Hypertrophic cardiomyopathy: a review

Preoperative evaluation of systolic murmur with point-of-care echocardiography before an elective thoracic surgery - A case report

BACKGROUND

Systolic murmur suggesting the association of aortic valve (AV) stenosis or obstructive pathology in the left ventricular outflow tract (LVOT) usually requires preoperative echocardiographic evaluation for elective surgery.

CASE

In a 63-year-old female patient undergoing elective thoracic surgery, the systolic murmur was auscultated on the right sternal border of the second intercostal space in the preoperative patient holding area. Point-of-care (POC) transthoracic echocardiography (TTE) demonstrated a systolic jet flow in the LVOT area. The peak systolic velocity of the continuous wave Doppler tracing, aligned to the LVOT and the AV, was approximately 1.5 m/s. The peak/mean pressure gradient was 11/6 mmHg for the AV and 9/5 mmHg for the LVOT. Anesthesia was induced under continuous TTE imaging. Intraoperative transesophageal echocardiography also confirmed the absence of any cardiac pathology.

CONCLUSIONS

POC echocardiography offered a thorough preoperative evaluation of an unexpectedly identified systolic murmur, avoiding a potential delay in the operation schedule for conventional preoperative echocardiographic evaluation.

Cardiac Remodeling and Functional Changes in Patients With Hypertrophic Cardiomyopathy: A Longitudinal Observational Study

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a hereditary cardiac disorder characterized by abnormal thickening of the left ventricular myocardium. This can lead to various clinical manifestations, including sudden death.

AIM

To investigate the cardiac remodeling and functional changes in patients with HCM over a specific time period and explore the impact of different treatment regimens on disease progression.

METHODS

We conducted a prospective longitudinal observational study involving 100 patients diagnosed with HCM. Baseline clinical data, including demographics, medical history, and echocardiographic measurements, were collected. Follow-up assessments were performed at regular intervals over 24 months to track changes in cardiac structure, function, and clinical status. Statistical analysis, including paired t-tests and subgroup analysis, was conducted to identify significant associations and differences between treatment groups.

RESULTS

A total of 100 patients (mean age = 55 years, 50% male) were enrolled in the study. At baseline, echocardiography revealed increased left ventricular wall thickness (mean = 18.5 mm), left atrial dimensions (mean = 39 mm), and ventricular mass (mean = 230 g). During the follow-up period, there was a progressive increase in left ventricular wall thickness (mean change = 1.0 mm/year, p < 0.001), left atrial dimensions (mean change = 3.0 mm/year, p < 0.001), and ventricular mass (mean change = 8 g/year, p = 0.003). Additionally, alterations in diastolic and systolic function parameters were noted, with a decline in E/A ratio (mean change = -0.1 units/year, p = 0.008) and a reduction in ejection fraction (mean change = -2.0% per year, p = 0.001).

CONCLUSION

Our longitudinal observational study provides important insights into the cardiac remodeling and functional changes in patients with HCM over time. The progressive increase in cardiac parameters indicates ongoing disease progression. Additionally, beta-blocker therapy was associated with a slower rate of left ventricular wall thickening. These findings contribute to a better understanding of HCM's natural history and may guide targeted therapeutic approaches to improve patient outcomes.

A Cardiac Magnetic Resonance Study: Comparison of Biventricular Longitudinal Function in Hypertrophic Cardiomyopathy Patients and Normal Individuals

OBJECTIVE

 Hypertrophic cardiomyopathy (HCM) is a genetic disease with an incidence of 0.2%-0.5%. It has a wide range of clinical presentations varying from coincidental diagnoses to heart failure, ventricular arrhythmias and sudden cardiac death. Mitral annular plane systolic excursion (MAPSE) and tricuspid annular plane systolic excursion (TAPSE) are M-mode-derived practical and reproducible measurements of systolic longitudinal displacement of the annular plane. These two measures may be used as markers of the left ventricular and right ventricular longitudinal functions. Currently, there are only a few studies on cardiac magnetic resonance (CMR)-derived TAPSE and MAPSE measurement comparison between the HCM group and normal control group. The aim of our study is to show the differences in CMR-derived TAPSE and MAPSE values between the HCM and normal population.

METHODS

 We evaluated CMR exams of patients diagnosed with HCM and of normal individuals scanned between 2020 and 2021 retrospectively. The patients were from our own institution's and other hospitals' in- and out-patient departments. Data was collected on 36 HCM patients and 34 adults with no known history of cardiac and non-cardiac diseases. All CMR exams were performed on a 1.5 T (Magnetom Avanto, Siemens Healthcare, Erlangen, Germany) scanner. CMR-derived MAPSE and TAPSE were measured on standard four-chamber steady-state free precession (SSFP) cine images and given in millimeters.

