Myocardial stiffness in patients with heart failure and a preserved ejection fraction: contributions of collagen and titin

Comprehensive Echocardiographic and Cardiac Magnetic Resonance Evaluation Differentiates Among Heart Failure With Preserved Ejection Fraction Patients, Hypertensive Patients, and Healthy Control Subjects

OBJECTIVES

The aim of this study was to investigate the utility of a comprehensive imaging protocol including echocardiography and cardiac magnetic resonance in the diagnosis and differentiation of hypertensive heart disease and heart failure with preserved ejection fraction (HFpEF).

BACKGROUND

Hypertension is present in up to 90% of patients with HFpEF and is a major etiological component. Despite current recommendations and diagnostic criteria for HFpEF, no noninvasive imaging technique has as yet shown the ability to identify any structural differences between patients with hypertensive heart disease and HFpEF.

METHODS

We conducted a prospective cross-sectional study of 112 well-characterized patients (62 with HFpEF, 22 with hypertension, and 28 healthy control subjects). All patients underwent cardiopulmonary exercise and biomarker testing and an imaging protocol including echocardiography with speckle-tracking analysis and cardiac magnetic resonance including T₁ mapping pre- and post-contrast.

RESULTS

Echocardiographic global longitudinal strain (GLS) and extracellular volume (ECV) measured by cardiac magnetic resonance were the only variables able to independently stratify among the 3 groups of patients. ECV was the best technique for differentiation between hypertensive heart disease and HFpEF (ECV area under the curve: 0.88; GLS area under the curve: 0.78; p < 0.001 for both). Using ECV, an optimal cutoff of 31.2% gave 100% sensitivity and 75% specificity. ECV was significantly higher and GLS was significantly reduced in subjects with reduced exercise capacity (lower peak oxygen consumption and higher minute ventilation-carbon dioxide production) (p < 0.001 for both ECV and GLS).

CONCLUSIONS

Both GLS and ECV are able to independently discriminate between hypertensive heart disease and HFpEF and identify patients with prognostically significant functional limitation. ECV is the best diagnostic discriminatory marker of HFpEF and could be used as a surrogate endpoint for therapeutic studies.

Relaxation and the Role of Calcium in Isolated Contracting Myocardium From Patients With Hypertensive Heart Disease and Heart Failure With Preserved Ejection Fraction

BACKGROUND

Relaxation characteristics and Ca²⁺ homeostasis have not been studied in isolated myocardium from patients with hypertensive heart disease (HHD) and heart failure with preserved ejection fraction (HFpEF). Prolonged myocardial relaxation is believed to play an important role in the pathophysiology of these conditions. In this study, we evaluated relaxation parameters, myocardial calcium (Ca²⁺), and sodium (Na⁺) handling, as well as ion transporter expression and tested the effect of Na⁺-influx inhibitors on relaxation in isolated myocardium from patients with HHD and HFpEF.

METHODS AND RESULTS

Relaxation characteristics were studied in myocardial strip preparations under physiological conditions at stimulation rates of 60 and 180 per minute. Intracellular Ca²⁺ and Na⁺ were simultaneously assessed using Fura-2 and AsanteNATRIUMGreen-2, whereas elemental analysis was used to measure total myocardial concentrations of Ca, Na, and other elements. Quantitative polymerase chain reaction was used to measure expression levels of key ion transport proteins. The lusitropic effect of Na⁺-influx inhibitors ranolazine, furosemide, and amiloride was evaluated. Myocardial left ventricular biopsies were obtained from 36 control patients, 29 HHD and 19 HHD+HFpEF. When compared with control patients, half maximal relaxation time (RT₅₀) at 60 per minute was prolonged by 13% in HHD and by 18% in HHD+HFpEF (both P<0.05). Elevated resting Ca²⁺ levels and a tachycardia-induced increase in diastolic Ca²⁺ were associated with incomplete relaxation and an increase in diastolic tension in HHD and HHD+HFpEF. Na⁺ levels were not increased, and expression levels of Ca²⁺- or Na⁺-handling proteins were not altered. Na⁺-influx inhibitors did not improve relaxation or prevent incomplete relaxation at high stimulation rates.

CONCLUSIONS

Contraction and relaxation are prolonged in isolated myocardium from patients with HHD and HHD+HFpEF. This leads to incomplete relaxation at higher rates. Elevated calcium levels in HFpEF are neither a result of an impaired Na⁺ gradient nor expression changes in key ion transporters and regulatory proteins.

Current Perspectives on Systemic Hypertension in Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a prevalent but incompletely understood syndrome. Traditional models of HFpEF pathophysiology revolve around systemic HTN and other causes of increased left ventricular afterload leading to left ventricular hypertrophy (LVH) and diastolic dysfunction. However, emerging models attribute the development of HFpEF to systemic proinflammatory changes secondary to common comorbidities which include HTN. Alterations in passive ventricular stiffness, ventricular-arterial coupling, peripheral microvascular function, systolic reserve, and chronotropic response occur. As a result, HFpEF is heterogeneous in nature, making it difficult to prescribe uniform therapies to all patients. Nonetheless, treating systemic HTN remains a cornerstone of HFpEF management. Antihypertensive therapies have been linked to LVH regression and improvement in diastolic dysfunction. However, to date, no therapies have definitive mortality benefit in HFpEF. Non-pharmacologic management for HTN, including dietary modification, exercise, and treating sleep disordered breathing, may provide some morbidity benefit in the HFpEF population. Future research is need to identify effective treatments, perhaps in more specific subgroups, and focus may need to shift from reducing mortality to improving exercise capacity and symptoms. Tailoring antihypertensive therapies to specific phenotypes of HFpEF may be an important component of this strategy.

The Effects of Guizhi Gancao Decoction on Pressure Overload-Induced Heart Failure and Posttranslational Modifications of Tubulin in Mice

Guizhi Gancao Decoction (GGD), a traditional Chinese medical recipe, has been widely used in the treatment of cardiovascular diseases in China for centuries. The present study was carried out to determine whether GGD exerts direct protective effects against pressure overload-induced heart failure. Moreover, we investigated whether GGD affects tubulin expression and posttranslational modifications. We demonstrated that GGD ameliorated TAC caused cardiac hypertrophy by gravimetric and echocardiography analysis in C57BL/6 mice. We found that GGD abrogated TAC-induced myocardium fibrosis by Masson's staining and collagen volume fraction (CVF) analysis. By using pressure-volume hemodynamic measurements, we found that GGD prevented TAC-induced cardiac systolic and diastolic dysfunction. Immunoblotting and immunofluorescent analysis revealed that GGD abrogated TAC-induced detyrosination and acetylation abnormalities on microtubules. Our present study demonstrated potential therapeutic effects of GGD against pressure overload-induced heart failure.

INDIE-HFpEF (Inorganic Nitrite Delivery to Improve Exercise Capacity in Heart Failure With Preserved Ejection Fraction): Rationale and Design

Approximately half of patients with heart failure have preserved ejection fraction. There is no proven treatment that improves outcome. The pathophysiology of heart failure with preserved ejection fraction is complex and includes left ventricular systolic and diastolic dysfunction, pulmonary vascular disease, endothelial dysfunction, and peripheral abnormalities. Multiple lines of evidence point to impaired nitric oxide (NO)-cGMP bioavailability as playing a central role in each of these abnormalities. In contrast to traditional organic nitrate therapies, an alternative strategy to restore NO-cGMP signaling is via inorganic nitrite. Inorganic nitrite, previously considered to be an inert byproduct of NO metabolism, functions as an important in vivo reservoir for NO generation, particularly under hypoxic and acidosis conditions. As such, inorganic nitrite becomes most active at times of greater need for NO signaling, as during exercise when left ventricular filling pressures and pulmonary artery pressures increase. Herein, we present the rationale and design for the INDIE-HFpEF trial (Inorganic Nitrite Delivery to Improve Exercise Capacity in Heart Failure with Preserved Ejection Fraction), which is a multicenter, randomized, double-blind, placebo-controlled cross-over study assessing the effect of inhaled inorganic nitrite on peak exercise capacity, conducted in the National Heart, Lung, and Blood Institute-sponsored Heart Failure Clinical Research Network.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02742129.

