Molecular basis of familial cardiomyopathies

Cardiomyopathic troponin mutations predominantly occur at its interface with actin and tropomyosin

Reversible Ca2+ binding to troponin is the primary on-off switch of the contractile apparatus of striated muscles, including the heart. Dominant missense mutations in human cardiac troponin genes are among the causes of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy. Structural understanding of troponin action has recently advanced considerably via electron microscopy and molecular dynamics studies of the thin filament. As a result, it is now possible to examine cardiomyopathy-inducing troponin mutations in thin-filament structural context, and from that to seek new insight into pathogenesis and into the troponin regulatory mechanism. We compiled from consortium reports a representative set of troponin mutation sites whose pathogenicity was determined using standardized clinical genetics criteria. Another set of sites, apparently tolerant of amino acid substitutions, was compiled from the gnomAD v2 database. Pathogenic substitutions occurred predominantly in the areas of troponin that contact actin or tropomyosin, including, but not limited to, two regions of newly proposed structure and long-known implication in cardiomyopathy: the C-terminal third of troponin I and a part of the troponin T N terminus. The pathogenic mutations were located in troponin regions that prevent contraction under low Ca2+ concentration conditions. These regions contribute to Ca2+-regulated steric hindrance of myosin by the combined effects of troponin and tropomyosin. Loss-of-function mutations within these parts of troponin result in loss of inhibition, consistent with the hypercontractile phenotype characteristic of HCM. Notably, pathogenic mutations are absent in our dataset from the Ca2+-binding, activation-producing troponin C (TnC) N-lobe, which controls contraction by a multi-faceted mechanism. Apparently benign mutations are also diminished in the TnC N-lobe, suggesting mutations are poorly tolerated in that critical domain.

Differential responses of induced pluripotent stem cell-derived cardiomyocytes to anisotropic strain depends on disease status

Primary dilated cardiomyopathy (DCM) is a non-ischemic heart disease with impaired pumping function of the heart. In this study, we used human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from a healthy volunteer and a primary DCM patient to investigate the impact of DCM on iPSC-CMs׳ responses to different types of anisotropic strain. A bioreactor system was established that generates cardiac-mimetic forces of 150 kPa at 5% anisotropic cyclic strain and 1 Hz frequency. After confirming cardiac induction of the iPSCs, it was determined that fibronectin was favorable to other extracellular matrix protein coatings (gelatin, laminin, vitronectin) in terms of viable cell area and density, and was therefore selected as the coating for further study. When iPSC-CMs were exposed to three strain conditions (no strain, 5% static strain, and 5% cyclic strain), the static strain elicited significant induction of sarcomere components in comparison to other strain conditions. However, this induction occurred only in iPSC-CMs from a healthy volunteer ("control iPSC-CMs"), not in iPSC-CMs from the DCM patient ("DCM iPSC-CMs"). The donor type also significantly influenced gene expressions of cell-cell and cell-matrix interaction markers in response to the strain conditions. Gene expression of connexin-43 (cell-cell interaction) had a higher fold change in healthy versus diseased iPSC-CMs under static and cyclic strain, as opposed to integrins α-5 and α-10 (cell-matrix interaction). In summary, our iPSC-CM-based study to model the effects of different strain conditions suggests that intrinsic, genetic-based differences in the cardiomyocyte responses to strain may influence disease manifestation in vivo.

Clinical significance of left ventricular apical aneurysms in hypertrophic cardiomyopathy patients: the role of diagnostic electrocardiography

OBJECTIVES

Some patients with hypertrophic cardiomyopathy (HCM) develop left ventricular apical aneurysm, leading to serious cardiovascular complications. The aims of this study were to identify the incidence and clinical course of HCM patients with apical aneurysms in Japan, and to evaluate the role of electrocardiography (ECG) as a screening test to detect apical aneurysms in HCM patients.

METHODS AND RESULTS

In a retrospective, single center analysis of a population of 247 HCM patients, 21 patients (8.5%) had left ventricular apical aneurysms. Their mean age was 60 ± 14 years (range: 23-77 years) at study entry. Over 4.7 ± 3.3 years of follow-up, 10 patients (47.6%) experienced an adverse clinical event (annual event rate: 10.1%/y), including five implantable cardioverter-defibrillator (ICD) implantations for ventricular tachycardia/ventricular fibrillation (VT/VF), an appropriate discharge of ICD for VT/VF, and four nonfatal thromboembolic strokes. Two patients developed systolic dysfunction (ejection fraction <50%). No sudden cardiac death or progressive heart failure was detected. Fourteen patients showed ST-segment elevation (≥ 1 mm) in V3 through V5 of ECG. In four patients, progression of the ST-segment elevation was recognized. When the ST-segment elevation was used to identify apical aneurysms in HCM patients, the sensitivity was 66.7%, and the specificity was 98.7%.

CONCLUSION

Apical aneurysms in HCM patients in Japan are not rare, and are associated with serious cardiovascular complications. The early diagnosis of apical aneurysms can be achieved by serial ECG.

Alteration of Time Intervals in Patients With Hypertrophic Cardiomyopathy During an Exercise Echocardiography

Background

Hypertrophic cardiomyopathy (HCM) is often associated with diastolic dysfunction. Theoretically, a more marked alteration of diastolic function is revealed during exercise.

Methods and Results

We studied 84 persons: 1) 25 patients with HCM, 2) 25 patients with essential arterial hypertension (AH) and 3) 34 healthy controls. Each person performed a treadmill echocardiography. Before and after work, the following parameters were measured: the time interval between the QRS complex and the onset of mitral early diastolic filling velocity (TE), the interval between the QRS complex and the onset of peak early tissue mitral annular velocity (Te’), the isovolumetric relaxation time over the difference of TE and Te’ ratio (IVRT/(TE-Te’)), and changes of the time parameters during the stress test. In comparison with hypertensive and control groups, HCM patients at rest showed a significantly longer TE (448 ± 55 vs. 423 ± 33 vs. 417 ± 24 ms, P < 0.04) and Te’ (446 ± 48 vs. 403 ± 44 vs. 416 ± 38 ms, P < 0.003). After stress the HCM group had a longer Te’ (355 ± 59 vs. 299 ± 40 vs. 292 ± 30 ms, P < 0.000004) and a higher IVRT/(TE-Te’) ratio (3.1 ± 1.5 vs. 0.9 ± 2.4 vs. 1.7 ± 1.2, P < 0.002).

Conclusions

HCM patients show an alteration in the time parameters not only compared to healthy persons but to hypertensive patients as well.

Rapamycin reverses hypertrophic cardiomyopathy in a mouse model of LEOPARD syndrome-associated PTPN11 mutation

LEOPARD syndrome (LS) is an autosomal dominant "RASopathy" that manifests with congenital heart disease. Nearly all cases of LS are caused by catalytically inactivating mutations in the protein tyrosine phosphatase (PTP), non-receptor type 11 (PTPN11) gene that encodes the SH2 domain-containing PTP-2 (SHP2). RASopathies typically affect components of the RAS/MAPK pathway, yet it remains unclear how PTPN11 mutations alter cellular signaling to produce LS phenotypes. We therefore generated knockin mice harboring the Ptpn11 mutation Y279C, one of the most common LS alleles. Ptpn11(Y279C/+) (LS/+) mice recapitulated the human disorder, with short stature, craniofacial dysmorphia, and morphologic, histologic, echocardiographic, and molecular evidence of hypertrophic cardiomyopathy (HCM). Heart and/or cardiomyocyte lysates from LS/+ mice showed enhanced binding of Shp2 to Irs1, decreased Shp2 catalytic activity, and abrogated agonist-evoked Erk/Mapk signaling. LS/+ mice also exhibited increased basal and agonist-induced Akt and mTor activity. The cardiac defects in LS/+ mice were completely reversed by treatment with rapamycin, an inhibitor of mTOR. Our results demonstrate that LS mutations have dominant-negative effects in vivo, identify enhanced mTOR activity as critical for causing LS-associated HCM, and suggest that TOR inhibitors be considered for treatment of HCM in LS patients.

