Hypertrophic cardiomyopathy: histopathological features of sudden death in cardiac troponin T disease

[Advances in the molecular pathogenesis of hypertrophic cardiomyopathy]

Hypertrophic Cardiomyopathy (HCM) is a primary cardiac disorder characterized by asymmetric thickening of the septum and left ventricular wall. HCM affects 1 in 500 individuals in the general population, and it is the most common cause of sudden death in the young and athletes. The clinic phenotype of HCM is highly variable with respect to age at onset, degree of symptoms, and risk of sudden death. HCM is usually inherited as a Mendelian autosomal dominant trait. To date, over 900 mutations have been reported in HCM, which were mainly located in 13 genes encoding cardiac sarcomere protein, e.g., MYH7, MYBPC3, and TnT. In addition, more and more mitochondrial DNA mutations were reported to be associated with the pathogenesis of HCM. Based on the description of the clinical phenotype and morphological characteristics, this review focuses on the research in the molecular pathogenic mechanism of HCM and its recent advances.

Thin filament mutations: developing an integrative approach to a complex disorder

Sixteen years ago, mutations in cardiac troponin (Tn)T and α-tropomyosin were linked to familial hypertrophic cardiomyopathy, thus transforming the disorder from a disease of the β-myosin heavy chain to a disease of the cardiac sarcomere. From the outset, studies suggested that mutations in the regulatory thin filament caused a complex, heterogeneous pattern of ventricular remodeling with wide variations in clinical expression. To date, the clinical heterogeneity is well matched by an extensive array of nearly 100 independent mutations in all components of the cardiac thin filament. Significant advances in our understanding of the biophysics of myofilament activation, coupled to the emerging evidence that thin filament linked cardiomyopathies are progressive, suggests that a renewed focus on the most proximal events in both the molecular and clinical pathogenesis of the disease will be necessary to achieve the central goal of using genotype information to manage affected patients. In this review, we examine the existing biophysical and clinical evidence in support of a more proximal definition of thin filament cardiomyopathies. In addition, new high-resolution, integrated approaches are presented to help define the way forward as the field works toward developing a more robust link between genotype and phenotype in this complex disorder.

The development of familial hypertrophic cardiomyopathy: from mutation to bedside

Hypertrophic cardiomyopathy (HCM) is a familial disorder characterized by left ventricular hypertrophy in the absence of other cardiac or systemic disease likely to cause this hypertrophy. HCM is considered a disease of the sarcomere as most causal mutations are identified in genes encoding sarcomeric proteins, although several other disorders have also been linked to the HCM phenotype. The clinical course of HCM is characterized by a large inter- and intrafamilial variability, ranging from severe symptomatic HCM to asymptomatic individuals. The general picture emerges that the underlying pathophysiology of HCM is complex and still scarcely clarified. Recent findings indicated that both functional and morphological (macroscopic and microscopic) changes of the HCM muscle are present before the occurrence of HCM phenotype. This review aims to provide an overview of the myocardial alterations that occur during the gradual process of wall thickening in HCM on a myofilament level, as well as the structural and functional abnormalities that can be observed in genetically affected individuals prior to the development of HCM with state of the art imaging techniques, such as tissue Doppler echocardiography and cardiovascular magnetic resonance imaging. Additionally, present and future therapeutic options will be briefly discussed.

Fetal cardiac troponin isoforms rescue the increased Ca2+ sensitivity produced by a novel double deletion in cardiac troponin T linked to restrictive cardiomyopathy: a clinical, genetic, and functional approach

A novel double deletion in cardiac troponin T (cTnT) of two highly conserved amino acids (Asn-100 and Glu-101) was found in a restrictive cardiomyopathic (RCM) pediatric patient. Clinical evaluation revealed the presence of left atrial enlargement and marked left ventricle diastolic dysfunction. The explanted heart examined by electron microscopy revealed myofibrillar disarray and mild fibrosis. Pedigree analysis established that this mutation arose de novo. The patient tested negative for six other sarcomeric genes. The single and double recombinant cTnT mutants were generated, and their functional consequences were analyzed in porcine skinned cardiac muscle. In the adult Tn environment (cTnT3 + cardiac troponin I), the single cTnT3-ΔN100 and cTnT3-ΔE101 mutations had opposing effects on the Ca(2+) sensitivity of force development compared with WT, whereas the double deletion cTnT3-ΔN100/ΔE101 increased the Ca(2+) sensitivity + 0.19 pCa units. In addition, cTnT3-ΔN100/ΔE101 decreased the cooperativity of force development, suggesting alterations in intrafilament protein-protein interactions. In the fetal Tn environment, (cTnT1 + slow skeletal troponin I), the single (cTnT1-ΔN110) and double (cTnT1-ΔN110/ΔE111) deletions did not change the Ca(2+) sensitivity compared with control. To recreate the patient's heterozygous genotype, we performed a reconstituted ATPase activity assay. Thin filaments containing 50:50 cTnT3-ΔN100/ΔE101:cTnT3-WT also increased the myofilament Ca(2+) sensitivity compared with WT. Co-sedimentation of thin filament proteins indicated that no significant changes occurred in the binding of Tn containing the RCM cTnT mutation to actin-Tm. This report reveals the protective role of Tn fetal isoforms as they rescue the increased Ca(2+) sensitivity produced by a cTnT-RCM mutation and may account for the lack of lethality during gestation.

Myocardial blood flow and fibrosis in hypertrophic cardiomyopathy

BACKGROUND

We investigated the relationship between myocardial blood flow (MBF), fibrosis, risk factors for sudden death, and clinical manifestations in hypertrophic cardiomyopathy (HCM).

METHODS AND RESULTS

Sixty-two patients with HCM (45 men, overall mean age 47 ± 16 years), 15 acromegalic patients with left ventricular hypertrophy (9 man, overall mean age 47 ± 12 years), and 20 healthy subjects underwent cardiac magnetic resonance. Resting MBF was measured as the ratio between coronary sinus flow measured by phase-contrast technique and left ventricular mass. Myocardial fibrosis was evaluated by late gadolinium enhancement (LGE) technique. In HCM patients, MBF was significantly lower than in control subjects and acromegalic patients. Patients with LGE had lower MBF than those without it (0.46 ± 0.2 vs 0.66 ± 0.29 mL·min(-1)·g(-1); P < .005). Patients with ventricular tachycardia at Holter monitoring had lower MBF (0.4 ± 0.14 vs 0.6 ± 0.29 mL·min(-1)·g(-1); P < .04). Among patients with preserved systolic function, those in New York Heart Association (NYHA) functional class ≥II had lower MBF than those in NYHA functional class I (0.46 ± 0.2 vs 0.69 ± 0.3 mL·min(-1)·g(-1); P < .003). MBF was the only independent predictor of worse clinical status (NYHA ≥II; P = .01).

CONCLUSIONS

In HCM patients low resting MBF is associated with the presence of fibrosis. MBF is a predictor of worse clinical status.