The link between exercise and titin passive stiffness

NEW FINDINGS

What is the topic of this review? This review focuses on how in vivo and molecular measurements of cardiac passive stiffness can predict exercise tolerance and how exercise training can reduce cardiac passive stiffness. What advances does it highlight? This review highlights advances in understanding the relationship between molecular (titin-based) and in vivo (left ventricular) passive stiffness, how passive stiffness modifies exercise tolerance, and how exercise training may be therapeutic for cardiac diseases with increased passive stiffness. Exercise can help alleviate the negative effects of cardiovascular disease and cardiovascular co-morbidities associated with sedentary behaviour; this may be especially true in diseases that are associated with increased left ventricular passive stiffness. In this review, we discuss the inverse relationship between exercise tolerance and cardiac passive stiffness. Passive stiffness is the physical property of cardiac muscle to produce a resistive force when stretched, which, in vivo, is measured using the left ventricular end diastolic pressure-volume relationship or is estimated using echocardiography. The giant elastic protein titin is the major contributor to passive stiffness at physiological muscle (sarcomere) lengths. Passive stiffness can be modified by altering titin isoform size or by post-translational modifications. In both human and animal models, increased left ventricular passive stiffness is associated with reduced exercise tolerance due to impaired diastolic filling, suggesting that increased passive stiffness predicts reduced exercise tolerance. At the same time, exercise training itself may induce both short- and long-term changes in titin-based passive stiffness, suggesting that exercise may be a treatment for diseases associated with increased passive stiffness. Direct modification of passive stiffness to improve exercise tolerance is a potential therapeutic approach. Titin passive stiffness itself may be a treatment target based on the recent discovery of RNA binding motif 20, which modifies titin isoform size and passive stiffness. Translating these discoveries that link exercise and left ventricular passive stiffness may provide new methods to enhance exercise tolerance and treat patients with cardiovascular disease.

Right Ventricular Myocardial Stiffness in Experimental Pulmonary Arterial Hypertension: Relative Contribution of Fibrosis and Myofibril Stiffness

Supplemental Digital Content is available in the text.

Background—

The purpose of this study was to determine the relative contribution of fibrosis-mediated and myofibril-mediated stiffness in rats with mild and severe right ventricular (RV) dysfunction.

Methods and Results—

By performing pulmonary artery banding of different diameters for 7 weeks, mild RV dysfunction (Ø=0.6 mm) and severe RV dysfunction (Ø=0.5 mm) were induced in rats. The relative contribution of fibrosis- and myofibril-mediated RV stiffness was determined in RV trabecular strips. Total myocardial stiffness was increased in trabeculae from both mild and severe RV dysfunction in comparison to controls. In severe RV dysfunction, increased RV myocardial stiffness was explained by both increased fibrosis-mediated stiffness and increased myofibril-mediated stiffness, whereas in mild RV dysfunction, only myofibril-mediated stiffness was increased in comparison to control. Histological analyses revealed that RV fibrosis gradually increased with severity of RV dysfunction, whereas the ratio of collagen I/III expression was only elevated in severe RV dysfunction. Stiffness measurements in single membrane-permeabilized RV cardiomyocytes demonstrated a gradual increase in RV myofibril stiffness, which was partially restored by protein kinase A in both mild and severe RV dysfunction. Increased expression of compliant titin isoforms was observed only in mild RV dysfunction, whereas titin phosphorylation was reduced in both mild and severe RV dysfunction.

Conclusions—

RV myocardial stiffness is increased in rats with mild and severe RV dysfunction. In mild RV dysfunction, stiffness is mainly determined by increased myofibril stiffness. In severe RV dysfunction, both myofibril- and fibrosis-mediated stiffness contribute to increased RV myocardial stiffness.

Heart Failure With Preserved Ejection Fraction and Atrial Fibrillation: Vicious Twins

Heart failure with preserved ejection fraction (HFpEF) and atrial fibrillation (AF) are age-related conditions that are increasing in prevalence, commonly coexist, and share clinical features. This review provides a practical update on the epidemiology, pathophysiology, diagnosis, and management of patients with concomitant HFpEF and AF. Epidemiological studies highlight the close and complex links between HFpEF and AF, the shared risk factors, the high AF occurrence in the natural history of HFpEF, and the independent contribution of each condition to poor outcomes. Diagnosis of HFpEF in the setting of AF is challenging because the symptoms overlap. AF is associated with changes in echocardiographic parameters and circulating natriuretic peptides that confound HFpEF diagnosis. Symptomatic improvement with diuretic therapy supports the presence of HFpEF in patients with concomitant AF. Important knowledge gaps need to be addressed by a multidisciplinary and translational research approach to develop novel therapies that can improve prognosis.

Functional Status, Pulmonary Artery Pressure, and Clinical Outcomes in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Patients with heart failure with preserved ejection fraction have functional impairment resulting in reduced quality of life. Specific pathological mechanisms underlying symptoms have not yet been defined.

OBJECTIVES

The aim of this study was to identify hemodynamic and other patient-related variables that are associated with New York Heart Association (NYHA) functional class and to analyze functional class in perspective with other clinical, laboratory, imaging, and hemodynamic parameters with respect to its influence on outcomes.

METHODS

Between January 2011 and February 2015, 193 patients with confirmed heart failure with preserved ejection fraction were enrolled.

RESULTS

Those in more advanced NYHA functional classes (III and IV; n = 136) were older (p = 0.008), had higher body mass indexes (p = 0.004), and had higher levels of N-terminal pro-brain natriuretic peptide (p = 0.001) compared with less symptomatic patients (NYHA class II; n = 57). Furthermore, parameters reflecting left ventricular diastolic dysfunction were more pronounced in advanced NYHA classes (early mitral inflow velocity/early diastolic mitral annular velocity; p = 0.023) as well as parameters reflecting right ventricular afterload (diastolic pulmonary artery pressure; p < 0.001). By multivariate regression analysis, age (p = 0.007), body mass index (p = 0.002), N-terminal pro-brain natriuretic peptide (p < 0.001), early mitral inflow velocity/mitral peak velocity of late filling (p = 0.031), and diastolic pulmonary artery pressure (p < 0.001) were independently associated with advanced NYHA class. After 21.9 months of follow-up, 64 patients (33.2%) reached the combined endpoint, defined as hospitalization for heart failure and/or cardiac death. By multivariate Cox analysis, NYHA functional class was independently associated with outcome (hazard ratio: 2.133; p = 0.040), as well as N-terminal pro-brain natriuretic peptide (hazard ratio: 1.655; p < 0.001) and impaired right ventricular function (hazard ratio: 2.360; p = 0.001).

CONCLUSIONS

Symptoms of breathlessness in patients with heart failure with preserved ejection fraction are multifactorial and largely related to body mass index, left ventricular diastolic function, and the pulmonary vasculature. Clinically meaningful therapeutic interventions should target body weight, left ventricular stiffness, and concomitant pulmonary vascular disease.

[Myocardial fibrosis: Current aspects of the problem]

Fibrosis is one of the main components in the progression of most cardiovascular diseases, including coronary heart disease, by causing structural changes in the myocardium and vascular wall. The quantitative and qualitative characteristics of fibrosis of the myocardium are responsible for decreasing its elastic properties, developing diastolic dysfunction, impairing myocardial contractility, developing systolic dysfunction and cardiac arrhythmias, and worsening coronary blood flow in patients with heart failure of different etiologies. The important aspect of studying fibrosis is not only its interpretation as a model of the typical pathological process, but also its consideration as a systemic lesion of various organs and tissues. At the same time, the identification of myocardial fibrosis biomarkers that are available for their determination in circulating blood is of particular interest. Since there was evidence for the role of fibrosis in developing dysfunction of various organs and ensuring the systematicity of most diseases, especially at their development stages, the process of fibrosis came to be regarded as a promising therapeutic target. It is relevant to further investigate myocardial fibrosis, which is aimed at increasing the efficiency of its diagnosis and predicting its course and pathogenetically sound therapy.