RESULTS

 From February 2020 to December 2021, a total of 150 patients were diagnosed with hypertrophic cardiomyopathy. After exclusion, 36 patients with HCM were included in the study and the normal control group comprised 34 individuals. The mean age of the HCM group was 43.2 + 13.5 years, while it was 37.5 + 11.3 in the control group. The female ratio of the HCM group was found to be 36%, while it was 56% in the healthy control group. MAPSE values were significantly higher in the normal control group when compared to the HCM patient group (MAPSE: 14.5 ± 2.9 mm vs. 11.7 ± 3.2 mm; p<0.001), while TAPSE values did not depict a significant difference between the two groups (p=0.627).

CONCLUSIONS

 This study suggests that MAPSE values are significantly lower in the HCM patient group in comparison with the normal control group on CMR scans. Although not statistically significant, TAPSE values are also lower in the HCM group.

Diabetes outcomes in heart failure patients with hypertrophic cardiomyopathy

Aims: We aimed to assess diabetes outcomes in heart failure (HF) patients with hypertrophic cardiomyopathy (HCM). Methods: The National Inpatient Sample database was analyzed to identify records from 2005 to 2015 of patients hospitalized for HF with concomitant HCM. We examined the prevalence of diabetes in those patients, assessed the temporal trend of in-hospital mortality, ventricular fibrillation, atrial fibrillation, and cardiogenic shock and compared diabetes patients to their non-diabetes counterparts. Results: Among patients with HF, 0.26% had HCM, of whom 29.3% had diabetes. Diabetes prevalence increased from 24.8% in 2005 to 32.7% in 2015. The mean age of patients with diabetes decreased from 71 ± 13 to 67.6 ± 14.2 (p < 0.01), but the prevalence of cardiovascular risk factors significantly increased. In-hospital mortality decreased from 4.3% to 3.2% between 2005 and 2015. Interestingly, cardiogenic shock, VF, and AF followed an upward trend. Age (OR = 1.04 [1.03-1.05]), female gender (OR = 1.50 [0.72-0.88]), and cardiovascular risk factors were associated with a higher in-hospital mortality risk in diabetes. Compared to non-diabetes patients, the ones with diabetes were younger and had more comorbidities. Unexpectedly, the adjusted risks of in-hospital mortality (aOR = 0.88 [0.76-0.91]), ventricular fibrillation (aOR = 0.79 [0.71-0.88]) and atrial fibrillation (aOR 0.80 [0.76-0.85]) were lower in patients with diabetes, but not cardiogenic shock (aOR 1.01 [0.80-1.27]). However, the length of stay was higher in patients with diabetes, and so were the total charges per stay. Conclusion: In total, we observed a temporal increase in diabetes prevalence among patients with HF and HCM. However, diabetes was paradoxically associated with lower in-hospital mortality and arrhythmias.

Mavacamten: A First-in-class Oral Modulator of Cardiac Myosin for the Treatment of Symptomatic Hypertrophic Obstructive Cardiomyopathy

Hypertrophic cardiomyopathy is the most common monogenic cardiovascular disease that is caused by sarcomeric protein gene mutations. A hallmark of the most common form of the disease is outflow obstruction secondary to systolic narrowing of the left ventricular outflow tract from septal hypertrophy, mitral valve abnormalities and, most importantly, hyperdynamic contractility. Recent mechanistic studies have identified excessive myosin adenosine triphosphatase activation and actin-myosin cross-bridging as major underlying causes. These studies have led to the development of mavacamten, a first-in-class myosin adenosine triphosphatase inhibitor and the first specific therapy for hypertrophic obstructive cardiomyopathy. Preclinical and subsequent pivotal clinical studies have demonstrated the efficacy and safety of mavacamten. A remarkable improvement among treated patients in peak oxygen consumption, functional capacity, symptom relief and post-exercise left ventricular outflow tract gradient, along with dramatic reductions in heart failure biomarkers, suggests that this new medication will be transformative for the symptom management of hypertrophic obstructive cardiomyopathy. There is also hope and early evidence that mavacamten may delay or obviate the need for invasive septal reduction therapies. In this article, we review the current evidence for the efficacy and safety of mavacamten and highlight important considerations for its clinical use.

