Hypertrophic Cardiomyopathy Disease Progression Research Articles

Left atrioventricular coupling index is an independent associate of new-onset AF and stroke in hypertrophic cardiomyopathy: a CMR study

Abstract Background Left atrial (LA) dysfunction is an important marker of disease progression in hypertrophic cardiomyopathy (HCM). LA volumes and functional parameters are associated with new-onset atrial fibrillation (AF) and its complications including stroke. The association between left atrioventricular coupling (LACI), a parameter reflecting the contribution of the left ventricular and LA remodeling to LA dysfunction, with the occurrence of new-onset AF and stroke has not been evaluated. Aim To investigate the association between LACI and the occurrence of new-onset AF or stroke in patients with HCM. Methods In patients with an established diagnosis of HCM and cardiac magnetic resonance (CMR) data, LACI was calculated as the ratio between the LA and the LV end-diastolic volumes. New-onset AF or occurrence of stroke comprised the primary combined endpoint. Cumulative event-free survival rates for the occurrence of the primary endpoint were estimated with the population divided according to a LACI cut-off value of 40%. The association between clinical and CMR variables and the primary endpoint was assessed with univariable and multivariable Cox proportional hazard regression models. Results Of 114 patients with HCM, (mean age 54±16 years, 33 (29%) female, LV ejection fraction 67.0±8.4%), 71 patients (49%) had a LACI > 40% (left atrioventricular uncoupling). During a median follow-up of 4.1 (1.8-6.4) years, 19 (16.7%) patients experienced new-onset AF or stroke. Patients with preserved left atrioventricular coupling (LACI ≤ 40%) had a lower cumulative rate of events compared to those with left atrioventricular uncoupling (log-rank p=0.031, Fig. 1). LACI was independently associated with new-onset AF or stroke after adjusting by the presence of late gadolinium enhancement (LGE) sex and age (HR=23.27, p=0.016). Conclusions In patients with HCM, the presence of left atrioventricular uncoupling is independently associated with the occurrence of new-onset AF or stroke.

The effect of atrial morphology on atrial function in hypertrophic cardiomyopathy

Abstract Background Atrial dysfunction is a relevant marker of disease progression in hypertrophic cardiomyopathy (HCM). Left atrial (LA) longitudinal functional parameters and volumes derived from cardiac magnetic resonance (CMR) are associated with new-onset atrial fibrillation (AF) and its complications. The asymmetrical shape of the LA and its morphological alterations may influence LA function and could provide new mechanistic insights into HCM. Objective To assess the association between CMR derived functional and morphological LA characteristics in HCM patients. Methods Patients with an established diagnosis of HCM were included. HCM patients with a history of AF or without available CMR were excluded. CMR acquisitions used for clinical indication of heart failure diagnosis and etiology were retrospectively analyzed to obtain LA reservoir (LAres), booster (LAboost), and conduit (LAcond) strain on 2-chamber views (Medis Suite v3.2). Strain measurements of the other cardiac chambers were also performed. Manual tracing of LA endocardial border at the LA orthogonal longitudinal and transverse diameters on 2-, 3-, and 4-chamber views was performed (Philips Portal v10.1). Univariable and multivariable forward linear regression was employed to assess associations between functional and morphological LA measures. Results A total of 81 HCM patients were included, mean age 52±16 years, 59 (73%) male, and left ventricular ejection fraction 72.0±8.3%. Mean LAres was 27.2±11.0%, LAboost -14.9%±6.4%, and LAcond -12.5%±7.5%. LA morphological parameters are summarized in Table 1. The strongest correlates in multivariable regression for LAres were longitudinal LA diameter on 2-chamber view (Figure 1) and transverse LA diameter ratio between 4- and 2-chamber view (R2 0.30, p<0.001). The strongest correlates in multivariable regression for LAboost were longitudinal LA diameter on 2- and 4-chamber view, antero-posterior LA diameter on 3-chamber view, and LA area on 4-chamber view (R2 0.29, p<0.001). Longitudinal 2-chamber LA diameter also correlated with LAcond, but the strongest correlates of LAcond in multivariable regression were longitudinal-transversal LA diameter ratio on 2-chamber view, LA area on 3-chamber view, and LA sphericity (R2 0.25, p<0.001). Conclusions CMR-derived LA functions in HCM patients differently correlated with LA morphology. LA longitudinal 2-chamber diameter had a strong influence on all LA functions.Left atrial measures in HCMLA function and diameter correlations

