Hypertrophic Cardiomyopathy Phenotype Research Articles

The molecular and cellular landscape of hypertrophic cardiomyopathy phenotypes: transition from obstructive to end-stage heart failure.

Hypertrophic cardiomyopathy (HCM) is a myocardial disorder which commonly presents as an obstructive or end-stage disease. This study aims to investigate the transcriptomic changes related to cardiac cell-specific expression profiles that underpin the molecular transition between the HCM phenotypes. This study utilizes bioinformatics meta-analysis to integrate independent datasets to generate a comprehensive gene expression profile of obstructive HCM and end-stage HCM phenotypes compared to donor hearts. Gene set enrichment and cellular deconvolution were applied to identify ontologies and pathways related to each phenotype and to enumerate cell abundances. The intersection between cell lineage genes and meta-genes was identified to explore the cellular contribution to the phenotypic molecular signatures. Meta-analysis revealed, enhanced muscle function and myocardial remodeling, alongside impaired immune and inflammatory processes in obstructive HCM. In contrast, enriched tissue matrix remodeling pathways and altered metabolic and signaling cascades were identified in end-stage HCM, indicating a shift towards cellular dysfunction and loss of homeostasis. These molecular profiles were associated with an altered cellular landscape, with increased cardiomyocytes and lower immune cell populations in obstructive samples but increased fibroblasts and smooth muscle cells in end-stage HCM, implicating extensive tissue remodeling. This study provides novel insights into the cellular contributions of contractile, immune, homeostatic, and vascular alterations underpinning each of the HCM phenotypes. KEY MESSAGES: HCM phenotypes are characterized by distinct molecular and cellular profiles. Obstructive HCM has an enriched contractile profile underpinned by an expanded cardiomyocyte population. End-stage HCM shifts the cellular profile towards extracellular and vascular remodeling.

Genetic variations in PTPN11 lead to a recurrent Left Ventricular Outflow Tract Obstruction phenotype in childhood hypertrophic cardiomyopathy

ObjectiveLeft ventricular septal myotomy provides a favorable prognosis for children with hypertrophic obstructive cardiomyopathy (HOCM). However, some children still suffer from recurrent left ventricular outflow tract obstruction (LVOTO) after surgery. Poor prognosis exists for HOCM caused by PTPN11 mutation. Therefore, the aim of this study was to determine the clinical features of recurrent obstruction in children with HOCM caused by pathogenic mutations in the PTPN11 gene. MethodsA total of 56 children were diagnosed with HOCM underwent septal myectomies. Whole exome sequencing of 49 pediatric cardiomyopathies associated genes (including PTPN11) were performed. We performed hematoxylin-eosin(H&E), Masson, and wheat germ agglutinin (WGA)staining of tissues positive for PTPN11 and those negative for PTPN11 were conducted. ResultsWhole exome sequencing results showed 11 PTPN11 mutation (19.6%) children. In long-term follow-up (median 37 months, maximum 9 years), children with PTPN11 mutation had 6(54.5%) recurrent LVOTO compared with other groups (P=.015), but similar survival rates(P=.514). The mean postoperative time to recurrent obstruction was 22±27 months. Children with PTPN11 mutation were 9-fold more likely to experience the risk associated with recurrent obstruction (95% CI = 1.77-45.81, P<.001). H&E, Masson and WGA staining also revealed more cardiomyocyte hypertrophy in PTPN11 mutation tissues. See Figure 4 for a graphical abstract of the study. ConclusionChildren with PTPN11 mutation-associated hypertrophic cardiomyopathy have a higher risk of recurrent LVOTO.

Distinct mechanisms drive divergent phenotypes in hypertrophic and dilated cardiomyopathy associated TPM1 variants.

Hypertrophic and dilated cardiomyopathies (HCM and DCM, respectively) are inherited disorders that may be caused by mutations to the same sarcomeric protein but have completely different clinical phenotypes. The precise mechanisms by which point mutations within the same gene bring about phenotypic diversity remain unclear. Our objective has been to develop a mechanistic explanation of diverging phenotypes in two TPM1 mutations, E62Q (HCM) and E54K (DCM). Drawing on data from the literature and experiments with stem cell-derived cardiomyocytes expressing the TPM1 mutations of interest, we constructed computational simulations that provide plausible explanations of the distinct muscle contractility caused by each variant. In E62Q, increased calcium sensitivity and hypercontractility was explained most accurately by a reduction in effective molecular stiffness of tropomyosin and alterations in its interactions with the actin thin filament that favor the 'closed' regulatory state. By contrast, the E54K mutation appeared to act via long-range allosteric interactions to increase the association rate of the C-terminal troponin I mobile domain to tropomyosin/actin. These mutation-linked molecular events produced diverging alterations in gene expression that can be observed in human engineered heart tissues. Modulators of myosin activity confirmed our proposed mechanisms by rescuing normal contractile behavior in accordance with predictions.