α-B Crystallin Reverses High Diastolic Stiffness of Failing Human Cardiomyocytes

BACKGROUND

Cardiomyocytes with a less distensible titin and interstitial collagen contribute to the high diastolic stiffness of failing myocardium. Their relative contributions and mechanisms underlying loss of titin distensibility were assessed in failing human hearts.

METHODS AND RESULTS

Left ventricular tissue was procured in patients with aortic stenosis (AS, n=9) and dilated cardiomyopathy (DCM, n=6). Explanted donor hearts (n=8) served as controls. Stretches were performed in myocardial strips, and an extraction protocol differentiated between passive tension (F_passive) attributable to cardiomyocytes or to collagen. F_passive-cardiomyocytes was higher in AS and DCM at shorter muscle lengths, whereas F_passive-collagen was higher in AS at longer muscle lengths and in DCM at shorter and longer muscle lengths. Cardiomyocytes were stretched to investigate titin distensibility. Cardiomyocytes were incubated with alkaline phosphatase, subsequently reassessed after a period of prestretch and finally treated with the heat shock protein α-B crystallin. Alkaline phosphatase shifted the F_passive-sarcomere length relation upward only in donor. Prestretch shifted the F_passive-sarcomere length relation further upward in donor and upward in AS and DCM. α-B crystallin shifted the F_passive-sarcomere length relation downward to baseline in donor and to lower than baseline in AS and DCM. In failing myocardium, confocal laser microscopy revealed α-B crystallin in subsarcolemmal aggresomes.

CONCLUSIONS

High cardiomyocyte stiffness contributed to stiffness of failing human myocardium because of reduced titin distensibility. The latter resulted from an absent stiffness-lowering effect of baseline phosphorylation and from titin aggregation. High cardiomyocyte stiffness was corrected by α-B crystallin probably through relief of titin aggregation.

Employing Extracellular Volume Cardiovascular Magnetic Resonance Measures of Myocardial Fibrosis to Foster Novel Therapeutics

Quantifying myocardial fibrosis (MF) with myocardial extracellular volume measures acquired during cardiovascular magnetic resonance promises to transform clinical care by advancing pathophysiologic understanding and fostering novel therapeutics. Extracellular volume quantifies MF by measuring the extracellular compartment depicted by the myocardial uptake of contrast relative to plasma. MF is a key domain of dysfunctional but viable myocardium among others (eg, microvascular dysfunction and cardiomyocyte/mitochondrial dysfunction). Although anatomically distinct, these domains may functionally interact. MF represents pathological remodeling in the heart associated with cardiac dysfunction and adverse outcomes likely mediated by interactions with the microvasculature and the cardiomyocyte. Reversal of MF improves key measures of cardiac dysfunction, so reversal of MF represents a likely mechanism for improved outcomes. Instead of characterizing the myocardium as homogenous tissue and using important yet still generic descriptors, such as thickness (hypertrophy) and function (diastolic or systolic), which lack mechanistic specificity, paradigms of cardiac disease have evolved to conceptualize myocardial disease and patient vulnerability based on the extent of disease involving its various compartments. Specifying myocardial compartmental involvement may then implicate cellular/molecular disease pathways for treatment and targeted pharmaceutical development and above all highlight the role of the cardiac-specific pathology in heart failure among myriad other changes in the heart and beyond. The cardiology community now requires phase 2 and 3 clinical trials to examine strategies for the regression/prevention of MF and eventually biomarkers to identify MF without reliance on cardiovascular magnetic resonance. It seems likely that efficacious antifibrotic therapy will improve outcomes, but definitive data are needed.

Dual Endothelin-A/Endothelin-B Receptor Blockade and Cardiac Remodeling in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Despite the increasing prevalence of heart failure with preserved ejection fraction (HFpEF) in humans, there remains no evidence-based therapies for HFpEF. Endothelin-1 (ET-1) antagonists are a possibility because elevated ET-1 levels are associated with adverse cardiovascular effects, such as arterial and pulmonary vasoconstriction, impaired left ventricular (LV) relaxation, and stimulation of LV hypertrophy. LV hypertrophy is a common phenotype in HFpEF, particularly when associated with hypertension.

METHODS AND RESULTS

In the present study, we found that ET-1 levels were significantly elevated in patients with chronic stable HFpEF. We then sought to investigate the effects of chronic macitentan, a dual ET-A/ET-B receptor antagonist, on cardiac structure and function in a murine model of HFpEF induced by chronic aldosterone infusion. Macitentan caused LV hypertrophy regression independent of blood pressure changes in HFpEF. Although macitentan did not modulate diastolic dysfunction in HFpEF, it significantly reduced wall thickness and relative wall thickness after 2 weeks of therapy. In vitro studies showed that macitentan decreased the aldosterone-induced cardiomyocyte hypertrophy. These changes were mediated by a reduction in the expression of cardiac myocyte enhancer factor 2a. Moreover, macitentan improved adverse cardiac remodeling, by reducing the stiffer cardiac collagen I and titin n2b expression in the left ventricle of mice with HFpEF.

CONCLUSIONS

These findings indicate that dual ET-A/ET-B receptor inhibition improves HFpEF by abrogating adverse cardiac remodeling via antihypertrophic mechanisms and by reducing stiffness. Additional studies are needed to explore the role of dual ET-1 receptor antagonists in patients with HFpEF.

Titin-Truncating Variants Increase the Risk of Cardiovascular Death in Patients With Hypertrophic Cardiomyopathy

BACKGROUND

Titin-truncating variants (TTNtv) have been detected in a variety of cardiomyopathies and represent the most common cause of dilated cardiomyopathy. However, their significance in hypertrophic cardiomyopathy (HCM) is still unclear.

METHODS

The titin gene (TTN) was sequenced for truncating variants in a cohort of 529 Chinese patients with HCM and 307 healthy controls. Baseline and follow-up clinical data (for 4.7 ± 3.2 years) from these patients were obtained.

RESULTS

We identified 13 and 8 TTNtv in patients with HCM (13 of 529 [2.5%]) and controls (8 of 307 [2.6%]), respectively. The prevalence of TTNtv in patients with HCM and in healthy controls was comparable (P = 0.895). There were no significant differences in baseline characteristics between patients with and those without TTNtv. However, during follow-up, patients with TTNtv (3 of 13 [23.1%]) were more likely to experience cardiovascular death compared with those without TTNtv (39 of 516 [7.6%]) [adjusted hazard ratio, 6.88; 95% confidence interval, 2.04-23.20; P = 0.002).

CONCLUSIONS

Our study suggests that TTNtv might be a genetic modifier of HCM and confer an increased risk for cardiovascular death.

Experimental cardiac radiation exposure induces ventricular diastolic dysfunction with preserved ejection fraction

Breast cancer radiotherapy increases the risk of heart failure with preserved ejection fraction (HFpEF). Cardiomyocytes are highly radioresistant, but radiation specifically affects coronary microvascular endothelial cells, with subsequent microvascular inflammation and rarefaction. The effects of radiation on left ventricular (LV) diastolic function are poorly characterized. We hypothesized that cardiac radiation exposure may result in diastolic dysfunction without reduced EF. Global cardiac expression of the sodium-iodide symporter (NIS) was induced by cardiotropic gene (adeno-associated virus serotype 9) delivery to 5-wk-old rats. SPECT/CT (¹²⁵I) measurement of cardiac iodine uptake allowed calculation of the ¹³¹I doses needed to deliver 10- or 20-Gy cardiac radiation at 10 wk of age. Radiated (Rad; 10 or 20 Gy) and control rats were studied at 30 wk of age. Body weight, blood pressure, and heart rate were similar in control and Rad rats. Compared with control rats, Rad rats had impaired exercise capacity, increased LV diastolic stiffness, impaired LV relaxation, and elevated filling pressures but similar LV volume, EF, end-systolic elastance, preload recruitable stroke work, and peak +dP/dt Pathology revealed reduced microvascular density, mild concentric cardiomyocyte hypertrophy, and increased LV fibrosis in Rad rats compared with control rats. In the Rad myocardium, oxidative stress was increased and in vivo PKG activity was decreased. Experimental cardiac radiation exposure resulted in diastolic dysfunction without reduced EF. These data provide insight into the association between cardiac radiation exposure and HFpEF risk and lend further support for the importance of inflammation-related coronary microvascular compromise in HFpEF.NEW & NOTEWORTHY Cardiac radiation exposure during radiotherapy increases the risk of heart failure with preserved ejection fraction. In a novel rodent model, cardiac radiation exposure resulted in coronary microvascular rarefaction, oxidative stress, impaired PKG signaling, myocardial fibrosis, mild cardiomyocyte hypertrophy, left ventricular diastolic dysfunction, and elevated left ventricular filling pressures despite preserved ejection fraction.

