Myocyte Disarray Research Articles

Genetic insights and clinical implication of inherited hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is one of the most common inherited genetic diseases of myocardium. It is the leading cause of unexpected mortality among young people and athletes. H.C.M. has been regarded as a sarcomere illness for the past few decades, usually with incomplete penetrance and varied expressivity arising from autosomal dominance. For the purpose of risk and treatment stratification, all diagnostic techniques—such as tissue biopsy, genetic counselling, magnetic resonance imaging, transthoracic and transoesophageal echocardiography, heart catheterization, and genetic counselling—must be used. Additionally, each patient's results should be customized based on their genotype and phenotype. About one-third of people have left ventricular outflow tract blockage at rest, and another third may be prompted to develop it. Interstitial fibrosis and myocyte hypertrophy and disarray are among the histological characteristics of H.C.M. Another common complication of the hypertrophy is left ventricular diastolic dysfunction. The pathogenesis of H.C.M is complex, and its clinical profile is variable. Functional disability resulting from heart failure and stroke (induced by atrial fibrillation) is also attributed to H.C.M. The goal of the current treatments for H.C.M., which include medication, myectomy, alcohol septal ablation, and implanted cardiac defibrillators (I.C.Ds) to avoid SCD, is to slow down the disease's progression and relieve symptoms. Multidisciplinary approaches are best suited for the diagnosis and treatment of patients with H.C.M. More individualized care and better results for this patient population have been made possible by this, as well as the enhanced safety and effectiveness of medicinal, percutaneous, and surgical therapy for H.C.M. In this review the molecular pathophysiology of H.C.M will be reviewed in light of current knowledge. In addition, describing how genetic testing is used for diagnosis and outlining the range of clinical manifestations.

Reduced connexin-43 expression, slow conduction and repolarisation dispersion in a model of hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is an inherited heart muscle disease that is characterised by left ventricular wall thickening, cardiomyocyte disarray and fibrosis, and is associated with arrhythmias, heart failure and sudden death. However, it is unclear to what extent the electrophysiological disturbances that lead to sudden death occur secondary to structural changes in the myocardium or as a result of HCM cardiomyocyte electrophysiology. In this study, we used an induced pluripotent stem cell model of the R403Q variant in myosin heavy chain 7 (MYH7) to study the electrophysiology of HCM cardiomyocytes in electrically coupled syncytia, revealing significant conduction slowing and increased spatial dispersion of repolarisation - both well-established substrates for arrhythmia. Analysis of rhythmonome protein expression in MYH7 R403Q cardiomyocytes showed reduced expression of connexin-43 (also known as GJA1), sodium channels and inward rectifier potassium channels - a three-way hit that reduces electrotonic coupling and slows cardiac conduction. Our data represent a previously unreported, biophysical basis for arrhythmia in HCM that is intrinsic to cardiomyocyte electrophysiology. Later in the progression of the disease, these proarrhythmic phenotypes may be accentuated by myocyte disarray and fibrosis to contribute to sudden death.

Multimodality Imaging in Patients with Hypertrophic Cardiomyopathy and Atrial Fibrillation.

Ventricular hypertrophy is associated with diastolic dysfunction, resulting in increased left atrial (LA) pressure, enlargement, fibrosis, and decreased LA function. Hypertrophic cardiomyopathy (HCM) is characterized by myocyte disarray, myocardial fibrosis, and hypertrophy. Notably, a thickened and noncompliant LV results in the impairment of diastolic function. These conditions promote LA remodeling and enlargement, which contribute to developing and maintaining atrial fibrillation (AF). AF is an atrial arrhythmia that occurs frequently in HCM, and evaluating the morphology and physiology of the atrium and ventricle is important for treatment and prognosis determination in HCM patients with AF. In addition, it provides a clue that can predict the possibility of new AF, even in patients not previously diagnosed with AF. Cardiac magnetic resonance (CMR), which can overcome the limitations of transthoracic echocardiography (TTE), has been widely used traditionally and even enables tissue characterization; moreover, it has emerged as an essential imaging modality for patients with HCM. Here, we review the role of multimodal imaging in patients with HCM and AF.

Spatial Transcriptomic Analysis of Focal and Normal Areas of Myocyte Disarray in Human Hypertrophic Cardiomyopathy.

