventricular Pacing for Cardiac Resynchronization Therapy: Where Are We Heading?

Over the last few years, pacing of the conduction system (CSP) has emerged as the new standard pacing modality for bradycardia indications, allowing a more physiological ventricular activation compared to conventional right ventricular pacing. CSP has also emerged as an alternative modality to conventional biventricular pacing for the delivery of cardiac resynchronization therapy (CRT) in heart failure patients. However, if the initial clinical data seem to support this new physiological-based approach to CRT, the lack of large randomized studies confirming these preliminary results prevents CSP from being used routinely in clinical practice. Furthermore, concerns are still present regarding the long-term performance of pacing leads when employed for CSP, as well as their extractability. In this review article, we provide the state-of-the-art of CSP as an alternative to biventricular pacing for CRT delivery in heart failure patients. In particular, we describe the physiological concepts supporting this approach and we discuss the future perspectives of CSP in this context according to the implant techniques (His bundle pacing and left bundle branch area pacing) and the clinical data published so far.

[Recent research on childhood hypertrophic cardiomyopathy caused by MYH7 gene mutations]

Hypertrophic cardiomyopathy (HCM) is the most common monogenic inherited myocardial disease in children, and mutations in sarcomere genes (such as MYH7 and MYBPC3) are the most common genetic etiology of HCM, among which mutations in the MYH7 gene are the most common and account for 30%-50%. MYH7 gene mutations have the characteristics of being affected by environmental factors, coexisting with multiple genetic variations, and age-dependent penetrance, which leads to different or overlapping clinical phenotypes in children, including various cardiomyopathies and skeletal myopathies. At present, the pathogenesis, course, and prognosis of HCM caused by MYH7 gene mutations in children remain unclear. This article summarizes the possible pathogenesis, clinical phenotype, and treatment of HCM caused by MYH7 gene mutations, in order to facilitate the accurate prognostic evaluation and individualized management and treatment of the children with this disorder.

Left Bundle Branch Pacing for Bradycardia in Non-obstructive Hypertrophic Cardiomyopathy Patients: Feasibility, Safety, and Effect

PURPOSE

Left bundle branch pacing (LBBP) is as an innovative physiological pacing approach. The research on LBBP in non-obstructive hypertrophic cardiomyopathy (NOHCM) patients is scarce. This study aimed to assess the feasibility, safety, and effect of LBBP in bradycardia NOHCM patients with permanent pacemaker (PPM) implantation indication.

METHODS

Thirteen consecutive patients with NOHCM who received LBBP were retrospectively enrolled as a hypertrophic cardiomyopathy (HCM) group. Following 1:3 matching, 39 patients without HCM were randomly matched as a control group. Echocardiographic index and pacing parameters were collected.

RESULTS

The successful LBBP was achieved in 96.2% of all cases (50/52), and the success rate of the HCM group was 92.3% (12/13). In the HCM group, the paced QRS duration (from the pacing stimulus to QRS end) was 145.6±20.8 ms. The stimulus to left ventricular activation time (s-LVAT) was 87.4±15.2 ms. In the control group, the paced QRS duration was 139.4±17.2 ms, and the s-LVAT was 79.9±14.1 ms. During the implantation, R-wave sensing and the pacing threshold of the HCM group were significantly higher than the control group (20.2±10.5 vs 12.5±5.9 mV, P < 0.05; 0.8±0.3 vs 0.6±0.2V/0.4 ms, P < 0.05). In addition, the fluoroscopic duration and procedural duration were longer in the HCM group (14.8±8.3 vs 10.3±6.6min, P = 0.07; 131.8±50.5 vs 101.4±41.6 min, P < 0.05). The lead insertion depth was 15±2 mm in the HCM group, and no procedure-related complications occurred. During the 12-month follow-up, pacing parameters remained stable and were of no significance in the two groups. The cardiac function did not deteriorate, and the left ventricular outflow tract gradient (LVOTG) did not increase in the follow-up.

CONCLUSION

LBBP might be feasible and safe for NOHCM patients with conventional bradycardia pacing indication, and there is no deterioration in cardiac function and LVOTG of patients with NOHCM.