MEK-ERK pathway modulation ameliorates disease phenotypes in a mouse model of Noonan syndrome associated with the Raf1(L613V) mutation

Hypertrophic cardiomyopathy (HCM) is a leading cause of sudden death in children and young adults. Abnormalities in several signaling pathways are implicated in the pathogenesis of HCM, but the role of the RAS-RAF-MEK-ERK MAPK pathway has been controversial. Noonan syndrome (NS) is one of several autosomal-dominant conditions known as RASopathies, which are caused by mutations in different components of this pathway. Germline mutations in RAF1 (which encodes the serine-threonine kinase RAF1) account for approximately 3%-5% of cases of NS. Unlike other NS alleles, RAF1 mutations that confer increased kinase activity are highly associated with HCM. To explore the pathogenesis of such mutations, we generated knockin mice expressing the NS-associated Raf1(L613V) mutation. Like NS patients, mice heterozygous for this mutation (referred to herein as L613V/+ mice) had short stature, craniofacial dysmorphia, and hematologic abnormalities. Valvuloseptal development was normal, but L613V/+ mice exhibited eccentric cardiac hypertrophy and aberrant cardiac fetal gene expression, and decompensated following pressure overload. Agonist-evoked MEK-ERK activation was enhanced in multiple cell types, and postnatal MEK inhibition normalized the growth, facial, and cardiac defects in L613V/+ mice. These data show that different NS genes have intrinsically distinct pathological effects, demonstrate that enhanced MEK-ERK activity is critical for causing HCM and other RAF1-mutant NS phenotypes, and suggest a mutation-specific approach to the treatment of RASopathies.

Mutations in the beta-myosin heavy chain gene in southern Chinese families with hypertrophic cardiomyopathy

In this study, 14 unrelated hypertrophic cardiomyopathy (HCM) probands were scanned by polymerase chain reaction-single-strand conformation polymorphism analysis and DNA sequencing. Three mis-sense mutations of the beta-myosin heavy chain gene, MYH7, were found: valine (Val) 606 methionine (Met), arginine (Arg) 694 leucine (Leu), and Arg 723 glycine (Gly). All are reported here for the first time in Chinese subjects. The results showed that: Val606Met is an intermediate malignancy mutation; Arg694Leu is a novel mutation with a benign phenotype; and the Arg723Gly mutation is linked to malignancy - it can lead not only to HCM but also to dilated cardiomyopathy at various ages. The clinical symptoms associated with Arg723Gly emerged early and caused more severe clinical manifestation and poorer prognosis in females than in males. Mis-sense mutations were not detected in the myosin binding protein C, cardiac, cardiac troponin T type 2, or cardiac troponin I type 3 genes. The MYH7 gene may be an HCM mutation hotspot in the Chinese and have unique features in this study population.

Midregional pro-atrial natriuretic peptide: a novel marker of myocardial fibrosis in patients with hypertrophic cardiomyopathy

We aimed to determine the diagnostic performance of biomarkers in predicting myocardial fibrosis assessed by late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (CMR) in patients with hypertrophic cardiomyopathy (HCM). LGE CMR was performed in 40 consecutive patients with HCM. Left and right ventricular parameters, as well as the extent of LGE were determined and correlated to the plasma levels of midregional pro-atrial natriuretic peptide (MR-proANP), midregional pro-adrenomedullin (MR-proADM), carboxy-terminal pro-endothelin-1 (CT-proET-1), carboxy-terminal pro-vasopressin (CT-proAVP), matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1) and interleukin-8 (IL-8). Myocardial fibrosis was assumed positive, if CMR indicated LGE. LGE was present in 26 of 40 patients with HCM (65%) with variable extent (mean: 14%, range: 1.3-42%). The extent of LGE was positively associated with MR-proANP (r = 0.4; P = 0.01). No correlations were found between LGE and MR-proADM (r = 0.1; P = 0.5), CT-proET-1 (r = 0.07; P = 0.66), CT-proAVP (r = 0.16; P = 0.3), MMP-9 (r = 0.01; P = 0.9), TIMP-1 (r = 0.02; P = 0.85), and IL-8 (r = 0.02; P = 0.89). After adjustment for confounding factors, MR-proANP was the only independent predictor associated with the presence of LGE (P = 0.007) in multivariate analysis. The area under the ROC curve (AUC) indicated good predictive performance (AUC = 0.882) of MR-proANP with respect to LGE. The odds ratio was 1.268 (95% confidence interval 1.066-1.508). The sensitivity of MR-proANP at a cut-off value of 207 pmol/L was 69%, the specificity 94%, the positive predictive value 90% and the negative predictive value 80%. The results imply that MR-proANP serves as a novel marker of myocardial fibrosis assessed by LGE CMR in patients with HCM.

Rationale and design of the CAREFUL study : The yield of CARdiogenetic scrEening in First degree relatives of sudden cardiac and UnexpLained death victims <45 years

Background. Sudden cardiac death (SCD) in the young (1-45 years) is a strong risk factor for the presence of inherited cardiac diseases in surviving first-degree relatives. Postmortem investigation of the victim and cardiogenetic evaluation of the first-degree relatives is indicated to detect inherited cardiac diseases and treat relatives at an early stage to prevent SCD. In the Netherlands, postmortem investigation is often not performed and relatives of SCD and sudden unexplained death (SUD) victims are rarely evaluated for inherited cardiac diseases.Methods. A prospective population-based follow-up study carried out in two intervention regions and two control regions. In the intervention regions a comprehensive intervention (stimulate autopsy and storage of victims DNA and the referral of first-degree relatives for cardiogenetic evaluation) is applied in a 'top down' and 'bottom up' mode. In each region, young sudden death victims are registered and for all cases performance of autopsy and evaluation of relatives in a cardiogenetics outpatient clinic will be determined.Expected results. The study will provide information on the incidence of sudden death in the young and the proportion of diagnosed inherited cardiac diseases. Moreover, the additional value of the introduction of two different preventive strategies directed at early detection of inherited cardiac diseases in first-degree relatives to usual care will be evaluated. Conclusion. The CAREFUL study will help to set a new standard of care in the evaluation of young sudden death victims and their relatives to identify the presence of inherited cardiac diseases, in order to prevent sudden death. (Neth Heart J 2010;18:286-90.).

Sudden cardiac death in a 20-year-old male swimmer

In young adults, hypertrophic obstructive cardiomyopathy (HOCM) is an acknowledged risk factor for sudden cardiac death (SCD) in an otherwise healthy and active patient. While the incidence of SCD in young people is not high enough for extensive, wide-scale examinations, the potential for prevention of some deaths via pre-exercise imaging may be beneficial in certain patient populations, such as those with a family history of SCD or professional athletes. We present the case of a healthy 20-year-old man with no past medical history who died while swimming in a river, likely secondary to cardiac arrest in the setting of HOCM.