Three-dimensional Feature Tracking Cardiac Magnetic Resonance in Hypertrophic Cardiomyopathy: Comparison with Two-Dimensional Algorithm

Abstract Aim The aims of this study were to: 1) determine whether 2D and 3D feature tracking cardiac magnetic resonance (FT-CMR) are equivalent in patients with hypertrophic cardiomyopathy (HCM), 2) compare 3D FT-CMR values in HCM and healthy volunteers and 3) compare FT-CMR in most frequent HCM phenotypes. Methods Consecutive patients with HCM and LVEF&gt;55% were included in the study. FT-CMR parameters included left ventricular (LV) global longitudinal (GLS), circumferential (GCS) and radial (GRS) strain, which were calculated using both 2D and 3D FT-CMR derived from multi-slice 2D cine image stacks in the LV short and long axis plane. FT was calculated using Circle Cvi42 software. Results Sixty HCM patients (66.7% male, mean age 58.2 ± 15.8 years) were included (56.7% septal HCM, 25% apical HCM). FT analysis was feasible in all individuals. Seventy-two percent of patients exhibited focal fibrosis in 2 [0-4] segments. As previously reported for healthy individuals, myocardial strain evaluated using 3D FT-CMR was consistently lower compared to 2D FT-CMR. The highest level of agreement was noted between the 2D and 3D values of GCS, with a mean difference of -0.3% (95% CI -1.81 to 1.2, p=0.68), while GRS showed the lowest agreement. In patients with apical HCM GLS 3D was significantly more reduced than in patients with septal HCM (-7.4% ± 4.1 vs. -10.5% ± 2.9, p=0.004). Conclusions 3D FT-CMR is feasible in HCM patients. 3D FT is advantageous as it does not require additional scanning time, making it suitable for HCM patients with limited acoustic window and abnormal geometry.

Diagnostic capabilities of cardiac computed tomography in the preoperative diagnosis of hypertrophic cardiomyopathy

BACKGROUND: A comprehensive approach to studying hypertrophic cardiomyopathy with diagnostic equipment and the latest scanning methods will ensure quality control and effective treatment of patients with this condition. The implementation of innovative technologies and computer calculation using next-generation scanners may become relevant and promising in studying various phenotypes of left ventricular remodeling in combination with abnormalities of the chordopapillary apparatus of the mitral valve and myocardial structure. AIM: To examine the diagnostic capabilities of computed tomography in the preoperative examination of various hypertrophic cardiomyopathy phenotypes. MATERIALS AND METHODS: The retrospective data analysis included 47 patients with hypertrophic cardiomyopathy (mean age, 52±7 full years) before surgical correction. computed tomography was performed using our protocol with automatic bolus tracking in the left atrium with a 90 HU threshold and biphasic contrast injection to assess the heart chambers and coronary arteries anatomy and mitral valve morphology. Moreover, to assess myocardial structure remodeling, iodine dual-energy computed tomography maps obtained with delayed contrast enhancement were analyzed. All patients with hypertrophic cardiomyopathy were classified by morphological types. The anatomy of chordopapillary apparatus was evaluated in each case. RESULTS: This study demonstrated variability in hypertrophic cardiomyopathy phenotypes, which were conventionally divided into five morphological categories, but not restricted by them. Among the patients, 26 (55%) had diffuse septum hypertrophic cardiomyopathy, 5 (11%) had midventricular hypertrophic cardiomyopathy, 2 (4%) had midventricular obstruction and apical aneurysm, 8 (18%) had focal basal septum hypertrophic cardiomyopathy, 4 (8%) had concentric hypertrophic cardiomyopathy, and the remaining 4 (8%) had apical hypertrophic cardiomyopathy. Most patients were diagnosed with chordopapillary abnormalities of the mitral valve, categorized by papillary muscle number and position, and the ratio of chords to muscles. In 10 (21%) patients, data on the myocardial bridge of a coronary artery were obtained, whereas 3 (14%) of them had dynamic stenosis. All patients had focal iodine uptake on dual-energy computed tomography maps. An extracellular volume increase was observed in 10 out of 13 (76%) patients. As shown by dual-energy computed tomography, the mean extracellular volume of the left ventricular myocardium was 30.58% (95% confidence interval, 27–34%). CONCLUSION: Our scanning protocols developed with computed tomography scanners of various generations enable to evaluate the specific morphological patterns of hypertrophic cardiomyopathy in a single study and provide a detailed interpretation of the geometry of cardiac valves and chambers, left ventricular function, state of the coronary bed, and structural changes of the left ventricular myocardium.

Screening for Fabry disease in patients with hypertrophic cardiomyopathy using cardiac magnetic resonance imaging.

Fabry disease (FD) usually mimics hypertrophic cardiomyopathy (HCM). Decreased native T1 mapping and a unique late gadolinium enhancement (LGE) pattern by cardiac magnetic resonance (CMR) imaging are specific imaging markers for FD. Explore the performance of multiparametric CMR imaging in screening for FD in patients with a HCM phenotype. A prospective cohort of 602 patients with a HCM phenotype was assessed from April 2012 to December 2022. Participants underwent CMR imaging and genetic testing. FD diagnosis was according to genetic testing and enzyme-activity test of α-galactosidase A. Multiparameter CMR imaging included cardiac function, native T1 mapping, extracellular volume (ECV), T2 mapping, LGE, and myocardial strains. Diagnostic performance of CMR parameters in identifying FD from HCM was done by analysis of receiver operating characteristic (ROC) curves. FD prevalence was 1.8% (11 cases) in this cohort with HCM. Native T1 mapping was significantly lower in FD compared with HCM (FD vs. HCM: native T1 mapping: 1174.08 ± 60.60 vs. 1293.94 ± 55.86, p < 0.001). Ventricular function, mass, ventricular wall thickness, and strains did not show significant differences between the two groups. Binary logistic regression and analysis of ROC curves demonstrated myocardial native T1 mapping of the left ventricular basal slice had the best performance in screening for FD in patients with a HCM phenotype (cutoff: 1216 ms; AUC: 0.947; sensitivity: 91%; specificity: 90%). Native T1 mapping is the best parameter for screening FD in a Chinese population with a HCM phenotype. Question The prevalence of Fabry Disease (FD) in the study population is unknown and the efficacy of cardiac MRI (CMR) parameter screening for FD needs validating. Findings We report the prevalence of FD among a Chinese hypertrophic cardiomyopathy (HCM) cohort and found T1 mapping is the best CMR parameter for screening FD. Clinical relevance Native T1 mapping is the best CMR parameter for screening FD in the HCM cohort, providing an effective method for rapid screening of FD in clinic, which may help identify patients for early treatment of FD.