The Ace of Spades: Apical Hypertrophic Cardiomyopathy in an African Male Patient

We present a case of a 52-year-old African male patient diagnosed with apical hypertrophic cardiomyopathy. He was initially diagnosed with hypertensive heart disease and placed on anti-failure treatment. Following multiple subsequent presentations and on closer review of his signs and symptoms, apical hypertrophic cardiomyopathy was considered. The diagnosis was made five years after his initial presentation and confirmed by echocardiography and cardiac magnetic resonance imaging. This case report explores his presentation and aims to provide further literature on the aetiology, description, and management of apical hypertrophic cardiomyopathy, particularly within the African population. 

Anatomical-MRI Correlations in Adults and Children with Hypertrophic Cardiomyopathy

Hypertrophic Cardiomyopathy (HCM) is the most frequent hereditary cardiovascular disease and the leading cause of sudden cardiac death in young individuals. Advancements in CMR imaging have allowed for earlier identification and more accurate prognosis of HCM. Interventions aimed at slowing or stopping the disease’s natural course may be developed in the future. CMR has been validated as a technique with high sensitivity and specificity, very few contraindications, a low risk of side effects, and is overall a good tool to be employed in the management of HCM patients. The goal of this review is to evaluate the magnetic resonance features of HCM, starting with distinct phenotypic variants of the disease and progressing to differential diagnoses of athlete’s heart, hypertension, and infiltrative cardiomyopathies. HCM in children has its own section in this review, with possible risk factors that are distinct from those in adults; delayed enhancement in children may play a role in risk stratification in HCM. Finally, a number of teaching points for general cardiologists who recommend CMR for patients with HCM will be presented.

NATURAL LANGUAGE PROCESSING BASED MACHINE LEARNING MODEL USING CARDIAC MRI REPORTS TO IDENTIFY HYPERTROPHIC CARDIOMYOPATHY PATIENTS

Hypertrophic Cardiomyopathy (HCM) is the most common genetic heart disease in the US and is known to cause sudden death (SCD) in young adults. While significant advancements have been made in HCM diagnosis and management, there is a need to identify HCM cases from electronic health record (EHR) data to develop automated tools based on natural language processing guided machine learning (ML) models for accurate HCM case identification to improve management and reduce adverse outcomes of HCM patients. Cardiac Magnetic Resonance (CMR) Imaging, plays a significant role in HCM diagnosis and risk stratification. CMR reports, generated by clinician annotation, offer rich data in the form of cardiac measurements as well as narratives describing interpretation and phenotypic description. The purpose of this study is to develop an NLP-based interpretable model utilizing impressions extracted from CMR reports to automatically identify HCM patients. CMR reports of patients with suspected HCM diagnosis between the years 1995 to 2019 were used in this study. Patients were classified into three categories of yes HCM, no HCM and, possible HCM. A random forest (RF) model was developed to predict the performance of both CMR measurements and impression features to identify HCM patients. The RF model yielded an accuracy of 86% (608 features) and 85% (30 features). These results offer promise for accurate identification of HCM patients using CMR reports from EHR for efficient clinical management transforming health care delivery for these patients.

Sex differences in the prognosis of patients with hypertrophic cardiomyopathy

We investigated sex-related differences in the prognosis of patients with hypertrophic cardiomyopathy (HCM) using the Korea National Health Insurance Service database. From 2010 to 2016, 9524 patients diagnosed with HCM and had more than 1-year follow-up period were analyzed. The primary endpoint was the composite of cardiovascular death or new-onset heart failure (HF) admission. Propensity score-matching analysis was performed to adjust for different baseline characteristics. With a 4.4-years’ median follow-up interval (range 2.0–6.6 years) and male predominance (77.6%), women with HCM were older (52.6 ± 9.7 vs. 51.4 ± 9.1, p < 0.001), had lower incomes, more comorbidities based on Charlson comorbidity index. Women with HCM had a higher incidence of the primary endpoint than men (incidence rate: 34.15 vs. 22.83 per 1000 person-years, log-rank p < 0.001). Multivariable Cox analysis showed that female sex was a poor prognostic factor for the primary endpoint (HR 1.43, 95% CI 1.24–1.64, p < 0.001). This was mainly driven by a higher incidence of new-onset HF admission (HR 1.55, 95% CI 1.34–1.80). However, there was no difference in the incidence of cardiovascular death between the sexes. This result was concordant in the propensity score-matched cohort. In conclusion, women with HCM have worse prognosis, which was mainly driven by a higher new-onset HF admission.