Increased Left Ventricular Diastolic Stiffness Is Associated With Heart Failure Symptoms in Aortic Stenosis Patients With Preserved Ejection Fraction

BACKGROUND

Clinical risk factors associated with heart failure (HF) symptoms in aortic stenosis (AS) patients with preserved ejection fraction (EF) have not been fully identified. We hypothesized that left ventricular (LV) diastolic stiffness is associated with HF symptoms in patients with AS.

METHODS AND RESULTS

We retrospectively evaluated 275 patients with at least moderate AS (aortic valve area <1.5 cm²) and preserved EF (≥50%). LV diastolic stiffness was evaluated with the use of echocardiographic parameters, diastolic wall strain (DWS, a measure of LV wall stiffness), and K_LV (a marker of LV chamber stiffness). There were 69 patients with HF. Patients with HF were older, were more likely to be African American, had a higher body mass index, and had more hypertension and coronary artery disease (P < .05 for all). Aortic valve area index and mean pressure gradient across the aortic valve were not different between patients with and without HF. Despite similar echocardiographic parameters of AS severity, patients with HF had stiffer LV (DWS 0.21 ± 0.06 vs 0.25 ± 0.06 [P < .01], K_LV 0.17 ± 0.11 vs 0.13 ± 0.08 [P < .01]). Logistic regression analyses revealed that after adjusting for age, race, body mass index, history of hypertension, and coronary artery disease, LV diastolic stiffness parameters remained significantly associated with HF symptoms.

CONCLUSIONS

LV diastolic stiffness is independently associated with HF in AS patients with preserved EF.

Effect of exercise on passive myocardial stiffness in mice with diastolic dysfunction

Heart failure with preserved ejection fraction (HFpEF) is a complex syndrome, characterized by increased diastolic stiffness and a preserved ejection fraction, with no effective treatment options. Here we studied the therapeutic potential of exercise for improving diastolic function in a mouse model with HFpEF-like symptoms, the TtnΔIAjxn mouse model. TtnΔIAjxn mice have increased diastolic stiffness and reduced exercise tolerance, mimicking aspects of HFpEF observed in patients. We investigated the effect of free-wheel running exercise on diastolic function. Mechanical studies on cardiac muscle strips from the LV free wall revealed that both TtnΔIAjxn and wildtype (WT) exercised mice had a reduction in passive stiffness, relative to sedentary controls. In both genotypes, this reduction is due to an increase in the compliance of titin whereas ECM-based stiffness was unaffected. Phosphorylation of titin's PEVK and N2B spring elements were assayed with phospho-site specific antibodies. Exercised mice had decreased PEVK phosphorylation and increased N2B phosphorylation both of which are predicted to contribute to the increased compliance of titin. Since exercise lowers the heart rate we examined whether reduction in heart rate per se can improve passive stiffness by administering the heart-rate-lowering drug ivabradine. Ivabradine lowered heart rate in our study but it did not affect passive tension, in neither WT nor TtnΔIAjxn mice. We conclude that exercise is beneficial for decreasing passive stiffness and that it involves beneficial alterations in titin phosphorylation.

Heart Failure with Preserved Ejection Fraction: Diagnosis and Management

Heart failure with preserved ejection fraction (HFpEF) is a prevalent condition with substantial individual and societal burden. In this article, we review the current status of understanding of HFpEF, focusing on the challenges and uncertainties regarding diagnosis and treatment. We then propose a scientific roadmap to facilitate research that may translate into improved clinical outcomes.

Cardiovascular consequences of metabolic syndrome

The metabolic syndrome (MetS) is defined as the concurrence of obesity-associated cardiovascular risk factors including abdominal obesity, impaired glucose tolerance, hypertriglyceridemia, decreased HDL cholesterol, and/or hypertension. Earlier conceptualizations of the MetS focused on insulin resistance as a core feature, and it is clearly coincident with the above list of features. Each component of the MetS is an independent risk factor for cardiovascular disease and the combination of these risk factors elevates rates and severity of cardiovascular disease, related to a spectrum of cardiovascular conditions including microvascular dysfunction, coronary atherosclerosis and calcification, cardiac dysfunction, myocardial infarction, and heart failure. While advances in understanding the etiology and consequences of this complex disorder have been made, the underlying pathophysiological mechanisms remain incompletely understood, and it is unclear how these concurrent risk factors conspire to produce the variety of obesity-associated adverse cardiovascular diseases. In this review, we highlight current knowledge regarding the pathophysiological consequences of obesity and the MetS on cardiovascular function and disease, including considerations of potential physiological and molecular mechanisms that may contribute to these adverse outcomes.

Pharmacological Strategies to Retard Cardiovascular Aging

Aging is the major risk factor for cardiovascular diseases, which are the leading cause of death in the United States. Traditionally, the effort to prevent cardiovascular disease has been focused on addressing the conventional risk factors, including hypertension, hyperglycemia, hypercholesterolemia, and high circulating levels of triglycerides. However, recent preclinical studies have identified new approaches to combat cardiovascular disease. Calorie restriction has been reproducibly shown to prolong lifespan in various experimental model animals. This has led to the development of calorie restriction mimetics and other pharmacological interventions capable to delay age-related diseases. In this review, we will address the mechanistic effects of aging per se on the cardiovascular system and focus on the prolongevity benefits of various therapeutic strategies that support cardiovascular health.

Role of Biomarkers for the Prevention, Assessment, and Management of Heart Failure: A Scientific Statement From the American Heart Association

BACKGROUND AND PURPOSE

Natriuretic peptides have led the way as a diagnostic and prognostic tool for the diagnosis and management of heart failure (HF). More recent evidence suggests that natriuretic peptides along with the next generation of biomarkers may provide added value to medical management, which could potentially lower risk of mortality and readmissions. The purpose of this scientific statement is to summarize the existing literature and to provide guidance for the utility of currently available biomarkers.

METHODS

The writing group used systematic literature reviews, published translational and clinical studies, clinical practice guidelines, and expert opinion/statements to summarize existing evidence and to identify areas of inadequacy requiring future research. The panel reviewed the most relevant adult medical literature excluding routine laboratory tests using MEDLINE, EMBASE, and Web of Science through December 2016. The document is organized and classified according to the American Heart Association to provide specific suggestions, considerations, or contemporary clinical practice recommendations.

RESULTS

A number of biomarkers associated with HF are well recognized, and measuring their concentrations in circulation can be a convenient and noninvasive approach to provide important information about disease severity and helps in the detection, diagnosis, prognosis, and management of HF. These include natriuretic peptides, soluble suppressor of tumorgenicity 2, highly sensitive troponin, galectin-3, midregional proadrenomedullin, cystatin-C, interleukin-6, procalcitonin, and others. There is a need to further evaluate existing and novel markers for guiding therapy and to summarize their data in a standardized format to improve communication among researchers and practitioners.

CONCLUSIONS

HF is a complex syndrome involving diverse pathways and pathological processes that can manifest in circulation as biomarkers. A number of such biomarkers are now clinically available, and monitoring their concentrations in blood not only can provide the clinician information about the diagnosis and severity of HF but also can improve prognostication and treatment strategies.