Gene-echocardiography: unmasking the covert role of fatty acid metabolism gene mutations in adult cardiomyopathy

Abstract Background Although the role of fatty acid metabolic deficiencies in cardiomyopathy is established, the precise identity of causative genes and their respective phenotypes in adult cardiomyopathy remains unclear. Methods We implemented a combination of echocardiography and whole exome sequencing in clinically diagnosed cardiomyopathy patients to uncover this relationship. This involved recording cardiac phenotypes, identifying genes associated with disrupted fatty acid metabolism, and subsequently followed up with these patients. Results Out of 802 cardiomyopathy patients, 27 exhibited mutations in genes tied to fatty acid metabolism. Specifically, 16 patients demonstrated a hypertrophic cardiomyopathy (HCM) phenotype, and 11 showed a dilated cardiomyopathy (DCM) phenotype. The implicated genes were SLC22A5 (n=7), ACADVL (n=6), ACADS (n=4), ACADM (n=3), SLC25A20 (n=3), ACADL (n=2), HADH (n=1), and AGK (n=1), with a higher prevalence in males. Among these, the SLC22A5 mutation was predominant and correlated with HCM phenotype. Notably, compound mutations were frequently observed (16/27), leading to earlier disease onset and diminished aortic sinus dimension. Further investigation showed that smaller aortic sinus dimensions resulted from abnormal left ventricular myocardial work. HCM phenotype mutation carriers showed more consistent left ventricular hypertrophy and a higher probability of right ventricular hypertrophy, while DCM phenotype mutation carriers exhibited impaired contractile function across all left ventricle segments. After a 24-month follow-up, the DCM phenotype group demonstrated higher cardiovascular risk, including two fatalities. Conclusion Our investigation highlights the significant prevalence of mutations related to abnormal fatty acid metabolism in adult cardiomyopathy patients, underscoring the utility of a gene-echocardiography approach for diagnosis.

Global and national insights into the decline of hypertrophic cardiomyopathy as a cause of sudden death in the young

Abstract Background &amp; Objective Hypertrophic cardiomyopathy (HCM) has been reported as a leading cause of sudden cardiac death (SCD) in the young but appears less common in contemporary cohorts of young SCD. This research aimed to determine if HCM is a common cause of SCD in the young and whether this has changed over time. Methods We analysed three national databases, the National Echo Database Australia (NEDA), Centre for Disease Control Wide-ranging Online Data for Epidemiologic Research (CDC-WONDER) and the National Coronial Information System of Australia (NCIS) to determine incidence of SCD due to HCM in ≤ 35 years old from 1999-2017. Sub-analyses assessed for differences in sex and obstructive and non-obstructive HCM phenotypes. Results NEDA: Of 40,738 individual echocardiograms 2005-2017, 868 (2.13%) exhibited the HCM phenotype. 982 patients died ≤ 35 years, of which 4 deaths were attributable to HCM (0.4%). CDC-WONDER: 41% reduction in HCM related mortality/million people across 1999-2016 (p&amp;lt;.0001). Similar reduction was seen when stratified for age, sex and non-obstructive/obstructive HCM phenotype. NCIS: 36% reduction in HCM-related SCD was observed between 2001-2010 and 2011-2016 periods (p=.049). Conclusions HCM rarely causes SCD and accounts for &amp;lt;5% of SCD in the young. Rates of HCM-related SCD have been decreasing over the last two decades. Improved survival likely relates to improved case detection and medical management.Abstract Figure

Determinants of right ventricular - pulmonary arterial uncoupling in hypertrophic cardiomyopathy

Abstract Background Right ventricular (RV) – pulmonary arterial (PA) coupling, assessed by echocardiography, is a non-invasive surrogate on how the RV is adapted to an increased afterload in the pulmonary circulation. In cases of exhaustion of compensatory RV remodeling, the ratio decreases and there is RV-PA uncoupling. Our objective was to identify what are the determinants of this parameter in patients with hypertrophic cardiomyopathy (HCM). Methods This prospective cohort study enrolled patients with HCM without obstructive epicardial coronary artery disease, that underwent a comprehensive evaluation. Echocardiography was used to assess RV-PA coupling as the ratio of tricuspid annular plane systolic excursion (TAPSE) to pulmonary artery systolic pressure (PASP). In addition, coronary flow reserve in the left anterior descending artery (CFR_LAD) was also evaluated: diastolic coronary flow velocity was measured in basal conditions and in hyperemia and CFR was calculated as the ratio of hyperemic and basal peak diastolic flow velocities. This was used as a surrogate marker of coronary microvascular dysfunction. Cardiac magnetic resonance (CMR) was also performed to evaluate RV function (volumes and ejection fraction), and the extent of late gadolinium enhancement (LGE) in the left ventricle (LV). Results We enrolled 62 patients, with a mean age of 55 (15) years, 64% males. In 64% it was an asymmetrical septal hypertrophy phenotype, in 31% an apical hypertrophy, and in 27%, it was an obstructive HCM. Mean TAPSE/PASP was 0.556 (0.23) and median was 0.50. All patients had a normal LV ejection fraction. Univariable linear regression analysis showed that age, maximal wall thickness, E/E’, indexed left atrial volume (LAVi), CFR-LAD, %LGE and % hypoperfusion (by CMR) were correlated with RV-PA uncoupling. The HCM phenotype or the presence of obstruction were not associated with uncoupling. Multivariable stepwise linear regression analysis showed that the independent predictors of RV-PA uncoupling were age (b-estimate: - 0.180, p=0.009), LAVi (b-estimate: -0.645, p=&amp;lt;0.001), CFR-LAD (b-estimate: 0.183, p=0.011) and %LGE (b-estimate: -0.270, p=&amp;lt;0.001). Conclusion In patients with HCM, the presence of coronary microcirculation abnormalities and the extent of LGE in the LV are independent predictors of RV-PA uncoupling.