Mutation type is not clinically useful in predicting prognosis in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM), or clinically unexplained hypertrophy of the heart, is a common genetic cardiovascular disorder marked by genetic and phenotypic heterogeneity. As the genetic mutations underlying the pathogenesis of this disease have been identified, investigators have attempted to link mutations to clearly defined alterations in survival in hopes of identifying prognostically relevant biomarkers of disease. While initial studies labeling particular MYH7 -encoded beta myosin heavy chain and TNNT2 -encoded cardiac troponin T mutations as “malignant” or “benign” raised hopes for mutation-specific risk stratification in HCM, a series of subsequent investigations identified mutations in families with contradictory disease phenotypes. Furthermore, subsequent proband-based cohort studies indicated that the clinical prognostic relevance of individual mutations labeled as “malignant” or “benign” in large referral centers is negligible. Herein, we seek to summarize the controversy and dispute the notion that mutation-specific risk stratification in HCM is possible at the present time. We provide evidence for clinicians and basic scientists alike to move beyond simple mutation descriptors to a more nuanced understanding of HCM mutations that fully captures the multi-factorial nature of HCM disease expression.

Impact of Mendelian inheritance in cardiovascular disease

Cardiovascular disease is a leading cause of mortality worldwide. While the etiology for the majority of cardiovascular disease is presumed to be a combination of genetic and environmental factors, developments in understanding the basic biology of cardiac disorders have been greatly advanced through discoveries made studying heart diseases that exhibit Mendelian forms of inheritance. Most of these diseases primarily affect children and young adults and include cardiomyopathies, arrhythmias, aortic aneurysms, and congenital heart defects. The discovery of the genetic etiologies for these diseases have had significant impact on our understanding of more complex forms of cardiovascular disease and in some cases have led to novel diagnostic and treatment modalities. In this review, we will summarize these seminal genetic discoveries, highlighting a few that have resulted in significant impact on human disease, and discuss the potential utility of studying Mendelian-inherited heart disease with the development of new genetic technologies and our increased understanding of the human genome.

Cardiac troponin mutations and restrictive cardiomyopathy

Mutations in sarcomeric proteins have recently been established as heritable causes of Restrictive Cardiomyopathy (RCM). RCM is clinically characterized as a defect in cardiac diastolic function, such as, impaired ventricular relaxation, reduced diastolic volume and increased end-diastolic pressure. To date, mutations have been identified in the cardiac genes for desmin, α-actin, troponin I and troponin T. Functional studies in skinned muscle fibers reconstituted with troponin mutants have established phenotypes consistent with the clinical findings which include an increase in myofilament Ca²⁺ sensitivity and basal force. Moreover, when RCM mutants are incorporated into reconstituted myofilaments, the ability to inhibit the ATPase activity is reduced. A majority of the mutations cluster in specific regions of cardiac troponin and appear to be mutational “hot spots”. This paper highlights the functional and clinical characteristics of RCM linked mutations within the troponin complex.

Increased myofilament Ca2+-sensitivity and arrhythmia susceptibility

Increased myofilament Ca(2+) sensitivity is a common attribute of many inherited and acquired cardiomyopathies that are associated with cardiac arrhythmias. Accumulating evidence supports the concept that increased myofilament Ca(2+) sensitivity is an independent risk factor for arrhythmias. This review describes and discusses potential underlying molecular and cellular mechanisms how myofilament Ca(2+) sensitivity affects cardiac excitation and leads to the generation of arrhythmias. Emphasized are downstream effects of increased myofilament Ca(2+) sensitivity: altered Ca(2+) buffering/handling, impaired energy metabolism and increased mechanical stretch, and how they may contribute to arrhythmogenesis.

Evolving molecular diagnostics for familial cardiomyopathies: at the heart of it all

Cardiomyopathies are an important and heterogeneous group of common cardiac diseases. An increasing number of cardiomyopathies are now recognized to have familial forms, which result from single-gene mutations that render a Mendelian inheritance pattern, including hypertrophic cardiomyopathy, dilated cardiomyopathy, restrictive cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy and left ventricular noncompaction cardiomyopathy. Recently, clinical genetic tests for familial cardiomyopathies have become available for clinicians evaluating and treating patients with these diseases, making it necessary to understand the current progress and challenges in cardiomyopathy genetics and diagnostics. In this review, we summarize the genetic basis of selected cardiomyopathies, describe the clinical utility of genetic testing for cardiomyopathies and outline the current challenges and emerging developments.

Molecular basis of hereditary cardiomyopathy: abnormalities in calcium sensitivity, stretch response, stress response and beyond

Cardiomyopathy is caused by functional abnormality of cardiac muscle. The functional abnormality involved in its etiology includes both extrinsic and intrinsic factors, and cardiomyopathy caused by the intrinsic factors is called as idiopathic or primary cardiomyopathy. There are several clinical types of primary cardiomyopathy including hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). Linkage studies and candidate gene approaches have explored the disease genes for hereditary primary cardiomyopathy. The most notable finding was that mutations in the same disease gene can be found in different clinical types of cardiomyopathy. Functional analyses of disease-related mutations have revealed that characteristic functional alterations are associated with the clinical types, such that increased and decreased Ca(2+) sensitivity due to sarcomere mutations are associated with HCM and DCM, respectively. In addition, our recent studies have suggested that mutations in the Z-disc components found in HCM and DCM may result in increased and decreased stiffness of sarcomere; that is, stiff sarcomere and loose sarcomere, respectively, and hence altered stretch response. More recently, mutations in the components of I region were found in hereditary cardiomyopathy and the functional analyses of the mutations suggested that the altered stress response was associated with cardiomyopathy, further complicating the etiology and pathogenesis. However, elucidation of genetic etiology and functional alterations caused by the mutations shed lights on the new therapeutic approaches to hereditary cardiomyopathy, such that treatment of DCM with a Ca(2+) sensitizer prevented the disease in a mouse model.

Mutations in Troponin that cause HCM, DCM AND RCM: what can we learn about thin filament function?

Troponin (Tn) is a critical regulator of muscle contraction in cardiac muscle. Mutations in Tn subunits are associated with hypertrophic, dilated and restrictive cardiomyopathies. Improved diagnosis of cardiomyopathies as well as intensive investigation of new mouse cardiomyopathy models has significantly enhanced this field of research. Recent investigations have showed that the physiological effects of Tn mutations associated with hypertrophic, dilated and restrictive cardiomyopathies are different. Impaired relaxation is a universal finding of most transgenic models of HCM, predicted directly from the significant changes in Ca(2+) sensitivity of force production. Mutations associated with HCM and RCM show increased Ca(2+) sensitivity of force production while mutations associated with DCM demonstrate decreased Ca(2+) sensitivity of force production. This review spotlights recent advances in our understanding on the role of Tn mutations on ATPase activity, maximal force development and heart function as well as the correlation between the locations of these Tn mutations within the thin filament and myofilament function.

Histologic characterization of hypertrophic cardiomyopathy with and without myofilament mutations

BACKGROUND

Between 30% and 60% of clinical cases of hypertrophic cardiomyopathy (HC) can be attributed to mutations in the genes encoding cardiac myofilament proteins. Interestingly, it appears that the likelihood of an underlying myofilament mutation can be predicted by echocardiographic assessment of left ventricular morphology. However, it is not known whether genotypically characterized HC exists as a separate entity with discrete phenotypic morphology and histology or to what extent recognized polymorphisms of the renin-angiotensin-aldosterone system (RAAS) influence this relationship. The presence of cardiac myofilament and mutations and RAAS polymorphisms will have a strong association with the severity of histologic features of HC and characteristic septal shape.