Cardiac Resynchronization Therapy and Hypertrophic Cardiomyopathy: A Comprehensive Review

Hypertrophic cardiomyopathy (HCM) is an inherited primary myocardial disease characterized by asymmetrical/symmetrical left ventricle (LV) hypertrophy, with or without LV outflow tract (LVOT) dynamic obstruction, and poor prognosis. Cardiac resynchronization therapy (CRT) has emerged as a minimally invasive tool for patients with heart failure (HF) with decreased LV ejection fraction (LVEF) and prolonged QRS duration of over 120 ms with or without left bundle branch block (LBBB). Several HCM patients are at risk of developing LBBB because of disease progression or secondary to septal myomectomy, while others might develop HF with decreased LVEF, alleged end-stage/dilated HCM, especially those with thin myofilament mutations. Several studies have shown that patients with myectomy-induced LBBB might benefit from left bundle branch pacing or CRT to relieve symptoms, improve exercise capacity, and increase LVEF. Otherwise, patients with end-stage/dilated HCM and prolonged QRS interval could gain from CRT in terms of NYHA class improvement, LV systolic performance increase and, to some degree, LV reverse remodeling. Moreover, several electrical and imaging parameters might aid proper selection and stratification of HCM patients to benefit from CRT. Nonetheless, current available data are scarce and further studies are still required to accurately clarify the view. This review reassesses the importance of CRT in patients with HCM based on current research by contrasting and contextualizing data from various published studies.

Left ventricular pacing in the treatment of pediatric cardiac dysfunction caused by idiopathic complete left bundle branch block

OBJECTIVE

This study aimed to investigate the feasibility and effectiveness of transthoracic epicardial dual-chamber pacemaker implantation in the treatment of cardiac dysfunction caused by idiopathic complete left bundle branch block (CLBBB) in children.

METHODS

Nine children diagnosed with cardiac dysfunction due to idiopathic CLBBB were included in this study. All patients underwent transthoracic epicardial dual-chamber pacemaker implantation. Cardiac function was evaluated using echocardiography during the follow-up. Additionally, intraventricular synchronization parameters were assessed using two-dimensional speckle tracking echocardiography (STE).

RESULTS

Nine children (mean age, 3.0 ± 2.6 years) were included in this study. The median follow-up duration was 2 (interquartile range, 1-3) years. The cardiac function of all patients recovered to normal levels within 1 year postoperatively. The postoperative QRS duration on electrocardiography (142 ± 21 ms) was significantly shorter than that at baseline (106 ± 12 ms) (p < .05). Cardiac dyssynchrony in patients who manifested preoperatively achieved complete correction after pacemaker implantation. The comparison of preoperative and postoperative (last follow-up visit) synchronization parameters were as follows: longitudinal standard deviation of the time to peak strain, 99.0 ± 41.9 versus 36.8 ± 5.0 ms (p = .004); delay time of peak longitudinal strain, 252.2 ± 131.4 versus 35.0 ± 22.9 ms (p = .002); and longitudinal systolic dyssynchrony index, 2.8 ± 0.8% versus 1.0 ± 0.3% (p = .001), respectively.

CONCLUSION

Transthoracic epicardial dual-chamber pacemaker implantation (with left atrial sensing and left ventricular single-site pacing) can be used for the treatment of cardiac dysfunction caused by idiopathic CLBBB in children.

Case report: Rare restrictive cardiomyopathy with ventricular fibrillation as initial symptom rescued by automatic external defibrillator in a pediatric patient

Restrictive cardiomyopathy (RCM) is a rare form of heart muscle disease with poor prognosis. Its primary manifestations were caused by systemic or pulmonary circulation congestion. Here, we reported a case of RCM with ventricular fibrillation as initial symptom in a 7-year-old boy. The child suffered cardiac and respiratory arrest suddenly while exercising at school and immediately was given external chest compression and defibrillation by the school’s equipped automatic external defibrillator (AED). The rescue was successful. At the time of the AED discharge, his electrocardiogram (ECG) indicated ventricular fibrillation. Upon further examination, the echocardiogram revealed enlarged bilateral atria, decreased diastolic function and normal ventricular thickness. Genetic analysis identified a heterozygous missense mutation [c.611(exon8)G&gt;A,p.R204H] of TNNI3 in the proband boy. This case contributes to our understanding of RCM in children and emphasizes the importance of having AEDs available in public places.

Characteristics of Primary Bradyarrhythmia in Hypertrophic Cardiomyopathy: A 10-Year, Single-Center Analysis

Background: Secondary bradyarrhythmias in hypertrophic cardiomyopathy (HCM) have been extensively reported. The prevalence and characteristics of primary bradyarrhythmias in HCM have yet to be investigated. Methods: We retrospectively enrolled 101 consecutive patients with HCM who were referred to the arrhythmia center from May 2010 to October 2020. The clinical features of patients with bradyarrhythmias were analyzed. Results: Twenty-nine (28.7%) patients had primary bradyarrhythmias, and six (5.9%) patients had secondary third-degree atrioventricular block (AVB). Of the 29 patients, 17 (58.6%) had sinus node dysfunction (SND), 14 (48.3%) had AVB, and two (6.9%) had both SND and AVB. The median age was 62 years old, and 69% were male. Six (20.7%) patients had left ventricular obstructive outflow tract obstruction, 15 (51.7%) had a history of syncope, and one (3.4%) had a family history of HCM. Most patients (86.2%) had New York Heart Association functional class I or II, and the median left ventricular ejection fraction was 63%. A total of 22 patients received pacemaker implantation, including 17 (77.3%) dual-chamber pacing, four (18.2%) single-chamber ventricular pacing, and one (4.5%) cardiac resynchronization therapy. Conclusions: Primary bradyarrhythmias need to be evaluated in HCM patients with arrhythmia-related symptoms. Patients with HCM might need pacemaker implantation for primary bradyarrhythmias.