Left atrial reservoir strain differentiates cardiac amyloidosis and hypertrophic cardiomyopathy

Abstract Aims Availability of mortality-reducing therapies for cardiac amyloidosis (CA) has led to an increase in referral rates to tertiary care centers. Investigations to improve diagnosis rates are urgently needed, as diagnosis of CA requires a multimodal approach and its early diagnosis is crucial due to high mortality in untreated patients. The aim of this study is to evaluate the accuracy of the left atrial reservoir strain (LASr) in differentiating CA patients from patients with hypertrophic cardiomyopathy (HCM). Methods This is a cross-sectional analysis from the Graz HCM Registry, a prospective single-center cohort study enrolling consecutive patients with a HCM phenotype. This analysis included HCM and CA patients with valid standardized transthoracic echocardiographic examinations. Blinded investigators performed post-processing echocardiographic analyses in 100 HCM and 95 CA patients. Results Compared to HCM patients, CA patients were more frequently male [79 (83%) vs. 54 (54%); p&amp;lt;0.001] and older [78 (73-81) vs. 58 (47-70) years; p&amp;lt;0.001]. Moreover, CA patients had a lower BMI [25.0 (22.8-26.9) vs. 26.5 (24.3-29.7) kg/m²; p=0.002] as well as lower systolic [134±20 vs. 142±25 mmHg; p=0.018] and diastolic blood pressure [78±12 vs. 84±12 mmHg; p&amp;lt;0.001]. Additionally, CA patients had higher NT-proBNP [2533.0 (1146.0-5016.0) vs. 543.0 (195.0-1381.0) pg/ml; p&amp;lt;0.001] and lower eGFR [58.4±19.1 vs. 80.1±22.2 ml/min/1.73m²; p&amp;lt;0.001]. LASr was significantly worse in CA patients compared to HCM patients [9.2 (5.6-13.0) vs. 21.7 (14.8-27.6) %; p&amp;lt;0.001]. Multivariable logistic regression analysis revealed LASr as an independent predictor of CA [OR=0.936 (95% CI 0.877-0.998)], adjusting for covariates. ROC analysis showed an AUC of 0.80 (95% CI 0.73-0.86) for LASr to discriminate CA from HCM. LASr ≤14.3% demonstrated a 80% sensitivity and 79% specificity for the identification of CA patients. Sensitivity analyses involving 74 sex- and age-matched patients yielded materially unchanged results. Conclusion Compared to HCM patients, LASr was diminished in CA patients and an independent predictor of CA. Moreover, LASr showed high diagnostic accuracy in differentiating CA and HCM patients. Prospective studies are needed to evaluate the added value of left atrial strain in the diagnostic work-up of CA patients.ROC curve of LASr

MRPL44 haploinsufficient mouse spontaneously develops hypertrophic cardiomyopathy and shows systolic dysfunction after aldosterone treatment

Abstract Introduction It has been recently reported there are big differences in pathophysiological and molecular phenotypes in mouse and human hypertrophic cardiomyopathy. These differences are observed all in terms of myocyte redox, mitochondrial number and respiration, mitochondrial reactive oxygen species generation and Ca2+ handling. Therefore we should search for molecules to be able to induce similar phenotype and molecular signaling both in mice and human. Mitochondrial ribosomal large subunit 44 (MRPL44) knockout mice were embryonic lethal, for which mutations are known to cause mitochondrial infantile cardiomyopathy and hypertrophic cardiomyopathy. Purpose Our purpose is to investigate the effect of MRPL44 haploinsufficiency in mice. Methods MRPL44 haploinsufficient (MRPL44+/-) mice were generated. Mineralocorticoid receptor-associated hypertension mice were induced in MRPL44+/- and wild-type (WT, MRPL44+/+) mice with subcutaneous infusion of aldosterone(Aldo) and 8% NaCl food for 4 weeks after uninephrectomy. Systolic blood pressure was measured by tail cuffs every week. WB, qPCR, cardiac echo, and histological examinations were performed. RNA sequencing analysis, electron microscopy examinations and mitochondrial activity assay were performed to find differences between MRPL44+/- and MRPL44+/+ mice. Results MRPL44 haploinsufficient mice spontaneously developed left ventricular hypertrophy in 6 weeks old. Heart rate, blood pressure, and cardiac systolic function were normal in MRPL44 haploinsufficient mice. MRPL44 was decreased about to 70% in MRPL44 haploinsufficient mice and mitochondrial arrangement were impaired in electron microscopic analysis. After Aldo treatment, blood pressure elevation were similar, however, MRPL44 haploinsufficient mice developed left ventricular systolic dysfunction and dilation compared with MRPL44+/+ mice. WB showed mitochondrial electron transport chain protein complex IV expression was significantly decreased. Furthermore, mitochondrial activity assay showed MRPL44 haploinsufficient mice had a significant reduction in complex IV activity, whereas complex I and II activity were similar to MRPL44+/+ mice. RNA sequencing analysis showed the significant changes in the expression of ribosomal subunits coded by nucleus in addition to mitochondrial ribosomal subunits. These results indicate MRPL44 plays an important role in the cardiac function of mitochondrial electron transport chain protein complexes via the expression of ribosomal protein subunits coded by both nucleus and mitochondria. Conclusions MRPL44 haploinsufficient mice spontaneously develop left ventricular hypertrophy and shows systolic dysfunction after aldosterone treatment accompanied with oxidative phosphorylation enzyme dysfunction.