Cardiac sympathetic activity in the asymmetrically hypertrophied septum in patients with hypertension or hypertrophic cardiomyopathy

BACKGROUND

In patients with essential hypertension (HT), proportional (symmetric) left ventricular hypertrophy (LVH) is common. In contrast, hypertrophic cardiomyopathy (HCM) is characterized by disproportional LVH and, in particular, asymmetric septal hypertrophy (ASH); however, some hypertensive patients also develop ASH. It has not been determined whether such cases represent a distinct type of hypertensive LVH or HCM combined with hypertension.

HYPOTHESIS

The study was undertaken to evaluate sympathetic activity in the interventricular septum in patients with HT and ASH or in patients with HCM.

METHODS

The patients were evaluated by I-123 meta-iodobenzylguanidine (MIBG) and thallium-201 (201Tl) single-photon emission computed tomography (SPECT), respectively. They were divided into three groups: patients with essential HT and symmetric septal hypertrophy (Group A), patients with HT and ASH (Group B), and patients with HCM and ASH (Group C).

RESULTS

Compared with the lateral wall, early uptake of MIBG in the septum was significantly higher in Group B than in Group A, but not significantly different between Groups A and C. Compared with the lateral wall, early uptake of 201Tl in the septum did not differ among the three groups. No significant difference in the MIBG clearance in the lateral wall was seen among the three groups. By contrast, MIBG clearances in the septum and apex were significantly greater in Group C than in Groups A and B. There was an inverse correlation between systolic thickening and MIBG clearance in the septum.

CONCLUSION

These findings suggest that sympathetic activity in the septum differs between patients with HT and ASH and patients with HCM.

Aerobic capacity-dependent differences in cardiac gene expression

Aerobic capacity is a strong predictor of cardiovascular mortality. To determine the relationship between inborn aerobic capacity and cardiac gene expression we examined genome-wide gene expression in hearts of rats artificially selected for high and low running capacity (HCR and LCR, respectively) over 16 generations. The artificial selection of LCR caused accumulation of risk factors of cardiovascular disease similar to the metabolic syndrome seen in human, whereas HCR had markedly better cardiac function. We also studied alterations in gene expression in response to exercise training in these animals. Left ventricle gene expression of both sedentary and exercise-trained HCR and LCR was characterized by microarray and gene ontology analysis. Out of 28,000 screened genes, 1,540 were differentially expressed between sedentary HCR and LCR. Only one gene was found differentially expressed by exercise training, but this gene had unknown name and function. Sedentary HCR expressed higher amounts of genes involved in lipid metabolism, whereas sedentary LCR expressed higher amounts of the genes involved in glucose metabolism. This suggests a switch in cardiac energy substrate utilization from normal mitochondrial fatty acid β-oxidation in HCR to carbohydrate metabolism in LCR, an event that often occurs in diseased hearts. LCR were also associated with pathological growth signaling and cellular stress. Hypoxic conditions seemed to be a common source for several of these observations, triggering hypoxia-induced alterations of transcription. In conclusion, inborn high vs. low aerobic capacity was associated with differences in cardiac energy substrate, growth signaling, and cellular stress.

Recent and ongoing selection in the human genome

The recent availability of genome-scale genotyping data has led to the identification of regions of the human genome that seem to have been targeted by selection. These findings have increased our understanding of the evolutionary forces that affect the human genome, have augmented our knowledge of gene function and promise to increase our understanding of the genetic basis of disease. However, inferences of selection are challenged by several confounding factors, especially the complex demographic history of human populations, and concordance between studies is variable. Although such studies will always be associated with some uncertainty, steps can be taken to minimize the effects of confounding factors and improve our interpretation of their findings.

Screening of the endothelin1 gene (EDN1) in a cohort of patients with essential left ventricular hypertrophy

Our objective was to analyse the role of endothelin1 gene (EDN1) variation in essential left ventricular hypertrophy (LVH). We searched for EDN1 variants in 145 Spanish patients with an essential form of LVH (not secondary to hypertension, aortic stenosis, or any other disease that could explain the hypertrophy). The five EDN1 coding exons and 1.5 kilobases of the promoter region were analysed through single strand conformation analysis and direct sequencing. We found four nucleotide changes: -1224 C/A (promoter), -131 ins/del A (exon 1, 5'-non-translated sequence), A/G in codon 106 (exon 3, silent), and G/T in codon 198 (exon 5, lys198asn). To determine the association between these polymorphisms and cardiac hypertrophy, we compared the genotype frequencies from these 145 patients with 250 healthy controls. We found a higher frequency of patients homozygous for 198 lys (198 KK) (65% vs. 52%; p = 0.01; OR = 1.76) and for -1224 AA (73% vs. 66%; p = 0.19). Homozygotes for -1224 A + 198 K (AA+KK) were significantly more frequent in patients (62% vs. 45%; p = 0.0007; OR = 2.10; 95% CI = 1.35-3.25). The expression of the -1224 C/A and exon 5 K198N variants was analysed with cells in culture. These in vitro studies showed that these variations did not differ in their expression levels. In conclusion, our work has shown that EDN1 variation, and in particular homozygosity for the -1224A/198K haplotype, is associated with the risk of developing cardiac hypertrophy. However, these EDN1 variants do not affect in vitro gene expression.

Electrocardiographic markers of sudden death

The 12-lead ECG has limited utility to predict the risk for sudden cardiac death in common cardiac diseases such as coronary artery disease and idiopathic dilated cardiomyopathy. However, it is quite useful in diagnosing less common cardiac conditions that are associated with an increased risk for sudden death.

Significance and relation between magnitude of left ventricular hypertrophy and heart failure symptoms in hypertrophic cardiomyopathy

In hypertrophic cardiomyopathy (HC), an important subgroup of patients develop progressive and disabling symptoms that are related to heart failure and death. Although a direct relation has been demonstrated between left ventricular (LV) wall thickness and likelihood of sudden and unexpected death (usually in patients who are asymptomatic or mildly symptomatic), it is unresolved whether magnitude of hypertrophy is similarly associated with severity of heart failure. To determine the relation of LV wall thickness to heart failure symptoms in HC, 700 consecutive patients who had HC were assessed by 2-dimensional echocardiography. The relation between maximum level of heart failure symptoms by New York Heart Association functional class and maximum LV wall thickness was not linear but rather parabolic. Therefore, marked symptoms were most commonly associated with moderate degrees of LV hypertrophy (wall thickness 16 to 24 mm; 27%) but less frequently with extreme hypertrophy (>/=30 mm 13%) or mild hypertrophy (</=15 mm; 19%, p = 0.0001). Mean New York Heart Association functional class showed a similar pattern with respect to moderate hypertrophy (1.9 +/- 0.8), mild hypertrophy (1.6 +/- 0.9), and extreme hypertrophy (1.6 +/- 0.7, p = 0.005). Multivariable regression analysis showed the parabolic relation between heart failure symptoms and magnitude of LV hypertrophy to be independent of other hypertrophic cardiomyopathy related clinical variables. In conclusion, no direct relation was evident between symptoms of heart failure and magnitude of LV wall thickness, with implications for the natural history of HC.