Tampering with springs: phosphorylation of titin affecting the mechanical function of cardiomyocytes

Reversible post-translational modifications of various cardiac proteins regulate the mechanical properties of the cardiomyocytes and thus modulate the contractile performance of the heart. The giant protein titin forms a continuous filament network in the sarcomeres of striated muscle cells, where it determines passive tension development and modulates active contraction. These mechanical properties of titin are altered through post-translational modifications, particularly phosphorylation. Titin contains hundreds of potential phosphorylation sites, the functional relevance of which is only beginning to emerge. Here, we provide a state-of-the-art summary of the phosphorylation sites in titin, with a particular focus on the elastic titin spring segment. We discuss how phosphorylation at specific amino acids can reduce or increase the stretch-induced spring force of titin, depending on where the spring region is phosphorylated. We also review which protein kinases phosphorylate titin and how this phosphorylation affects titin-based passive tension in cardiomyocytes. A comprehensive overview is provided of studies that have measured altered titin phosphorylation and titin-based passive tension in myocardial samples from human heart failure patients and animal models of heart disease. As our understanding of the broader implications of phosphorylation in titin progresses, this knowledge could be used to design targeted interventions aimed at reducing pathologically increased titin stiffness in patients with stiff hearts.

Reversal of maladaptive fibrosis and compromised ventricular function in the pressure overloaded heart by a caveolin-1 surrogate peptide

Chronic ventricular pressure overload (PO) results in congestive heart failure (CHF) in which myocardial fibrosis develops in concert with ventricular dysfunction. Caveolin-1 is important in fibrosis in various tissues due to its decreased expression in fibroblasts and monocytes. The profibrotic effects of low caveolin-1 can be blocked with the caveolin-1 scaffolding domain peptide (CSD, a caveolin-1 surrogate) using both mouse models and human cells. We have studied the beneficial effects of CSD on mice in which PO was induced by trans-aortic constriction (TAC). Beneficial effects observed in TAC mice receiving CSD injections daily included: improved ventricular function (increased ejection fraction, stroke volume, and cardiac output; reduced wall thickness); decreased collagen I, collagen chaperone HSP47, fibronectin, and CTGF levels; decreased activation of non-receptor tyrosine kinases Pyk2 and Src; and decreased activation of eNOS. To determine the source of cells that contribute to fibrosis in CHF, flow cytometric studies were performed that suggested that myofibroblasts in the heart are in large part bone marrow-derived. Two CD45+ cell populations were observed. One (Zone 1) contained CD45+/HSP47-/macrophage marker+ cells (macrophages). The second (Zone 2) contained CD45^moderate/HSP47+/macrophage marker- cells often defined as fibrocytes. TAC increased the number of cells in Zones 1 and 2 and the level of HSP47 in Zone 2. These studies are a first step in elucidating the mechanism of action of CSD in heart fibrosis and promoting the development of CSD as a novel treatment to reduce fibrosis and improve ventricular function in CHF patients.

Diagnostic and Prognostic Value of CMR T1-Mapping in Patients With Heart Failure and Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) presents a major challenge in modern cardiology. Although this syndrome is of increasing prevalence and is associated with unfavorable outcomes, treatment trials have failed to establish effective therapies. Currently, solutions to this dilemma are being investigated, including categorizing and characterizing patients more diversely to individualize treatment. In this regard, new imaging techniques might provide important information. Diastolic dysfunction is a diagnostic and pathophysiological cornerstone in HFpEF and is believed to be caused by systemic inflammation with the development of interstitial myocardial fibrosis and myocardial stiffening. Cardiac magnetic resonance (CMR) T₁-mapping is a novel tool, which allows noninvasive quantification of the extracellular space and diffuse myocardial fibrosis. This review provides an overview of the potential of myocardial tissue characterization with CMR T₁ mapping in HFpEF patients, outlining its diagnostic and prognostic implications and discussing future directions. We conclude that CMR T₁ mapping is potentially an effective tool for patient characterization in large-scale epidemiological, diagnostic, and therapeutic HFpEF trials beyond traditional imaging parameters.

Role of Myocardial Collagen in Severe Aortic Stenosis With Preserved Ejection Fraction and Symptoms of Heart Failure

INTRODUCTION AND OBJECTIVES

We investigated the anatomical localization, biomechanical properties, and molecular phenotype of myocardial collagen tissue in 40 patients with severe aortic stenosis with preserved ejection fraction and symptoms of heart failure.

METHODS

Two transmural biopsies were taken from the left ventricular free wall. Mysial and nonmysial regions of the collagen network were analyzed. Myocardial collagen volume fraction (CVF) was measured by picrosirius red staining. Young's elastic modulus (YEM) was measured by atomic force microscopy in decellularized slices to assess stiffness. Collagen types I and III were measured as C_IVF and C_IIIVF, respectively, by confocal microscopy in areas with YEM evaluation.

RESULTS

Compared with controls, patients exhibited increased mysial and nonmysial CVF and nonmysial:mysial CVF ratio (P < .05). In patients, nonmysial CVF (r = 0.330; P = .046) and the nonmysial:mysial CVF ratio (r = 0.419; P = .012) were directly correlated with the ratio of maximal early transmitral flow velocity in diastole to early mitral annulus velocity in diastole. Both the C_IVF:C_IIIVF ratio and YEM were increased (P ≤ .001) in nonmysial regions compared with mysial regions in patients, with a direct correlation (r = 0.895; P < .001) between them.

CONCLUSIONS

These findings suggest that, in patients with severe aortic stenosis with preserved ejection fraction and symptoms of heart failure, diastolic dysfunction is associated with increased nonmysial deposition of collagen, predominantly type I, resulting in increased extracellular matrix stiffness. Therefore, the characteristics of collagen tissue may contribute to diastolic dysfunction in these patients.

Mechanisms underlying the cardiac antifibrotic effects of losartan metabolites

Excessive myocardial collagen deposition and cross-linking (CCL), a process regulated by lysyl oxidase (LOX), determines left ventricular (LV) stiffness and dysfunction. The angiotensin II antagonist losartan, metabolized to the EXP3179 and EXP3174 metabolites, reduces myocardial fibrosis and LV stiffness in hypertensive patients. Our aim was to investigate the differential influence of losartan metabolites on myocardial LOX and CCL in an experimental model of hypertension with myocardial fibrosis, and whether EXP3179 and EXP3174 modify LOX expression and activity in fibroblasts. In rats treated with N^G-nitro-L-arginine methyl ester (L-NAME), administration of EXP3179 fully prevented LOX, CCL and connective tissue growth factor (CTGF) increase, as well as fibrosis, without normalization of blood pressure (BP). In contrast, administration of EXP3174 normalized BP and attenuated fibrosis but did not modify LOX, CCL and CTGF. In TGF-β₁-stimulated fibroblasts, EXP3179 inhibited CTGF and LOX expression and activity with lower IC50 values than EXP3174. Our results indicate that, despite a lower antihypertensive effect, EXP3179 shows higher anti-fibrotic efficacy than EXP3174, likely through its ability to prevent the excess of LOX and CCL. It is suggested that the anti-fibrotic effect of EXP3179 may be partially mediated by the blockade of CTGF-induced LOX in fibroblasts.

Targeting Obesity and Diabetes to Treat Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a major unmet medical need that is characterized by the presence of multiple cardiovascular and non-cardiovascular comorbidities. Foremost among these comorbidities are obesity and diabetes, which are not only risk factors for the development of HFpEF, but worsen symptoms and outcome. Coronary microvascular inflammation with endothelial dysfunction is a common denominator among HFpEF, obesity, and diabetes that likely explains at least in part the etiology of HFpEF and its synergistic relationship with obesity and diabetes. Thus, pharmacological strategies to supplement nitric oxide and subsequent cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) signaling may have therapeutic promise. Other potential approaches include exercise and lifestyle modifications, as well as targeting endothelial cell mineralocorticoid receptors, non-coding RNAs, sodium glucose transporter 2 inhibitors, and enhancers of natriuretic peptide protective NO-independent cGMP-initiated and alternative signaling, such as LCZ696 and phosphodiesterase-9 inhibitors. Additionally, understanding the role of adipokines in HFpEF may lead to new treatments. Identifying novel drug targets based on the shared underlying microvascular disease process may improve the quality of life and lifespan of those afflicted with both HFpEF and obesity or diabetes, or even prevent its occurrence.