Skeletal and respiratory muscle weakness contributes to decreased exercise capacity in hypertrophic cardiomyopathy

Abstract Background and Aims Although decreased exercise capacity (due to dyspnea or angina-like symptoms) constitutes the fundamental characteristics of hypertrophic cardiomyopathy (HCM), the pathophysiology of these symptoms remains only partly understood. We investigated clinical and functional determinants of decreased exercise capacity in a broad range of HCM patients irrespective of primary disease aetiology (either genetic disorder or e.g. infiltrative phenocopies in the course of cardiac amyloidosis), overt heart failure (HF) and the presence of haemodynamically significant left ventricular outflow tract obstruction (LVOTO). Further, we deterimined the contribution of skeletal and respiratory muscle weakness to decresed exercise capacity. Methods We analyzed clinical data and functional assessments (skeletal and respiratory muscle strength, physical fitness) in relation to symptomatology and sub-maximal exercise capacity in 82 clinically stable patients with HCM (females: 32 %; age: 62±16 years; left ventricular ejection fraction [LVEF] 59±7%; intraventricular septum wall thickness [IVS] 19±4 mm; median plasma N-terminal pro-B-type natriuretic peptide [NT-proBNP]: 818 pg/mL [lower and upper quartile: 208-1917]; New York Heart Association [NYHA] class 0/I/II/III: 38/18/33/11 % [0 indicates no HF]; significant LVOTO: 29%). Results HCM patients with more severe symptomatology (NYHA class II-III vs 0-I) were older, had more frequently significant LVOTO and greater comorbidity burden, and had higher NT-proBNP and worse estimated renal function (all p≤0.03). Gender distribution, percentage of beta-blocker therapy and implanted device, body mass index, major echocardiography parameters (including LVEF, left ventricular end-diastolic diameter and IVS), high-sensitive (hs) cardiac troponin type I and hs-C-reactive protein were comparable in these 2 groups of subjects (all p&amp;gt;0.05). In multivariable linear regression models more advanced age, higher circulating natriuretic peptides (NT-proBNP) and previous coronary revascularization were independent predictors of more advanced NYHA class (standardized β-coefficient=0.30, p&amp;lt;0.01; β=0.27, p&amp;lt;0.01; and β=0.22, p&amp;lt;0.05; respectively). Similarly, more advanced age, female sex and higher NT-proBNP were independent correlates of shorter distance in 6-minute walking test (6MWT) (β=-0.46, p&amp;lt;0.001; β=-0.26, p&amp;lt;0.001; and β=-0.36, p&amp;lt;0.001; respectively). All analyzed muscle parameters (including respiratory muscle strength parameters) and objective measures of physical fitness (Functional Fitness Test for older adults) remained independently associated with 6MWT distance (all p&amp;lt;0.001) when adjusted for aforementioned clinical and laboratory correlates of 6MWT. Conclusions Muscle weakness and low physical fitness are related to decreased exercise capacity in HCM and may be potential therapeutic targets to alleviate disease symptoms also in non-obstructive HCM phenotype.

Genotype-phenotype relationship in hypertrophic cardiomyopathy

Abstract Background/Introduction Hypertrophic cardiomyopathy (HCM) is an inherited highly heterogeneous disease with variable penetrance and expression, but the exact relationship between the underlying genetic cause and the clinical course remains elusive. Purpose The aim of our study was to analyse the phenotypic and molecular characteristics of individuals with HCM examined and treated at our University Hospital. Methods Clinical data from adult HCM patients treated at our hospital between 2005 and 2023 were analysed. Informed consents to participate in the study were obtained from all participants. Clinical manifestation, instrumental examination and next generation sequencing (NGS) data of HCM related genes were collected. The Mann–Whitney U for two groups and Kruskal–Wallis tests for more than two groups were used to compare continuous variables. Univariate logistic regression was used to analyze categorical variables. Results The study involved 191 unrelated individuals, 58.6% males, the median age at HCM diagnosis was 50, interquartile range 37 – 60 years. A median follow-up was 3.9 [1.6-6.4] years. Pathogenic and likely pathogenic (P/LP) variants were identified in 45.5% (N=87) of affected individuals. Truncating variants were observed in 31 individuals. MYBPC3 P/LP variants were the most common (N=47), following by MYH7 (N=22) and other (N=18). Individuals with MYBPC3 P/LP truncating variants had higher HCM estimated 5-year risk of sudden cardiac death (SCD) during primary evaluation (3.1 [2.5-4.6]) compared to individuals with P/LP variants in other genes (2.4 [1.9-3.7]) and individuals with negative NGS results (1.8 [1.5-2.7], p&amp;lt;0,001). Patients with MYBPC3 P/LP variants experienced the earliest onset of symptoms (median age 37.0 [30.5-50.0] years) and HCM diagnosis (median age 38.0 [31.0-51.5] years) compared to individuals with other genes P/LP variants (median age 46.0 [31.0-56.2] years and 47.5 [31.5 – 59.5] years, respectively) and genotype negative individuals (median age 51.5 [44.0-61.0] years and 52.0 [45.0-63.2] years, respectively), p&amp;gt;0,001). The presence of P/LP variant was associated with significantly thicker left ventricular wall (maximal thickness) on cardiac imaging in comparison with negative NGS results (18.0 [15.0-21.0] mm vs. 16.0 [14.0-18.0] mm, p=0.002 on transthoracic echocardiography and 20.0 [17.0-22.5] mm vs. 18.0 [16.0-20.0] mm, p&amp;lt;0,001 on cardiac magnetic resonance). The presence of MYBPC3 truncating variants were associated with the greatest risk of ventricular tachycardia in comparison with negative NGS results (OR 3.05, 95% CI:1.3, 8.0, p=0.025). Conclusion More severe HCM phenotype is associated with detection of P/LP variants in HCM related genes. The presence of the MYBPC3 P/LP variant is associated with an earlier onset of the disease and truncating variants of this gene are related to a higher risk for ventricular tachycardia and an estimated 5-year risk of SCD.