METHODS

We conducted a retrospective review of histology specimens, obtained at septal myectomy among 181 patients with medically refractory symptomatic HC. All patients underwent comprehensive genetic analysis for mutations in 8 myofilament-encoding genes; a subset was genotyped for 6 known RAAS-polymorphisms. Patients underwent comprehensive echocardiography by an expert blinded to genotype and microscopic status.

RESULTS

Microscopically, severity of myocyte hypertrophy appears to be associated with the presence of recognized HC cardiac myofilament mutations (P = .03). Other histologic features characteristic of HC were not consistently associated with myofilament mutation status. A higher burden of pro-LVH RAAS polymorphisms also appeared to predict only myocyte hypertrophy (P = .01). The presence of RAAS polymorphisms was not associated with the development of a specific septal morphology (P = .6).

CONCLUSION

Myofilament-positive HC does not appear to represent a distinct clinical phenotypic entity as evidenced by specific histologic characteristics and septal shape.

Abnormal blood pressure response to exercise occurs more frequently in hypertrophic cardiomyopathy patients with the R92W troponin T mutation than in those with myosin mutations

Abnormal blood pressure response to exercise is reported to occur in up to a third of hypertrophic cardiomyopathy (HCM) cases and is associated with an increased risk of death, particularly in the young, but it is not known whether the HCM-causing mutation influences blood pressure response to exercise. The purpose of this article is to ascertain whether the blood pressure response to exercise differs among carriers of the R92W mutation in the cardiac troponin T gene (TNNT2), which has been associated with an increased risk of sudden cardiac death in young males; carriers of mutations in the cardiac β-myosin heavy chain gene (MYH7); and their noncarrier relatives. Thirty R92W_TNNT2 carriers, 51 MYH7 mutation carriers, and 68 of their noncarrier relatives were subjected to bicycle ergonometric exercise testing to assess blood pressure response to, as well as heart rate recovery after, exercise. Additional echocardiographic and demographic details were documented for all participants. R92W_TNNT2 carriers demonstrated significantly more abnormal blood pressure responses to exercise (P = .021; odds ratio 3.03; confidence interval 1.13–8.12) and smaller increases in systolic blood pressure than MYH7 mutation carriers or related noncarrier control individuals. Although abnormal blood pressure response occurred at similar frequencies in males in all groups (23%–26%), the percentage of R92W_TNNT2 females with abnormal blood pressure response was 64%, compared with 25% for MYH7 and 22% for noncarriers. Therefore, these results show that blood pressure response to exercise is influenced by genotype and gender in patients with HCM.

Diagnostic synergy of non-invasive cardiovascular magnetic resonance and invasive endomyocardial biopsy in troponin-positive patients without coronary artery disease

AIMS

Only few data are available regarding a direct comparison of both non-invasive CMR and invasive EMB with respect to conformity of procedure-derived diagnoses in the same patients. The aim of this study was to elucidate the diagnostic performance of non-invasive cardiovascular magnetic resonance imaging (CMR) and endomyocardial biopsy (EMB) in patients with troponin-I (TnI) positive acute chest pain in the absence of significant coronary artery disease (CAD).

METHODS AND RESULTS

One thousand one hundred and seventy-four consecutive patients who were admitted with TnI-positive acute chest pain between March 2004 and July 2007 underwent coronary angiography. In 1012 patients (86%), significant CAD (stenosis >50%) was detected as underlying reason for the acute chest pain. In 82 out of the remaining 162 patients without significant CAD, further workup was performed including both CMR and EMB. Cardiovascular magnetic resonance imaging alone enabled a diagnosis in 66/82 (80%) and EMB alone in 72/82 (88%) patients (P = 0.31). Myocarditis was the most frequent diagnosis by both CMR and EMB in this cohort and was detected with a higher frequency by EMB (58 vs. 81%; P < 0.001). With the combined approach comprising CMR and EMB, a final diagnosis could be established applying the 'Believe-The-Positive-Rule' in 78/82 patients (95%). This combined approach turned out to yield more diagnoses than either CMR (P < 0.001) or EMB (P = 0.03) as single techniques, respectively. Comparison of diagnostic CMR procedures with the corresponding diagnostic EMBs demonstrated a substantial match of diagnoses (kappa = 0.70).

CONCLUSION

Cardiovascular magnetic resonance imaging and EMB have good diagnostic performances as single techniques in patients with TnI-positive acute chest pain in the absence of CAD. The combined application of CMR and EMB yields a considerable diagnostic synergy by overcoming some limitations of CMR and EMB as individually applied techniques.

Diagnostic, prognostic, and therapeutic implications of genetic testing for hypertrophic cardiomyopathy

Over the last 2 decades, the pathogenic basis for the most common heritable cardiovascular disease, hypertrophic cardiomyopathy (HCM), has been investigated extensively. Affecting approximately 1 in 500 individuals, HCM is the most common cause of sudden death in young athletes. In recent years, genomic medicine has been moving from the bench to the bedside throughout all medical disciplines including cardiology. Now, genomic medicine has entered clinical practice as it pertains to the evaluation and management of patients with HCM. The continuous research and discoveries of new HCM susceptibility genes, the growing amount of data from genotype-phenotype correlation studies, and the introduction of commercially available genetic tests for HCM make it essential that the modern-day cardiologist understand the diagnostic, prognostic, and therapeutic implications of HCM genetic testing.

Long-term survival after cardiac arrest in hypertrophic cardiomyopathy

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) and aborted cardiac arrest are generally regarded as a high-risk subgroup susceptible to future major cardiac events and an unfavorable prognosis. However, outcome over extended time periods after major arrhythmic events is unresolved in such HCM patients.

OBJECTIVE

This study sought to more completely define the natural history of HCM.

METHODS

Of 916 HCM patients in the Minneapolis Heart Institute registry, 39 experienced either cardiac arrest (n = 21) or an appropriate shock from a prophylactically implanted cardioverter-defibrillator (ICD) (n = 18), and were assessed prospectively.

RESULTS

Age at initial arrhythmic event was 34 +/- 17 years (range 8 to 68; 67% <40 years). Of the 39 study patients, 32 (82%) survived after their initial cardiac event (for 9.4 +/- 7.6 years; up to 30 years), including 14 patients for >or=10 years (36%) and 4 patients >or=20 years (10%). Of the 32 survivors, 15 (47%) have not experienced subsequent events, and 17 (53%) had >or=1 additional cardiac arrest or appropriate ICD intervention. Annual HCM-related mortality was 1.4%, similar to general HCM populations, and 88% of patients were free of HCM-related death over the follow-up period. Survival from potentially lethal arrhythmias was associated with no or only mild heart failure symptoms in 29 of 32 patients (91%) at most recent evaluation.

CONCLUSION

In HCM, long-term survival up to 30 years may follow cardiac arrest with or without ICD intervention. Disabling heart failure symptoms were uncommon after these arrhythmic events, at last follow-up. These novel observations regarding the natural history of HCM underscore the unpredictability of the arrhythmogenic substrate, which may remain dormant over extended periods of time.

