Risk stratification for sudden cardiac death in hypertrophic cardiomyopathy: Dutch cardiologists and the care of mutation carriers

Background. Patients with hypertrophic cardiomyopathy (HCM) and HCM mutation carriers are at risk of sudden cardiac death (SCD). Both groups should therefore be subject to regular cardiological testing – including risk stratification for SCD – according to international guidelines. We evaluated Dutch cardiologists' knowledge of and adherence to international guidelines on risk stratification and prevention of SCD in mutation carriers with and without manifest HCM. Methods. A questionnaire was sent to 1109 Dutch cardiologists (in training) containing case-based questions. Results. The response rate was 21%. Own general knowledge on HCM care was rated as insufficient by 63% of cardiologists. The percentage of correct answers (i.e. in agreement with international guidelines), on the case-based questions ranged from 37 to 96%, being lowest in cases with an unknown number of risk factors for SCD. A substantial portion of correct answers was based on the correct answer ‘ask an expert opinion’. Significantly more correct answers were provided in cases with manifest HCM. There was little difference between the answers of cardiologists with different self-reported levels of knowledge, with different numbers of HCM patients in their practice or with different numbers of carriers without manifest HCM. Conclusion. Knowledge on risk stratification and preventive therapy was mediocre, and knowledge gaps exist, especially on HCM mutation carriers without manifest disease. Fortunately, experts are frequently asked for their opinion which might bring patient care to an adequate level. Hopefully, our results will stimulate cardiologists to follow developments in this field, thereby increasing quality of care for HCM patients and mutation carriers. (Neth Heart J 2009:17:464–9.).     

A missense mutation in a ubiquitously expressed protein, vinculin, confers susceptibility to hypertrophic cardiomyopathy

The R975W mutation, in the alternatively spliced exon 19 of vinculin (VCL) which yields the isoform metavinculin, was associated previously with hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM), and shown to alter in vivo organization of intercalated discs. We tested the hypothesis that alterations in the ubiquitously expressed, VCL-encoded protein, vinculin, may provide a pathogenic substrate for HCM. Comprehensive mutational analysis of VCL's 22 translated exons was performed in a cohort of 228 unrelated patients with genotype negative HCM, having no identifiable mutations in 12 HCM-associated myofilament/Z-disc-encoding genes. A novel missense mutation, L277M-VCL, involving a conserved residue was identified in a patient with severely obstructive, mid-ventricular hypertrophy. This mutation was not detected in 400 reference alleles. Immunohistochemical analysis of the proband's myectomy specimen demonstrated markedly reduced vinculin levels in the intercalated discs. We provide the first report of a cardiomyopathy associated mutation in vinculin. Despite its ubiquitous expression, the HCM-associated VCL mutation clinically yielded a cardiac-specific phenotype.     

ACE I/D polymorphism in Indian patients with hypertrophic cardiomyopathy and dilated cardiomyopathy

Aim The study was carried to determine the association of angiotensin converting enzyme (ACE) insertion/deletion (I/D) polymorphism with the risk of hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), and restrictive cardiomyopathy (RCM). Methods and results A total of 174 patients diagnosed with cardiomyopathy (118 with HCM, 51 with DCM, and 5 with RCM) and 164 ethnically, age- and gender-matched controls were included in the study. ACE I/D genotyping was performed by PCR. In total, 25.86% of the patients were in New York Heart Association (NYHA) class III and IV at presentation. A total of 67.24% patients had dyspnea, 56.89% had angina pectoris, and 25.28% of the patients had at least one event of syncope. Frequency of occurrence of the disease was more in male patients compared to female patients (P < 0.05). After adjustment for age, sex, body mass index (BMI), and smoking habit, the prevalence of ACE DD genotype, and ACE ‘D’ allele was significantly higher in patients as compared to controls and was associated with increased risk (DD: OR 2.11, 95% CI 1.27–3.52, P < 0.05; ‘D’: OR 1.91, 95% CI 1.08–3.35, P < 0.05). The mean septal thickness was higher for DD and ID genotypes (20.40 ± 3.73 mm and 21.82 ± 5.35 mm, respectively) when compared with II genotype (18.63 ± 6.69 mm) in HCM patients, however, the differences were not significant statistically (P > 0.05). The DCM patients with ID genotype showed significantly decreased left ventricular ejection fraction (LVEF) at enrolment (26.50 ± 8.04%) (P = 0.04). Conclusion Our results suggest that D allele of ACE I/D polymorphism significantly influences the HCM and DCM phenotypes.     