P21-Activated Kinases Present a New Drug Target for Hypertrophic Cardiomyopathy

Expert review p21-Activated Kinases Present a New Drug Target for Hypertrophic Cardiomyopathy He Yu , and Lei Ming , * Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK * Correspondence: ming.lei@pharm.ox.ac.uk Received: 17 February 2023 Accepted: 26 March 2023 Published: 21 August 2023 Abstract: Hypertrophic cardiomyopathy (HCM), primarily involving mutations in sarcomeric proteins, is the most common form of inherited heart disease and a leading cause of sudden death in young adults and athletes. HCM patients present with cardiac hypertrophy, fibrosis, and diastolic dysfunction often in a progressive manner. Despite significant progress made in understanding the molecular genetic basis of HCM, there remains a lack of effective and specific treatment for preventing disease progression in HCM. This article first provides an overview of recent progress in understanding the pathogenic basis of disease progression in HCM, in particular dysfunctional calcium handling, mitochondrial impairment, and endoplasmic reticulum stress. This article then analyses the evidence for critical roles of the multifunctional enzymes P21-activated kinase-1 and 2 (Pak1/2) in the heart and our opinion on their therapeutic value as a promising druggable target in pathological hypertrophy and associated ventricular arrhythmias.

Abstract P3123: Sex-related Differences In Cardiac Biomarkers And Ventricular Fibrosis In A Minipig Model Of Hypertrophic Cardiomyopathy

Hypertrophic Cardiomyopathy (HCM) is characterized by ventricular hypertrophy and stiffness resulting in part from interstitial fibrosis. While associated with autosomal dominant mutations in sarcomere proteins, it has been reported that males and females may have different clinical presentations and disease courses. We have previously shown that minipigs carrying the R403Q mutation in MYH7 demonstrate a phenotype that recapitulates human non-obstructive HCM with increased hypertrophy, markers of cardiac stress, and diastolic dysfunction. Under the hypothesis that sex-dependent differences in cardiac physiology can independently modulate disease phenotype, we evaluated ventricular fibrosis and cardiac biomarkers in both male and female mutant pigs. Purpose-bred Yucatan R403Q MYH7 heterozygous mutant minipigs of either sex (M: n=8, F: n=6) and wild-type littermates (M: n=4, F: n=14) were used; for the purposes of these comparisons, cloned male pigs were also included (R403Q: 8). Males were castrated, and all pigs received soybean-based feed. Circulating levels of both cardiac troponin T (cTnT) and brain natriuretic peptide (BNP), markers of cardiac injury and stress, were assessed. Interstitial fibrosis was assessed in left ventricular free wall (LV-FW) and apical tissue samples utilizing picrosirius red staining and semi-automated quantification (HALO). Male HCM pigs died earlier (<9M of age, P<0.05) and had higher serum biomarkers than females (cTnT levels (M: 143±17 vs F: 44±7 ng/L, P<0.05; BNP 1536±335 vs 4881±414 ng/L, P<0.05) Consistent with the higher cTnT levels, male HCM pigs had greater fibrosis areas than females in both LV-FW (11±3% vs 7±2%, P<0.05) and apical regions (13±1% vs. 8±2%, respectively, P<0.05). All HCM pigs had significantly increased fibrotic area vs WT controls (R403Q: 10±3% vs WT: 3±2%, P<0.05). Our findings demonstrate that despite a common genotype, female and male carriers of the HCM pathogenic R403Q mutation present different disease phenotypes, with castrated males showing greater fibrotic burden. Future studies to understand the mechanistic drivers of these differences should not only help elucidate the role of sex in HCM disease progression, but also the development of sex-informed therapies.

Association of left atrial size and function by cardiac magnetic resonance imaging with long term outcomes in patients with hypertrophic cardiomyopathy.