Genetic and clinical profile of Indian patients of idiopathic restrictive cardiomyopathy with and without hypertrophy

Both idiopathic restrictive cardiomyopathy (IRCM) and hypertrophic cardiomyopathy (HCM) are part of the same disease spectrum and are due to sarcomeric gene mutations. A patient with restrictive physiology without left ventricular hypertrophy (LVH) would be diagnosed as IRCM, while one with LVH would be diagnosed as HCM with restrictive physiology. We studied a group of patients with restrictive physiology for mutations in beta-myosin heavy chain (MYH7) and troponin I (TNNI3) gene. Consecutive probands in the HCM and IRCM cohort over a 4-year period were considered for this study. These included 10 IRCM and 102 HCM patients. All were Asian Indians. Among the 17 patients who had restrictive physiology 10 were IRCM patients and seven were HCM patients. Of the HCM patients, seven (6.9%) had restrictive physiology. Mean age of these 17 patients was 40.1 +/- 19.2 years (range: 15-67 ), six (35.3%) were males. Maximal left ventricular wall thickness of the seven HCM probands was 20.7 +/- 5.2 mm (range: 16-31), while it was normal in the IRCM probands. Ten probands (58.8%) were in NYHA class III or IV. Seven patients (41.2%) had atrial fibrillation. All the probands were screened for mutations in selected exons of MYH7 and TNNI3 genes. One IRCM patient was found to have p.Arg721Lys mutation in the MYH7 gene. She died due to progressive congestive cardiac failure at the age of 47 years. One HCM proband with a maximal left ventricular wall thickness of 17 mm had p.Arg192His mutation in the TNNI3 gene. She had features consistent with restrictive physiology. Her father and sister had died of restrictive cardiomyopathy. IRCM and HCM with restrictive physiology, both are part of the clinical expression of MYH7 and TNNI3 mutations and lead to worse clinical onset and progression of the disease.

The role of Akt/GSK-3beta signaling in familial hypertrophic cardiomyopathy

Mutations in cardiac troponin T (TnT) are a cause of familial hypertrophic cardiomyopathy (FHC). Transgenic mice expressing a missense mutation (R92Q) or a splice site donor mutation (Trunc) in the cardiac TnT gene have mutation-specific phenotypes but mice of both models have smaller hearts compared to wild type and exhibit hemodynamic dysfunction. Because growth-related signaling pathways in the hearts of mice expressing TnT mutations are not known, we evaluated the impact of increased Akt or glycogen synthase kinase-3beta (GSK-3beta) activity in both mutant TnT mice; molecules that increase heart size via physiologic pathways and block pathologic growth, respectively. Expression of activated Akt dramatically augments heart size in both R92Q and Trunc mice; however, this increase in heart size is not beneficial, since Akt also increases fibrosis in both TnT mutants and causes some pathologic gene expression shifts in the R92Q mice. Activated GSK-3beta results in further decreases in left ventricular size in both R92Q and Trunc hearts, but this decrease is associated with significant mutation-specific phenotypes. Among many pathologic consequences, activating GSK-3beta in R92Q hearts decreases phosphorylation of troponin I and results in early mortality. In contrast, increased GSK-3beta activity in Trunc hearts does not significantly impact cardiac phenotypes. These findings demonstrate that increased Akt and its downstream target, GSK-3beta can impact both cardiac size and phenotype in a mutation-specific manner. Moreover, increased activity of these molecules implicated in beneficial cardiac phenotypes exacerbates the progression of disease in the R92Q TnT mutant.

Familial hypertrophic cardiomyopathy: basic concepts and future molecular diagnostics

Familial hypertrophic cardiomyopathies (FHC) are the most common genetic heart diseases in the United States, affecting nearly 1 in 500 people. Manifesting as increased cardiac wall thickness, this autosomal dominant disease goes mainly unnoticed as most affected individuals are asymptomatic. Up to 1-2% of children and adolescents and 0.5-1% adults with FHC die of sudden cardiac death, making it critical to quickly and accurately diagnose FHC to institute therapy and potentially reduce mortality. However, due to the heterogeneity of the genetic defects in mainly sarcomere proteins, this is a daunting task even with current diagnostic methods. Exciting new methods utilizing high-throughput microarray technology to identify FHC mutations by a method known as array-based resequencing has recently been described. Additionally, next generation sequencing methodologies may aid in improving FHC diagnosis. In this review, we discuss FHC pathophysiology, the rationale for testing, and discuss the limitations and advantages of current and future diagnostics.

Decreased contractility due to energy deprivation in a transgenic rat model of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is associated with cardiac hypertrophy, diastolic dysfunction, and sudden death. Recently, it has been suggested that inefficient energy utilization could be a common molecular pathway of HCM-related mutations. We have previously generated transgenic Sprague-Dawley rats overexpressing a truncated cardiac troponin T (DEL-TNT) molecule, displaying typical features of HCM such as diastolic dysfunction and an increased susceptibility to ventricular arrhythmias. We now studied these rats using 31P magnetic resonance spectroscopy (MRS). MRS demonstrated that cardiac energy metabolism was markedly impaired, as indicated by a decreased phosphocreatine to ATP ratio (-31%, p < 0.05). In addition, we assessed contractility of isolated cardiomyocytes. While DEL-TNT and control cardiomyocytes showed no difference under baseline conditions, DEL-TNT cardiomyocytes selectively exhibited a decrease in fractional shortening by 28% after 1 h in glucose-deprived medium (p < 0.05). Moreover, significant decreases in contraction velocity and relaxation velocity were observed. To identify the underlying molecular pathways, we performed transcriptional profiling using real-time PCR. DEL-TNT hearts exhibited induction of several genes critical for cardiac energy supply, including CD36, CPT-1/-2, and PGC-1alpha. Finally, DEL-TNT rats and controls were studied by radiotelemetry after being stressed by isoproterenol, revealing a significantly increased frequency of arrhythmias in transgenic animals. In summary, we demonstrate profound energetic alterations in DEL-TNT hearts, supporting the notion that inefficient cellular ATP utilization contributes to the pathogenesis of HCM.

Delayed enhancement on cardiac magnetic resonance and clinical, morphological, and electrocardiographical features in hypertrophic cardiomyopathy

BACKGROUND

The clinical, morphological, and electrocardiographical relevance of delayed enhancement (DE) in cardiac magnetic resonance (CMR) was studied in patients with hypertrophic cardiomyopathy (HCM).

METHODS AND RESULTS

A total of 56 patients underwent both gadolinium-enhanced CMR and 12-lead electrocardiogram. The CMR demonstrated DE at the left ventricular (LV) wall in 39 patients. The patients with DE included more cases with dilated phase of HCM, higher New York Heart Association (NYHA) classes and incidence of ventricular tachyarrhythmias (VT), lower LV ejection fraction (LVEF) and mean LV wall thickness (WT), and a larger ratio of maximum to minimum LVWT. The QRS duration was prolonged and the QRS axis deviated toward left with increases in the DE volume (r = 0.58 and r = 0.41, P < .01). Abnormal Q waves were present in 5 patients and the location coincided with the DE segments in 4 patients, but the concordance was not significant. The amplitude of T waves correlated with the ratio of the apex to basal LVWT (r = 0.38, P < .01) and was more negative in cases with DE at the apex.