Spectrum and prognostic significance of arrhythmias on ambulatory Holter electrocardiogram in hypertrophic cardiomyopathy

OBJECTIVES

The goal of this study was to assemble a profile and assess the significance of arrhythmias in a nontertiary-based hypertrophic cardiomyopathy (HCM) cohort.

BACKGROUND

Hypertrophic cardiomyopathy is associated with arrhythmia-related consequences, particularly sudden death. Ventricular tachyarrhythmias on Holter electrocardiograms (ECG) have been reported as markers for sudden death in highly selected HCM populations.

METHODS

We assessed the profile of ventricular and supraventricular ectopy and bradyarrhythmia on ambulatory 24-h Holter ECG and also related these findings to clinical outcome in 178 HCM patients.

RESULTS

Of the 178 study patients, 157 (88%) had premature ventricular complexes (PVCs), including 21 (12%) with >/=500 PVCs, 74 (42%) had couplets, 67 (37%) had supraventricular tachycardia (SVT), and 56 (31%) had nonsustained ventricular tachycardia (NSVT). Mean number of PVCs was 330 +/- 763 (range 1 to 5,435) and increased with age (p < 0.01); NSVT was associated with greater left ventricular hypertrophy (p = 0.01) and severe symptoms (New York Heart Association functional classes III and IV) (p = 0.04); SVT occurred more commonly in patients with outflow obstruction (p = 0.02). Over a follow-up of 5.5 +/- 3.4 years, 11 (6%) patients died suddenly (annual mortality rate, 1.1%) including 5 patients with NSVT. For sudden death, NSVT on Holter ECG had negative and positive predictive values of 95% and 9%, and sensitivity and specificity of 45% and 69%, respectively.

CONCLUSIONS

In this nontertiary-based HCM cohort, ventricular and supraventricular tachyarrhythmias were particularly frequent and demonstrated a broad spectrum on ambulatory (Holter) ECG. Paradoxically, despite such a highly arrhythmogenic substrate, sudden death events proved to be relatively uncommon. Ventricular tachyarrhythmias had a low positive and relatively high negative predictive value for sudden death in this HCM population.

Proposal for contemporary screening strategies in families with hypertrophic cardiomyopathy

Screening families with hypertrophic cardiomyopathy (HCM) presents a common clinical problem to practicing cardiologists, internists, and pediatricians. The traditional recommended strategy for screening relatives in most HCM families calls for such evaluations with echocardiography (and electrocardiogram [ECG]) on a 12- to 18-month basis, usually beginning at about age 12 years. If such tests show no evidence of left ventricular hypertrophy, i.e., without one or more segments of abnormally increased wall thickness by the time full growth and maturation is achieved (at the age of about 18 to 21 years), it has been customary practice to conclude that HCM is probably absent and reassure family members accordingly that further echocardiographic testing is unnecessary. However, novel developments in the definition of the genetic causes of HCM have defined both substantial molecular diversity and heterogeneity of the disease expression including (in some relatives) incomplete phenotypic penetrance and delayed, late-onset left ventricular hypertrophy well into adulthood. These observations have unavoidably reshaped the customary practice of genetic counseling and established a new proposed paradigm for clinical family screening of HCM families. Therefore, in the absence of genetic testing, strong consideration should be given to extending diagnostic serial echocardiography past adolescence and into mid-life for those family members with a normal echocardiogram and ECG. Of note, recent developments in laboratory DNA-based diagnosis for HCM could potentially avoid the necessity for serial echocardiography in many such relatives.

Hypertrophic cardiomyopathy in childhood

Hypertrophic cardiomyopathy (HCM) is a heterogeneous and relatively common genetic cardiac disease that has been the subject of intense scrutiny and investigation for over 40 years. HCM is an important cause of disability and death in patients of all ages, although unexpected sudden death in the young is perhaps the most devastating component of the natural history. Therefore, while HCM is uncommon in pediatric cardiology practice, it is nevertheless a disease of great importance to young people and those clinicians charged with their care. Due to marked heterogeneity in clinical expression, natural history and prognosis, diagnostic and management strategies often represent a dilemma (and even the source of controversy) to both primary care clinicians and cardiovascular specialists. Consequently, it is timely to place perspective and clarify many of these relevant clinical issues, and profile the rapidly evolving concepts regarding HCM, especially as they may impact on this disease in childhood.

Role of genetic factors in the etiopathogenesis of cerebrovascular accidents: from an animal model to the human disease

1. The present work summarizes current knowledge on the genetic susceptibility to stroke, a complex cardiovascular phenotypic trait due to both gene/environment and gene/ gene interactions. 2. Evidence for the existence of genes directly contributing to stroke occurrence was first obtained in the animal model of the stroke-prone (sp) spontaneously hypertensive rat (SHR) through a linkage analysis approach in F2 segregating hybrid populations. In fact, several Quantitative Trait Loci (QTLs) were detected in different chromosomes of the rat. Candidate genes were identified (ANP, BNP, Adrenomedullin) and subsequently analyzed to obtain information on the fine disease mechanisms possibly dependent from specific sequence mutations. 3. The most important achievement was represented by the fact that the gene encoding ANP appeared to play a role in the disease of both rats and humans, thus providing a suggestive parallelism between the animal model and the human cerebrovascular disease. A more extensive analysis is required to identify the potential pathogenic role of genetic factors involved in human stroke.

Effect of MyBP-C binding to actin on contractility in heart muscle

In contrast to skeletal muscle isoforms of myosin binding protein C (MyBP-C), the cardiac isoform has 11 rather than 10 fibronectin or Ig modules (modules are identified as C0 to C10, NH2 to COOH terminus), 3 phosphorylation sites between modules C1 and C2, and 28 additional amino acids rich in proline in C5. Phosphorylation between C1 and C2 increases maximum Ca-activated force (Fmax), alters thick filament structure, and increases the probability of myosin heads on the thick filament binding to actin on the thin filament. Unphosphorylated C1C2 fragment binds to myosin, but phosphorylation inhibits the binding. MyBP-C also binds to actin. Using two types of immunoprecipitation and cosedimentation, we show that fragments of MyBP-C containing C0 bind to actin. In low concentrations C0-containing fragments bind to skinned fibers when the NH2 terminus of endogenous MyBP-C is bound to myosin, but not when MyBP-C is bound to actin. C1C2 fragments bind to skinned fibers when endogenous MyBP-C is bound to actin but not to myosin. Disruption of interactions of endogenous C0 with a high concentration of added C0C2 fragments produces the same effect on contractility as extraction of MyBP-C, namely decrease in Fmax and increase in Ca sensitivity. These results suggest that cardiac contractility can be regulated by shifting the binding of the NH2 terminus of MyBP-C between actin and myosin. This mechanism may have an effect on diastolic filling of the heart.