Heat shock proteins and small nucleolar RNAs are dysregulated in a Drosophila model for feline hypertrophic cardiomyopathy

In cats, mutations in myosin binding protein C (encoded by the MYBPC3 gene) have been associated with hypertrophic cardiomyopathy (HCM). However, the molecular mechanisms linking these mutations to HCM remain unknown. Here, we establish Drosophila melanogaster as a model to understand this connection by generating flies harboring MYBPC3 missense mutations (A31P and R820W) associated with feline HCM. The A31P and R820W flies displayed cardiovascular defects in their heart rates and exercise endurance. We used RNA-seq to determine which processes are misregulated in the presence of mutant MYBPC3 alleles. Transcriptome analysis revealed significant downregulation of genes encoding small nucleolar RNA (snoRNAs) in exercised female flies harboring the mutant alleles compared to flies that harbor the wild-type allele. Other processes that were affected included the unfolded protein response and immune/defense responses. These data show that mutant MYBPC3 proteins have widespread effects on the transcriptome of co-regulated genes. Transcriptionally differentially expressed genes are also candidate genes for future evaluation as genetic modifiers of HCM as well as candidate genes for genotype by exercise environment interaction effects on the manifestation of HCM; in cats as well as humans.

Heat shock proteins and small nucleolar RNAs are dysregulated in a Drosophila model for feline hypertrophic cardiomyopathy

In cats, mutations in myosin binding protein C (encoded by the MYBPC3 gene) have been associated with hypertrophic cardiomyopathy (HCM). However, the molecular mechanisms linking these mutations to HCM remain unknown. Here, we establish Drosophila melanogaster as a model to understand this connection by generating flies harboring MYBPC3 missense mutations (A31P and R820W) associated with feline HCM. The A31P and R820W flies displayed cardiovascular defects in their heart rates and exercise endurance. We used RNA-seq to determine which processes are misregulated in the presence of mutant MYBPC3 alleles. Transcriptome analysis revealed significant downregulation of genes encoding small nucleolar RNA (snoRNAs) in exercised female flies harboring the mutant alleles compared to flies that harbor the wild-type allele. Other processes that were affected included the unfolded protein response and immune/defense responses. These data show that mutant MYBPC3 proteins have widespread effects on the transcriptome of co-regulated genes. Transcriptionally differentially expressed genes are also candidate genes for future evaluation as genetic modifiers of HCM as well as candidate genes for genotype by exercise environment interaction effects on the manifestation of HCM; in cats as well as humans.

[Echocardiography in the Assessment of Intraventricular Flows and Pressure Gradients in Obstructive Hypertrophic Cardiomyopathy]

Aim      To evaluate results of myomectomy by intraventricular pressure gradients (IVPG) and blood flows in patients with obstructive hypertrophic cardiomyopathy (OHCMP).Material and methods  The study included a total of 76 subjects, 42 patients with OHCMP (mean age, 39±7 years) and 34 healthy volunteers (mean age, 41±3 years). Prior to and after myomectomy, transthoracic echocardiography was performed and followed by digital image processing and calculation of IVPG and left ventricular (LV) vortex flows. Vector analysis was used to estimate the myocardial displacement rate (V), vortex flows, and LV apex-to-base pressure gradients.Results The study showed a dynamic decrease in the LV apex-to-outflow IVPG by more than 50% and recovery of myocardial contraction velocity in the septal area (р&lt;0.001). The decrease in LV cavity pressure gradient serves as an index for evaluating the effectiveness of OHCMP correction. Myomectomy reduces the load on the myocardium and abolishes mitral valve regurgitation with improvement of LV blood flows as also evidenced by the dynamics of long axis velocity change during the cardiac cycle (dL / dt) and the myocardial contraction velocity (V).Conclusion      Effectiveness of the surgical correction of OHCMP is based on the dynamics of myocardial contraction velocities, vortex blood flows, and a decrease in LV apex-to-base IVPG.

Multiscale Modeling of Cardiovascular Function Predicts That the End-Systolic Pressure Volume Relationship Can Be Targeted via Multiple Therapeutic Strategies