Left atrial (LA) function and strain are being investigated as markers of disease progression in hypertrophic cardiomyopathy (HCM). To assess LA function and strain by cardiac magnetic resonance imaging (MRI) in patients with HCM and evaluate the association of these parameters with long-term clinical outcomes. We retrospectively evaluated 50 HCM patients and 50 patients with no significant cardiovascular disease (control) who underwent clinically indicated cardiac MRI. We calculated LA volumes using the Simpson area-length method to derive LA ejection fraction and expansion index. MRI-derived left atrial reservoir (ƐR), conduit (ƐCD), and contractile strain (ƐCT) were measured using dedicated software. A multivariate regression analysis with endpoints of ventricular tachyarrhythmias (VTA) and heart failure hospitalization (HFH) was performed. HCM patients had significantly higher LV mass, higher LA volumes and lower LA strain compared to controls. During the median follow up of 15.6months (interquartile range 8.4-35.4months), 11 patients (22%) experienced a HFH, while 10 patients (20%) had VTA. Multivariate analysis demonstrated that ƐCT (odds ratio (OR) 0.96, confidence interval (CI) 0.83-1.00) and LA ejection fraction (OR 0.89, CI 0.79-1.00) were significantly associated with VTA and HFH respectively.

Prediction of worsening heart failure in patients with hypertrophic cardiomyopathy using plasma proteomics profiling

Abstract Background While hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disease affecting 1 in 200–500 people, it is a heterogeneous disease. Only a subset of patients with HCM develop heart failure (HF; prevalence 35–50%). Prediction of worsening HF using clinical measures alone (e.g., cardiac imaging, genetic testing) remains limited. Furthermore, the underlying mechanism by which patients with HCM develop worsening HF has not been fully investigated. Proteomics profiling measures concentrations of thousands of proteins simultaneously and has been used to predict worsening of HF and to highlight which signaling pathways mediate worsening HF in non-HCM populations. Purpose In patients with HCM, we aimed to develop a plasma proteomics-based model to predict which patients with HCM would develop worsening HF and to identify signaling pathways that are differentially regulated in those who subsequently develop worsening HF. Methods We conducted a prospective cohort study in our multi-center biorepository of patients with HCM. We performed plasma proteomics profiling of 5032 proteins. We then developed a random forest model to predict worsening HF using proteomics profiling data from patients enrolled through one institution (training set). The outcome of worsening HF was defined as an increase in New York Heart Association functional class by at least 1 class. We externally validated this model in independent samples from patients enrolled through a different institution (test set). Further, we executed pathway analysis of proteins significantly dysregulated (i.e., univariable p<0.05) in patients who developed worsening HF compared to those who did not. Pathways with false discovery rate [FDR]<0.05 were considered to be dysregulated. Results There were 398 patients included in the study, with 278 in the training set and 120 in the test set. During a median follow-up of 1.8 years [interquartile range, 1.2–2.6], 60 (15%) patients developed worsening HF symptoms (45 patients in the training set and 15 patients in the test set). Using the proteomics-based model derived from the training set, the area under the receiver-operating-characteristic curve to predict worsening HF was 0.85 (95% confidence interval: 0.75–0.95) in the test set (Figure 1). Pathway analysis revealed that the Ras-MAPK pathway (FDR<0.00001) and its upstream PI3K-Akt pathway (FDR<0.00001) were dysregulated in patients who subsequently developed worsening HF (Figure 2). Conclusions Our study is the first to apply proteomics profiling to the prediction of worsening HF symptoms in patients with HCM, identifying patients who are at high risk of worsening HF and elucidating that the Ras-MAPK and related signaling pathways as potential underlying mechanisms. These findings support the potential application of proteomics profiling to clinical risk stratification and the investigation of signaling pathways underlying disease progression in HCM. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): NIH/NHLBI R01 grant

Copper chelation in patients with hypertrophic cardiomyopathy

BackgroundDisturbances of copper (Cu) homeostasis can lead to hypertrophic cardiac phenotypes (eg, Wilson’s disease). We previously identified abnormal Cu homeostasis in patients with hypertrophic cardiomyopathy (HCM) and, therefore, hypothesised that...