CONCLUSIONS

In HCM, the DE was associated with higher NYHA classes and prevalence of VT, impaired global LV function and asymmetrical hypertrophy, and conduction disturbance, abnormal Q waves, and giant negative T waves.

Myofilament Ca2+ sensitization causes susceptibility to cardiac arrhythmia in mice

In human cardiomyopathy, anatomical abnormalities such as hypertrophy and fibrosis contribute to the risk of ventricular arrhythmias and sudden death. Here we have shown that increased myofilament Ca2+ sensitivity, also a common feature in both inherited and acquired human cardiomyopathies, created arrhythmia susceptibility in mice, even in the absence of anatomical abnormalities. In mice expressing troponin T mutants that cause hypertrophic cardiomyopathy in humans, the risk of developing ventricular tachycardia was directly proportional to the degree of Ca2+ sensitization caused by the troponin T mutation. Arrhythmia susceptibility was reproduced with the Ca2+-sensitizing agent EMD 57033 and prevented by myofilament Ca2+ desensitization with blebbistatin. Ca2+ sensitization markedly changed the shape of ventricular action potentials, resulting in shorter effective refractory periods, greater beat-to-beat variability of action potential durations, and increased dispersion of ventricular conduction velocities at fast heart rates. Together these effects created an arrhythmogenic substrate. Thus, myofilament Ca2+ sensitization represents a heretofore unrecognized arrhythmia mechanism. The protective effect of blebbistatin provides what we believe to be the first direct evidence that reduction of Ca2+ sensitivity in myofilaments is antiarrhythmic and might be beneficial to individuals with hypertrophic cardiomyopathy.

Myocardial fibrosis in patients with symptomatic obstructive hypertrophic cardiomyopathy: correlation with echocardiographic measurements, sarcomeric genotypes, and pro-left ventricular hypertrophy polymorphisms involving the renin-angiotensin-aldosterone system

INTRODUCTION

Hypertrophic cardiomyopathy (HCM) is a heterogeneous disorder of the cardiac sarcomere, resulting in myocyte hypertrophy and disarray, interstitial fibrosis, and cardiac dysfunction. Our aim was to determine whether the amount of fibrosis in HCM correlates with echocardiographic measures of diastolic dysfunction, presence of HCM-susceptibility mutations, or polymorphisms in the renin-angiotensin-aldosterone system (RAAS).

METHODS

Surgical specimens from patients with obstructive HCM undergoing septal myectomy at the Mayo Clinic (2001-2004) were examined and compared with autopsy-derived tissues from age- and sex-matched normal controls. Digital image analysis was used to quantitate the fibrosis in representative microscopic sections. Genotyping was performed for myofilament-HCM using polymerase chain reaction, high-performance liquid chromatography, and direct DNA sequencing. RAAS polymorphism status was similarly established.

RESULTS

The study included 59 HCM cases and 44 controls. Patients with HCM exhibited more fibrosis (mean 17%, range 3-45%) than controls (mean 8%, range 3-17%) (P<.0001). A significant relationship existed between amount of fibrosis and maximum wall thickness (P=.02), left ventricular ejection fraction (P=.02), and peak early/late diastolic mitral annulus velocity (E/A ratio) (P=.002). Although there was no association between amount of fibrosis and myofilament-HCM genotype status or polymorphisms in the RAAS cascade, there was a trend toward more fibrosis in patients with > or =1 C-encoding allele in CYP11B2-encoded aldosterone synthase.

CONCLUSIONS

Patients with HCM undergoing septal myectomy had significantly more myocardial interstitial fibrosis than controls. The amount of fibrosis in HCM patients correlated with degree of septal hypertrophy and left ventricular systolic and diastolic function. Notably, neither mutations in cardiac myofilament proteins or polymorphisms in RAAS exhibited strong associations with severity of myocardial fibrosis.

Spatial relationship between coronary microvascular dysfunction and delayed contrast enhancement in patients with hypertrophic cardiomyopathy

To clarify the spatial relationship between coronary microvascular dysfunction and myocardial fibrosis in hypertrophic cardiomyopathy (HCM), we compared the measurement of hyperemic myocardial blood flow (hMBF) by PET with the extent of delayed contrast enhancement (DCE) detected by MRI.

METHODS

In 34 patients with HCM, PET was performed using (13)N-labeled ammonia during hyperemia induced by intravenous dipyridamole. DCE and systolic thickening were assessed by MRI. Left ventricular myocardial segments were classified as with DCE, either transmural (DCE-T) or nontransmural (DCE-NT), and without DCE, either contiguous to DCE segments (NoDCE-C) or remote from them (NoDCE-R).

RESULTS

In the group with DCE, hMBF was significantly lower than in the group without DCE (1.81 +/- 0.94 vs. 2.13 +/- 1.11 mL/min/g; P < 0.001). DCE-T segments had lower hMBF than did DCE-NT segments (1.43 +/- 0.52 vs. 1.91 +/- 1 mL/min/g, P < 0.001). Similarly, NoDCE-C segments had lower hMBF than did NoDCE-R (1.98 +/- 1.10 vs. 2.29 +/- 1.10 mL/min/g, P < 0.01) and had no significant difference from DCE-NT segments. Severe coronary microvascular dysfunction (hMBF in the lowest tertile of all segments) was more prevalent among NoDCE-C than NoDCE-R segments (33% vs. 24%, P < 0.05). Systolic thickening was inversely correlated with percentage transmurality of DCE (Spearman rho = -0.37, P < 0.0001) and directly correlated with hMBF (Spearman rho = 0.20, P < 0.0001).

CONCLUSION

In myocardial segments exhibiting DCE, hMBF is reduced. DCE extent is inversely correlated and hMBF directly correlated with systolic thickening. In segments without DCE but contiguous to DCE areas, hMBF is significantly lower than in those remote from DCE and is similar to the value obtained in nontransmural DCE segments. These results suggest that increasing degrees of coronary microvascular dysfunction might play a causative role for myocardial fibrosis in HCM.

Occurrence and frequency of arrhythmias in hypertrophic cardiomyopathy in relation to delayed enhancement on cardiovascular magnetic resonance

OBJECTIVES

Our aim was to determine whether myocardial fibrosis, detected by cardiovascular magnetic resonance (CMR), represents an arrhythmogenic substrate in hypertrophic cardiomyopathy (HCM).

BACKGROUND

Myocardial fibrosis is identified frequently in HCM; however, the clinical significance of this finding is uncertain.

METHODS

We studied prevalence and frequency of tachyarrhythmias on 24-h ambulatory Holter electrocardiogram (ECG) with regard to delayed enhancement (DE) on contrast-enhanced CMR in 177 HCM patients (age 41 +/- 16 yrs; 95% asymptomatic or mildly symptomatic).