Hypertrophic Cardiomyopathy (HCM) is a common inherited disorder that can lead to heart failure and sudden cardiac death, characterized at the histological level by focal areas of myocyte disarray, hypertrophy and fibrosis, and only a few disease-targeted therapies exist. To identify the focal and spatially restricted alterations in the transcriptional pathways and reveal novel therapeutic targets, we performed a spatial transcriptomic analysis of the areas of focal myocyte disarray compared to areas of normal tissue using a commercially available platform (GeoMx, nanoString). We analyzed surgical myectomy tissue from four patients with HCM and the control interventricular septum tissue from two unused organ donor hearts that were free of cardiovascular disease. Histological sections were reviewed by an expert pathologist, and 72 focal areas with varying degrees of myocyte disarray (normal, mild, moderate, severe) were chosen for analysis. Areas of interest were interrogated with the Human Cancer Transcriptome Atlas designed to profile 1800 transcripts. Differential expression analysis revealed significant changes in gene expression between HCM and the control tissue, and functional enrichment analysis indicated that these genes were primarily involved in interferon production and mitochondrial energetics. Within the HCM tissue, differentially expressed genes between areas of normal and severe disarray were enriched for genes related to mitochondrial energetics and the extracellular matrix in severe disarray. An analysis of the gene expression of the ligand-receptor pair revealed that the HCM tissue exhibited downregulation of platelet-derived growth factor (PDGF), NOTCH, junctional adhesion molecule, and CD46 signaling while showing upregulation of fibronectin, CD99, cadherin, and amyloid precursor protein signaling. A deconvolution analysis utilizing the matched single nuclei RNA-sequencing (snRNA-seq) data to determine cell type composition in areas of interest revealed significant differences in fibroblast and vascular cell composition in areas of severe disarray when compared to normal areas in HCM samples. Cell composition in the normal areas of the control tissue was also divergent from the normal areas in HCM samples, which was consistent with the differential expression results. Overall, our data identify novel and potential disease-modifying targets for therapy in HCM.

Cytoskeletal disarray increases arrhythmogenic vulnerability during sympathetic stimulation in a model of hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (FHC) patients are advised to avoid strenuous exercise due to increased risk of arrhythmias. Mice expressing the human FHC-causing mutation R403Q in the myosin heavy chain gene (MYH6) recapitulate the human phenotype, including cytoskeletal disarray and increased arrhythmia susceptibility. Following in vivo administration of isoproterenol, mutant mice exhibited tachyarrhythmias, poor recovery and fatigue. Arrhythmias were attenuated with the β-blocker atenolol and protein kinase A inhibitor PKI. Mutant cardiac myocytes had significantly prolonged action potentials and triggered automaticity due to reduced repolarization reserve and connexin 43 expression. Isoproterenol shortened cycle length, and escalated electrical instability. Surprisingly isoproterenol did not increase CaV1.2 current. We found alterations in CaV1.2-β1 adrenergic receptor colocalization assessed using super-resolution nanoscopy, and increased CaV1.2 phosphorylation in mutant hearts. Our results reveal for the first time that altered ion channel expression, co-localization and β-adrenergic receptor signaling associated with myocyte disarray contribute to electrical instability in the R403Q mutant heart.

Genetics, patterns of hypertrophy and fibrosis on myocardial mechanics in hypertrophic cardiomyopathy

Abstract Funding Acknowledgements Type of funding sources: None. Background Asymmetrical hypertrophy, myocyte disarray and fibrosis due to genetic cause are underlying pathology of hypertrophic cardiomyopathy (HCM). However, their contribution to myocardial functional mechanics are not extensively evaluated yet. Purpose In this study, we sought to investigate effects of genetic mutation, patterns of ventricular hypertrophy and fibrosis on myocardial mechanics in HCM. Methods In 133 patients with HCM, chamber geometry, segmental late gadolinium enhancement (LGE), extracellular volume fraction (ECV) by cardiac magnetic resonance imaging (CMR), echo-derived diastolic function analyses and genetic test were performed. Left ventricular (LV) segmental and global longitudinal strain (LS), circumferential strain (CS), and rotation were measured by feature tracking analysis of CMR. Results Patients with sarcomere gene mutation (SM) had lower LV-CS (global and all three slices) along with higher prevalence of midwall type LGE, LGE amount and ECV. Despite global LS was not lower in SM, anteroseptal-LS was significantly impaired accompanying with higher septal wall thickness. To compensate impaired anteroseptal LS, basal endocardial rotation was paradoxically increased in SM. Augmented basal segmental was significantly related to obstructive HCM. In apical HCM, although apical segmental LS was significantly lower, higher apical rotation and preserved apical CS along with lower prevalence of SM. The E/e’ was significantly related to LV mass index, LGE extent but not with SM. Conclusion Circumferential myocardial function was significantly reduced in SM independent of fibrosis extent, suggesting primary phenotype. However, longitudinal fiber function was more related to hypertrophy regardless of SM. LV diastolic function was more related to LV mass, extent and degree of fibrosis including non-thickened myocardium regardless of SM.