Prevalence of cardiomyopathy and cardiac mortality in a colony of non-purebred cats in New Zealand

ABSTRACT Aims To evaluate the prevalence of subclinical cardiomyopathy and cardiac mortality in a research colony of non-purebred cats, established as a model of the wider cat population in New Zealand. Methods All apparently healthy, compliant, non-pregnant, non-neonatal cats in the colony at the Centre for Feline Nutrition (Massey University, Palmerston North, NZ) underwent physical examination and echocardiography using a 4.4–6.2-MHz probe by a board-certified veterinary cardiologist. Cardiac phenotype was classified following current guidelines. Hypertrophic cardiomyopathy (HCM) phenotype was defined as an end-diastolic left ventricular wall thickness ≥ 6 mm. Colony mortality data from February 2012 to February 2022 was reviewed to determine cardiac mortality. Results Cats (n = 132; 65 females and 67 males) included in the study had a median age of 4.1 (IQR 3.0–8.0) years. Thirty-two (24%) cats had a heart murmur, and three (2%) cats had an arrhythmia. Echocardiography revealed heart disease in 24 (18.2%) cats, including 23 with an HCM phenotype and one with a restrictive cardiomyopathy phenotype. Of the cats with the HCM phenotype, 3/23 had systemic hypertension or hyperthyroidism or both, and these cats were excluded from the final diagnosis of HCM (20/132; 15.2 (95% CI = 9.5–22.4)%). Between 2012 and 2022, 168 colony cats died, with 132 undergoing post-mortem examination. Heart disease was considered the cause of death in 7/132 (5.3%; 95% CI = 2.2–10.6%) cats; five had HCM, one a congenital heart defect, and one myocarditis. The overall prevalence of death related to HCM in the colony during this period was 3.8% (95% CI = 1.2–8.6%). Three cats with HCM and the cat with a congenital heart defect died unexpectedly without prior clinical signs, while congestive heart failure was observed prior to death in two cats with HCM and the cat with myocarditis. Additionally, 30/132 (22.7%) cats had cardiac abnormalities but died for non-cardiac reasons. Conclusions Subclinical cardiomyopathy, specifically HCM, was common in cats in the colony. Given that the colony originated as a convenience selection of non-purebred cats in New Zealand, the true prevalence of HCM in the wider New Zealand population is likely to fall within the 95% CI (9.5–22%). The proportion of deaths of colony cats due to HCM was lower (3.8%) supporting the conclusion that subclinical cardiomyopathy may not progress to clinical disease causing death. Clinical relevance Veterinarians should be aware of the high prevalence of subclinical HCM when treating cats. Abbreviations CAM: Systolic anterior motion of the chordae tendineae; CFN: Centre for Feline Nutrition; HCM: Hypertrophic cardiomyopathy; LA/Ao: Left atrial to aortic ratio; LV FS: Left ventricular fractional shortening; LVIDd: Left ventricular internal diameters in end-diastole; LVIDs: Left ventricular internal diameter in end-systole; LVWT: Max Maximum left ventricular wall thickness; SAM: Systolic anterior motion of the mitral valve; 2D: Two-dimensional

Carrying both the heterozygous Myh6-R453C and Tnnt2-R92W mutations aggravate the hypertrophic cardiomyopathy phenotype in mice

Hypertrophic cardiomyopathy (HCM) is an inherited disease of the heart muscle that is dominated by variations in eight genes encoding sarcomere proteins. Although there are clinical or basic research reports that carrying double mutations can lead to more severe HCM phenotypes, there are also research reports that after reanalyzing the reported mutations, the severity of clinical symptoms in patients with double mutations did not significantly increase compared to patients with only one mutation. To determine whether double pathogenic mutations can aggravate the phenotype of hypertrophic cardiomyopathy in mice, we constructed mice carrying single pathogenic heterozygous mutation Myh6-R453C or Tnnt2-R92W and mice carrying both pathogenic heterozygous mutations. Our results showed that mice with double heterozygous mutations exhibited significant hypertrophic cardiomyopathy phenotypes at 4 weeks of age, and the degree of hypertrophy was significantly higher than that of single heterozygous mutant mice of the same age. Our study suggests that carrying the two pathogenic heterozygous mutations simultaneously can aggravate the phenotype of HCM in mice, which provides experimental evidence for the genotype-phenotype relationship of double pathogenic mutations and provides reference significance for clinical risk stratification of HCM patients.