RESULTS

Premature ventricular contractions (PVCs), couplets, and nonsustained ventricular tachycardia (NSVT) were more common in patients with DE than those without DE (PVCs: 89% vs. 72%; couplets: 40% vs. 17%; NSVT: 28% vs. 4%; p < 0.0001 to 0.007). Patients with DE also had greater numbers of PVCs (202 +/- 655 vs. 116 +/- 435), couplets (1.9 +/- 5 vs. 1.2 +/- 10), and NSVT runs (0.4 +/- 0.8 vs. 0.06 +/- 0.4) than non-DE patients (all p < 0.0001); DE was an independent predictor of NSVT (relative risk 7.3, 95% confidence interval 2.6 to 20.4; p < 0.0001). However, extent (%) of DE was similar in patients with and without PVCs (8.2% vs. 9.1%; p = 0.93), couplets (8.5% vs. 8.4%; p = 0.99), or NSVT (8.3% vs. 8.5%; p = 0.35).

CONCLUSIONS

In this large HCM cohort with no or only mild symptoms, myocardial fibrosis detected by CMR was associated with greater likelihood and increased frequency of ventricular tachyarrhythmias (including NSVT) on ambulatory Holter ECG. Therefore, contrast-enhanced CMR identifies HCM patients with increased susceptibility to ventricular tachyarrhythmias.

Genetic determinants of cardiac hypertrophy

PURPOSE OF REVIEW

Cardiac hypertrophy is a common phenotypic response of the heart to stimulants. It is associated with increased morbidity and mortality in various cardiovascular disorders. Genetic factors are important determinants of phenotypic expression of cardiac hypertrophy, whether in single-gene disorders or in complex traits. We focus on the molecular genetics of cardiac hypertrophy in various conditions with an emphasis on hypertrophic cardiomyopathy, a genetic paradigm of cardiac hypertrophic response.

RECENT FINDINGS

The molecular genetic basis of cardiac hypertrophy in single-gene disorders has been partially elucidated. Likewise, the impact of genetics on the expression of cardiac hypertrophy in the general population has been demonstrated. Identification of mutations in the Z disk proteins has expanded the spectrum of causal mutations beyond the thin and thick filaments of the sarcomeres. In addition, modifier loci have been mapped and shown to impart considerable effects on the expression of cardiac hypertrophy in hypertrophic cardiomyopathy. Elucidation of the molecular genetics of sarcomeric hypertrophic cardiomyopathy and many of the phenocopies has highlighted the limitations of clinical diagnosis as a determinant of management and prognostic advice. The findings have raised the importance of diagnosis and treatment algorithms, which are based on both genotype and phenotype information.

SUMMARY

Cardiac hypertrophy, regardless of the cause, is the phenotypic consequence of complex interactions between genetic and nongenetic factors.

Utilities and limitations of genetic testing for hypertropic cardiomyopathy

BACKGROUND

Hypertropic cardiomyopathy (HCM) is a primary disease of cardiac myocytes, diagnosed clinically by the presence of cardiac hypertrophy in the absence of any known cause. Over a dozen causal genes and several hundred mutations for HCM have been identified.

OBJECTIVE

The utilities of genetic testing in accurate diagnosis, prognostication and treatment of HCM are reviewed.

METHODS

The existing data are reviewed.

RESULTS/CONCLUSIONS

There is considerable interest in genetic testing for HCM. However, heterogeneity of the causal genes and alleles has hampered the efforts to develop a simple comprehensive genetic screening test. At present, it is feasible to screen for the 5 most common causal genes, which collectively account for ∼ 60% of the HCM. Advances of deep resequencing technologies are expected to increase the yield considerably and, hence, increase the use of genetic testing in clinical practice. However, the utility of genetic testing for risk stratification is expected to be limited, as factors other than the causal genes also contribute to the development of the phenotype. A comprehensive approach that includes the information content of the causal mutations, the modifier genes and the non-genetic factors will be necessary for accurate risk stratification and genetic-based interventions.

The utility of magnetic resonance imaging in the evaluation of arrhythmogenic right ventricular cardiomyopathy

PURPOSE OF REVIEW

Perceptions of the utility of cardiovascular magnetic resonance in the evaluation of arrhythmogenic right ventricular cardiomyopathy have changed considerably in the past decade. This review offers an up-to-date perspective on the diagnostic role of cardiovascular magnetic resonance in the genetics era.

RECENT FINDINGS

Originally hailed as a putative gold standard in arrhythmogenic cardiomyopathy, cardiovascular magnetic resonance has received a more guarded reception lately owing to interobserver variability and lack of standardized protocols. Recent studies have nonetheless affirmed its value as an integral component of the diagnostic work-up. Quantitative volume analysis is relatively robust, but visualization of myocardial fat by spin-echo imaging is less reliable. Interpretation of wall motion abnormalities appears reproducible among expert readers. Emerging data suggest a key role for late gadolinium enhancement in detection of left ventricular involvement.

SUMMARY

Cardiovascular magnetic resonance in arrhythmogenic cardiomyopathy is facilitated by appropriate patient selection and preparation, experienced readers and operators, and a dedicated, comprehensive protocol. Indications for magnetic resonance assessment include proven arrhythmogenic cardiomyopathy in the family, unexplained ventricular arrhythmia, inverted T-waves in the right precordial or lateral leads, and/or family history of sudden cardiac death. Arrhythmia suppression is essential for optimal electrocardiographic triggering and image acquisition.

Structural effects of the slow/b-cardiac myosin heavy chain R453C mutation in cardiac and skeletal muscle

OBJECTIVES

Hypertrophic cardiomyopathy (HCM) represents an important cause of sudden cardiac death particularly in otherwise healthy young individuals. In some families, HCM is caused by distinct mutations of the cardiac beta myosin heavy chain gene (MYH7).

DESIGN

We have analyzed the expression of the malignant MYH7Arg453Cys mutation, in cardiac and skeletal muscle, and related it to morphological alterations.

RESULTS

Morphological investigation revealed hypertrophic cardiomyocytes but regularly arranged myofibrils. Skeletal muscle showed no sign of structural alterations.

CONCLUSIONS

Our results indicate that cardiomyocyte hypertrophy is secondary, due to impaired function, and that the mutation causes no structural alteration in myofibrillar structure in cardiac or skeletal muscle.