Discordant clinical features of identical hypertrophic cardiomyopathy twins

Hypertrophic cardiomyopathy (HCM) is a disease of heart muscle, which affects ∼1 in 500 individuals and is characterized by increased left ventricular wall thickness. While HCM is caused by pathogenic variants in any one of eight sarcomere protein genes, clinical expression varies considerably, even among patients with the same pathogenic variant. To determine whether background genetic variation or environmental factors drive these differences, we studied disease progression in 11 pairs of monozygotic HCM twins. The twin pairs were followed for 5 to 14 y, and left ventricular wall thickness, left atrial diameter, and left ventricular ejection fraction were collected from echocardiograms at various time points. All nine twin pairs with sarcomere protein gene variants and two with unknown disease etiologies had discordant morphologic features of the heart, demonstrating the influence of nonhereditable factors on clinical expression of HCM. Whole genome sequencing analysis of the six monozygotic twins with discordant HCM phenotypes did not reveal notable somatic genetic variants that might explain their clinical differences. Discordant cardiac morphology of identical twins highlights a significant role for epigenetics and environment in HCM disease progression.

Preventative therapeutic approaches for hypertrophic cardiomyopathy.

Sarcomeric gene mutations are associated with the development of hypertrophic cardiomyopathy (HCM). Current drug therapeutics for HCM patients are effective in relieving symptoms, but do not prevent or reverse disease progression. Moreover, due to heterogeneity in the clinical manifestations of the disease, patients experience variable outcomes in response to therapeutics. Mechanistically, alterations in calcium handling, sarcomeric disorganization, energy metabolism and contractility participate in HCM disease progression. While some similarities exist, each mutation appears to lead to mutation‐specific pathophysiology. Furthermore, these alterations may precede or proceed development of the pathology. This review assesses the efficacy of HCM therapeutics from studies performed in animal models of HCM and human clinical trials. Evidence suggests that a preventative rather than corrective therapeutic approach may be more efficacious in the treatment of HCM. In addition, a clear understanding of mutation‐specific mechanisms may assist in informing the most effective therapeutic mode of action.

Fropofol prevents disease progression in mice with hypertrophic cardiomyopathy

Increased myofilament contractility is recognized as a crucial factor in the pathogenesis of hypertrophic cardiomyopathy (HCM). Direct myofilament desensitization might be beneficial in preventing HCM disease progression. Here, we tested whether the small molecule fropofol prevents HCM phenotype expression and disease progression by directly depressing myofilament force development. Force, intracellular Ca2+, and steady-state activation were determined in isolated trabecular muscles from wild-type (WT) and transgenic HCM mice with heterozygous human α-myosin heavy chain R403Q mutation (αMHC 403/+). αMHC 403/+ HCM mice were treated continuously with fropofol by intraperitoneal infusion for 12 weeks. Heart tissue was analysed with histology and real-time PCR of prohypertrophic and profibrotic genes. Fropofol decreased force in a concentration-dependent manner without significantly altering [Ca2+]i in isolated muscles from both WT and αMHC 403/+ HCM mouse hearts. Fropofol also depressed maximal Ca2+-activated force and increased the [Ca2+]i required for 50% activation during steady-state activation. In whole-animal studies, chronic intra-abdominal administration of fropofol prevented hypertrophy development and diastolic dysfunction. Chronic fropofol treatment also led to attenuation of prohypertrophic and profibrotic gene expression, reductions in cell size, and decreases in tissue fibrosis. Direct inhibition of myofilament contraction by fropofol prevents HCM disease phenotypic expression and progression, suggesting that increased myofilament contractile force is the primary trigger for hypertrophy development and HCM disease progression.

Identification of a Multiplex Biomarker Panel for Hypertrophic Cardiomyopathy Using Quantitative Proteomics and Machine Learning.