Traditional Chinese Medication Qiliqiangxin Protects Against Cardiac Remodeling and Dysfunction in Spontaneously Hypertensive Rats

Qiliqiangxin (QLQX), a traditional Chinese herbs medication, exerted protective effect in chronic heart failure patients in a multicenter randomized double-blind study. QLQX has also been found to improve cardiac function and reduce cardiac fibrosis in spontaneously hypertension animal model. However, the effect of longterm treatment with QLQX in such a condition and the related molecular mechanisms remain largely unknown. In the present study, thirteen-week-old spontaneously hypertensive rats (SHRs) were treated by daily intragastric administration of QLQX or saline for one year. Echocardiography, electron microscopy, and Masson's trichrome staining were used to determine cardiac function, mitochondria ultrastructure, and cardiac fibrosis, respectively. Quantitative reverse transcription polymerase chain reactions (qRT-PCRs) and Western blotting were used to determine gene expressions. We found that QLQX significantly improved cardiac function and reduced gene markers of pathological hypertrophy including ANP, BNP, and Myh7. QLQX also attenuated cardiac fibrosis and apoptosis in SHRs as evidenced by downregulation of α-SMA, collagen I, collagen III, and TGF-β expressions and reduction of Bax to Bcl-2 ratio. Moreover, the damage of mitochondrial ultrastructure was greatly improved and the reduction of PPAR-α, PPAR-γ, and PGC-1α expression levels was significantly restored in SHRs by treatment with QLQX. In conclusion, longterm treatment with QLQX protects against cardiac remodeling and dysfunction in hypertension by increasing PPARs and PGC-1α.

Deliberations on Diastolic Heart Failure

Studies of left ventricular diastolic dysfunction and diastolic heart failure (DHF), published during the past 4 decades, include a prodigious number and wide variety of research efforts. This review report considers some of the historical literature and incorporates more recent information supporting the idea that patients with DHF constitute a subgroup of the heterogeneous population of patients with heart failure and a preserved ejection fraction. Clinical investigation, particularly therapeutic trials, should be directed at specific targets within the population of interest, not at the broad heart failure with preserved ejection fraction population. To accomplish this, it is important to stipulate criteria for the diagnosis of DHF and to limit our attention to specific subgroups or phenotypes.

ω3-Polyunsaturated fatty acids for heart failure: Effects of dose on efficacy and novel signaling through free fatty acid receptor 4

Heart failure (HF) affects 5.7 million in the U.S., and despite well-established pharmacologic therapy, the 5-year mortality rate remains near 50%. Furthermore, the mortality rate for HF has not declined in years, highlighting the need for new therapeutic options. Omega-3 polyunsaturated fatty acids (ω3-PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are important regulators of cardiovascular health. However, questions of efficacy and mechanism of action have made the use of ω3-PUFAs in all cardiovascular disease (CVD) controversial. Here, we review recent studies in animal models of HF indicating that ω3-PUFAs, particularly EPA, are cardioprotective, with the results indicating a threshold for efficacy. We also examine clinical studies suggesting that ω3-PUFAs improve outcomes in patients with HF. Due to the relatively small number of clinical studies of ω3-PUFAs in HF, we discuss EPA concentration-dependency on outcomes in clinical trials of CVD to gain insight into the perceived questionable efficacy of ω3-PUFAs clinically, with the results again indicating a threshold for efficacy. Ultimately, we suggest that the main failing of ω3-PUFAs in clinical trials might be a failure to reach a therapeutically effective concentration. We also examine mechanistic studies suggesting that ω3-PUFAs signal through free fatty acid receptor 4 (Ffar4), a G-protein coupled receptor (GPR) for long-chain fatty acids (FA), thereby identifying an entirely novel mechanism of action for ω3-PUFA mediated cardioprotection. Finally, based on mechanistic animal studies suggesting that EPA prevents interstitial fibrosis and diastolic dysfunction, we speculate about a potential benefit for EPA-Ffar4 signaling in heart failure preserved with ejection fraction.

Diastolic Left Ventricular Function in Relation to Urinary and Serum Collagen Biomarkers in a General Population

Current knowledge on the pathogenesis of diastolic heart failure predominantly rests on case-control studies involving symptomatic patients with preserved ejection fraction and relying on invasive diagnostic procedures including endomyocardial biopsy. Our objective was to gain insight in serum and urinary biomarkers reflecting collagen turnover and associated with asymptomatic diastolic LV dysfunction. We randomly recruited 782 Flemish (51.3% women; 50.5 years). We assessed diastolic LV function from the early and late diastolic peak velocities of the transmitral blood flow and of the mitral annulus. By sequencing urinary peptides, we identified 70 urinary collagen fragments. In serum, we measured carboxyterminal propeptide of procollagen type 1 (PICP) as marker of collagen I synthesis and tissue inhibitor of matrix metalloproteinase type 1 (TIMP-1), an inhibitor of collagen-degrading enzymes. In multivariable-adjusted analyses with Bonferroni correction, we expressed effect sizes per 1-SD in urinary collagen I (uCI) or collagen III (uCIII) fragments. In relation to uCI fragments, e’ decreased by 0.183 cm/s (95% confidence interval, 0.017 to 0.350; p = 0.025), whereas E/e’ increased by 0.210 (0.067 to 0.353; p = 0.0012). E/e’ decreased with uCIII by 0.168 (0.021 to 0.316; p = 0.018). Based on age-specific echocardiographic criteria, 182 participants (23.3%) had subclinical diastolic LV dysfunction. Partial least squares discriminant analysis contrasting normal vs. diastolic LV dysfunction confirmed the aforementioned associations with the uCI and uCIII fragments. PICP and TIMP-1 increased in relation to uCI (p<0.0001), whereas these serum markers decreased with uCIII (p≤0.0006). Diastolic LV dysfunction was associated with higher levels of TIMP-1 (653 vs. 696 ng/mL; p = 0.013). In a general population, the non-invasively assessed diastolic LV function correlated inversely with uCI and serum markers of collagen I deposition, but positively with uCIII. These observations generalise previous studies in patients to randomly recruited people, in whom diastolic LV function ranged from normal to subclinical impairment, but did not encompass overt diastolic heart failure.

Cardiac extracellular matrix is associated with adverse outcome in patients with chronic heart failure

AIMS

Accumulation of extracellular matrix (ECM) is known to play a crucial role in the pathophysiology of heart failure (HF). However, its prognostic relevance is poorly investigated.

METHODS AND RESULTS

A total of 73 HF patients who underwent LV endomyocardial biopsy were enrolled in our study. ECM area was quantified by TissueFAXS and ImageJ software. Patients were followed-up at 6-month intervals. The study endpoint was defined as hospitalization for a cardiac reason and/or cardiac death. Furthermore, the influence of the ECM on invasively measured haemodynamic parameters was tested. During a median follow-up period of 9.0 months, 34 patients (46.6%) reached the combined endpoint. Median ECM area was 30.5%. Patients with ECM area ≥30.5% experienced significantly more events (67.6% vs. 25.0%, P < 0.001) in comparison with patients with an ECM area <30.5%. ECM area was independently associated with outcome in the total HF cohort [hazard ratio (HR) 1.041, 95% confidence interval (CI) 1.017-1.066, P = 0.001] as well as in HF patients with preserved (HR 1.079, 95% CI 1.001-1.163, P =0 .046) or reduced ejection fraction (HR 1.149, 95% CI 1.036-1.275, P = 0.009). Positive correlations were found between ECM area and LV end-diastolic pressure (P = 0.021, R = 0.303), pulmonary artery wedge pressure (P = 0.042, R = 0.249), mean pulmonary arterial pressure (P = 0.035, R = 0.258), as well as right atrial pressure (P = 0.003, R = 0.353).

CONCLUSION

ECM area within the LV myocardium correlates with left and right heart haemodynamics and is associated with clinical course in various non-ischaemic HF types.

Left Atrial Remodeling and Atrioventricular Coupling in a Canine Model of Early Heart Failure With Preserved Ejection Fraction

BACKGROUND

Left atrial (LA) compliance and contractility influence left ventricular stroke volume. We hypothesized that diminished LA compliance and contractile function occur early during the development of heart failure with preserved ejection fraction (HFpEF) and impair overall cardiac performance.