Most patients who develop heart failure are unable to elevate their cardiac output on demand due to impaired contractility and/or reduced ventricular filling. Despite decades of research, few effective therapies for heart failure have been developed. In part, this may reflect the difficulty of predicting how perturbations to molecular-level mechanisms that are induced by drugs will scale up to modulate system-level properties such as blood pressure. Computer modeling might help with this process and thereby accelerate the development of better therapies for heart failure. This manuscript presents a new multiscale model that uses a single contractile element to drive an idealized ventricle that pumps blood around a closed circulation. The contractile element was formed by linking an existing model of dynamically coupled myofilaments with a well-established model of myocyte electrophysiology. The resulting framework spans from molecular-level events (including opening of ion channels and transitions between different myosin states) to properties such as ejection fraction that can be measured in patients. Initial calculations showed that the model reproduces many aspects of normal cardiovascular physiology including, for example, pressure-volume loops. Subsequent sensitivity tests then quantified how each model parameter influenced a range of system level properties. The first key finding was that the End Systolic Pressure Volume Relationship, a classic index of cardiac contractility, was ∼50% more sensitive to parameter changes than any other system-level property. The second important result was that parameters that primarily affect ventricular filling, such as passive stiffness and Ca²⁺ reuptake via sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA), also have a major impact on systolic properties including stroke work, myosin ATPase, and maximum ventricular pressure. These results reinforce the impact of diastolic function on ventricular performance and identify the End Systolic Pressure Volume Relationship as a particularly sensitive system-level property that can be targeted using multiple therapeutic strategies.

Heart Failure in Humans Reduces Contractile Force in Myocardium From Both Ventricles

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Contractile assays were performed using multicellular preparations isolated from the left and right ventricles of organ donors and patients with heart failure.

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Heart failure reduced maximum force and power by approximately 30% in the myocardium from both ventricles.

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Heart failure increased the Ca²⁺ sensitivity of contraction, but the effect was bigger in right ventricular tissue than in left ventricular samples.

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The changes in Ca²⁺ sensitivity may reflect ventricle-specific post-translational modifications to sarcomeric proteins.

This study measured how heart failure affects the contractile properties of the human myocardium from the left and right ventricles. The data showed that maximum force and maximum power were reduced by approximately 30% in multicellular preparations from both ventricles, possibly because of ventricular remodeling (e.g., cellular disarray and/or excess fibrosis). Heart failure increased the calcium (Ca²⁺) sensitivity of contraction in both ventricles, but the effect was bigger in right ventricular samples. The changes in Ca²⁺ sensitivity were associated with ventricle-specific changes in the phosphorylation of troponin I, which indicated that adrenergic stimulation might induce different effects in the left and right ventricles.

Isogenic models of hypertrophic cardiomyopathy unveil differential phenotypes and mechanism-driven therapeutics

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a prevalent and complex cardiovascular condition. Despite being strongly associated with genetic alterations, wide variation of disease penetrance, expressivity and hallmarks of progression complicate treatment. We aimed to characterize different human isogenic cellular models of HCM bearing patient-relevant mutations to clarify genetic causation and disease mechanisms, hence facilitating the development of effective therapeutics.

METHODS

We directly compared the p.β-MHC-R453C and p.ACTC1-E99K HCM-associated mutations in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and their healthy isogenic counterparts, generated using CRISPR/Cas9 genome editing technology. By harnessing several state-of-the-art HCM phenotyping techniques, these mutations were investigated to identify similarities and differences in disease progression and hypertrophic signaling pathways, towards establishing potential targets for pharmacological treatment. CRISPR/Cas9 knock-in of the genetically-encoded calcium indicator R-GECO1.0 to the AAVS1 locus into these disease models resulted in calcium reporter lines.

RESULTS

Confocal line scan analysis identified calcium transient arrhythmias and intracellular calcium overload in both models. The use of optogenetics and 2D/3D contractility assays revealed opposing phenotypes in the two mutations. Gene expression analysis highlighted upregulation of CALM1, CASQ2 and CAMK2D, and downregulation of IRF8 in p.β-MHC-R453C mutants, whereas the opposite changes were detected in p.ACTC1-E99K mutants. Contrasting profiles of nuclear translocation of NFATc1 and MEF2 between the two HCM models suggest differential hypertrophic signaling pathway activation. Calcium transient abnormalities were rescued with combination of dantrolene and ranolazine, whilst mavacamten reduced the hyper-contractile phenotype of p.ACTC1-E99K hiPSC-CMs.

CONCLUSIONS

Our data show that hypercontractility and molecular signaling within HCM are not uniform between different gene mutations, suggesting that a 'one-size fits all' treatment underestimates the complexity of the disease. Understanding where the similarities (arrhythmogenesis, bioenergetics) and differences (contractility, molecular profile) lie will allow development of therapeutics that are directed towards common mechanisms or tailored to each disease variant, hence providing effective patient-specific therapy.