Abstract We133: In Silico Model of Cardiomyopathy Caused by a MYBPC3-induced HCM Mutation

Introduction: Hypertrophic cardiomyopathy (HCM) is the most frequent hereditary cardiomyopathy and a leading cause of sudden cardiac death, particularly in adolescent. Despite recent improved prognosis and FDA approved drugs, current cardiac therapeutics cannot efficiently prevent remodeling across all HCM patient populations due to genetic variability. Therefore, we require a systems biology approach to understand how the complex cardiac signaling networks regulate cardiomyocyte shape and size due to an HCM mutation. This study leverages a computational systems approach to explore MYBPC3-induced HCM mutation regulation of cardiomyocyte hypertrophy. Method: For the signaling network model, we employed a logic-based differential equations model (NETFLUX) to construct a signaling network validated using in vitro data from published studies. This model captured signaling dynamics and cross talks between pathways governing cardiomyocyte size and shape. Additionally, a MYBPC3 HCM mutation is integrated in the model as an input providing a comparison between a control and simulated HCM responses. Sensitivity analyses are performed to investigate the most influential signaling pathways that mediate changes in mass. Results: We created a MYBPC3-induced HCM model by integrating an additional cardiac myosin binding protein-C node to a previously validated inherited cardiomyopathy signaling network. This updated model predicted an increase in mass when the HCM mutation is simulated. The simulated inhibition of each node in the model revealed that inhibition of calcium pathway, growth factor receptor, and titin stiffness could mitigate the HCM phenotype by reducing mass. The sensitivity analysis results also suggested PI3K, Ras, and ERK1/2 pathways as potential mechanisms mediating the decrease in mass and served as potential therapeutic targets. Discussion and Future Work: Our systems approach gave insights on the mechanisms governing the cardiomyocyte response to a MYBPC3-induced HCM mutation. This will be further validated via a MYBPC3-HCM model using human iPSC-CMs with MYBPC3-induced mutations. This will create a cell line that will provide genetically precise comparisons for identifying new molecular mechanisms of disease, thereby offering a strategy for advancing precision medicine.

Clonal haematopoiesis is associated with major adverse cardiovascular events in patients with hypertrophic cardiomyopathy.

The heterogeneous phenotype of hypertrophic cardiomyopathy (HCM) is still not fully understood. Clonal haematopoiesis (CH) is emerging as a cardiovascular risk factor potentially associated with adverse clinical events. The prevalence, phenotype and outcomes related to CH in HCM patients were evaluated. Patients with HCM and available biospecimens from the Peter Munk Cardiac Centre Cardiovascular Biobank were subjected to targeted sequencing for 35 myeloid genes associated with CH. CH prevalence, clinical characteristics, morphological phenotypes assessed by echocardiogram and cardiac magnetic resonance and outcomes were assessed. All patients were evaluated for a 71-plex cytokines/chemokines, troponin I and B-type natriuretic peptide analysis. Major adverse cardiovascular events (MACE) were defined as appropriate implantable cardioverter-defibrillator shock, stroke, cardiac arrest, orthotopic heart transplant and death. Among the 799 patients, CH was found in 183 (22.9%) HCM patients with sarcomeric germline mutations. HCM patients with CH were more symptomatic and with a higher burden of fibrosis than those without CH. CH was associated with MACE in those HCM patients with sarcomeric germline mutations (adjusted hazard ratio [HR] 6.89, 95% confidence interval [CI] 1.78-26.6; p = 0.005), with the highest risk among those that had DNMT3A, TET2 and ASXL1 mutations (adjusted HR 5.76, 95% CI 1.51-21.94; p = 0.010). Several cytokines (IL-1ra, IL-6, IL-17F, TGFα, CCL21, CCL1, CCL8, and CCL17), and troponin I were upregulated in gene-positive HCM patients with CH. These results indicate that CH in patients with HCM is associated with worse clinical outcomes. In the absence of CH, gene-positive patients with HCM have lower rates of MACE.

Identification of a novel likely pathogenic TPM1 variant linked to hypertrophic cardiomyopathy in a family with sudden cardiac death.

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant genetic cardiac disorder characterized by unexplained left ventricular hypertrophy. It can cause a wide spectrum of clinical manifestations, ranging from asymptomatic to heart failure and sudden cardiac death (SCD). Approximately half of HCM cases are caused by variants in sarcomeric proteins, including α-tropomyosin (TPM1). In this study, we aimed to characterize the clinical and molecular phenotype of HCM in an Iranian pedigree with SCD. The proband and available family members underwent comprehensive clinical evaluations, including echocardiography, cardiac magnetic resonance (CMR) imaging and electrocardiography (ECG). Whole-exome sequencing (WES) was performed in all available family members to identify the causal variant, which was validated, and segregation analysis was conducted via Sanger sequencing. WES identified a novel missense variant, c.761A>G:p.D254G (NM_001018005.2), in the TPM1 gene, in the proband, his father and one of his sisters. Bioinformatic analysis predicted it to be likely pathogenic. Clinical features in affected individuals were consistent with HCM. The identification of a novel TPM1 variant in a family with HCM and SCD underscores the critical role of genetic screening in at-risk families. Early detection of pathogenic variants can facilitate timely intervention and management, potentially reducing the risk of SCD in individuals with HCM.