Myofilament mechanical performance is enhanced by R403Q myosin in mouse myocardium independent of sex

Male but not female mice carrying a single R403Q missense allele for cardiac alpha-myosin heavy chain (M-alphaMHC(R403Q/+) and F-alphaMHC(R403Q/+), respectively) develop significant hypertrophic cardiomyopathy (HCM) compared with male and female wild-type mice (M-alphaMHC(+/+) and F-alphaMHC(+/+), respectively) after approximately 30 wk of age. We tested the hypothesis that myofilament mechanical performance differs between M-alphaMHC(R403Q/+) and F-alphaMHC(R403Q/+) at younger ages (10-20 wk) and could account for sex differences in HCM development. The sensitivity of chemically skinned myocardial strips to Ca(2+) activation (pCa(50)) was significantly (P < 0.05) enhanced in male mice independent of genotype (M-alphaMHC(R403Q/+): 5.70 +/- 0.06, M-alphaMHC(+/+): 5.63 +/- 0.05, F-alphaMHC(R403Q/+): 5.57 +/- 0.03, F-alphaMHC(+/+): 5.54 +/- 0.04) by two-way ANOVA, whereas maximum developed tension was significantly enhanced in alpha-MHC(R403Q/+) independent of sex (M-alphaMHC(R403Q/+): 29.3 +/- 2.3, M-alphaMHC(+/+): 26.0 +/- 1.4, F-alphaMHC(R403Q/+): 30.2 +/- 2.1, F-alphaMHC(+/+): 26.2 +/- 1.2 mN/mm(2)). The frequency of maximum work generated by sinusoidal length perturbation was significantly higher in alphaMHC(R403Q/+) mice than in sex-matched controls (M-alphaMHC(R403Q/+): 2.26 +/- 0.47, M-alphaMHC(+/+): 1.29 +/- 0.18, F-alphaMHC(R403Q/+): 3.21 +/- 0.33, F-alphaMHC(+/+): 2.52 +/- 0.36 Hz). Unloaded shortening velocity was significantly enhanced in alphaMHC(R403Q/+) and in female mice (M-alphaMHC(R403Q/+): 2.26 +/- 0.47, M-alphaMHC(+/+): 1.29 +/- 0.18, F-alphaMHC(R403Q/+): 3.21 +/- 0.33, F-alphaMHC(+/+): 2.52 +/- 0.36 muscle lengths/s), and normalized mechanical power, calculated from the tension-velocity relationship, was significantly enhanced in alphaMHC(R403Q/+) independent of sex (M-alphaMHC(R403Q/+): 60 +/- 2 10(-3), M-alphaMHC(+/+): 37 +/- 3 10(-3), F-alphaMHC(R403Q/+): 57 +/- 3 10(-3), F-alphaMHC(+/+) 25 +/- 3 10(-3) muscle lengths/s x normalized tension). We did not find a statistically significant sex x mutation interaction for any measure of myofilament performance. Therefore, sarcomeric incorporation of the R403Q myosin similarly enhanced left ventricular myofilament mechanical performance in both male and female mice. The sex-dependent development of HCM due to the R403Q myosin may then be inhibited by female sex hormones, which may additionally underlie the observed sex differences for pCa(50) and unloaded shortening velocity.

Hypertrophic cardiomyopathy: the genetic determinants of clinical disease expression

Hypertrophic cardiomyopathy (HCM), defined clinically by the presence of unexplained left ventricular hypertrophy, is the most common inherited cardiac disorder. This condition is the major cause of sudden death in the young (<30 years of age) and in athletes. The clinical phenotype is heterogeneous, and mutations in a number of sarcomeric contractile-protein genes are responsible for causing the disease in approximately 60% of individuals with HCM. Other inherited syndromes, as well as metabolic and mitochondrial disorders, can present as clinical phenocopies and can be distinguished by their associated cardiac and noncardiac features and on the basis of their unique molecular genetics. The mode of inheritance, natural history and treatment of phenocopies can differ from those of HCM caused by mutations in sarcomere genes. Detailed clinical evaluation and mutation analysis are, therefore, important in providing an accurate diagnosis in order to enable genetic counseling, prognostic evaluation and appropriate clinical management. This Review summarizes current knowledge on the genetics, disease mechanisms, and correlations between phenotype and genotype in patients with HCM, and discusses the implications of genetic testing in routine clinical practice.

The mystery of sudden death: mechanisms for risks

This review addresses the possible overlapping mechanisms that may apply to the risk of sudden unexpected death occurring in epilepsy and in cardiac disease. It explores the interaction between the central and peripheral autonomic nervous systems and the cardiopulmonary systems. Included is a discussion of the potential interactive role of genetically determined subtle cardiac risk factors for arrhythmias with a predisposition for seizure-related cardiac arrhythmias. We address the possible mechanisms that are operant in producing both epileptogenic and cardiogenic arrhythmias. Finally, we speculate about potential preventive measures to minimize the risk of both sudden unexpected death in epilepsy and sudden cardiac death.

Genetic basis of hypertrophic cardiomyopathy: from bench to the clinics

Hypertrophic cardiomyopathy (HCM) is a common inherited cardiac disorder that characterized by marked thickening of the left ventricular wall that occurs in the absence of increased external load. HCM is the most common cause of sudden cardiac death under 35 years and in addition causes heart failure. HCM is usually inherited as an autosomal dominant mutation in genes that encode protein constituents of the sarcomere. To date, more than 450 different mutations have been identified within 13 myofilament-related genes. This review focuses current research involved in the discovery of other causative genes, investigation of the mechanisms by which sarcomere genes mutations produce hypertrophy and arrhythmia, and identification of modifying factors that influence clinical expression in HCM patients. The clinical implications of molecular advances in HCM are discussed.

Usefulness of delayed enhancement magnetic resonance imaging to differentiate dilated phase of hypertrophic cardiomyopathy and dilated cardiomyopathy

BACKGROUND

The dilated phase of hypertrophic cardiomyopathy (HCM) has a poor prognosis. For correct recognition of such patients, we compared the findings in cardiac delayed enhancement (DE)-magnetic resonance imaging (MRI) between HCM and dilated cardiomyopathy (DCM) patients.

METHODS AND RESULTS

Sixty-five patients (HCM 39, DCM 26) underwent gadolinium-DTPA-enhanced MRI. The HCM patients were divided into those with preserved (HCM-P, n = 30) and those with impaired systolic function (HCM-I, n = 9). DE-MRI demonstrated focal or diffuse DE at the left ventricular (LV) wall in 60% of HCM-P and 100% of HCM-I, but in only 12% of DCM. The DE distributed mainly septal to the anterior wall of LV, but the DE volume against whole LV muscle volume was much larger in HCM-I than in HCM-P and DCM (4.1 +/- 6.1% in HCM-P, 14.6 +/- 11.9% in HCM-I, and 0.8 +/- 2.4% in DCM, means +/- SD, P < .05). In HCM, there were weak but significant correlations between DE volume, and LV end-diastolic volume and LV end-systolic volume. In HCM-P, the percent of length shortening in the segments with DE was lower than that without DE.

CONCLUSIONS

The HCM patients had more DE than the DCM patients, and DE volume correlated to lower global and local LV function. DE-MRI may be useful to evaluate myocardial damage in HCM patients, and to differentiate the dilated phase of HCM from DCM.

Is sudden cardiac death predictable in LEOPARD syndrome?

We report the sudden cardiac death of a young male presenting with classic clinical features of LEOPARD syndrome, shown to be due to a mutation in the PTPN11 gene, and severe non obstructive hypertrophic cardiomyopathy. We also discuss briefly the usefulness of prophylactic risk stratification in patients with syndromic and non syndromic hypertrophic cardiomyopathy.

Pathophysiology and Treatment of Hypertrophic Cardiomyopathy

All patients with hypertrophic cardiomyopathy (HCM) should have five aspects of care addressed. An attempt should be made to detect the presence or absence of risk factors for sudden arrhythmic death. If the patient appears to be at high risk, discussion of the benefits and risks of ICD are indicated, and many such patients will be implanted. Symptoms are appraised and treated. Bacterial endocarditis prophylaxis is recommended. Patients are advised to avoid athletic competition and extremes of physical exertion. First degree family members should be screened with echocardiography and ECG.