Evidence for microstructural alteration and microvascular disease in subclinical and overt hypertrophic cardiomyopathy

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): British Heart Foundation - Clinical Research Training Fellowship Background Disarray and microvascular disease (MVD) are implicated in adverse events in hypertrophic cardiomyopathy (HCM). Advances in CMR permit quantification of microstructural indices reflecting disarray, and microvascular disease. As novel myosin inhibitors provide promise for disease modification, early and disease-specific biomarkers are a rapidly emerging clinical priority. Purpose Using latest imaging techniques, we investigated MVD and disarray in 3 HCM groups: overt disease, either genotype positive (G+LVH+) or negative (G-LVH+), and subclinical HCM (G+LVH-), exploring relationships to electrical changes and genetic substrate. Methods A 207 subject, multi-centre consortium: 102 patients with overt HCM (52 G+LVH+, 50 G-LVH+), 77 subclinical (G+LVH-) and 28 matched healthy volunteers (HV). All underwent ECG, quantitative perfusion (measuring myocardial blood flow (MBF), perfusion reserve (MPR) and perfusion defects) and cardiac diffusion tensor imaging (cDTI) to investigate for evidence of disarray, measured as fractional anisotropy (FA – the directional variability of diffusion, reflecting myocyte disarray), mean diffusivity (MD – reflecting myocyte packing and intra- and extracellular volume) and absolute second eigenvector angle (E2A –measuring orientation of sheetlets, functional units of myocytes that re-orientate to facilitate wall-thickening). Results Compared to HV, overt HCM had evidence of microstructural alteration (lower FA (suggestive of disarray), higher MD and higher E2A, all p<0.001) and MVD (lower stress MBF and MPR p<0.001). Compared to G+LVH+, G-LVH+ had elevated E2A (64.4°(58.7–66.5) vs 60.1°(55.6–63.7 p = 0.006)). Perfusion defects were found in all G+ but not all G- overt disease (100%(52/52) vs 82%(41/50) p = 0.001). Compared to HV, subclinical HCM (G+LVH-) had evidence of microstructural alteration (lower FA suggestive of disarray, higher MD and higher E2A, all p<0.001) and MVD (reduced stress MBF (2.43±0.52 vs 2.77±0.62ml/g/min p = 0.006) with perfusion defects in 29% (vs 0 HV p = 0.001)). Microstructural markers and MVD were independently associated, in both overt and subclinical disease (overt: E2A and stress MBF: β=-0.29, p = 0.002; subclinical: those with perfusion defects (vs without) had lower FA & higher E2A). Disarray markers and MVD independently associated with pathological ECG abnormalities in both overt and subclinical disease, after adjustment for degree of fibrosis and LVH (overt: FA odds ratio (OR) for abnormal ECG=3.2, p = 0.014; stress MBF OR=2.8, p = 0.013; subclinical: FA OR=3.4, p = 0.006, MPR OR=4.0 p = 0.008). Conclusions In Hypertrophic Cardiomyopathy, sarcomere mutation carriers without hypertrophy have microstructural alterations and microvascular disease that are detectable, correlate, and associate with pathological ECG changes. These are more prominent once LVH is present, with genotype positive and genotype negative overt disease patients having differing phenotypes.

700 EPICARDIAL ADIPOSE TISSUE AND ATRIAL FIBRILLATION, A REVIEW

Abstract Aims Atrial fibrillation (AF) is the most common cardiac arrhythmia closely associated with stroke, heart failure, and decreased quality of life. Excess adiposity has long been associated with increased cardiovascular disease and risk factor of AF. Methods Epicardial Adipose Tissue (EAT) is the fat depot located between the myocardium and the epicardium supplied by branches of the coronary arteries. By contrast, pericardial adipose tissue (PAT) is located externally and is supplied by non-​coronary arteries. EAT fat thickness was first visualized by and measured with Transthoracic Two-dimensional (2D) Echocardiography because is visible as an echo free space between the outer wall of the myocardium and the visceral layer of the pericardium. Moreover, computed tomography (CT) has been used to measure EAT through accurate volumetric measurement. CMR imaging is instead considered the ‘gold standard’ modality for imaging adipose tissue.EAT function and morphology in normal conditions is protective but it function changes under pathological conditions.Lots of studies, infact, indicated higher pericardial fat volume was associated with a nearly 40% higher odds of prevalent AF, and the association remained significant even after adjustment for other AF risk factors including age, sex, myocardial infarction, heart failure, BMI, and other regional fat deposits. Infact, EAT volume is related to impaired diastolic function, elevated left ventricular mass, and enlarged left atrium. Moreover, a higher degree of EAT accumulation is often observed in patients with systematic inflammatory disease and oxidative stress, such as rheumatoid arthritis and psoriasis, compared with those without systematic inflammatory disease even after adjusting other risk factors. Free fatty acids can be transported from EAT to the myocardium and lead to electromechanical changes in atrial tissue: they separate cardiomyocytes and this situation result in conduction slowing, loss of side-​to-​side cell connections and myocardial disorganization that leads to conduction delay and re-​entry. Results EAT is a modifiable cardiovascular risk factor and a potential novel therapeutic target owing to its responsiveness to drugs with pleiotropic effects such as GLP1R agonists (visceral fat reduction is one of the non-​glycaemic effects of the GLP1R agonists), SGLT2 inhibitors (reduction of intramyocardial lipid content by increasing EAT lipolysis and ketone body oxidation) and statins (reduction of EAT thickness through modulation of peroxisome proliferator-​activated receptors (PPARs)). Furthemore, suppression of AF after injecting botulinum toxin into EAT in patients with paroxysmal AF, both during postoperative cardiac surgery and catheter ablation of epicardial fat pad can also result in EAT reduction. Conclusion EAT is a measurable and modifiable cardiovascular risk factor that adds qualitative value to the stratification of cardiovascular risk. In the context of atrial fibrillation, EAT represents a new pathogenic substrate through the regional secretion of factors that induce fibrosis and neurohormonal disarray of the atrial myocytes. Genetic studies are also optional to uncover pathophysiological mechanism of EAT-AF interaction and clarify causal relationship. Finally, more efforts should be made to realize application of EAT quantification in risk evaluation and management for AF.