METHODS AND RESULTS

Cardiac magnetic resonance imaging, echocardiography, left ventricular and LA pressure-volume studies, and tissue analyses were performed in a model of early HFpEF (elderly dogs, renal wrap-induced hypertension, exogenous aldosterone; n=9) and young control dogs (sham surgery; n=13). Early HFpEF was associated with LA enlargement, cardiomyocyte hypertrophy, and enhanced LA contractile function (median active emptying fraction 16% [95% confidence interval, 13-24]% versus 12 [10-14]%, P=0.008; end-systolic pressure-volume relationship slope 2.4 [1.9-3.2]mm Hg/mL HFpEF versus 1.5 [1.2-2.2]mm Hg/mL controls, P=0.01). However, atrioventricular coupling was impaired and the curvilinear LA end-reservoir pressure-volume relationship was shifted upward/leftward in HFpEF (LA stiffness constant [β_LA] 0.16 [0.11-0.18]mm Hg/mL versus 0.06 [0.04-0.10]mm Hg/mL controls; P=0.002), indicating reduced LA compliance. Impaired atrioventricular coupling and lower LA compliance correlated with lower left ventricular stroke volume. Total fibrosis and titin isoform composition were similar between groups; however, titin was hyperphosphorylated in HFpEF and correlated with β_LA. LA microvascular reactivity was diminished in HFpEF versus controls. LA microvascular density tended to be lower in HFpEF and inversely correlated with β_LA.

CONCLUSIONS

In early-stage hypertensive HFpEF, LA cardiomyocyte hypertrophy, titin hyperphosphorylation, and microvascular dysfunction occur in association with increased systolic and diastolic LA chamber stiffness, impaired atrioventricular coupling, and decreased left ventricular stroke volume. These data indicate that maladaptive LA remodeling occurs early during HFpEF development, supporting a concept of global myocardial remodeling.

Left atrial changes in early stages of heart failure with preserved ejection fraction

BACKGROUND AND AIM

Increased left atrial (LA) mass was introduced as a compensatory mechanism in heart failure (HF) patients. Furthermore, atrial conduction time and LA emptying fraction is are deteriorated in HF with preserved ejection fraction (HFpEF). The aim of this study was to assess the early LA changes in HFpEF patients.

METHODS

In 79 consecutive patients with HFpEF (age 61±8 years, NYHA class I-III, LV EF ≥45%), a complete 2-dimensional, M-mode, and Doppler echocardiographic study was performed. According to the diastolic dysfunction (DD), patients were divided into three groups: Group I-29 healthy subjects (control group); Group II-HFpEF patients with mild DD; and Group III-HFpEF patients with moderate DD.

RESULTS

The LV mass was increased (P<.05), septal s', lateral s', septal and lateral MAPSE were decreased (P<.05, for all), E/e' ratio was increased (P<.001), LA mass and minimal volume were increased (P<.001, P<.05), LA emptying fraction was decreased (P<.05), and LA dyssynchrony was deteriorated (P<.05) in patients with mild DD compared to controls. These changes were of the same nature in patients with moderate LV DD.

CONCLUSIONS

In early stage of DD, in patients with HFpEF, in addition to LV hypertrophy and compromised LV longitudinal systolic function, the LA emptying fraction is reduced, LA mass and LAV min are increased and LA dyssynchrony is significant, despite normal LA dimensions. These findings suggest early LA function deterioration irrespective of normal cavity measurements, hence a need for optimum therapy.

Early-stage heart failure with preserved ejection fraction in the pig: a cardiovascular magnetic resonance study

BACKGROUND

The hypertensive deoxy-corticosterone acetate (DOCA)-salt-treated pig (hereafter, DOCA pig) was recently introduced as large animal model for early-stage heart failure with preserved ejection fraction (HFpEF). The aim of the present study was to evaluate cardiovascular magnetic resonance (CMR) of DOCA pigs and weight-matched control pigs to characterize ventricular, atrial and myocardial structure and function of this phenotype model.

METHODS

Five anesthetized DOCA and seven control pigs underwent 3 T CMR at rest and during dobutamine stress. Left ventricular/atrial (LV/LA) function and myocardial mass (LVMM), strains and torsion were evaluated from (tagged) cine imaging. 4D phase-contrast measurements were used to assess blood flow and peak velocities, including transmitral early-diastolic (E) and myocardial tissue (E') velocities and coronary sinus blood flow. Myocardial perfusion reserve was estimated from stress-to-rest time-averaged coronary sinus flow. Global native myocardial T1 times were derived from prototype modified Look-Locker inversion-recovery (MOLLI) short-axis T1 maps. After in-vivo measurements, transmural biopsies were collected for stereological evaluation including the volume fractions of interstitium (V_V(int/LV)) and collagen (V_V(coll/LV)). Rest, stress, and stress-to-rest differences of cardiac and myocardial parameters in DOCA and control animals were compared by t-test.

RESULTS

In DOCA pigs LVMM (p < 0.001) and LV wall-thickness (end-systole/end-diastole, p = 0.003/p = 0.007) were elevated. During stress, increase of LV ejection-fraction and decrease of end-systolic volume accounted for normal contractility reserves in DOCA and control pigs. Rest-to-stress differences of cardiac index (p = 0.040) and end-diastolic volume (p = 0.042) were documented. Maximal (p = 0.042) and minimal (p = 0.012) LA volumes in DOCA pigs were elevated at rest; total LA ejection-fraction decreased during stress (p = 0.006). E' was lower in DOCA pigs, corresponding to higher E/E' at rest (p = 0.013) and stress (p = 0.026). Myocardial perfusion reserve was reduced in DOCA pigs (p = 0.031). T1-times and V_V(int/LV) did not differ between groups, whereas V_V(coll/LV) levels were higher in DOCA pigs (p = 0.044).

CONCLUSIONS

LA enlargement, E' and E/E' were the markers that showed the most pronounced differences between DOCA and control pigs at rest. Inadequate increase of myocardial perfusion reserve during stress might represent a metrics for early-stage HFpEF. Myocardial T1 mapping could not detect elevated levels of myocardial collagen in this model.

TRIAL REGISTRATION

The study was approved by the local Bioethics Committee of Vienna, Austria (BMWF-66.010/0091-II/3b/2013).

Early-stage heart failure with preserved ejection fraction in the pig: a cardiovascular magnetic resonance study

BACKGROUND

The hypertensive deoxy-corticosterone acetate (DOCA)-salt-treated pig (hereafter, DOCA pig) was recently introduced as large animal model for early-stage heart failure with preserved ejection fraction (HFpEF). The aim of the present study was to evaluate cardiovascular magnetic resonance (CMR) of DOCA pigs and weight-matched control pigs to characterize ventricular, atrial and myocardial structure and function of this phenotype model.

METHODS

Five anesthetized DOCA and seven control pigs underwent 3 T CMR at rest and during dobutamine stress. Left ventricular/atrial (LV/LA) function and myocardial mass (LVMM), strains and torsion were evaluated from (tagged) cine imaging. 4D phase-contrast measurements were used to assess blood flow and peak velocities, including transmitral early-diastolic (E) and myocardial tissue (E') velocities and coronary sinus blood flow. Myocardial perfusion reserve was estimated from stress-to-rest time-averaged coronary sinus flow. Global native myocardial T1 times were derived from prototype modified Look-Locker inversion-recovery (MOLLI) short-axis T1 maps. After in-vivo measurements, transmural biopsies were collected for stereological evaluation including the volume fractions of interstitium (VV(int/LV)) and collagen (VV(coll/LV)). Rest, stress, and stress-to-rest differences of cardiac and myocardial parameters in DOCA and control animals were compared by t-test.

RESULTS

In DOCA pigs LVMM (p < 0.001) and LV wall-thickness (end-systole/end-diastole, p = 0.003/p = 0.007) were elevated. During stress, increase of LV ejection-fraction and decrease of end-systolic volume accounted for normal contractility reserves in DOCA and control pigs. Rest-to-stress differences of cardiac index (p = 0.040) and end-diastolic volume (p = 0.042) were documented. Maximal (p = 0.042) and minimal (p = 0.012) LA volumes in DOCA pigs were elevated at rest; total LA ejection-fraction decreased during stress (p = 0.006). E' was lower in DOCA pigs, corresponding to higher E/E' at rest (p = 0.013) and stress (p = 0.026). Myocardial perfusion reserve was reduced in DOCA pigs (p = 0.031). T1-times and VV(int/LV) did not differ between groups, whereas VV(coll/LV) levels were higher in DOCA pigs (p = 0.044).