Early biomarkers of disease in hypertrophic cardiomyopathy: does telomere length matter?

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Biomedical Research Institute of Murcia (IMIB-Arrixaca) Introduction Hypertrophic cardiomyopathy (HCM) is the leading cause of sudden death in people under 35 years of age. (1) The variability of the phenotype together with its incomplete penetrance has been an obstacle to a complete understanding of the clinical spectrum and consequences of the disease. In recent years, there has been increasing interest in telomeric shortening and several authors have linked it to age-related diseases and HCM. (2, 3) Our aim was to study whether telomere length could affect the age at presentation and the severity of the HCM phenotype in genetic carriers. Methods Measurement of telomere length in circulating leukocytes (LTLc) was performed in 96 patients carrying a mutation in MYBPC3 causing HCM [58 affected (24 severely affected), 38 unaffected]. The variants included were c.2308+1G&amp;gt;A, p.Pro108Alafs*9, p.Arg891Alafs*160 and p.Glu258Lys, all considered founder mutations in our region. Peripheral venous blood samples were obtained from patients at the Inherited Heart Diseases Unit and stored at -80 ºC after informed consent had been signed by all participants. For telomere length analysis, a telomeric restriction fragment (TRF) assay was performed using the TeloTAGGGTelomereLenghtAssay kit (Roche, 12209136001) according to the manufacturer's protocol with slight modifications. Results Our results show a lower LTLc in those affected patients with a more severe HCM phenotype compared to the affected and unaffected group (p=0.023) independently of age and sex, which are two variables that affect LTLc. Similarly, a shorter telomere length was associated with greater severity of the phenotype, with patients presenting a larger left atrial size (p=0.032), septal size (p=0.023) and greater obstruction (p=0.044). The presence of atrial fibrillation (p=0.039) and sudden death (p=0.024) was also higher in patients with shorter telomeres. Conclusions Telomere length is a variable that influences the expression of the phenotype in HCM patients carrying a MYBPC3 variant. This is an observation that supports the thesis of numerous publications linking HCM and other age-related diseases, sometimes called telomeropathies,(2) to telomere shortening. It has also been linked to non-hereditary conditions(3). This fact sheds some light on the complex phenotypic variability present in HCM, raising LTL as a promising prognostic biomarker of the disease, as has already been suggested by other authors.(4, 5, 6).Workflow in the telomere legth analysisClinical associations of LTLc

Microtubule-induced restriction of nuclear deformability in hypertrophic cardiomyopathy

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Leducq foundation Background Hypertrophic cardiomyopathy (HCM) is characterized by abnormal thickening of the left ventricular (LV) wall in conjunction with diastolic dysfunction with a prevalence of ~1:200. HCM pathophysiology is incompletely understood. We hypothesized that misregulated mechanotransduction plays an important role in the disease process. Extensive cytoskeletal remodeling has been observed in HCM patients, with a robust increase in tubulin and desmin levels, with a concomitant increase in stabilizing post-translational modifications, which we previously showed contributes to diastolic dysfunction. Microtubules are connected to the nucleus by the LINC complex. Little is known about the interaction of the non-sarcomeric cytoskeleton with the nucleus and the role this may have in the development of HCM. Purpose Relate cytoskeleton changes to nuclear and chromatin morphology in HCM patient myocardium and assess nuclear deformability in contracting cardiomyocytes with and without microtubule destabilizing drugs. Methods Nuclear morphology and chromatin organization was assessed using electron microscopy in cardiac septal tissue from 19 patients with obstructive HCM and compared to samples from 4 non-failing donors (NF). Further nuclear changes were studied using wild type (WT) and homozygous Mybpc3 c.2373InsG mice (Mybpc3c.2373InsG, KI), which have a HCM phenotype. Nuclear morphology was assessed in slices of 6 WT and 6 Mybpc3c.2373InsG paraffin-embedded mouse hearts. To study nuclear deformability during contractions, adult cardiomyocytes were isolated, stained with live cell dyes and imaged live while electrically paced. Lastly, DNA damaged was assessed in 6 WT and 6 Mybpc3c.2373InsG paraffin-embedded mouse hearts. Results Cardiomyocyte nuclei of HCM patients had a significantly higher number of invaginations (0.32±0.09 invaginations/µm in HCM versus 0.18±0.03 invaginations/µm in NF hearts), were more irregular of shape and had altered chromatin organization compared to those from NF hearts. Nuclei of Mybpc3c.2373InsG mice were considerably larger (322±75 µm³ versus 221±24 µm³). While sarcomere shortening is similar (7.0±1.4% in Mybpc3c.2373InsG versus 6.5±1.7% in WT), nuclei from Mybpc3c.2373InsG mice are less deformable than WT nuclei (figure). Addition of microtubule destabilizer nocodazole or detyrosination inhibitor EPO-Y restored nuclear deformability to WT levels, indicating a role of detyrosinated microtubules in nuclear deformability. In addition, nuclei from Mybpc3c.2373InsG have more extensive DNA damage (19.7±3.4 foci in Mybpc3c.2373InsG versus 9.1±3.2 foci in WT). Conclusion Extensive nuclear changes are observed in HCM patients and a HCM mouse model. Cytoskeletal remodeling results in less deformable nuclei that might contribute to chromatin alterations and increased DNA damage. Nuclear deformability can be restored by microtubule modifying drugs, specifically those that decrease microtubule detyrosination.