A myomesin mutation associated with hypertrophic cardiomyopathy deteriorates dimerisation properties

Myomesin plays an important structural and functional role in the M-band of striated muscles. The C-terminal domain 13 of myomesin dimerises and forms antiparallel strands which cross-link neighboring Myosin filaments and titin in the M-line of the sarcomeres. These interactions stabilise the contractile apparatus during striated muscle contraction. Since myomesin is an important component of the M-band we screened the myomesin gene for genetic variants in patients with hypertrophic cardiomyopathy (HCM).We identified the missense mutation V1490I in domain 12 of myomesin in a family with inherited HCM. Analytical ultracentrifugation experiments, circular dichroism spectra, and surface plasmon resonance spectroscopy of myomesin fragments were carried out to investigate the effects of the mutation V1490I on structure and function of myomesin domains 11–13 and 12–13. Both the wild type and mutated myomesin domains My11–13 revealed similar secondary structures and formed stable dimers. Mutated myomesin domains My11–13 and My12–13 dimers revealed a reduced thermal stability and a significantly decreased dimerisation affinity, showing disturbed functional properties of V1490I mutated myomesin. However, monomeric myomesin domains My11–12, i.e. without dimerisation domain 13 showed no difference in thermal stability between wild type and V1490I mutated myomesin.In conclusion, the V1490I mutation associated with HCM lead to myomesin proteins with abnormal functional properties which affect dimerisation properties of myomesin domain 13. These effects may contribute to the pathogenesis of HCM.     

Identification and functional analysis of a caveolin-3 mutation associated with familial hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are caused by mutations in 14 and 15 different disease genes, respectively, in a part of the patients and the disease genes for cardiomyopathy overlap in part with that for limb-girdle muscular dystrophy (LGMD). In this study, we examined an LGMD gene encoding caveolin-3 (CAV3) for mutation in the patients with HCM or DCM. A Thr63Ser mutation was identified in a sibling case of HCM. Because the mutation was found at the residue that is involved in the LGMD-causing mutations, we investigate the functional change due to the Thr63Ser mutation as compared with the LGMD mutations by examining the distribution of GFP-tagged CAV3 proteins. It was observed that the Thr63Ser mutation reduced the cell surface expression of caveolin-3, albeit the change was mild as compared with the LGMD mutations. These observations suggest that HCM is a clinical spectrum of CAV3 mutations.     

磁共振成像对扩张型心肌病转基因模型小鼠左右心室对比分析

目的对cTnTR141W扩张型心肌病转基因模型小鼠左、右心室进行对比分析,研究cTnTR141W转基因小鼠作为右心室心肌病的动物模型的可行性。方法利用7.0 T高场强磁共振成像(MRI)技术,定量分析了2、4、6和8月龄对照组及cTnTR141W转基因模型小鼠左、右心室的舒张末容积(EDV)、收缩末容积(ESV)和射血分数(EF)的变化情况,同时对6月龄对照组cTnTR141W转基因模型小鼠心肌组织进行组织学分析。结果转基因阴性对照小鼠相比,cTnTR141W转基因小鼠左、右心室的容积在2月龄时已有增大趋势,而射血分数有减小趋势。右心室射血分数减小出现最早也最显著(P<0.05)。随年龄增加,cTnTR141W转基因小鼠与转基因阴性对照小鼠相比,右心室的结构和功能的病理生理变化与左心室同时趋于严重。该小鼠左、右心室在4月龄后表现典型的扩张型心肌病表型。结论 cTnTR141W转基因模型小鼠左心室和右心室的扩张性心肌病表型同时出现,该小鼠可作为右室性心肌病等右心室功能下降相关疾病研究的动物模型。     

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

Introduction

Hypertrophic 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.

Methods

Hypertrophic 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.

Endpoints

Our 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.     

Structural analysis of obscurin gene in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a cardiac disease characterized by left ventricular hypertrophy with diastolic dysfunction. Molecular genetic studies have revealed that HCM is caused by mutations in genes for sarcomere/Z-band components including titin/connectin and its associate proteins. However, disease-causing mutations can be found in about half of the patients, suggesting that other disease-causing genes remain to be identified. To explore a novel disease gene, we searched for obscurin gene (OBSCN) mutations in HCM patients, because obscurin interacts with titin/connectin. Two linked variants, Arg4344Gln and Ala4484Thr, were identified in a patient and functional analyses demonstrated that Arg4344Gln affected binding of obscurin to Z9-Z10 domains of titin/connectin, whereas Ala4484Thr did not. Myc-tagged obscurin showed that Arg4344Gln impaired obscurin localization to Z-band. These observations suggest that the obscurin abnormality may be involved in the pathogenesis of HCM.     