Hypertrophic cardiomyopathy (HCM) is defined by pathological left ventricular hypertrophy (LVH). It is the commonest inherited cardiac condition and a significant number of high risk cases still go undetected until a sudden cardiac death (SCD) event. Plasma biomarkers do not currently feature in the assessment of HCM disease progression, which is tracked by serial imaging, or in SCD risk stratification, which is based on imaging parameters and patient/family history. There is a need for new HCM plasma biomarkers to refine disease monitoring and improve patient risk stratification. To identify new plasma biomarkers for patients with HCM, we performed exploratory myocardial and plasma proteomics screens and subsequently developed a multiplexed targeted liquid chromatography-tandem/mass spectrometry-based assay to validate the 26 peptide biomarkers that were identified. The association of discovered biomarkers with clinical phenotypes was prospectively tested in plasma from 110 HCM patients with LVH (LVH+ HCM), 97 controls, and 16 HCM sarcomere gene mutation carriers before the development of LVH (subclinical HCM). Six peptides (aldolase fructose-bisphosphate A, complement C3, glutathione S-transferase omega 1, Ras suppressor protein 1, talin 1, and thrombospondin 1) were increased significantly in the plasma of LVH+ HCM compared with controls and correlated with imaging markers of phenotype severity: LV wall thickness, mass, and percentage myocardial scar on cardiovascular magnetic resonance imaging. Using supervised machine learning (ML), this six-biomarker panel differentiated between LVH+ HCM and controls, with an area under the curve of ≥ 0.87. Five of these peptides were also significantly increased in subclinical HCM compared with controls. In LVH+ HCM, the six-marker panel correlated with the presence of nonsustained ventricular tachycardia and the estimated five-year risk of sudden cardiac death. Using quantitative proteomic approaches, we have discovered six potentially useful circulating plasma biomarkers related to myocardial substrate changes in HCM, which correlate with the estimated sudden cardiac death risk.

Abstract P202: Targeting the Cardiac Sympathetic Afferent Reflex in Hypertrophic Cardiomyopathy

Sarcomere gene mutations cause hypertrophic cardiomyopathy (HCM). Hallmark features include cardiac hypertrophy, fibrosis, excessive cardiac sympathetic tone, and increased risk of arrhythmias and sudden death. The mechanism(s) of increased sympathetic tone is poorly understood. We hypothesized that cardiac spinal (sympathetic) afferents are sensitized by metabolites (e.g., H+) produced during myocyte energy depletion in HCM, resulting in an enhanced cardiac sympathetic afferent reflex (CSAR). We studied mice with cardiac-specific expression of mutated alpha-tropomyosin (Glu180Gly), an established model of HCM. The CSAR was assessed by measuring mean arterial pressure (MAP) and heart rate (HR) responses to epicardial application of the TRPV1 agonist capsaicin (2.5mM, 2μL) to the left ventricle in anesthetized, ventilated HCM (n=5) and wild-type (WT) littermate control (n=5) mice. Pressor and tachycardic responses to capsaicin were markedly enhanced in HCM mice (Table). Blocking the tonic influence of cardiac afferent activity by epicardial application of the local anesthetic lidocaine (2%) caused small, significant decreases in MAP in both groups of mice; but decreased HR markedly in HCM mice only (n=5) (Table). mRNA expression (qPCR) of acid-sensing ion channel 3 was increased by 2-fold in dorsal root ganglia (T1-T9) of HCM vs. WT mice (n=6 each, P<0.05), suggesting a mechanism for sensitization of cardiac sympathetic afferents in HCM. We conclude that the CSAR is enhanced in HCM mice and speculate that increased activity of cardiac ‘sympathetic’ afferent nerves contributes to increased sympathetic tone, arrhythmias and disease progression in HCM.

Efficacy and safety of the angiotensin II receptor blocker losartan for hypertrophic cardiomyopathy: the INHERIT randomised, double-blind, placebo-controlled trial