Novel point mutations in the mitochondrial DNA detected in patients with dilated cardiomyopathy by screening the whole mitochondrial genome

Dilated cardiomyopathy (DCM) is widely accepted as a pluricausal or multifactorial disease. Because of the linkage between energy metabolism in the mitochondria and cardiac muscle contraction, it is reasonable to assume that mitochondrial abnormalities may be responsible for some forms of DCM. We analysed the whole mitochondrial genome in a series of 45 patients with DCM for alterations and compared the findings with those of 62 control subjects. A total of 458 sequence changes could be identified. These sequence changes were distributed among the whole mitochondrial DNA (mtDNA). An increased number of novel missense mutations could be detected nearly in all genes encoding for protein subunits in DCM patients. In genes coding for NADH dehydrogenase subunits the number of mtDNA mutations detected in patients with DCM was significantly increased (p < 0.05) compared with control subjects. Eight mutations were found to occur in conserved amino acids in the above species. The c.5973G > A (Ala-Trp) and the c.7042T > G (Val-Asp) mutations were located in highly conserved domains of the gene coding for cytochrome c oxidase subunit. Two tRNA mutations could be detected in the mtDNA of DCM patients alone. The T-C transition at nt 15,924 is connected with respiratory enzyme deficiency, mitochondrial myopathy, and cardiomyopathy. The c.16189T > C mutation in the D-loop region that is associated with susceptibility to DCM could be detected in 15.6% of patients as well as in 9.7% of controls. Thus, mutations altering the function of the enzyme subunits of the respiratory chain can be relevant for the pathogenesis of dilated cardiomyopathy.

Efficacy of implantable cardioverter defibrillator therapy for primary and secondary prevention of sudden cardiac death in hypertrophic cardiomyopathy

Risk stratification and effectiveness of implantable cardioverter-defibrillator (ICD) therapy are unresolved issues in hypertrophic cardiomyopathy (HCM), a cardiac disease that is associated with arrhythmias and sudden death. We assessed ICD therapy in 132 patients with HCM: age at implantation was 34 +/- 17 years, and 44 (33%) patients were aged </= 20 years. Indications were sustained ventricular tachycardia (VT) or cardiac arrest (secondary prevention) in 47 (36%) patients, and clinical features associated with increased risk for sudden death (primary prevention) in 85 (64%) patients. There were 6 deaths and 55 appropriate interventions in 27 (20%) patients during a mean follow-up period of 4.8 +/- 4.2 years: 5-year survival and event-free rates were 96%+/- 2%and 75%+/- 5%, respectively. ICD intervention-free rates were significantly less for secondary than for primary prevention:64%+/- 7%versus 84%+/- 6%at 5 years,P = 0.02. Notably, 59 of 67 events (cardiac arrest and therapeutic ICD interventions), or 88%, occurred during sedentary or noncompetitive activity. Incidence of therapeutic shocks was related to age but not to other reported risk factors, including severity of cardiac hypertrophy, nonsustained VT during Holter monitoring, and abnormal blood pressure response to exercise. ICD related complications occurred in 38 (29%) patients, including 60 inappropriate ICD interventions in 30 (23%) patients. However, 8 (27%) of the patients with inappropriate shocks also had therapeutic interventions. ICD is effective for secondary prevention of sudden death in HCM. However, selection of patients for primary prevention of sudden death, and prevention of device related complications require further refinement.

Cardiac troponin T and familial hypertrophic cardiomyopathy: an energetic affair

It has long been noted that while patients with familial hypertrophic cardiomyopathy due to cardiac troponin T (cTnT) mutations often suffer sudden cardiac death, they do not develop significant ventricular hypertrophy, suggesting that a distinct cellular mechanism apart from alterations in myocardial contractility is responsible. A new study has revealed that a single missense mutation in cTnT causes a striking disruption to energy metabolism, leading to cardiomyopathy.

Hypertrophic cardiomyopathy: low frequency of mutations in the beta-myosin heavy chain (MYH7) and cardiac troponin T (TNNT2) genes among Spanish patients

BACKGROUND

Mutations in the cardiac beta-myosin heavy chain (MYH7) and cardiac troponin T (TNNT2) genes are reportedly responsible for up to 40% of familial cases with hypertrophic cardiomyopathy (HC). Although there are no mutational hotspots, most of the mutations are located in specific exons of the MYH7 and TNNT2 genes. Currently it is not possible to predict the phenotype in carriers of mutations in these genes, although it is widely accepted that mutations in the MYH7 gene predispose to severe HC, whereas TNNT2 mutations are frequently linked to sudden cardiac death (SCD) in spite of minimal hypertrophy.

METHODS

We sequenced exons 8, 9, 13-16, 19, 20, 22-24, and 30 of the MYH7 gene and exons 8, 9, 11, and 14-16 of the TNNT2 gene in 30 HC patients (18-60 years of age) from the region of Asturias (Northern Spain); 25 cases (80%) had a family history of the disease. Genomic DNA was amplified, and fragments were directly sequenced. Each DNA variant found in the patients was also analyzed in 200 healthy controls through single-strand conformation analysis.

RESULTS

Four of the probands had nucleotide changes absent in the healthy controls. Two cases had mutations previously described in the MYH7 gene (exon 14, Arg453Cys) or the TNNT2 gene (exon 16, Arg278Cys). Two cases had new mutations (MYH7 exon 22, Met822Val; TNNT2 exon 14, Lys247Arg) not found among the healthy controls. We found MYH7 Met822Val in a woman with a severe form of HC; the mutation was absent in her parents, indicating a de novo mutation. MYH7 R453C was present in a woman with mild HC, mother of a son who died from SCD. TNNT2 R278C was present in a woman with severe HC, but a sister and a daughter were mutation carriers and did not have hypertrophy. A patient with severe HC was carrier of TNNT2 247Arg.

CONCLUSIONS

Mutations in the MYH7 and TNNT2 genes can be found in patients without a family history of HC. However, compared with other populations MYH7 or TNNT2 mutations were rare among our HC patients. This study illustrates the extreme phenotypic heterogeneity in carriers of MYH7 or TNNT2 mutations.

Relation of left ventricular thickness to age and gender in hypertrophic cardiomyopathy

Left ventricular (LV) wall thickening is the most consistent clinical marker of hypertrophic cardiomyopathy (HC), and characteristically increases substantially during adolescence. In this study, we used 2-dimensional echocardiography to develop a cross-sectional profile of LV wall thicknesses in adult patients with HC. We studied a regional community-based cohort of 239 consecutively enrolled patients (aged 18 to 91 years). On average, maximum LV wall thickness decreased relative to increasing age (p = 0.007) within 4 age groups: 22.8 +/- 5.1 mm (18 to 39 years) to 22.1 +/- 5.1 mm (40 to 59 years) to 21.1 +/- 3.7 mm (60 to 74 years) to 20.8 +/- 3.6 mm (>or=75 years). The LV thickness index (summation of wall thicknesses in all 4 segments) also decreased with age (p = 0.017): 63.0 +/- 12.2 mm to 59.8 +/- 11.9 mm to 58.3 +/- 10.4 mm to 57.9 +/- 9.8 mm. Decreasing magnitude of LV hypertrophy was independently associated with increasing age, but not with other relevant disease variables, such as symptoms and outflow obstruction. However, when separated by gender, this inverse relation between age and LV wall thickness was statistically significant only for women (p = 0.007). In conclusion, in an unselected HC cohort, cross-sectional analysis showed a modest but statistically significant inverse relation between age and LV hypertrophy that was largely gender-specific for women. This association constitutes another facet of the natural history of this complex and heterogenous disease and may reflect disproportionate occurrence of premature death in young patients with HC with marked hypertrophy or possibly gradual LV remodeling.