903 NOVEL MALIGNANT MUTATION IN HYPERTROPHIC CARDIOMYOPATHY

Abstract Background Hypertrophic cardiomyopathy (HCM) is a common inherited disease almost invariably caused by mutations in sarcomeric genes. The HCM phenotype is clinically heterogeneous with myocyte hypertrophy, disarray, and myocardial fibrosis as histological hallmarks. This condition is recognized as an important cause of sudden cardiac death (SCD) in the youth and of heart failure (HF) in the elderly. Current guidelines mandate genetic analysis as a class I indication in HCM. Indeed, the advent of the next generation sequencing in the medical practice has led to decipher the molecular etiology of HCM and to assess the disease risk in family members with relevant insights into the clinical course. Clinical case A 62-year-old man followed-up at another Hospital with a non-obstructive HCM diagnosis, was referred to our Hospital for therapy optimization and clinical follow-up. Past medical history included third degree atrioventricular block at age 40 treated with dual chamber pacemaker (PM) and, at age of 60, atrial flutter with high ventricular response complicated with cardiogenic shock and stroke. Due to worsening systolic function and ventricular sustained tachycardia he was upgraded to implantable cardioverter defibrillator which delivered appropriate shocks. Echocardiography performed during current hospitalization showed a moderate concentric hypertrophy (intraventricular septum 17 mm, cardiac mass index 258 g/m2), dilated ventricle with reduced ejection fraction (33%) and akinesis of the mid inferior and infero-septal walls of the left ventricle and of the apex, with a stratified thrombotic apposition. Magnetic resonance was contraindicated because of non-compatible PM. Due to alteration in serum proteins and free light chain, to rule out systemic disease, extensive imaging diagnosis was performed including bone scintigraphy and abdominal ultrasonography which resulted negative. While waiting for bone marrow aspiration and biopsy the patient rapidly deteriorated with worsening renal failure, ensuing proteinuria until exitus. After an appropriate pre-test counseling the family consented to genetic test in the proband. Clinical exome sequencing revealed the presence of a missense mutation in MYH7 gene. This new mutation is characterized by the substitution of cysteine residue by a serine in 905 codon of MYH7 gene. Cys905Ser results in a semi-conservative amino acid substitution which may impact disulfide bond formation in the MYH7 protein. To date no study has described this mutation as a cause of HCM. A mutation affecting this same codon, Cys905Phe was reported in only one patient with HCM. From a biological point of view, this variant lies in the head region of the protein where the majority of the missense variants are grouped and statistically associated to HCM phenotype. Several studies reported that the occurrence of atrial fibrillation (AF) tends to be more prevalent in patients carrying the MYH7 mutation. Furthermore, AF is associated with substantial risk for HF-related mortality, stroke, and severe functional disability. Awareness regarding the spectrum of MYH7 mutations probably related to SCD or HF combined with a thorough patient characterization for molecular and clinical features, may help to improve the genotype and phenotype correlation. This important challenge could elucidate better the mechanism of HCM enabling cardiologists to a better clinical decision-making and patients’ care.

Fatal Case of Hypertrophic Cardiomyopathy in a Donor Heart: A Case Report

Hypertrophic cardiomyopathy is a genetically determined heart muscle disease, and patients are at an increased risk for sudden cardiac death. We report the case of a 39-year-old White man who was found dead at home unexpectedly. He had a cardiac transplant for congenital heart disease at the age of 12 and his condition was maintained with immunosuppression ever since with good cardiac function and right bundle branch block. At autopsy, the heart was enlarged with a weight of 591 g and had fibrous adhesions of the pericardium with endothelialized sutures in the atria and great vessels in keeping with heart transplant. There was focal septal hypertrophy noted on short axis cut. There was diffuse thickening of the coronary arteries, but no significant stenosis was noted. On microscopic examination of the heart, sections of right and left ventricle showed myocyte hypertrophy with extensive widespread myocyte disarray and replacement fibrosis. The histologic appearance was that of hypertrophic cardiomyopathy, which was responsible for his sudden unexpected death. This postmortem diagnosis of hypertrophic cardiomyopathy in a transplanted heart has major implications for the donor family because of the inherited nature of the condition. Follow-up with the donor family is essential in this unique case. This case highlights the importance of autopsy in transplant death cases. Hypertrophic cardiomyopathy in the donor heart most likely did not manifest phenotypically at the time of transplant in this case because the majority present in adolescence and early adulthood, rarely in childhood. This is first report of such a case.