Myofibrillar remodeling in cardiac hypertrophy, heart failure and cardiomyopathies

BACKGROUND

A wide variety of pathological conditions have been shown to result in cardiac remodelling and myocardial dysfunction. However, the mechanisms of transition from adaptive to maladaptive alterations, as well as those for changes in cardiac performance leading to heart failure, are poorly understood.

OBSERVATIONS

Extensive studies have revealed a broad spectrum of progressive changes in subcellular structures and function, as well as in signal transduction and metabolism in the heart, among different cardiovascular disorders. The present review is focused on identifying the alterations in molecular and biochemical structure of myofibrils (myofibrillar remodelling) in hypertrophied and failing myocardium in different types of heart diseases. Numerous changes at the level of gene expression for both contractile and regulatory proteins have already been reported in failing hearts and heart diseases; these changes are potential precursors for heart failure such as cardiac hypertrophy and cardiomyopathies. Myofibrillar remodelling, as a consequence of proteolysis, oxidation, and phosphorylation of some functional groups in both contractile and regulatory proteins in hearts failing due to different etiologies, has also been described.

CONCLUSIONS

Although myofibrillar remodelling appears to be associated with cardiac dysfunction, alterations in both contractile and regulatory proteins are dependent on the type and stage of heart disease.

Delayed hyperenhancement in magnetic resonance imaging of left ventricular hypertrophy caused by aortic stenosis and hypertrophic cardiomyopathy: visualisation of focal fibrosis

OBJECTIVE

To compare the extent and distribution of focal fibrosis by gadolinium contrast-enhanced magnetic resonance imaging (MRI; delayed hyperenhancement) in severe left ventricular (LV) hypertrophy in patients with pressure overload caused by aortic stenosis (AS) and with genetically determined hypertrophic cardiomyopathy (HCM).

METHODS

44 patients with symptomatic valvular AS (n = 22) and HCM (n = 22) were studied. Cine images were acquired with fast imaging with steady-state precession (trueFISP) on a 1.5 T scanner (Sonata, Siemens Medical Solutions). Gadolinium contrast-enhanced MRI was performed with a segmented inversion-recovery sequence. The location, extent and enhancement pattern of hyperenhanced myocardium was analysed in a 12-segment model.

RESULTS

Mean LV mass was 238.6 (SD 75.3) g in AS and 205.4 (SD 80.5) g in HCM (p = 0.17). Hyperenhancement was observed in 27% of patients with AS and in 73% of patients with HCM (p < 0.01). In AS, hyperenhancement was observed in 60% of patients with a maximum diastolic wall thickness >or= 18 mm, whereas no patient with a maximum diastolic wall thickness < 18 mm had hyperenhancement (p < 0.05). Patients with hyperenhancement had more severe AS than patients without hyperenhancement (aortic valve area 0.80 (0.09) cm(2)v 0.99 (0.3) cm(2), p < 0.05; maximum gradient 98 (22) mm Hg v 74 (24) mm Hg, p < 0.05). In HCM, hyperenhancement was predominant in the anteroseptal regions and patients with hyperenhancement had higher end diastolic (125.4 (36.9) ml v 98.8 (16.9) ml, p < 0.05) and end systolic volumes (38.9 (18.2) ml v 25.2 (1.7) ml, p < 0.05). The volume of hyperenhancement (percentage of total LV myocardium), where present, was lower in AS than in HCM (4.3 (1.9)% v 8.6 (7.4)%, p< 0.05). Hyperenhancement was observed in 4.5 (3.1) and 4.6 (2.7) segments in AS and HCM, respectively (p = 0.93), and the enhancement pattern was mostly patchy with multiple foci.

CONCLUSIONS

Focal scarring can be observed in severe LV hypertrophy caused by AS and HCM, and correlates with the severity of LV remodelling. However, focal scarring is significantly less prevalent in adaptive LV hypertrophy caused by AS than in genetically determined HCM.

Antifibrotic effects of antioxidant N-acetylcysteine in a mouse model of human hypertrophic cardiomyopathy mutation

OBJECTIVES

The objective was to determine the effects of antioxidant N-acetylcysteine (NAC) on reversal and attenuation of established interstitial fibrosis in the cardiac troponin T (cTnT) mouse model of human hypertrophic cardiomyopathy (HCM) mutation.

BACKGROUND

Interstitial fibrosis is a characteristic pathological feature of HCM and a risk factor for sudden cardiac death. The cTnT-Q92 transgenic mice, generated by cardiac-restricted expression of human HCM mutation, show a two- to four-fold increase in interstitial fibrosis.

METHODS

We randomized the cTnT-Q92 mice to treatment with a placebo or NAC (250, 500, or 1,000 mg/kg/day) and included non-transgenic mice as controls (N = 5 to 13 per group). We performed echocardiography before and 24 weeks after therapy, followed by histologic and molecular characterization.

RESULTS

There were no significant differences in the baseline characteristics of the groups. Treatment with NAC reduced myocardial concentrations of malondialdehyde and 4-hydroxy-2(E)-nonenal, markers of oxidative stress, by 40%. Collagen volume fractions comprised 1.94 +/- 0.76% of the myocardium in non-transgenic, 6.2 +/- 1.65% in the placebo, and 1.56 +/- 0.98% in the NAC (1,000 mg/kg/day) groups (p < 0.001). Expression levels of Col1a1 and Col1a2 were also reduced significantly, as were levels of phosphorylated but not total p44/42, p38, and c-Jun NH2-terminal kinase. Levels of oxidized mitochondrial and nuclear DNA were not significantly different.

CONCLUSIONS

Treatment with NAC reduced myocardial oxidative stress, stress-responsive signaling kinases, and fibrosis in a mouse model of HCM. The potential beneficial effects of NAC in reversal of cardiac phenotype in human HCM, the most common cause of sudden cardiac death in the young, merits investigation.

GENES, CALCIUM AND MODIFYING FACTORS IN HYPERTROPHIC CARDIOMYOPATHY

1. Familial hypertrophic cardiomyopathy (FHC) is a primary disorder of the myocardium characterized by remarkable diversity in clinical presentations, ranging from no symptoms to severe heart failure and sudden cardiac death. 2. Over the past 15 years, at least 11 genes have been identified, defects of which cause FHC. Most of these genes encode proteins that comprise the basic contractile unit of the heart (i.e. the sarcomere). 3. Genetic studies are now beginning to have a major impact on the diagnosis in FHC, as well as in guiding treatment and preventative strategies. Although much is known about which genes cause disease, relatively little is known about the molecular steps leading from the gene defect to the clinical phenotype and what factors modify the expression of the mutant genes. 4. Concurrent studies in cell culture and animal models of FHC are now beginning to shed light on the signalling pathways involved in FHC and the role of both environmental and genetic modifying factors. Calcium dysregulation appears to be important in the pathogenesis of FHC. 5. Understanding these basic molecular mechanisms will ultimately improve our knowledge of the basic biology of heart muscle function and will therefore provide new avenues for diagnosis and treatment not only for FHC, but also for a range of human cardiovascular diseases.