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

Blood Pressure Response to Treadmill Cardiopulmonary Exercise Test in Children with Normal Cardiac Anatomy and Function

OBJECTIVES

To describe blood pressure (BP) responses during cardiopulmonary exercise testing (CPET) and propose criteria for abnormal BP responses in children with normal hearts.

STUDY DESIGN

Treadmill CPET data of children <18 years with normal hearts were retrospectively analyzed to evaluate BP responses to exercise at the Children's Hospital of Michigan over an 8-year period (2011-2018).

RESULTS

Our cohort included 1085 children (boys, 59%) aged 7-17 years. Analysis of variance for systolic BP at peak exercise (peak SBP) and SBP change (Δ) showed significant age and sex effects and age-sex interaction effects (P < .01). In the multiple linear regression model (P < .001, R square 0.298, standard error of the estimate 17.15), peak SBP (mm Hg) was predicted as 132.27 + 1.37 × age (years) + (3.31 × age (years) - 31.88) × sex [boys 1, girls 0]. The following criteria for abnormal BP responses in children were proposed: hypertensive BP response was defined by peak SBP with a 90% CI upper limit of reference values based on age and sex, and blunted BP response as ΔSBP <10 mm Hg for aged 7-11 years, <20 mm Hg for boys aged 12-17 years, and ΔSBP <10 mm Hg in girls.

CONCLUSIONS

BP responses to treadmill CPET depend on age and sex in children with normal hearts. The proposed criteria for abnormal BP responses in children during CPET will need to be verified in a large pediatric cohort.

Genetics of inherited cardiomyopathies in Africa

In sub-Saharan Africa (SSA), the burden of noncommunicable diseases (NCDs) is rising disproportionately in comparison to the rest of the world, affecting urban, semi-urban and rural dwellers alike. NCDs are predicted to surpass infections like human immunodeficiency virus, tuberculosis and malaria as the leading cause of mortality in SSA over the next decade. Heart failure (HF) is the dominant form of cardiovascular disease (CVD), and a leading cause of NCD in SSA. The main causes of HF in SSA are hypertension, cardiomyopathies, rheumatic heart disease, pericardial disease, and to a lesser extent, coronary heart disease. Of these, the cardiomyopathies deserve greater attention because of the relatively poor understanding of mechanisms of disease, poor outcomes and the disproportionate impact they have on young, economically active individuals. Morphofunctionally, cardiomyopathies are classified as dilated, hypertrophic, restrictive and arrhythmogenic; regardless of classification, at least half of these are inherited forms of CVD. In this review, we summarise all studies that have investigated the incidence of cardiomyopathy across Africa, with a focus on the inherited cardiomyopathies. We also review data on the molecular genetic underpinnings of cardiomyopathy in Africa, where there is a striking lack of studies reporting on the genetics of cardiomyopathy. We highlight the impact that genetic testing, through candidate gene screening, association studies and next generation sequencing technologies such as whole exome sequencing and targeted resequencing has had on the understanding of cardiomyopathy in Africa. Finally, we emphasise the need for future studies to fill large gaps in our knowledge in relation to the genetics of inherited cardiomyopathies in Africa.

The Role of Exercise Stress Echocardiography for Determination of Subclinical Cardiac Involvement in β-Thalassemia Major

β-Thalassemia major (β-TM) patients are at increased risk for cardiovascular diseases. Determination of subclinical cardiac involvement is essential for preventive measures. Thus, we aimed to evaluate the role of stress echocardiography for identification of subclinical cardiac dysfunction in β-TM patients. In this prospective study, 45 β-TM patients who were referred for cardiac evaluation, were enrolled. Exclusion criteria included non sinus rhythm and overt cardiac disease. Stress echocardiography levels and cardiac magnetic resonance imaging (MRI) results were obtained from β-TM patients. Patients were divided into two groups of normal vs. iron overload from cardiac T2* greater or less than 20 msec, respectively. Resting and peak exercise right ventricular stroke volume (RVSV) and left ventricular SV (LVSV) were significantly lower in iron overload vs. normal β-TM patients, respectively (p value <0.05). At peak LV global longitudinal strain (GLS) and myocardial performance index (MPI) were significantly decreased and increased compared with resting in iron overload vs. normal β-TM patients, respectively (p value <0.05). There was a significant relationship between inappropriate hemodynamic response to exercise and lower age (p value = 0.032). Resting LVSV and RVSV seemed better prognosticators for iron overload than LV ejection fraction (LVEF). Decreased GLS and increased MPI at peak exercise could also predict the presence of cardiac iron overload. These measurements by stress echocardiography could be evaluated when cardiac T2* could not be determined.