The importance of cardiac MRI as a diagnostic tool in viral myocarditis-induced cardiomyopathy

Myocarditis is an acute or chronic inflammatory disease of the myocardium which can be viral, postinfectious immune or primarily organ-specific autoimmune. Clinical manifestations of acute and chronic myocarditis are extremely varied, ranging from mild to severe. Affected patients may recover or develop (dilated) cardiomyopathy (DCM) with life-threatening symptoms including heart failure, conduction disturbances, arrhythmias, cardiogenic shock or sudden cardiac death. The diagnosis of myocarditis is a challenging process and not only because of a diverse presentation; other problems are limited sensitivity of endomyocardial biopsies (EMB) and overlapping symptoms. Furthermore, the diagnosis is not well defined. However, early diagnosis is mandatory to address specific aetiology-directed therapeutic management in myocarditis that influences patient morbidity and mortality. Currently, EMB remains the only way to confirm the presence of a viral genome and other histopathological findings allowing proper treatment to be implemented in cases of myocarditis. Increased recognition of the role of myocardial inflammatory changes has given rise to interest in noninvasive imaging as a diagnostic tool, especially cardiovascular magnetic resonance imaging (CMR). In this review we discuss the current role of CMR in the evaluation of myocarditis-induced inflammatory cardiomyopathies. (Neth Heart J 2009;17:481–6.)     

Hypertrophic cardiomyopathy: two homozygous cases with "typical" hypertrophic cardiomyopathy and three new mutations in cases with progression to dilated cardiomyopathy

About 10% of cases of hypertrophic cardiomyopathy (HCM) evolve into dilated cardiomyopathy (DCM) with unknown causes. We studied 11 unrelated patients (pts) with HCM who progressed to DCM (group A) and 11 who showed "typical" HCM (group B). Mutational analysis of the beta-myosin heavy chain (MYH7), myosin-binding protein C (MYBPC3), and cardiac troponin T (TNNT2) genes demonstrated eight mutations affecting MYH7 or MYBPC3 gene, five of which were new mutations. In group A-pts, the first new mutation occurred in the myosin head-rod junction and the second occurred in the light chain-binding site. The third new mutation leads to a MYBPC3 lacking titin and myosin binding sites. In group B, two pts with severe HCM carried two homozygous MYBPC3 mutations and one with moderate hypertrophy was a compound heterozygous for MYBPC3 gene. We identified five unreported mutations, potentially "malignant" defects as for the associated phenotypes, but no specific mutations of HCM/DCM.     

Obstructive hypertrophic cardiomyopathy is associated with reduced expression of vinculin in the intercalated disc

Mutations in the cardiac-specific insert of vinculin, metavinculin, rarely cause hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). Subsequently, a missense mutation in the ubiquitously expressed vinculin was discovered in a patient with obstructive HCM. Microscopic examination of both myectomy specimens from patients bearing genetic defects in metavinculin and vinculin showed a marked reduction of vinculin/metavinculin expression in the intercalated disc, but normal expression in the Z-disc. Given that distinct functional domains were altered by the metavinculin and vinculin mutations, we hypothesized that the intercalated disc-specific reduction of vinculin may stem from left ventricular tract obstruction in general rather than rarely observed perturbations in VCL-encoded vinculin. To test this hypothesis, we examined the localization of vinculin/metavinculin in hypertrophied human heart tissue from patients with cardiovascular conditions associated with obstruction and hemodynamic overload using an immunohistochemistry approach. Tissue specimens derived from patients with obstructive HCM and aortic stenosis (AS) showed a universal defect of vinculin/metavinculin expression in the intercalated disc but preserved expression in the cardiac Z-disc, whereas tissue specimens derived from patients with either DCM, hypertensive heart disease (HTN), or pulmonary hypertension (PHTN) exhibited normal expression of vinculin/metavinculin in both the Z- and the intercalated disc despite being associated with hypertrophy. Results of this study suggest that cardiac hypertrophy may be associated with different expression of the marker vinculin/metavinculin depending on the underlying pathophysiology; hemodynamic overload may not affect the localization whereas obstructive disease substantially reduces the expression of vinculin preferentially in the intercalated disc.     