Hypertrophic cardiomyopathy in a large community-based population: clinical outcome and identification of risk factors for sudden cardiac death and clinical deterioration

OBJECTIVES

This study evaluates the clinical course and identifies risk factors for sudden cardiac death (SCD) and clinical deterioration in hypertrophic cardiomyopathy (HCM) in a large community-based population. Comparison was made with data from six tertiary referral and six nonreferral institutions.

BACKGROUND

Hypertrophic cardiomyopathy is a disease with marked heterogeneity in clinical presentation and prognosis. Risk factors for SCD are not well defined in patients free of referral bias.

METHODS

Between 1970 and 1999, 225 consecutive patients (mean age [+/-SD] 41+/-16 years) were examined and followed at yearly intervals.

RESULTS

Forty-four deaths were recorded of which 27 cases were cardiovascular. Fourteen patients died suddenly, six were successfully resuscitated, and seven patients died of congestive heart failure. The annual mortality, annual cardiac mortality, and annual mortality due to sudden death were 1.3%, 0.8%, and 0.6%, respectively. At least one New York Heart Association (NYHA) functional class deterioration was reported in 33% of the patients with a significant (> or =50 mm Hg) left ventricular outflow tract (LVOT) gradient in contrast to 7% without obstruction. The presence of syncope was related to SCD (p < 0.05). Younger age and more severe functional limitation distinguishes patients from in hospital-based centers from the ones in community-based centers.

CONCLUSIONS

Hypertrophic cardiomyopathy is a benign disease in an unselected population with a low incidence of cardiac death. Syncope was associated with a higher incidence of SCD and patients with a significant LVOT obstruction were more susceptible to clinical deterioration.

Relationship of race to sudden cardiac death in competitive athletes with hypertrophic cardiomyopathy

OBJECTIVES

The goal of this study was to determine the impact of race on identification of hypertrophic cardiomyopathy (HCM).

BACKGROUND

Sudden death in young competitive athletes is due to a variety of cardiovascular diseases (CVDs) and, most commonly, HCM. These catastrophes have become an important issue for African Americans, although HCM has been previously regarded as rare in this segment of the U.S. population.

METHODS

We studied the relationship of race to the prevalence of CVDs causing sudden death in our national athlete registry, and compared these findings with a representative multicenter hospital-based cohort of patients with HCM.

RESULTS

Of 584 athlete deaths, 286 were documented to be due to CVD at ages 17 +/- 3 years; 156 (55%) were white, and 120 (42%) were African American. Most were male (90%), and 67% participated in basketball and football. Among the 286 cardiovascular deaths, most were due to HCM (n = 102; 36%) or anomalous coronary artery of wrong sinus origin (n = 37; 13%). Of the athletes who died of HCM, 42 (41%) were white, but 56 (55%) were African American. In contrast, of 1,986 clinically identified HCM patients, only 158 (8%) were African American (p < 0.001).

CONCLUSIONS

In this autopsy series, HCM represented a common cause of sudden death in young and previously undiagnosed African American male athletes, in sharp contrast with the infrequent clinical identification of HCM in a hospital-based population (i.e., by seven-fold). This discrepancy suggests that many HCM cases go unrecognized in the African American community, underscoring the need for enhanced clinical recognition of HCM to create the opportunity for preventive measures to be employed in high-risk patients with this complex disease.

Distinct gene-sex interactions regulate adult rat cardiomyocyte width and length independently

Wistar-Kyoto (WKY) and WKY-derived hyperactive (WKHA) rats are two genetically-related inbred strains of rats that are both normotensive yet exhibit differences in left ventricular mass (LVM). We had shown previously that cardiomyocytes from male WKHA are wider than that of male WKY, and that there was genetic linkage between LVM and a locus on chromosome 5 (RNO5) in the male progeny of a F2 WKHA/WKY cross. We show here that cardiomyocyte width is linked to the same RNO5 locus in male reciprocal congenic rats derived from WKHA and WKY. Contrary to males, we found no genetic linkage between LVM and the RNO5 locus in female rats. However, ventricular hypertrophy in females might be of a different nature, because cardiomyocytes from female WKHA were shorter than their WKY counterparts (with no difference in width). The RNO5 locus contains that of the natriuretic peptide precursor A (Nppa) gene. In male congenic rats, changes in cardiomyocyte width always correlated with reciprocal changes in the LV concentration of atrial natriuretic factor (ANF, i.e., the peptide product of Nppa). Taken together with other functional data, the small size of the RNO5 locus (approximately 63 cR) increased the likelihood that both cardiomyocyte width and LV ANF concentration could be linked to only one gene (possibly Nppa) in male rats. Moreover, our results support the notion that genes and sex interact to regulate cardiomyocyte width and length independently from one another.

Genetic causes of inherited cardiac hypertrophy: Robert L. Frye Lecture

Cardiac hypertrophy is well recognized as a cardiac manifestation of systemic disorders such as hypertension or intrinsic myocardial disease, but it can also reflect an underlying genetic defect. Molecular studies of inherited forms of cardiac hypertrophy have defined 2 novel pathways that lead to cardiac remodeling in adults, discoveries that increasingly provide insights relevant for both diagnosis and management. This article reviews the genetic studies that led to the current molecular understanding of hypertrophic cardiomyopathy and discusses more recently discovered causes of inherited cardiac hypertrophy.

Risk associated with pregnancy in hypertrophic cardiomyopathy

OBJECTIVES

We sought to assess mortality and morbidity in pregnant women with hypertrophic cardiomyopathy (HCM).

BACKGROUND

The risk associated with pregnancy in women with HCM is an important and increasingly frequent clinical issue for which systematic data are not available and a large measure of uncertainty persists.

METHODS

Maternal mortality in 91 consecutively evaluated families with HCM was compared with that reported in the general population. The study cohort included 100 women with HCM with one or more live births, for a total of 199 live births. Morbidity related to HCM during pregnancy was investigated in 40 women evaluated within five years of their pregnancy.

RESULTS

Two pregnancy-related deaths occurred, both in patients at a particularly high risk. The maternal mortality rate was 10 per 1,000 live births (95% confidence interval [CI] 1.1 to 36.2/1,000) and was in excess of the expected mortality in the general Italian population (relative risk 17.1, 95% CI 2.0 to 61.8). In the 40 patients evaluated within close proximity of their pregnancy, 1 (4%) of the 28 who were previously asymptomatic and 5 (42%) of the 12 with symptoms progressed to functional class III or IV during pregnancy (p < 0.01). One patient had atrial fibrillation and one had syncope, both of whom had already experienced similar and recurrent events before their pregnancy.

CONCLUSIONS

Maternal mortality is increased in patients with HCM compared with the general population. However, absolute maternal mortality is low and appears to be principally confined to women at a particularly high risk. In the presence of a favorable clinical profile, the progression of symptoms, atrial fibrillation, and syncope are also uncommon during pregnancy.

Hypertrophic cardiomyopathy: practical steps for preventing sudden death

Hypertrophic cardiomyopathy (HCM) is a rare cause of death among the many participants in sports and recreational athletics, but it attracts widespread attention because the deaths occur in young, apparently healthy people. Differentiating HCM from conditioning hypertrophy (athlete's heart) remains a challenge. Routine detection of HCM patients is most commonly done with family history, physical examination, electrocardiography, and echocardiography. Keys to the differential diagnosis include evidence of heterogenous left ventricle hypertrophy, left atrial enlargement, unusual ECG patterns, and family history or gene mutations. Molecular detection methods for known defective genes in HCM have not yet become routine clinical tools. Athletes with unequivocal HCM should not participate in competitive sports, except for perhaps some low-intensity ones.