No medical treatment has been reliably shown to halt or reverse disease progression in hypertrophic cardiomyopathy, but the results of several pilot studies have suggested beneficial effects of angiotensin II receptor blockers on left ventricular hypertrophy and fibrosis, which are predictive of an adverse outcome. We aimed to assess the effect of the angiotensin II receptor blocker losartan on left ventricular hypertrophy and fibrosis in patients with hypertrophic cardiomyopathy. In this single-centre, randomised, double-blind, placebo-controlled trial, adult patients (aged 18 years and older) with obstructive or non-obstructive hypertrophic cardiomyopathy were randomly assigned via computer-based system to losartan (100 mg per day) or placebo for 12 months. Patients and investigators were masked to assigned treatment. The primary endpoint was change in left ventricular mass as assessed by cardiac magnetic resonance imaging (CMR) or CT. Efficacy analyses were done in the modified intention-to-treat population (all patients with data available at the 12-month follow-up). The trial is registered with ClinicalTrials.gov, number NCT01447654. Between Dec 1, 2011, and May 1, 2013, 318 patients were screened. 133 patients (mean age 52 years [SD 13], 35% women) consented and were randomly assigned to placebo (n=69) or losartan (n=64). 124 (93%) patients completed the study and were included in the modified intention-to-treat analysis for the primary endpoint. After 12 months we noted no significant difference in the change in left ventricular mass between the placebo group and the losartan group (mean difference 1 g/m(2), 95% CI -3 to 6; p=0·60). A decrease in systolic blood pressure in the losartan group (from mean 127 mm Hg [SD 12] to 121 mm Hg [14]; p=0·0001) confirmed drug compliance; blood pressure did not decrease in the placebo group. Two (2%) patients, both in the placebo group, died from sudden cardiac death during follow-up. In the losartan group, one (1%) patient had angioedema, one (1%) had deterioration of renal function, and one (1%) had hyperkalaemia. Treatment was well tolerated by patients with left ventricular outflow obstruction at baseline. Our findings challenge the generally held view that angiotensin II receptor blockers reduce cardiac hypertrophy. Treatment with losartan was safe, suggesting that it can be used for other indications in patients with hypertrophic cardiomyopathy, irrespective of obstructive physiology. Additional studies are needed to assess the effect of angiotensin II receptor blockers in preclinical hypertrophic cardiomyopathy-eg, in genotype-positive but phenotype-negative individuals.

ENerGetIcs in hypertrophic cardiomyopathy: traNslation between MRI, PET and cardiac myofilament function (ENGINE study)

IntroductionHypertrophic cardiomyopathy (HCM) is an autosomal dominant heart disease mostly due to mutations in genes encoding sarcomeric proteins. HCM is characterised by asymmetric hypertrophy of the left ventricle (LV) in the absence of another cardiac or systemic disease. At present it lacks specific treatment to prevent or reverse cardiac dysfunction and hypertrophy in mutation carriers and HCM patients. Previous studies have indicated that sarcomere mutations increase energetic costs of cardiac contraction and cause myocardial dysfunction and hypertrophy. By using a translational approach, we aim to determine to what extent disturbances of myocardial energy metabolism underlie disease progression in HCM.MethodsHypertrophic obstructive cardiomyopathy (HOCM) patients and aortic valve stenosis (AVS) patients will undergo a positron emission tomography (PET) with acetate and cardiovascular magnetic resonance imaging (CMR) with tissue tagging before and 4 months after myectomy surgery or aortic valve replacement + septal biopsy. Myectomy tissue or septal biopsy will be used to determine efficiency of sarcomere contraction in-vitro, and results will be compared with in-vivo cardiac performance. Healthy subjects and non-hypertrophic HCM mutation carriers will serve as a control group.EndpointsOur study will reveal whether perturbations in cardiac energetics deteriorate during disease progression in HCM and whether these changes are attributed to cardiac remodelling or the presence of a sarcomere mutation per se. In-vitro studies in hypertrophied cardiac muscle from HOCM and AVS patients will establish whether sarcomere mutations increase ATP consumption of sarcomeres in human myocardium. Our follow-up imaging study in HOCM and AVS patients will reveal whether impaired cardiac energetics are restored by cardiac surgery.

Micro-RNA-195 and -451 Regulate the LKB1/AMPK Signaling Axis by Targeting MO25

BackgroundRecently, MicroRNAs (miR) and AMP-kinase (AMPK) have emerged as prominent players in the development of cardiac hypertrophy and heart failure. We hypothesized that components of the adenosine monophosphate-activated kinase (AMPK) pathway are targeted by miRs and alter AMPK signaling during pathological cardiac stress.Methodology/Principal FindingsUsing a mouse model of hypertrophic cardiomyopathy (HCM), we demonstrated early elevation of miR-195 and miR-451 in HCM hearts, which targets MO25, a central component of the MO25/STRAD/LKB1 complex that acts as an upstream kinase for AMPK. We show functional targeting of MO25 by miR-195 and -451. Further in vitro interrogation of MO25 as a functional target validated this hypothesis where over-expression of miR-195 in C2C12 cells knocked down MO25 expression levels and downstream AMPK signaling (phosphorylation of Acetyl CoA carboxylase [ACC] and AMPK activity assay), similar to MO25 knockdown in C2C12 cells by siRNA. Parallel changes were measured in 60 day R403Q HCM male hearts that were rescued by short-term administration of AICAR, an AMPK agonist.Conclusions/SignificanceElevated miR-195 targets the LKB1/AMPK signaling axis in HCM progression and implicates a functional role in HCM disease progression. MiR-195 may serve as potential therapeutics or therapeutic targets for heart disease.