Impact of gender on heart failure presentation in non-obstructive hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic cardiac disease that represents a broad spectrum of morphologic features and clinical presentations. However, little is known about the impact of gender differences in heart failure (HF) development in non-obstructive HCM. We assessed clinical and echocardiographic parameters according to gender in patients with non-obstructive HCM and evaluated the impact of gender on HF presentation and cardiovascular (CV) outcomes in this population. We investigated 202 consecutive patients with non-obstructive HCM. Clinical parameters and conventional echocardiographic measurements including tissue Doppler measurements were evaluated and compared according to gender. Additionally, left ventricular (LV) deformation was assessed with global longitudinal strain (GLS) utilizing 2D speckle tracking software. Of the 202 patients (age = 63 ± 14 years, male: female = 141: 61), 51 patients (24.8%) presented with HF and female patients had HF more frequently (52.5% vs. 12.8%, P < 0.001). Females were older, had a higher prevalence of atrial fibrillation, had increased left atrial volume (LAV), and a higher ratio of early diastolic mitral inflow to early annular velocity (E/e') than males (70 ± 12 years vs. 59 ± 14 years, P < 0.001 for age; 51.4 ± 19.3 mL/m² vs. 40.0 [Formula: see text] 13.4 mL/m², P < 0.001 for indexed LAV; 17.2 [Formula: see text] 6.0 vs. 13.0 [Formula: see text] 4.3, P < 0.001 for E/e'). While LV maximal thickness and LV ejection fraction were comparable between men and women, GLS was decreased significantly in female patients (- 13.5 [Formula: see text] 3.4% vs. - 15.6 [Formula: see text] 4.0%, P = 0.001 for GLS). Even after adjusting for clinical factors, female was independently associated with HF presentation (Odd ratio 5.19, 95% CI 2.24-12.03, P < 0.001). During a median follow-up duration 34.0 months, 20 patients (9.9%) had HF hospitalization or CV death. In a multivariable analysis, female gender was associated with higher risk of the composite of HF hospitalization or CV death and HF hospitalization alone than male (Adjusted hazard ratio [HR] = 3.31, 95% CI 1.17-9.35, P = 0.024 for primary composite outcome of HF hospitalization or CV death; adjusted HR = 4.78, 95% CI 1.53-14.96, P = 0.007 for HF hospitalization). In patients with non-obstructive HCM, female patients presented with HF more frequently and showed a higher risk of CV events than male patients. LA volume, E/e' and LV mechanics were different between the genders, suggesting that these might contribute to greater susceptibility to HF in women with HCM.

Hypertrophic cardiomyopathy-linked variants of cardiac myosin-binding protein C3 display altered molecular properties and actin interaction

The most common inherited cardiac disorder, hypertrophic cardiomyopathy (HCM), is characterized by thickening of heart muscle, for which genetic mutations in cardiac myosin-binding protein C3 (c-MYBPC3) gene, is the leading cause. Notably, patients with HCM display a heterogeneous clinical presentation, onset and prognosis. Thus, delineating the molecular mechanisms that explain how disparate c-MYBPC3 variants lead to HCM is essential for correlating the impact of specific genotypes on clinical severity. Herein, five c-MYBPC3 missense variants clinically associated with HCM were investigated; namely V1 (R177H), V2 (A216T), V3 (E258K), V4 (E441K) and double mutation V5 (V3 + V4), all located within the C1 and C2 domains of MyBP-C, a region known to interact with sarcomeric protein, actin. Injection of the variant complementary RNAs in zebrafish embryos was observed to recapitulate phenotypic aspects of HCM in patients. Interestingly, V3- and V5-cRNA injection produced the most severe zebrafish cardiac phenotype, exhibiting increased diastolic/systolic myocardial thickness and significantly reduced heart rate compared with control zebrafish. Molecular analysis of recombinant C0-C2 protein fragments revealed that c-MYBPC3 variants alter the C0-C2 domain secondary structure, thermodynamic stability and importantly, result in a reduced binding affinity to cardiac actin. V5 (double mutant), displayed the greatest protein instability with concomitant loss of actin-binding function. Our study provides specific mechanistic insight into how c-MYBPC3 pathogenic variants alter both functional and structural characteristics of C0-C2 domains leading to impaired actin interaction and reduced contractility, which may provide a basis for elucidating the disease mechanism in HCM patients with c- MYBPC3 mutations.