Mitochondrial dysfunction and autophagy activation are associated with cardiomyopathy developed by extended methamphetamine self-administration in rats

The recent rise in illicit use of methamphetamine (METH), a highly addictive psychostimulant, is a huge health care burden due to its central and peripheral toxic effects. Mounting clinical studies have noted that METH use in humans is associated with the development of cardiomyopathy; however, preclinical studies and animal models to dissect detailed molecular mechanisms of METH-associated cardiomyopathy development are scarce. The present study utilized a unique very long-access binge and crash procedure of METH self-administration to characterize the sequelae of pathological alterations that occur with METH-associated cardiomyopathy. Rats were allowed to intravenously self-administer METH for 96 h continuous weekly sessions over 8 weeks. Cardiac function, histochemistry, ultrastructure, and biochemical experiments were performed 24 h after the cessation of drug administration. Voluntary METH self-administration induced pathological cardiac remodeling as indicated by cardiomyocyte hypertrophy, myocyte disarray, interstitial and perivascular fibrosis accompanied by compromised cardiac systolic function. Ultrastructural examination and native gel electrophoresis revealed altered mitochondrial morphology and reduced mitochondrial oxidative phosphorylation (OXPHOS) supercomplexes (SCs) stability and assembly in METH exposed hearts. Redox-sensitive assays revealed significantly attenuated mitochondrial respiratory complex activities with a compensatory increase in pyruvate dehydrogenase (PDH) activity reminiscent of metabolic remodeling. Increased autophagy flux and increased mitochondrial antioxidant protein level was observed in METH exposed heart. Treatment with mitoTEMPO reduced the autophagy level indicating the involvement of mitochondrial dysfunction in the adaptive activation of autophagy in METH exposed hearts. Altogether, we have reported a novel METH-associated cardiomyopathy model using voluntary drug seeking behavior. Our studies indicated that METH self-administration profoundly affects mitochondrial ultrastructure, OXPHOS SCs assembly and redox activity accompanied by increased PDH activity that may underlie observed cardiac dysfunction.

Advanced microstructural substrate detection in pre-hypertrophic HCM and its relationship to arrhythmogenesis; a hybrid CMR-ECG-Imaging study

Abstract Background Hypertrophic cardiomyopathy is defined in three domains; clinically by unexplained hypertrophy, genetically by sarcomeric gene mutations and histologically by disarray, small vessel disease and fibrosis. Both ischaemia and myocyte disarray have been implicated in arrhythmogenesis and sudden cardiac death but whether disarray occurs before hypertrophy and its relationship to ischaemia is unknown. Diffusion-tensor CMR, perfusion mapping & ECG Imaging (ECGI) can measure disarray, ischaemia and electrical aberrance respectively in vivo. We aimed to investigate these in genotype positive (G+) subjects without hypertrophy (LVH−) to identify further subclinical manifestations of gene expression and whether these relate to ventricular arrhythmia formation. Methods Diffusion-tensor CMR (3-Tesla) using a motion-compensated spin-echo sequence was acquired in 3 short-axis slices. Quantitative adenosine stress perfusion mapping was performed using standard clinical protocols. A novel ECGI vest, containing 256 unipolar electrodes acquired a 5-minute recording of body-surface potentials to quantify conduction and repolarisation dynamics intervals. Results ECGI/CMR was performed on 68 mutation carriers from 64 families and 24 age sex and ethnicity matched healthy controls. Of the mutation carriers, median age was 33 (24–41 years), 57% (39) were female, and 79% (54) were white. Mutations were 39 (57%) MYBPC3, 19 (28%) MYH7, 1 (1%) MYL2 and 9 (12%) were thin filament/non-sarcomeric mutations. There was no significant difference in ejection fraction or LV mass, however G+LVH− had a higher maximum wall thickness (9 (9–10) vs 8 (7–9) mm p=0.003). Compared to healthy volunteers, G+LVH− individuals had more perfusion defects (18/64 (30%) vs 0, p=0.004), lower Fractional Anisotropy (FA) (suggestive of more disarray) (0.32±0.02 vs 0.34±0.02, p<0.0001) and more prolonged Activation–Recovery Intervals (ARI, a surrogate for action potential duration (259±40 vs 240±31 ms, p=0.03). In G+LVH−, patients with perfusion defects had more prolonged ARI (263 (248 vs 292) vs 246 (225–283) ms, p=0.03) and lower FA suggestive of more disarray (0.32±0.2 vs 0.31±0.1, p=0.04). Conclusion Ischaemia, myocyte disarray and electrical abnormalities occur even in the absence of hypertrophy in HCM. These abnormalities associate to form a complex a clinical phenotype. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): British Heart FoundationBarts Charity