Development of left ventricular hypertrophy in adults in hypertrophic cardiomyopathy caused by cardiac myosin-binding protein C gene mutations

OBJECTIVES

We sought to determine whether the development of left ventricular hypertrophy (LVH) can be demonstrated during adulthood in genetically affected relatives with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Hypertrophic cardiomyopathy is a heterogeneous cardiac disease caused by mutations in nine genes that encode proteins of the sarcomere. Mutations in cardiac myosin-binding protein C (MyBPC) gene have been associated with age-related penetrance.

METHODS

To further analyze dormancy of LVH in patients with HCM, we studied, using echocardiography and 12-lead electrocardiography, the phenotypic expression caused by MyBPC mutations in seven genotyped pedigrees.

RESULTS

Of 119 family members studied, 61 were identified with a MyBPC mutation, including 21 genetically affected relatives (34%) who did not express the HCM morphologic phenotype (by virtue of showing normal left ventricular wall thickness). Of these 21 phenotype-negative individuals, 9 were children, presumably in the prehypertrophic phase, and 12 were adults. Of the 12 adults with normal wall thickness < or = 12 mm (7 also with normal electrocardiograms), 5 subsequently underwent serial echocardiography prospectively over four to six years. Of note, three of these five adults showed development of LVH in mid-life, appearing for the first time at 33, 34 and 42 years of age, respectively, not associated with outflow obstruction or significant symptoms.

CONCLUSIONS

In adults with HCM, disease-causing MyBPC mutations are not uncommonly associated with absence of LVH on echocardiogram. Delayed remodeling with the development of LVH appearing de novo in adulthood, demonstrated here for the first time in individual patients with prospectively obtained serial echocardiograms, substantiates the principle of age-related penetrance for MyBPC mutations in HCM. These observations alter prevailing perceptions regarding the HCM clinical spectrum and family screening strategies and further characterize the evolution of LVH in this disease.

Clinical and molecular studies of a large family with desmin-associated restrictive cardiomyopathy

Patients with restrictive cardiomyopathy (RC) have impaired diastolic function, but intact systolic function until later stages of the disease, ultimately leading to heart failure. Primary RC is often sporadic, but also may be inherited in an autosomal dominant fashion, particularly the idiopathic forms. Recently there has been great interest in inherited cardiomyopathy associated with myocyte desmin deposition ('desminopathies'). In some such families, desmin or alpha-B crystallin gene mutation is the underlying cause, and the desmin accumulation affects skeletal muscle as well, usually causing skeletal myopathy. We describe a large family with apparent autosomal dominant inheritance of desmin-associated RC spanning four generations, with the age of onset and severity/rate of progression being highly variable. This family is relatively unique in that there is no symptom-based evidence of skeletal muscle involvement, and the known desminopathy and cardiomyopathy genes/loci have been ruled out. These data support literature suggesting that desmin deposition may be associated with different underlying gene defects, and that a novel desminopathy gene is responsible for the condition in this family.

Use of implantable pacemakers and implantable defibrillators in hypertrophic cardiomyopathy

Recent data have emerged to help guide the use of implantable pacemakers and implantable defibrillators in patients who have hypertrophic cardiomyopathy (HCM). Controlled studies of the use of dual chamber pacemakers to treat outflow tract obstruction in HCM have shown little benefit, and have raised the possibility that earlier favorable reports were demonstrating an element of placebo effect. In particular, there is no recent support for earlier claims of regression of ventricular hypertrophy from chronic dual chamber pacing. Several reports have added to our understanding of the risk factors for sudden death in HCM. A normal blood pressure response to exercise appears to identify a subset of patients at low risk for sudden death. In a recent study of a large number of HCM patients, the risk of sudden death was found to be directly proportional to the extent of left ventricular hypertrophy. There is accumulating evidence that the implantable defibrillator is highly effective in terminating malignant ventricular arrhythmias in HCM patients, and HCM patients thought to be at significant risk for sudden death should be offered defibrillator implantation.

Hemodynamic benefits of treatment modalities for hypertrophic cardiomyopathy: a case study

Hypertrophic cardiomyopathy is a primary disease of the cardiac muscle characterized by a hypertrophied and nondilated left ventricle in the absence of other cardiac or systemic disease. The disorder occurs twice as often in men than in women and is relatively more common in young adults. Early treatment of symptoms may improve hemodynamic benefits and prevent complications, including sudden death. This case illustrates various treatment modalities used to manage symptoms and describes the challenges in effectively maintaining hemodynamic stability.

Malignant hypertrophic cardiomyopathy caused by the Arg723Gly mutation in beta-myosin heavy chain gene

Mutations causing hypertrophic cardiomyopathy have been described in nine genes encoding sarcomeric proteins. We report a new mutation in three families, with a C-->G transversion in nucleotide 12 307 of the beta-myosin heavy chain gene, located at the essential light chain interacting region, resulting in the replacement of arginine by glycine at amino acid residue 723. PCR amplification of the selected regions followed by single strand conformation polymorphism analysis, DNA sequencing of the polymorphic patterns and restriction analysis were used to detect the mutation. A total of 23 individuals were diagnosed as carriers, and seven were obligate carriers or had been clinically diagnosed. The Arg723Gly mutation was associated with a malignant phenotype. Ten out of 30 affected members died suddenly or needed an implantable cardioverter-defibrillator at a mean age of 42, and seven members developed progressive heart failure, leading to death or heart transplant in five, at a mean age of 50 years. Echocardiography showed non-obstructive left ventricular hypertrophy in affected members older than 20 (sensitivity 68%). Mean survival of affected members was 51 years. In conclusion, a new mutation Arg723Gly in beta-myosin heavy chain gene is reported which shortens life expectancy because of sudden death and end-stage heart failure.

Hypertrophic cardiomyopathy: the interrelation of disarray, fibrosis, and small vessel disease

OBJECTIVE

To make a quantitative assessment of the relation between disarray, fibrosis, and small vessel disease in hypertrophic cardiomyopathy.

DESIGN

Detailed macroscopic and histological examination at 19 segments of the left and right ventricle and the left atrial free wall.

PATIENTS

72 patients with hypertrophic cardiomyopathy who had suffered sudden death or progression to end stage cardiac failure (resulting in death or heart transplantation).

MAIN OUTCOME MEASURES

The presence of scarring, atrial dilatation, and a mitral valve impact lesion were noted, and heart weight, wall thickness, per cent disarray, per cent fibrosis, and per cent small vessel disease quantitated for each heart.

RESULTS

Within an individual heart the magnitude of hypertrophy correlated with the severity of fibrosis (p = 0.006) and disarray (p = 0.0002). Overall, however, total heart weight related weakly but significantly to fibrosis (r = 0.4, p = 0.0001) and small vessel disease (r = 0.3, p = 0.03), but not to disarray. Disarray was greater in hearts with mild left ventricular hypertrophy (maximum wall thickness < 20 mm) and preserved systolic function (60.9 (26)% v 43 (20.4)% respectively, p = 0.02) and hearts without a mitral valve impact lesion (26.3% v 18.9%, p = 0.04), but was uninfluenced by sex. Fibrosis was influenced by sex (7% in male patients and 4% in female, p = 0.04), but not by the presence of an impact lesion. No relation was found between disarray, fibrosis, and small vessel disease.