Biventricular / left ventricular pacing in hypertrophic obstructive cardiomyopathy: an overview

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant inherited genetic disease characterized by compensatory pathological left ventricle (LV) hypertrophy due to sarcomere dysfunction. In an important proportion of patients with HCM, the site and extent of cardiac hypertrophy results in severe obstruction to LV outflow tract (LVOT), contributing to disabling symptoms and increasing the risk of sudden cardiac death (SCD). In patients with progressive and/or refractory symptoms despite optimal pharmacological treatment, invasive therapies that diminish or abolish LVOT obstruction relieve heart failure-related symptoms, improve quality of life and could be associated with long-term survival similar to that observed in the general population. The gold standard in this respect is surgical septal myectomy, which might be supplementary associated with a reduction in SCD. Percutaneous techniques, particularly alcohol septal ablation (ASA) and more recently radiofrequency (RF) septal ablation, can achieve LVOT gradient reduction and symptomatic benefit in a large proportion of HOCM patients at the cost of a supposedly limited septal myocardial necrosis and a 10-20% risk of chronic atrioventricular block. After an initial period of enthusiasm, standard DDD pacing failed to show in randomized trials significant LVOT gradient reductions and objective improvement in exercise capacity. However, case reports and recent small pilot studies suggested that atrial synchronous LV or biventricular (biV) pacing significantly reduce LVOT obstruction and improve symptoms (acutely as well as long-term) in a large proportion of severely symptomatic HOCM patients not suitable to other gradient reduction therapies. Moreover, biV/LV pacing in HOCM seems to be associated with significant LV reverse remodelling.     

Ubiquitin-proteasome system impairment caused by a missense cardiac myosin-binding protein C mutation and associated with cardiac dysfunction in hypertrophic cardiomyopathy

The ubiquitin-proteasome system is responsible for the disappearance of truncated cardiac myosin-binding protein C, and the suppression of its activity contributes to cardiac dysfunction. This study investigated whether missense cardiac myosin-binding protein C gene (MYBPC3) mutation in hypertrophic cardiomyopathy (HCM) leads to destabilization of its protein, causes UPS impairment, and is associated with cardiac dysfunction. Mutations were identified in Japanese HCM patients using denaturing HPLC and sequencing. Heterologous expression was investigated in COS-7 cells as well as neonatal rat cardiac myocytes to examine protein stability and proteasome activity. The cardiac function was measured using echocardiography. Five novel MYBPC3 mutations—E344K, ΔK814, Δ2864-2865GC, Q998E, and T1046M—were identified in this study. Compared with the wild type and other mutations, the E334K protein level was significantly lower, it was degraded faster, it had a higher level of polyubiquination, and increased in cells pretreated with the proteasome inhibitor MG132 (50 μM, 6 h). The electrical charge of its amino acid at position 334 influenced its stability, but E334K did not affect its phosphorylation. The E334K protein reduced cellular 20 S proteasome activity, increased the proapoptotic/antiapoptotic protein ratio, and enhanced apoptosis in transfected Cos-7 cells and neonatal rat cardiac myocytes. Patients carrying the E334K mutation presented significant left ventricular dysfunction and dilation. The conclusion is the missense MYBPC3 mutation E334K destabilizes its protein through UPS and may contribute to cardiac dysfunction in HCM through impairment of the ubiquitin-proteasome system.     

Predictors of outcome after alcohol septal ablation in patients with hypertrophic obstructive cardiomyopathy. Special interest for the septal coronary anatomy

Background

Alcohol septal ablation (ASA) provides symptomatic relief in most but not all patients with hypertrophic obstructive cardiomyopathy (HOCM). Therefore we investigated predictors of outcome after ASA.

Methods

Clinical, echocardiographic, angiographic and procedural characteristics were analysed in 113 consecutive patients. Successful ASA was defined as NYHA ≤ 2 with improvement of at least 1 class combined with a resting gradient < 30 mmHg and provoked gradient < 50 mmHg at 4-month follow-up.

Results

In 37 patients ASA was not successful. In multivariate analysis, baseline gradient (OR 1.06 (1.01–1.11) per 5 mmHg, p = 0.024) and distance to the ablated septal branch (OR 1.09 (1.03–1.16) per mm, p = 0.004) were predictors of unsuccessful outcome. The combined presence of a non-ablated septal branch and a distance ≥ 19 mm to the ablated branch was a predictor of unsuccessful outcome (OR 5.88 (2.06–16.7), p < 0.001).