Contractile Dysfunction Irrespective of the Mutant Protein in Human Hypertrophic Cardiomyopathy With Normal Systolic Function

Hypertrophic cardiomyopathy (HCM), typically characterized by asymmetrical left ventricular hypertrophy, frequently is caused by mutations in sarcomeric proteins. We studied if changes in sarcomeric properties in HCM depend on the underlying protein mutation. Comparisons were made between cardiac samples from patients carrying a MYBPC3 mutation (MYBPC3(mut); n=17), mutation negative HCM patients without an identified sarcomere mutation (HCM(mn); n=11), and nonfailing donors (n=12). All patients had normal systolic function, but impaired diastolic function. Protein expression of myosin binding protein C (cMyBP-C) was significantly lower in MYBPC3(mut) by 33±5%, and similar in HCM(mn) compared with donor. cMyBP-C phosphorylation in MYBPC3(mut) was similar to donor, whereas it was significantly lower in HCM(mn). Troponin I phosphorylation was lower in both patient groups compared with donor. Force measurements in single permeabilized cardiomyocytes demonstrated comparable sarcomeric dysfunction in both patient groups characterized by lower maximal force generating capacity in MYBPC3(mut) and HCM(mn,) compared with donor (26.4±2.9, 28.0±3.7, and 37.2±2.3 kN/m(2), respectively), and higher myofilament Ca(2+)-sensitivity (EC(50)=2.5±0.2, 2.4±0.2, and 3.0±0.2 μmol/L, respectively). The sarcomere length-dependent increase in Ca(2+)-sensitivity was significantly smaller in both patient groups compared with donor (ΔEC(50): 0.46±0.04, 0.37±0.05, and 0.75±0.07 μmol/L, respectively). Protein kinase A treatment restored myofilament Ca(2+)-sensitivity and length-dependent activation in both patient groups to donor values. Changes in sarcomere function reflect the clinical HCM phenotype rather than the specific MYBPC3 mutation. Hypocontractile sarcomeres are a common deficit in human HCM with normal systolic left ventricular function and may contribute to HCM disease progression.

Abstract P196: The Impact of MicroRNA195 on the Lkb1/AMPK Signaling Axis and Hypertrophic Cardiomyopathy

Objectives: MicroRNAs (miRs) have been identified as chief post-transcriptional regulators of cardiac disease progression. In addition, a critical role of the adenosine monophosphate-activated kinase (AMPK) pathway in the development of myocardial hypertrophy has been revealed. Yet, regulation of the AMPK pathway by miRs in the heart has not been addressed. We hypothesized that components of the AMPK pathway are targeted by miRs and alter AMPK signaling in a mouse model of hypertrophic cardiomyopathy (HCM). Methods and results: Using real-time PCR, a candidate miR screen that included 22 miRs implicated in pathological cardiac disease and/or metabolic dysregulation was performed on hearts from 60-, 120-, and 240-day-old transgenic HCM male mice harboring an R403Q mutation in the myosin heavy gene. Among early (60 day) elevated miRs were miR-195 and -451. Both miR-195 and -451 have conserved target sites in the 3′ UTR of CAB39 (MO25), a central component of the MO25/STRAD/LKB1 complex that acts as an upstream kinase for AMPK and its subsequent activation. We further confirmed the elevation of miR-195 and -451 by Northern blotting. Next, we demonstrated specific expression and a similar distribution pattern of miR-195 and -451 in cardiomyocytes of R403Q HCM hearts by in situ hybridization. To determine whether the conserved sites in MO25 3′ UTR acted as functional targets, either the miR-195 or miR-451 target sequence was cloned into a luciferase expression vector. MiR-195 but not miR-451 suppressed luciferase activity compared to the missense sequence control vector in C2C12 cells. In addition, over-expression of miR195 in C2C12 cells knocked down MO25 expression levels and downstream AMPK signaling (phosphorylation of Acetyl CoA carboxylase). Finally, parallel changes were measured in 60 day R403Q HCM male hearts that included reduced MO25 expression and lowered phosphorlation of AMPK and Acetyl CoA carboxylase. Conclusion: Our findings indicate that miR-195 targets the LKB1/AMPK signaling axis and suggest a functional role for miR-195 elevation in R403Q HCM disease progression.