A Systematically Assembled Signature of Genes to be Deep-Sequenced for Their Associations with the Blood Pressure Response to Exercise

: Background: Exercise is one of the best nonpharmacologic therapies to treat hypertension. The blood pressure (BP) response to exercise is heritable. Yet, the genetic basis for the antihypertensive effects of exercise remains elusive. Methods: To assemble a prioritized gene signature, we performed a systematic review with a series of Boolean searches in PubMed (including Medline) from earliest coverage. The inclusion criteria were human genes in major BP regulatory pathways reported to be associated with: (1) the BP response to exercise; (2) hypertension in genome-wide association studies (GWAS); (3) the BP response to pharmacotherapy; (4a) physical activity and/or obesity in GWAS; and (4b) BP, physical activity, and/or obesity in non-GWAS. Included GWAS reports disclosed the statistically significant thresholds used for multiple testing. Results: The search yielded 1422 reports. Of these, 57 trials qualified from which we extracted 11 genes under criteria 1, 18 genes under criteria 2, 28 genes under criteria 3, 27 genes under criteria 4a, and 29 genes under criteria 4b. We also included 41 genes identified from our previous work. Conclusions: Deep-sequencing the exons of this systematically assembled signature of genes represents a cost and time efficient approach to investigate the genomic basis for the antihypertensive effects of exercise.

Atomic resolution probe for allostery in the regulatory thin filament

Calcium binding and dissociation within the cardiac thin filament (CTF) is a fundamental regulator of normal contraction and relaxation. Although the disruption of this complex, allosterically mediated process has long been implicated in human disease, the precise atomic-level mechanisms remain opaque, greatly hampering the development of novel targeted therapies. To address this question, we used a fully atomistic CTF model to test both Ca(2+) binding strength and the energy required to remove Ca(2+) from the N-lobe binding site in WT and mutant troponin complexes that have been linked to genetic cardiomyopathies. This computational approach is combined with measurements of in vitro Ca(2+) dissociation rates in fully reconstituted WT and cardiac troponin T R92L and R92W thin filaments. These human disease mutations represent known substitutions at the same residue, reside at a significant distance from the calcium binding site in cardiac troponin C, and do not affect either the binding pocket affinity or EF-hand structure of the binding domain. Both have been shown to have significantly different effects on cardiac function in vivo. We now show that these mutations independently alter the interaction between the Ca(2+) ion and cardiac troponin I subunit. This interaction is a previously unidentified mechanism, in which mutations in one protein of a complex indirectly affect a third via structural and dynamic changes in a second to yield a pathogenic change in thin filament function that results in mutation-specific disease states. We can now provide atom-level insight that is potentially highly actionable in drug design.

Recent advances in the epidemiology, pathogenesis and prognosis of acute heart failure and cardiomyopathy in Africa

This review addresses recent advances in the epidemiology, pathogenesis and prognosis of acute heart failure and cardiomyopathy based on research conducted in Africa. We searched Medline/PubMed for publications on acute decompensated heart failure and cardiomyopathy in Africa for the past 5 years (ie, 1 January 2008 to 31 December 2012). This was supplemented with personal communications with colleagues from Africa working in the field. A large prospective registry has shown that acute decompensated heart failure is caused by hypertension, cardiomyopathy and rheumatic heart disease in 90% of cases, a pattern that is in contrast with the dominance of coronary artery disease in North America and Europe. Furthermore, acute heart failure is a disease of the young with a mean age of 52 years, occurs equally in men and women, and is associated with high mortality at 6 months (∼18%), which is, however, similar to that observed in non-African heart failure registries, suggesting that heart failure has a dire prognosis globally, regardless of aetiology. The molecular genetics of dilated cardiomyopathy, hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy in Africans is consistent with observations elsewhere in the world; the unique founder effects in the Afrikaner provide an opportunity for the study of genotype-phenotype correlations in large numbers of individuals with cardiomyopathy due to the same mutation. Advances in the understanding of the molecular mechanisms of peripartum cardiomyopathy have led to promising clinical trials of bromocriptine in the treatment of peripartum heart failure. The key challenges of management of heart failure are the urgent need to increase the use of proven treatments by physicians, and the control of hypertension in primary care and at the population level.

A systematic review and meta-analysis of genotype-phenotype associations in patients with hypertrophic cardiomyopathy caused by sarcomeric protein mutations

BACKGROUND

The genetic basis of familial hypertrophic cardiomyopathy (HCM) is well described, but the relation between genotype and clinical phenotype is still poorly characterised.