Cardiac MR Imaging of Hypertrophic Cardiomyopathy: Techniques, Findings, and Clinical Relevance

Hypertrophic cardiomyopathy (HCM) is a relatively common myocardial genetic disease having a wide variety of symptoms and prognoses. The most serious complications of HCM are sudden cardiac death induced by ventricular arrhythmia or inappropriate changes in blood pressure, and heart failure. Cardiac MR imaging is a valuable imaging method for detecting HCM because of its accurate measurement of wall thickness and myocardial mass without limited view and the unique ability of late gadolinium enhancement (LGE) to identify myocardial fibrosis related to the prognosis of HCM. Tagging and T₁ or T₂ mapping MR imaging techniques have emerged as quantitative methods for the evaluation of disease severity. In this review, we introduce the MR imaging techniques applied to HCM and demonstrate the typical phenotypes and some morphological characteristics of HCM. In addition, we discuss the clinical relevance of MR imaging for risk stratification and management of HCM.

Massively Parallel Sequencing of Genes Implicated in Heritable Cardiac Disorders: A Strategy for a Small Diagnostic Laboratory

Sudden cardiac death (SCD) in people before the age of 35 years is a devastating event for any family. The causes of SCD in the young can be broadly divided into two groups: heritable cardiac disorders that affect the heart structure (cardiomyopathies) and primary electrical disorders (cardiac ion channelopathies). Genetic testing is vital as those suffering from cardiac ion channelopathies have structurally normal hearts, and those with cardiomyopathies may only show subtle abnormalities in the heart and these signs may not be detected during an autopsy. Post-mortem genetic testing of SCD victims is important to identify the underlying genetic cause. This is important as family cascade screening may be undertaken to identify those who may be at risk and provide vital information about risk stratification and clinical management. The development of massively parallel sequencing (MPS) has made it possible for the simultaneous screening of multiple patients for hundreds of genes. In light of this, we opted to develop an MPS approach for SCD analysis that would allow us to screen for mutations in genes implicated in cardiomyopathies and cardiac ion channelopathies. The rationale behind this panel was to limit it to genes carrying the greatest mutation load. If no likely pathogenic gene variant were found then testing could cascade to whole exome/genome sequencing as a gene-discovery exercise. The overarching aim was to design and validate a custom-cardiac panel that satisfies the diagnostic requirements of LabPLUS (Auckland City Hospital, Auckland, NZ) and the guidelines provided by the Royal College of Pathologists of Australasia and the Association for Clinical Genetic Science.

Sudden cardiac death: focus on the genetics of channelopathies and cardiomyopathies

Sudden cardiac death (SCD) describes a natural and unexpected death from cardiac causes occurring within a short period of time (generally within 1 h of symptom onset) in the absence of any other potentially lethal condition. Most SCD-related diseases have a genetic basis; in particular congenital cardiac channelopathies and cardiomyopathies have been described as leading causes of SCD. Congenital cardiac channelopathies are primary electric disorders caused by mutations affecting genes encoding cardiac ion channels or associated proteins, whereas cardiomyopathies are related to mutations in genes encoding several categories of proteins, including those of sarcomeres, desmosomes, the cytoskeleton, and the nuclear envelope. The purpose of this review is to provide a general overview of the main genetic variants that have been linked to the major congenital cardiac channelopathies and cardiomyopathies. Functional alterations of the related proteins are also described.

MYBPC3 mutations are associated with a reduced super-relaxed state in patients with hypertrophic cardiomyopathy

The “super-relaxed state” (SRX) of myosin represents a ‘reserve’ of motors in the heart. Myosin heads in the SRX are bound to the thick filament and have a very low ATPase rate. Changes in the SRX are likely to modulate cardiac contractility. We previously demonstrated that the SRX is significantly reduced in mouse cardiomyocytes lacking cardiac myosin binding protein–C (cMyBP-C). Here, we report the effect of mutations in the cMyBP-C gene (MYBPC3) using samples from human patients with hypertrophic cardiomyopathy (HCM). Left ventricular (LV) samples from 11 HCM patients were obtained following myectomy surgery to relieve LV outflow tract obstruction. HCM samples were genotyped as either MYBPC3 mutation positive (MYBPC3_mut) or negative (HCM_smn) and were compared to eight non-failing donor hearts. Compared to donors, only MYBPC3_mut samples display a significantly diminished SRX, characterised by a decrease in both the number of myosin heads in the SRX and the lifetime of ATP turnover. These changes were not observed in HCM_smn samples. There was a positive correlation (p < 0.01) between the expression of cMyBP-C and the proportion of myosin heads in the SRX state, suggesting cMyBP-C modulates and maintains the SRX. Phosphorylation of the myosin regulatory light chain in MYBPC3_mut samples was significantly decreased compared to the other groups, suggesting a potential mechanism to compensate for the diminished SRX. We conclude that by altering both contractility and sarcomeric energy requirements, a reduced SRX may be an important disease mechanism in patients with MYBPC3 mutations.