High Prevalence of Abnormal Nocturnal Oximetry in Patients With Hypertrophic Cardiomyopathy

We sought to determine the prevalence of nocturnal oxygen desaturation and obstructive sleep apnea (OSA) in a population of patients with hypertrophic cardiomyopathy (HCM). The coexistence of sleep apnea and HCM, 2 common cardiovascular conditions, has been largely unrecognized in the treatment of patients with HCM. The nocturnal hypoxia-induced hyperadrenergic state in OSA is expected to worsen hemodynamics and outcomes in HCM. One hundred subjects with HCM between June 1, 2006, and July 14, 2008, were screened with nocturnal oximetry. Clinical variables were collected for statistical analysis. Oximetry was classified abnormal (suspicion of sleep-disordered breathing) in the presence of repetitive desaturation (> or =5 events/h) followed by a rapid return to baseline oxygen saturation (SaO(2)) level with a decrease of > or =4% and threshold of 90%. Seventy-one (71%) patients with HCM had abnormal nocturnal oximetry (71 +/- 9%, 95% confidence interval: 62% to 80%). Subjects with abnormal oximetry were older (age 59.5 +/- 15.3 years) and more were hypertensive (n = 39 [55%]) than those with normal oximetry (age 45.8 +/- 18.5 years, n = 9 [31%], p < 0.001, p = 0.03). Patients with HCM were more symptomatic in the presence of abnormal oximetry (New York Heart Association functional class II to III) (62% vs. 83%, p = 0.023). HCM patients had a higher prevalence of abnormal nocturnal oximetry (n = 71, 71%) compared with a control group of similar age and sex distribution (n = 49, 49%) (p = 0.001). Abnormal nocturnal oximetry is common in patients with HCM, suggesting that OSA is prevalent. OSA may impact hemodynamics and symptoms in HCM. Further studies are needed to determine the long-term benefit of OSA treatment on hemodynamics and disease progression in HCM.

Hypertrophic Cardiomyopathy

Hypertrophic Cardiomyopathy

756-3 Management and Prognosis of Asymptomatic Patients with Hypertrophic Cardiomyopathy

The clinical course of hypertrophic cardiomyopathy (HCM) is extremely heterogeneous; some patients develop severe symptoms of heart failure, some die suddenly, but many remain asymptomatic throughout life. The prognosis of patients who are asymptomatic at initial examination, however, has never been investigated systematically in a large study population. We examined the clinical course of all the patients with HCM who were evaluated in our department during 10 years and were asymptomatic or had only mild symptoms at initial examination. A total of 89 patients were followed for a mean of 4.9 yrs (0.3–10.8). Of these 89 patients, 50 (56%) were not treated with cardioactive medications during follow up. Annual mortality was 0.4% (95% confidence interval 0.1–1.4); only 2 patients died, both showing progressive deterioration before death. Seventy-nine patients (89%) remained clinically stable during follow up, 3 developed severe symptoms (functional class III), and 5 did not progress to class III but experienced sustained ventricular tachycardia or syncope. Echocardiographic assessment of cardiac morphology showed that the 2 patients who died were in the small group of 8 patients with particularly marked hypertrophy (≥30 mm) at initial examination. In conclusion, our results show that cardiac mortality is low in patients with HCM who are asymptomatic or have only mild symptoms, and that clinical deterioration usually occurs gradually. In the absence of data showing that therapy prevents cardiac death or delays disease progression in HCM, our results suggest that treatment should be used only for alleviation of symptoms.