Mitral valve abnormalities in decedents of sudden cardiac death due to hypertrophic cardiomyopathy and idiopathic left ventricular hypertrophy

Abstract Background The sole identification of left ventricular hypertrophy (LVH) in a young individual that died suddenly may often lead to an erroneous diagnosis of hypertrophic cardiomyopathy (HCM). Emerging data suggests that idiopathic LVH (ILVH) and HCM may be separate entities. Aim We aimed to report on the prevalence and nature of mitral valve (MV) abnormalities, in a cohort of sudden cardiac death (SCD) victims with a post-mortem examination consistent with HCM and ILVH. Methods We reviewed 6860 consecutive cases of SCD referred to our specialist cardiac pathology centre between 1994 and 2020. SCD was defined as death from a cardiovascular cause within 12 hours of apparent well-being. HCM was defined by the presence of LVH, in the absence of abnormal loading conditions and characterised by myocyte disarray at histology. ILVH was defined as unexplained LVH (heart weight >500 g in males and >400 g in females) and left ventricular (LV) wall thickness >15mm, in the absence of myocardial disarray or secondary causes of LVH. The MV was examined for patency, circumference, thickening, nodularity, ballooning, bulging between cords, perforation, and the presence of impact lesions in the LV outflow tract (LVOT) and aortic outlet. Results Of the total cases of SCD, 264 (4%) were due to HCM (mean age 41±18 years, 78% males, LV maximal wall thickness 19±6 mm) (Figure 1). Ante-mortem symptoms were reported in 44 (17%) cases and for the majority (n=217, 82%) HCM was established at post-mortem. Death was attributed to ILVH in 253 (3%) cases (mean age 43±16 years, 80% males, LV maximal wall thickness 18±4 mm). MV abnormalities were found in 58 (22%) decedents with HCM (mean age 38±17 years; 72% males) and in 13 (5%) decedents with ILVH (mean age 55±15 years; 77% male), p<0.001. Amongst the 58 (22%) cases with HCM and MV abnormalities, 15 (6%) cases had multiple MV abnormalities. These included impact lesions associated with thickening of the anterior leaflet of the MV (n=39) and degenerative changes (n=34) such as bulging and ballooning; and thickening and nodularity. Decedents with HCM exhibiting MV abnormalities were younger than decedents with a normal MV (38±17 versus 45±19 years; p=0.08). Among the 253 decedents with ILVH, 13 (5%) cases exhibited MV abnormalities, which largely included degenerative changes (n=12). Among decedents with HCM and ILVH exhibiting MV abnormalities, the former was significantly younger (38±17 versus 55±15; p=0.001). Myocardial fibrosis was observed in 162 (61%) cases of HCM and 99 (39%) cases of ILVH, p<0.001. Conclusions MV abnormalities are over four-fold more common in individuals with HCM than those with ILVH and may be considered as additional macroscopic features to differentiate between these two entities. Furthermore, the inherent descriptive terminologies used when assessing the MV, support a greater emphasis on the standardisation and quantification of MV abnormalities as part of the autopsy in victims of SCD. Funding Acknowledgement Type of funding sources: Other. Main funding source(s): Acknowledgements: We thank the charitable organisation, Cardiac Risk in the Young (CRY) who fund and support the CRY Cardiovascular Pathology Unit and CRY database.

Sudden cardiac death during exercise in young individuals with hypertrophic cardiomyopathy