Mutation Analysis of Three Exons of Myosin-Binding Protein C3 in Patients with Hypertrophic Cardiomyopathy

Background: Hypertrophic cardiomyopathy is a genetic disorder with a prevalence rate of 0.2% in the general population. It comes from mutations in sarcomeric proteins. Cardiac myosin-binding protein C3 is one of the critical genes in hypertrophic cardiomyopathy (HCM) and sudden cardiac death, accounting for about 20% of HCM-causing mutations. Genetic testing is recommended in patients with HCM. The aim of the current study was to find possible disease-causing mutations in 3 exons of the gene myosin-binding protein C (MYBPC3) in patients with HCM. Methods: Fifty subjects with documented known HCM were enrolled in the study. The patients were referred to the hospitals affiliated to Tehran University of Medical Sciences between 2008 and 2011. Peripheral blood samples were collected, as well as clinical and demographic data. The nucleotide sequences of the exons number 7, 16, and 18 of MYBPC3, whose relevance to the disease was previously reported, were amplified by polymerase chain reaction. Direct DNA sequencing was applied, and the Chromas software was used to analyze the sequences to find possible disease-causing mutations. Results: The study population comprised 73% male and 27% female patients. The mean age of the patients was 33.9 ± 20.08 years. Family history of sudden cardiac death was reported in 48.2% of the patients. About 79% of the studied subjects had a history of at least 1 other affected relative in their families. Laboratory findings did not show mutations or any nucleotide changes in the sequences of the 3 target exons in the genomic DNA of the studied patients with HCM. Conclusion: The nucleotide sequences of the exons number 7, 16, and 18 of MYBPC3 were not mutated in the 50 studied subjects with HCM.

Ablation of cardiac myosin binding protein-C disrupts the super-relaxed state of myosin in murine cardiomyocytes

Cardiac myosin binding protein-C (cMyBP-C) is a structural and regulatory component of cardiac thick filaments. It is observed in electron micrographs as seven to nine transverse stripes in the central portion of each half of the A band. Its C-terminus binds tightly to the myosin rod and contributes to thick filament structure, while the N-terminus can bind both myosin S2 and actin, influencing their structure and function. Mutations in the MYBPC3 gene (encoding cMyBP-C) are commonly associated with hypertrophic cardiomyopathy (HCM). In cardiac cells there exists a population of myosin heads in the super-relaxed (SRX) state, which are bound to the thick filament core with a highly inhibited ATPase activity. This report examines the role cMyBP-C plays in regulating the population of the SRX state of cardiac myosin by using an assay that measures single ATP turnover of myosin. We report a significant decrease in the proportion of myosin heads in the SRX state in homozygous cMyBP-C knockout mice, however heterozygous cMyBP-C knockout mice do not significantly differ from the wild type. A smaller, non-significant decrease is observed when thoracic aortic constriction is used to induce cardiac hypertrophy in mutation negative mice. These results support the proposal that cMyBP-C stabilises the thick filament and that the loss of cMyBP-C results in an untethering of myosin heads. This results in an increased myosin ATP turnover, further consolidating the relationship between thick filament structure and the myosin ATPase.

Vascular Endothelial Growth Factor Is Associated with the Morphologic and Functional Parameters in Patients with Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is mostly autosomal dominant disease of the myocardium, which is characterized by myocardial hypertrophy. Vascular endothelial growth factor (VEGF) is involved in myocyte function, growth, and survival. The aim of study was to analyze the clinical significance of VEGF in structural and functional changes in patient with HCM.

METHODS

In a group of 21 patients with nonobstructive HCM, we assessed serum VEGF and analyzed its association with morphological and functional parameters. Compared to healthy controls, serum VEGF was increased: 199 (IQR: 120.4-260.8) ng/L versus 20 (IQR: 14.8-37.7) ng/L, P < 0.001. VEGF levels were associated with left atrium diameter (r = 0.51, P = 0.01), left ventricle ejection fraction (r = -0.56, P = 0.01), fractional shortening (r = -0.54, P = 0.02), left ventricular mass (r = 0.61, P = 0.03), LV mass index (r = 0.46, P = 0.04), vena cava inferior diameter (r = 0.65, P = 0.01), and peak gradient of tricuspid regurgitation (r = 0.46, P = 0.03).

CONCLUSIONS

Increased VEGF level is associated with structural and functional parameters in patients with HCM and serves as a potential tool for diagnostic process of these patients.