OBJECTIVE

To summarise and critically review the current literature on genotype-phenotype associations in patients with HCM and to perform a meta-analysis on selected clinical features.

DATA SOURCES

PubMed/Medline was searched up to January 2013. Retrieved articles were checked for additional publications.

SELECTION CRITERIA

Observational, cross-sectional and prospectively designed English language human studies that analysed the relationship between the presence of mutations in sarcomeric protein genes and clinical parameters.

DATA EXTRACTION AND ANALYSIS

The pooled analysis was confined to studies reporting on cohorts of unrelated and consecutive patients in which at least two sarcomere genes were sequenced. A random effect meta-regression model was used to determine the overall prevalence of predefined clinical features: age at presentation, gender, family history of HCM, family history of sudden cardiac death (SCD), and maximum left ventricular wall thickness (MLVWT). The I(2) statistic was used to estimate the proportion of total variability in the prevalence data attributable to the heterogeneity between studies.

RESULTS

Eighteen publications (corresponding to a total of 2459 patients) were selected for the pooled analysis. The presence of any sarcomere gene mutation was associated with a younger age at presentation (38.4 vs 46.0 years, p<0.0005), a family history of HCM (50.6% vs 23.1%, p<0.0005), a family history of SCD (27.0% vs 14.9%, p<0.0005) and greater MLVWT (21.0 vs 19.3 mm, p=0.03). There were no differences when the two most frequently affected genes, MYBPC3 and MYH7, were compared. A total of 53 family studies were also included in the review. These were characterised by pronounced variability and the majority of studies reporting on outcomes analysed small cross-sectional cohorts and were unsuitable for pooled analyses.

CONCLUSIONS

The presence of a mutation in any sarcomere gene is associated with a number of clinical features. The heterogeneous nature of the disease and the inconsistency of study design precludes the establishment of more precise genotype-phenotype relationships. Large scale studies examining the relation between genotype, disease severity, and prognosis are required.

Abnormal heart rate regulation in murine hearts with familial hypertrophic cardiomyopathy-related cardiac troponin T mutations

Mutations in cardiac troponin T (cTnT), Δ160E and R92Q, have been linked to familial hypertrophic cardiomyopathy (FHC), and some studies have indicated that these mutations can lead to a high incidence of sudden cardiac death in the relative absence of significant ventricular hypertrophy. Alterations in autonomic function have been documented in patients with hypertrophic cardiomyopathy. We hypothesize that alterations in autonomic function may contribute to mutation-specific clinical phenotypes in cTnT-related FHC. Heart rate (HR) variability (HRV) has been used to assess autonomic function from an electrocardiograph. Nontransgenic, Δ160E, or R92Q mice were implanted with radiofrequency transmitters to obtain continuous electrocardiograph recordings during 24-h baseline and 30-min recordings after β-adrenergic receptor drug injections. Although Δ160E mice did not differ from nontransgenic mice for any 24-h HRV measurements, R92Q mice had impaired HR regulation, as measured by a decrease in the SD of the R-R interval, a decrease in the low frequency-to-high frequency ratio, a decrease in normalized low frequency, and an increase in normalized high frequency. β-Adrenergic receptor density measurements and HRV analysis after drug injections did not reveal any significant differences for Δ160E or R92Q mice versus nontransgenic mice. Arrhythmia analysis revealed both an increased incidence of heart block in R92Q mice at baseline and frequency of premature ventricular contractions after isoproterenol injections in Δ160E and R92Q mice. In addition, Δ160E and R92Q mice exhibited a prolonged P duration after drug injections. Therefore, between two independent and clinically severe cTnT mutations within the same functional domain, only R92Q mice exhibited altered autonomic function, whereas both mutations demonstrated abnormalities in conduction and ventricular ectopy.

Resilience and mental health

The relationship between disease and good health has received relatively little attention in mental health. Resilience can be viewed as a defence mechanism, which enables people to thrive in the face of adversity and improving resilience may be an important target for treatment and prophylaxis. Though resilience is a widely-used concept, studies vary substantially in their definition, and measurement. Above all, there is no common underlying theoretical construct to this very heterogeneous research which makes the evaluation and comparison of findings extremely difficult. Furthermore, the varying multi-disciplinary approaches preclude meta-analysis, so that clarification of research in this area must proceed firstly by conceptual unification. We attempt to collate and classify the available research around a multi-level biopsychosocial model, theoretically and semiotically comparable to that used in describing the complex chain of events related to host resistance in infectious disease. Using this underlying construct we attempt to reorganize current knowledge around a unitary concept in order to clarify and indicate potential intervention points for increasing resilience and positive mental health.