Abstract Background Sudden cardiac death (SCD) in young individuals and athletes is generally caused by hereditary cardiac conditions, including cardiomyopathies such as hypertrophic cardiomyopathy (HCM). Although historically HCM has been reported as the predominant cause of SCD in young athletes, it is unclear as to what degree exercise is a trigger for possible fatal arrhythmias. Aim We aimed to report on the circumstances of SCD in a cohort of young individuals aged ≥10 and <30 whose autopsy was consistent with HCM. Methods We reviewed 6860 consecutive cases of SCD referred to our specialist cardiac pathology centre 1994 and 2020. SCD was defined as death from a cardiovascular cause within 12 hours of apparent well-being. All cases underwent detailed autopsy evaluation of the heart, including histological analysis, by expert cardiac pathologists. A minimum of 10 blocks of tissue were taken for histological analysis. HCM was defined by the presence of increased heart weight or increased wall thickness and significant myocyte disarray at histological examination. Results Of the total cases of SCD, 264 (4%) were due to HCM. Our cohort of young decedents comprised of 66 individuals (average age 21±5 years, males 76%). For the majority (n=52, 79%) SCD was the first manifestation of HCM. The average heart weight was 507±152 grams and left ventricular (LV) fibrosis was found in 28 (42%) cases (Figure 1A). Death was more common between 16 and 20 years of age (n=24) (Figure 1B). Death occurred during exertion in 25 (38%) individuals and at rest or during daily activities in the remaining 41 (62%), including 5 individuals who died during sleep. Male sex was more represented among decedents who died during exertion (88% compared with 68% in the group that died at rest, p=0.07); LV fibrosis was more commonly observed in individuals who died during exertion (56% compared with 34% in the group who died at rest, p=0.08). Younger individuals between 10–15 years of age died mostly during exercise (80%), in other age groups death occurred mainly at rest (33% in age group 16–20 years, 30% in age group 21–25 years, 33% in age group 26–30 years) (Figure 1B). Conclusions We observed a high age-related variability in terms of circumstances of death. In the context of HCM, our findings suggest that individuals aged 10–15 years are the most vulnerable in terms of exercise-related-SCD. This exemplifies the importance of preventative cardiac screening in young individuals who might be harbouring quiescent cardiac conditions associated with young SCD. Funding Acknowledgement Type of funding sources: Other. Main funding source(s): Acknowledgements: We thank the charitable organisation, Cardiac Risk in the Young (CRY) who fund and support the CRY Cardiovascular Pathology Unit and CRY database.

Mitral valve abnormalities in decedents of sudden cardiac death due to hypertrophic cardiomyopathy and idiopathic left ventricular hypertrophy.

Mitral valve abnormalities in decedents of sudden cardiac death due to hypertrophic cardiomyopathy and idiopathic left ventricular hypertrophy.

Abstract P2052: Lowered Pro-fibrotic And Damage Associated Molecular Pattern Gene Expressions After Exercise Training In A Mouse Model Of Hypertrophic Cardiomyopathy

Background: Hypertrophic cardiomyopathy (HCM) is the most frequent inherited cardiac disease, most often caused by mutations in sarcomere genes. The disease is characterized by left ventricular (LV) hypertrophy, increased risk of arrhythmias and diastolic dysfunction, due to cardiomyocyte hypercontractility, myocyte disarray and fibrosis. Fibrosis is a marker of worse prognosis, adverse remodeling and an increased risk of sudden cardiac death. Hypothesis: We hypothesized that exercise training could attenuate fibrosis development in mice genetically predisposed to HCM. Methods: We allocated male α-Myh6 R403Q/+ to high intensity interval treadmill running or sedentary behavior (N=11 per group) for a total of 6 weeks. HCM was induced in all mice by cyclosporine A given via the feed for the last 3 of the 6 week exercise protocol. All mice underwent echocardiography and an exercise test at weeks 0, 3, and 6, before harvesting LVs for digital droplet PCR (ddPCR) and a qPCR immune array. Results: Exercise training lead to a 2-fold increase in exercise capacity as measured by total distance ran during exercise testing (p<0.0001). In exercised HCM mice, several key fibrosis-related genes were lowered compared to sedentary HCM mice as measured by ddPCR (N=11 per group): Collagen 1 by 51 % (p=0.03), collagen 3 by 54 % (p=0.02), fibronectin by 51 % (p=0.01) and lysyl oxidase by 42 % (p=0.05). An array of 87 selected immune-related genes showed that 39 genes were upregulated >1.5 fold in sedentary HCM mice compared to sedentary wild type controls (N=3 samples, pooled). Twelve upregulated genes belonged to damage associated-molecular patterns (DAMPs). Several of the DAMP genes were lower in exercised HCM mice compared to sedentary HCM mice (N=10-11 per group): Biglycan was lowered by 29 %, versican by 22 % and fibronectin by 55 %. Trends were also found for lowered expression of syndecan 1 (by 26 %), fibromodulin (by 55 %), and tenacin C (by 49 %) (0.07<p<0.08). There was no difference in maximal wall thickness or function measured by echocardiography. Conclusion: Exercise training led to a lower expression of key fibrosis-related genes in an inducible mouse model of HCM. Initial results indicate that attenuation of DAMP signaling might be involved in the mechanism for this effect.

Single-cell transcriptomics provides insights into hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is a genetic heart disease that is characterized by unexplained segmental hypertrophy that is usually most pronounced in the septum. While sarcomeric gene mutations are often the genetic basis for HCM, the mechanistic origin for the heterogeneous remodeling remains largely unknown. A better understanding of the gene networks driving the cardiomyocyte (CM) hypertrophy is required to improve therapeutic strategies. Patients suffering from HCM often receive a septal myectomy surgery to relieve outflow tract obstruction due to hypertrophy. Using single-cell RNA sequencing (scRNA-seq) on septal myectomy samples from patients with HCM, we identify functional links between genes, transcription factors, and cell size relevant for HCM. The data show the utility of using scRNA-seq on the human hypertrophic heart, highlight CM heterogeneity, and provide a wealth of insights into molecular events involved in HCM that can eventually contribute to the development of enhanced therapies.