Conclusions

Baseline gradient and a greater distance from the origin of the left anterior descending artery to the ablated septal branch combined with a non-ablated proximal septal branch are associated with an unsuccessful outcome after ASA.     

Left ventricular apical torsion and architecture are not inverted in situs inversus totalis

Occasionally, individuals have a complete, mirror-image reversal of their internal organ position, called situs inversus totalis (SIT). Whereas gross anatomy is mirror-imaged in SIT, this might not be the case for the internal architecture of organs, e.g. the myofiber pattern in the left cardiac ventricle. We performed a Magnetic Resonance Tagging study in nine controls and in eight subjects with SIT to assess the deformation pattern in the apical half of the LV wall. It appeared that both groups had the same LV apical deformation pattern. This implies that not only the superficial LV apical layers in SIT follow a normal, not inverted pattern, but the deeper layers as well. Apparently, the embryonic L/R controlling genetic pathway does determine situs-specific gross anatomy morphogenesis but it is not the only factor regulating fiber architecture within the apical part of the LV wall. We propose that mechanical forces generated in the not-inverted molecular structure of the basic right-handed helical contractile components of the sarcomere play a role in shaping the LV apex.     

Cellular and molecular aspects of familial hypertrophic cardiomyopathy caused by mutations in the cardiac troponin I gene

Mutations in the cardiac troponin I (CTnI) gene occur in 5% of families with familial hypertrophic cardiomyopathy (FHC) and 20 mutations in this gene that cause FHC have now been described. The clinical manifestations of CTnI mutations that cause FHC are diverse, ranging from asymptomatic with high life expectancy to severe heart failure and sudden cardiac death. Most of these FHC mutations in CTnI result in cardiac hypertrophy unlike cardiac troponin T FHC mutations. All CTnI FHC mutations investigated in vitro affect the physiological function of CTnI, but other factors such as environmental or genetic factors (other genes that may affect the CTnI gene) are likely to be involved in influencing the severity of the phenotype produced by these mutations, since the distribution of hypertrophy among affected individuals varies within and between families. CTnI mutations mainly alter myocardial performance via changes in the Ca²⁺-sensitivity of force development and in some cases alter the muscle relaxation kinetics due to haemodynamic or physical obstructions of blood flow from the left ventricle. (Mol Cell Biochem 263: 99–114, 2004)     

Dual chamber pacing in a patient of hypertrophic cardiomyopathy with failure to wean from mechanical ventilator

We discuss the case of a 63 years old female who required repeated intubation due to recurrent pulmonary edema. She was found to have hypertrophic cardiomyopathy with a gradient of 82 mmHg across the left ventricular outflow tract. Initially adequate rate control and treatment with negative inotropes did not help her condition. Finally a dual chamber pacemaker implantation and atrioventricular node modification lead to successful extubation.     

三种正常大鼠磁共振成像心功能基础数据采集和分析

目的大鼠是常用的制备心脏病模型的实验动物,而磁共振成像（MRI）技术已经成为评价心脏病模型病理进程和药效的重要技术手段,但是目前国内外没有正常大鼠心脏的磁共振成像技术参数,影响了这一技术的应用。本文利用磁共振成像技术,采集和定量分析Wistar、Sprague-Dawley和Lewis三种常用大鼠的左、右心室功能参数,为心脏病模型制备和分析提供参考数据。方法利用7．0T高场强MRI心脏电影（CINE）序列,分析这三种常用大鼠活体心脏组织的左、右心室心功能参数。结果获得三种大鼠左、右心室的8—9周龄功能参数,包括：左、右心室的舒张末容积（EDV）、收缩末容积（ESV）、射血分数（EF）;左心室乳头肌层面舒张末期内径（EDD）、收缩末期内径（ESD）、短轴缩短率（Fs）、舒张末前后室壁厚度（EDAWT,EDPWT）、收缩末前后室壁厚度（ESAWT,ESPWT）、前室壁增厚率（AWT）和后室壁增厚率（PwT）;右心室乳头肌层面舒张末室壁厚度（EDWT）、收缩末室壁厚度（ESWT）和室壁增厚率（WT）等十八项心脏主要功能和结构的正常值。结论本研究获得的三种大鼠十八项心脏主要功能和结构的正常值,可作为心脏病模型制备成模判定和病理进程、药物评价的参考数据。