Conduction System Pacing Following Septal Myectomy: Insights into Site of Conduction Block

INTRODUCTION

Septal myectomy for obstructive hypertrophic cardiomyopathy (HCM) is associated with conduction block; however, the electrophysiological characteristics of conduction block have not been well characterized. The aim of study was to assess the feasibility and safety of His bundle pacing (HBP) and left bundle branch area pacing (LBBAP) in patients with septal myectomy-associated conduction block.

METHODS AND RESULTS

Patients with HCM and indications for pacing or cardiac resynchronization therapy after septal myectomy were included. Electrophysiological mapping was performed to identify the site of block. The success rates and pacing characteristics of HBP and LBBAP were also recorded. The echocardiographic data and complications were documented and tracked during follow-up. Ten patients with atrioventricular block (AVB) or left bundle branch block (LBBB) post-myectomy were included in the study. The site of block was infranodal in the nine patients with AVB. HBP failed due to the lack of distal His bundle capture (N=7) or LBBB correction (N=3). LBBAP was successful in nine patients and failed in one. QRS duration narrowed from 163.3 ± 16.6 ms after surgery to 123.6 ± 15.8 ms during LBBAP (P<0.001). The mean depth of the leads was 13.3 ± 4.0 mm (range from 10 to 20 mm). At a mean follow-up of 5.3 ± 3.9 months, pacing parameters and left ventricular ejection fraction remained stable.

CONCLUSIONS

Electrophysiological mapping revealed that the site of block was infra-Hisian and not correctable with HBP in patients with HCM post-myectomy. LBBAP appears to be a more feasible physiological strategy for these patients. This article is protected by copyright. All rights reserved.

Left bundle branch pacing in hypertrophic cardiomyopathy-a novel approach

Symptomatic bradycardia attributed by sick sinus syndrome in hypertrophic cardiomyopathy (HCM) is not commonly seen. Dual chamber pacing with right ventricular apical lead placement is conventional strategy in such scenario. Now physiological pacing which includes left bundle branch (LBB) pacing emerging as new technology for pacemaker implantation. Use of this technique is difficult in HCM due to septal hypertrophy. There is no such case reported so far in the literature where LBB pacing was performed in adult HCM for sick sinus syndrome. Here we present a novel approach of treating irreversible, symptomatic sinus node dysfunction in non-obstructive HCM with implementation of left bundle pacing strategy. Pacing parameters remain stable after 3 months of follow-up.

Phenotypic Diversity of Cardiomyopathy Caused by an MYBPC3 Frameshift Mutation in a Korean Family: A Case Report

Restrictive cardiomyopathy (RCM) is one of the rarest cardiac disorders, with a very poor prognosis, and heart transplantation is the only long-term treatment of choice. We reported that a Korean family presented different cardiomyopathies, such as idiopathic RCM and hypertrophic cardiomyopathy (HCM), caused by the same MYBPC3 mutation in different individuals. A 74-year-old male was admitted for the evaluation of exertional dyspnea, palpitations, and pitting edema in both legs for several months. Transthoracic echocardiography (TTE) showed RCM with biatrial enlargement and pericardial effusion. Cardiac magnetic resonance (CMR) images revealed normal left ventricular chamber size, borderline diffuse left ventricular hypertrophy and very large atria. In contrast to the proband, CMR images showed asymmetric septal hypertrophy of the left ventricle, consistent with a diagnosis of HCM in the proband’s two daughters. Of the five heterozygous variants identified as candidate causes of inherited cardiomyopathy by whole exome sequencing in the proband, Sanger sequencing confirmed the presence of a heterozygous frameshift mutation (NM_000256.3:c.3313_3314insGG; p.Ala1105Glyfs*85) in MYBPC3 in the proband and his affected daughters, but not in his unaffected granddaughter. There is clinical and genetic overlap of HCM with restrictive physiology and RCM, especially when HCM is combined with severe myocardial fibrosis. Family screening with genetic testing and CMR imaging could be excellent tools for the evaluation of idiopathic RCM.