PO-668-06 AUTOMATED QUANTIFICATION OF ABNORMAL LOW-AMPLITUDE QRS PEAKS FROM HIGH-RESOLUTION ECGS PREDICTS LATE VENTRICULAR ARRHYTHMIAS IN HYPERTROPHIC CARDIOMYOPATHY: A 5-YEAR PROSPECTIVE MULTICENTER STUDY

Hypertrophic cardiomyopathy (HCM) patients are at risk of ventricular arrhythmias (VA) due to abnormal electrical activation arising from myocardial fibrosis and myocyte disarray. QRS fragmentation on the surface ECG is a manifestation of abnormal activation, but a robust, quantitative ECG metric has yet to be developed.

Prevention of doxorubicin-induced experimental cardiotoxicity by Nigella sativa in rats

IntroductionDoxorubicin (DOX) is an anthracycline cytotoxic chemotherapeutic drug that is commonly used in cancer treatment. A major side effect limiting the clinical use of DOX is cardiotoxicity due to oxidative injury. Nigella sativa (NS) is an annual flowering plant with antioxidant properties. Its seeds contain several bioactive constituents such as saturated and unsaturated fatty acids, thymoquinone, dithymoquinone, thymohydroquinone, and thymol. In this study, we investigated the effect of NS extract on DOX-induced cardiotoxicity. MethodsThe experimental study animals consisted of 28 male Sprague Dawley rats weighing between 300 and 400 g. Four study groups each of seven rats were defined: controls; NS extract; DOX; and DOX+NS. Control and DOX rats received standard food, while each rat in the NS and DOX+NS groups also received 100 mg/kg NS extract orally. At day 28 of follow-up, rats in the DOX groups were administered a single 10 mg/kg intraperitoneal dose of DOX, while rats in the control and NS groups received a single 10 mg/kg dose of physiological saline solution. All animals were monitored for 35 days. On day 35, the rats were decapitated and serum and cardiac tissue samples were obtained. Troponin and NT-proBNP levels were measured in blood sera, while malondialdehyde (MDA), nitric oxide, total antioxidant capacity (TAC), and total oxidative stress (TOS) levels were quantified in sera and tissue samples. Histological alterations that were assessed in cardiac tissue included myocyte disarray, small vessel disease, myocyte hypertrophy, and fibrosis. ResultsThe DOX group had significantly higher NT-proBNP, TOS, and MDA, with greater histopathological derangement. TAC was significantly elevated in the DOX+NS group, which also exhibited significantly lower troponin, TOS, and MDA, as well as significantly higher TAC compared to the DOX group. Histopathological examination showed that the significant structural derangement observed in DOX rats was markedly and significantly reduced in DOX+NS rats. ConclusionOur results suggest that NS extract may prevent DOX-induced cardiotoxicity and thus represents a promising cardioprotective agent.

Myofibril orientation as a metric for characterizing heart disease

Myocyte disarray is a hallmark of many cardiac disorders. However, the relationship between alterations in the orientation of individual myofibrils and myofilaments to disease progression has been largely underexplored. This oversight has predominantly been because of a paucity of methods for objective and quantitative analysis. Here, we introduce a novel, less-biased approach to quantify myofibrillar and myofilament orientation in cardiac muscle under near-physiological conditions and demonstrate its superiority as compared with conventional histological assessments. Using small-angle x-ray diffraction, we first investigated changes in myofibrillar orientation at increasing sarcomere lengths in permeabilized, relaxed, wild-type mouse myocardium from the left ventricle by assessing the angular spread of the 1,0 equatorial reflection (angle σ). At a sarcomere length of 1.9 μm, the angle σ was 0.23 ± 0.01 rad, decreased to 0.19 ± 0.01 rad at a sarcomere length of 2.1 μm, and further decreased to 0.15 ± 0.01 rad at a sarcomere length of 2.3 μm (p < 0.0001). Angle σ was significantly larger in R403Q, a MYH7 hypertrophic cardiomyopathy model, porcine myocardium (0.24 ± 0.01 rad) compared with wild-type myocardium (0.14 ± 0.005 rad; p < 0.0001), as well as in human heart failure tissue (0.19 ± 0.006 rad) when compared with nonfailing samples (0.17 ± 0.007 rad; p = 0.01). These data indicate that diseased myocardium suffers from greater myofibrillar disorientation compared with healthy controls. Finally, we showed that conventional, histology-based analysis of disarray can be subject to user bias and/or sampling error and lead to false positives. Our method for directly assessing myofibrillar orientation avoids the artifacts introduced by conventional histological approaches that assess myocyte orientation and only indirectly evaluate myofibrillar orientation, and provides a precise and objective metric for phenotypically characterizing myocardium. The ability to obtain excellent x-ray diffraction patterns from frozen human myocardium provides a new tool for investigating structural anomalies associated with cardiac diseases.