CONCLUSIONS

LA enlargement, E' and E/E' were the markers that showed the most pronounced differences between DOCA and control pigs at rest. Inadequate increase of myocardial perfusion reserve during stress might represent a metrics for early-stage HFpEF. Myocardial T1 mapping could not detect elevated levels of myocardial collagen in this model.

TRIAL REGISTRATION

The study was approved by the local Bioethics Committee of Vienna, Austria (BMWF-66.010/0091-II/3b/2013).

Phosphorylating Titin's Cardiac N2B Element by ERK2 or CaMKIIδ Lowers the Single Molecule and Cardiac Muscle Force

Titin is a large filamentous protein that is responsible for the passive force of the cardiac sarcomere. Titin's force is generated by its I-band region, which includes the cardiac-specific N2B element. The N2B element consists of three immunoglobulin domains, two small unique sequence insertions, and a large 575-residue unique sequence, the N2B-Us. Posttranslational modifications of the N2B element are thought to regulate passive force, but the underlying mechanisms are unknown. Increased passive-force levels characterize diastolic stiffening in heart-failure patients, and it is critical to understand the underlying molecular mechanisms and identify therapeutic targets. Here, we used single-molecule force spectroscopy to study the mechanical effects of the kinases calcium/calmodulin-dependent protein kinase II delta (CaMKIIδ) and extracellular signal-regulated kinase 2 (ERK2) on the single-molecule mechanics of the N2B element. Both CaMKIIδ and ERK2 were found to phosphorylate the N2B element, and single-molecule force spectroscopy revealed an increase in the persistence length (Lp) of the molecule, indicating that the bending rigidity of the molecule was increased. Experiments performed under oxidizing conditions and with a recombinant N2B element that had a simplified domain composition provided evidence that the Lp increase requires the N2B-Us of the N2B element. Mechanical experiments were also performed on skinned myocardium before and after phosphorylation. The results revealed a large (∼30%) passive force reduction caused by CaMKIIδ and a much smaller (∼6%) reduction caused by ERK2. These findings support the notion that the important kinases ERK2 and CaMKIIδ can alter the passive force of myocytes in the heart (although CaMKIIδ appears to be more potent) during physiological and pathophysiological states.

Experimentally Increasing the Compliance of Titin Through RNA Binding Motif-20 (RBM20) Inhibition Improves Diastolic Function In a Mouse Model of Heart Failure With Preserved Ejection Fraction

BACKGROUND

Left ventricular (LV) stiffening contributes to heart failure with preserved ejection fraction (HFpEF), a syndrome with no effective treatment options. Increasing the compliance of titin in the heart has become possible recently through inhibition of the splicing factor RNA binding motif-20. Here, we investigated the effects of increasing the compliance of titin in mice with diastolic dysfunction.

METHODS

Mice in which the RNA recognition motif (RRM) of one of the RNA binding motif-20 alleles was floxed and that expressed the MerCreMer transgene under control of the αMHC promoter (referred to as cRbm20^ΔRRM mice) were used. Mice underwent transverse aortic constriction (TAC) surgery and deoxycorticosterone acetate (DOCA) pellet implantation. RRM deletion in adult mice was triggered by injecting raloxifene (cRbm20^ΔRRM-raloxifene), with dimethyl sulfoxide (DMSO)-injected mice (cRbm20^ΔRRM-DMSO) as the control. Diastolic function was investigated with echocardiography and pressure-volume analysis; passive stiffness was studied in LV muscle strips and isolated cardiac myocytes before and after elimination of titin-based stiffness. Treadmill exercise performance was also studied. Titin isoform expression was evaluated with agarose gels.

RESULTS

cRbm20^ΔRRM-raloxifene mice expressed large titins in the hearts, called supercompliant titin (N2BAsc), which, within 3 weeks after raloxifene injection, made up ≈45% of total titin. TAC/DOCA cRbm20^ΔRRM-DMSO mice developed LV hypertrophy and a marked increase in LV chamber stiffness as shown by both pressure-volume analysis and echocardiography. LV chamber stiffness was normalized in TAC/DOCA cRbm20^ΔRRM-raloxifene mice that expressed N2BAsc. Passive stiffness measurements on muscle strips isolated from the LV free wall revealed that extracellular matrix stiffness was equally increased in both groups of TAC/DOCA mice (cRbm20^ΔRRM-DMSO and cRbm20^ΔRRM-raloxifene). However, titin-based muscle stiffness was reduced in the mice that expressed N2BAsc (TAC/DOCAcRbm20^ΔRRM-raloxifene). Exercise testing demonstrated significant improvement in exercise tolerance in TAC/DOCA mice that expressed N2BAsc.

CONCLUSIONS

Inhibition of the RNA binding motif-20-based titin splicing system upregulates compliant titins, which improves diastolic function and exercise tolerance in the TAC/DOCA model. Titin holds promise as a therapeutic target for heart failure with preserved ejection fraction.

Heart rate-induced modifications of concentric left ventricular hypertrophy: exploration of a novel therapeutic concept

Lowering the heart rate is considered to be beneficial in heart failure (HF) with reduced ejection fraction (HFrEF). In a dilated left ventricle (LV), pharmacological heart rate lowering is associated with a reduction in LV chamber size. In patients with HFrEF, this structural change is associated with better survival. HF with preserved ejection fraction (HFpEF) is increasingly prevalent but, so far, without any evidence-based treatment. HFpEF is typically associated with LV concentric remodeling and hypertrophy. The effects of heart rate on this structural phenotype are not known. Analogous with the benefits of a low heart rate on a dilated heart, we hypothesized that increased heart rates could lead to potentially beneficial remodeling of a concentrically hypertrophied LV. This was explored in an established porcine model of concentric LV hypertrophy and fibrosis. Our results suggest that a moderate increase in heart rate can be used to reduce wall thickness, normalize LV chamber volumes, decrease myocardial fibrosis, and improve LV compliance. Our results also indicate that the effects of heart rate can be titrated, are reversible, and do not induce HF. These findings may provide the rationale for a novel therapeutic approach for HFpEF and its antecedent disease substrate.

Alternative Splicing of Titin Restores Diastolic Function in an HFpEF-Like Genetic Murine Model (TtnΔIAjxn)

RATIONALE

Patients with heart failure with preserved ejection fraction (HFpEF) experience elevated filling pressures and reduced ventricular compliance. The splicing factor RNA-binding motif 20 (RBM20) regulates the contour length of titin's spring region and thereby determines the passive stiffness of cardiomyocytes. Inhibition of RBM20 leads to super compliant titin isoforms (N2BAsc) that reduce passive stiffness.

OBJECTIVE

To determine the therapeutic potential of upregulating compliant titin isoforms in an HFpEF-like state in the mouse.

METHODS AND RESULTS

Constitutive and inducible cardiomyocyte-specific RBM20-inhibited mice were produced on a Ttn(ΔIAjxn) background to assess the effect of upregulating compliant titin at the cellular and organ levels. Genetic deletion of the I-band-A-band junction (IAjxn) in titin increases strain on the spring region and causes a HFpEF-like syndrome in the mouse without pharmacological or surgical intervention. The increased strain represents a mechanical analog of deranged post-translational modification of titin that results in increased passive myocardial stiffness in patients with HFpEF. On inhibition of RBM20 in Ttn(ΔIAjxn) mice, compliant titin isoforms were expressed, diastolic function was normalized, exercise performance was improved, and pathological hypertrophy was attenuated.

CONCLUSIONS

We report for the first time a benefit from upregulating compliant titin isoforms in a murine model with HFpEF-like symptoms. Constitutive and inducible RBM20 inhibition improves diastolic function resulting in greater tolerance to exercise. No effective therapies exists for treating this pervasive syndrome; therefore, our data on RBM20 inhibition are clinically significant.