CONCLUSIONS

Myocyte disarray is probably a direct response to functional or structural abnormalities of the mutated sarcomeric protein, while fibrosis and small vessel disease are secondary phenomena unrelated to disarray, but modified by factors such as left ventricular mass, sex, and perhaps local autocrine factors.

Exercise-induced ST-segment depression and systolic dysfunction in patients with nonobstructive hypertrophic cardiomyopathy

BACKGROUND

ST-segment depression is common in patients with hypertrophic cardiomyopathy (HCM). However, it is not clear whether exercise-induced ST-segment depression in patients with HCM and patent coronary arteries is associated with changes in left ventricular function.

METHODS

Left ventricular function was continuously evaluated in 53 patients with nonobstructive HCM during supine ergometer exercise with a radionuclide ventricular function monitor equipped with a cadmium telluride detector. On the basis of the ST-segment changes during exercise, the patients were divided into 2 groups: group N had no ST-segment depression, and group D had >/=0.1 mV ST-segment depression.

RESULTS

Exercise duration, blood pressure, heart rate, and rate-pressure product during exercise did not differ between the 2 groups. End-diastolic volume at rest and at peak exercise did not differ between groups D and N. In contrast, the end-systolic volume in group N decreased during exercise, whereas in group D it increased. As a result, the left ventricular ejection fraction in group D decreased from 70% +/- 7% to 59% +/- 15% (P <.0001), whereas ejection fraction in group N increased from 65% +/- 8% to 71% +/- 11% (P =.0002). There was a strong correlation between exercise-induced ST-segment depression and changes in ejection fraction from rest to peak exercise (P <.0001).

CONCLUSIONS

These results suggest that the exercise-induced ST-segment depression seen in patients with nonobstructive HCM is associated with systolic dysfunction during exercise.

Genotype-phenotype analysis in four families with mutations in beta-myosin heavy chain gene responsible for familial hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy is a genetically heterogeneous disease in which one of the most frequently implicated gene is the gene encoding the beta-myosin heavy chain. To date, more than 40 distinct mutations have been found within this gene. In order to progress on the determination of genotype-phenotype relationship, we have screened the beta-myosin heavy chain gene for mutations in 18 probands from unrelated families. We identified the mutation implicated in the disease in four families. Two of them, the Glu930 codon deletion and the Ile263Thr mutation, are reported here for the first time. The two other mutations are the Arg723Cys mutation, that was previously described in a proband as a de novo mutation, and the Arg719Trp mutation. A poor prognosis was associated with the Glu930codon deletion (mean maximal wall thickness (MWT) = 19.5 mm +/- 5) and the Arg719Trp mutation (mean MWT = 15.3 mm +/- 7), whereas a good prognosis was associated with the Arg723Cys mutation (mean MWT = 20.1 mm +/- 7). The combination of clinical and genetic characteristics of each family member suggests that prognosis is related neither to the degree of left ventricular wall thickness nor to a change in the net electrical charge of the protein. Additional family studies are needed to confirm these findings and to contribute to stratify the prognosis according to the mutation involved.

Magnitude of left ventricular hypertrophy and risk of sudden death in hypertrophic cardiomyopathy

BACKGROUND

Sudden death is known to be a possible consequence of hypertrophic cardiomyopathy. Quantification of the risk of sudden death, however, remains imprecise for most patients with this disease.

METHODS

We assessed the relation between the magnitude of left ventricular hypertrophy and mortality in 480 consecutive patients with hypertrophic cardiomyopathy. The patients were categorized into five subgroups according to maximal wall thickness: 15 mm or less, 16 to 19 mm, 20 to 24 mm, 25 to 29 mm, and 30 mm or more. Their ages ranged from 1 to 89 years (median, 47).

RESULTS

Over a mean follow-up period of 6.5 years, 65 of the 480 patients (14 percent) died: 23 suddenly, 15 of heart failure, and 27 of noncardiac causes or stroke. The risk of sudden death increased progressively and in direct relation to wall thickness (P=0.001), ranging from 0 per 1000 person-years (95 percent confidence interval, 0 to 14.4) for a wall thickness of 15 mm or less to 18.2 per 1000 person-years (95 percent confidence interval, 7.3 to 37.6) for a wall thickness of 30 mm or more and almost doubling from each wall-thickness subgroup to the next. The cumulative risk 20 years after the initial evaluation was close to zero for patients with a wall thickness of 19 mm or less but almost 40 percent for wall thicknesses of 30 mm or more. As compared with the other subgroups, patients with extreme hypertrophy were the youngest (mean age, 31 years), and most (41 of 43) had mild symptoms or no symptoms; of the 12 patients who were less than 18 years old at the initial evaluation, 5 died suddenly.

CONCLUSIONS

In hypertrophic cardiomyopathy, the magnitude of hypertrophy is directly related to the risk of sudden death and is a strong and independent predictor of prognosis. Young patients with extreme hypertrophy, even those with few or no symptoms, appear to be at substantial long-term risk and deserve consideration for interventions to prevent sudden death. The majority of patients with mild hypertrophy are at low risk and can be reassured regarding their prognosis.

Morphology and significance of the left ventricular collagen network in young patients with hypertrophic cardiomyopathy and sudden cardiac death

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a primary cardiac disease with a diverse clinical spectrum, in which many of the abnormal structural and pathophysiologic features are consequences of inappropriate left ventricular hypertrophy.

METHODS

We analyzed the amount, distribution and structure of the cardiac collagen network in transmural sections of the ventricular septum (thickness 17 to 40 mm, mean 25 mm) in 16 previously asymptomatic children and young adults with HCM (11 to 31 years of age, mean 20 years) who died suddenly. The morphologic appearance and volume fractions of interstitial (matrix) and perivascular (adventitial) collagen were analyzed with polarization microscopy and computerized videodensitometry in picrosirius red-stained sections. Findings were compared with 16 structurally normal hearts, 5 with systemic hypertension and 6 infants who died of HCM.

RESULTS

Adults and young children with HCM had an eightfold greater amount of matrix collagen compared with normal controls (14.1 +/- 8.8% vs. 1.8 +/- 1% of the tissue section; p < 0.0001), and a threefold increase compared with patients with systemic hypertension (4.5 +/- 1.3%; p < 0.001) and infants with HCM (4.0 +/- 2.4%; p < 0.001). Compared with normal controls and hypertensives, adults and young children (and infants) with HCM showed increased numbers and thickness of each collagen fiber component of the matrix (perimysial coils, pericellular weaves and struts), which were often arranged in disorganized patterns. In HCM patients, the amount of collagen was not a consequence of other clinical, demographic and morphologic disease variables.

CONCLUSIONS

Left ventricular collagen matrix in young, previously asymptomatic patients with HCM who died suddenly is morphologically abnormal and substantially increased in size. The enlarged matrix collagen compartment is present in HCM at an early age, further expands during growth, is partially responsible for increased ventricular septal thickness and likely represents a primary morphologic abnormality in this disease. These findings support the view that the complex HCM disease process is not confined to sarcomere protein abnormalities, but also involves connective tissue elements.