Diastolic heart failure: a misNOmer

Novel aspects of excitation-contraction coupling in heart failure

Excitation-contraction coupling is the process by which electrical activation is translated into contraction of a cardiac myocyte and thus the heart. In heart failure, expression, phosphorylation, and function of several intracellular proteins that are involved in excitation-contraction coupling are altered. The present review article summarizes central principles and highlights novel aspects of alterations in heart failure, focusing especially on recent findings regarding altered sarcoplasmic reticulum Ca2+ -leak and late Na+ -current without being able to cover all changes in full detail. These two pathomechanisms seem to play interesting roles with respect to systolic and diastolic dysfunction and may also be important for cardiac arrhythmias. Furthermore, the article outlines the translation of these novel findings into potential therapeutic approaches.

Vinexin-β protects against cardiac hypertrophy by blocking the Akt-dependent signalling pathway

Cardiac hypertrophy is the heart's response to hypertrophic stimuli and is associated with increased mortality. Vinexin-β is a vinculin-binding protein that belongs to a family of adaptor proteins and mediates signal transduction and actin cytoskeleton organisation. A previous study has shown that Vinexin-β is ubiquitously expressed and that it is highly expressed in the heart. However, a critical role for Vinexin-β in cardiac hypertrophy has not been investigated. Therefore, to examine the role of Vinexin-β in pathological cardiac hypertrophy, we used Vinexin-β knockout mice and transgenic mice that overexpress human Vinexin-β in the heart. Cardiac hypertrophy was induced by aortic banding (AB). The extent of cardiac hypertrophy was quantitated by echocardiography and pathological and molecular analyses of heart samples. Our results demonstrated that Vinexin-β overexpression in the heart markedly attenuated cardiac hypertrophy, fibrosis, and cardiac dysfunction, whereas loss of Vinexin-β exaggerated the pathological cardiac remodelling and fibrosis response to pressure overload. Further analysis of the in vitro and in vivo signalling events indicated that beneficial Vinexin-β effects were associated with AKT signalling abrogation. Our findings demonstrate for the first time that Vinexin-β is a novel mediator that protects against cardiac hypertrophy by blocking the AKT signalling pathway.

Interferon regulatory factor 3 is a negative regulator of pathological cardiac hypertrophy

Interferon regulatory factor (IRF) 3, a member of the highly conserved IRF family transcription factors, plays a pivotal role in innate immune response, apoptosis, and oncogenesis. Recent studies have implicated IRF3 in a wide range of host defense. However, whether IRF3 induces defensive responses to hypertrophic stresses such as biomechanical stress and neurohumoral factors remains unclear. Herein, we employed an IRF3-deficient mouse model, cardiac-specific IRF3-overexpression mouse model and isolated cardiomyocytes to investigate the role of IRF3 in cardiac hypertrophy induced by aortic banding (AB) or isoproterenol (ISO). The extent of cardiac hypertrophy was quantitated by echocardiography as well as by pathological and molecular analysis. Our results demonstrate that IRF3 deficiency profoundly exacerbated cardiac hypertrophy, whereas overexpression of IRF3 in the heart significantly blunted pathological cardiac remodeling induced by pressure overload. Similar results were also observed in cultured cardiomyocytes upon the treatment with ISO. Mechanistically, we discovered that IRF3 interacted with ERK2 and thereby inhibited the ERK1/2 signaling. Furthermore, inactivation of ERK1/2 by U0126 offset the IRF3-deficient-mediated hypertrophic response induced by aortic banding. Altogether, these data demonstrate that IRF3 plays a protective role in AB-induced hypertrophic response by inactivating ERK1/2 in the heart. Therefore, IRF3 could be a new target for the prevention and therapy of cardiac hypertrophy and failure.

Impaired left ventricular function in the presence of preserved ejection in chronic hypertensive conscious pigs

Systolic function is often evaluated by measuring ejection fraction and its preservation is often assimilated with the lack of impairment of systolic left ventricular (LV) function. Considering the left ventricle as a muscular pump, we explored LV function during chronic hypertension independently of increased afterload conditions. Fourteen conscious and chronically instrumented pigs received continuous infusion of either angiotensin II (n = 8) or saline (n = 6) during 28 days. Hemodynamic recordings were regularly performed in the presence and 1 h after stopping angiotensin II infusion to evaluate intrinsic LV function. Throughout the protocol, the mean arterial pressure steadily increased by 55 ± 4 mmHg in angiotensin II-treated animals. There were no significant changes in stroke volume, LV fractional shortening or LV wall thickening, indicating the lack of alterations in LV ejection. In contrast, we observed maladaptive changes with (1) the lack of reduction in isovolumic contraction and relaxation durations with heart rate increases, (2) abnormally blunted isovolumic contraction and relaxation responses to dobutamine and (3) a linear correlation between isovolumic contraction and relaxation durations. None of these changes were observed in saline-infused animals. In conclusion, we provide evidence of impaired LV function with concomitant isovolumic contraction and relaxation abnormalities during chronic hypertension while ejection remains preserved and no sign of heart failure is present. The evaluation under unloaded conditions shows intrinsic LV abnormalities.

Diastolic tolerance to systolic pressures closely reflects systolic performance in patients with coronary heart disease

In animal experiments, elevating systolic pressures induces diastolic dysfunction and may contribute to congestion, a finding not yet translated to humans. Coronary surgery patients (63 ± 8 years) were studied with left ventricular (LV) pressure (n = 17) or pressure-volume (n = 3) catheters, immediately before cardiopulmonary bypass. Single-beat graded pressure elevations were induced by clamping the ascending aorta. Protocol was repeated after volume loading (n = 7). Consecutive patients with a wide range of systolic function were included. Peak isovolumetric LV pressure (LVP(iso)) ranged from 113 to 261 mmHg. With preserved systolic function, LVP elevations neither delayed relaxation nor increased filling pressures. With decreasing systolic function, diastolic tolerance to afterload progressively disappeared: relaxation slowed and filling pressures increased (diastolic dysfunction). In severely depressed systolic function, filling pressures increased even with minor LVP elevations, suggesting baseline load-dependent elevation of diastolic pressures. The magnitude of filling pressure elevation induced in isovolumetric heartbeats was closely and inversely related to systolic performance, evaluated by LVP(iso) (r = -0.96), and directly related to changes in the time constant of relaxation τ (r = 0.95). The maximum tolerated systolic LVP (without diastolic dysfunction) was similarly correlated with LVP(iso) (r = 0.99). Volume loading itself accelerated relaxation, but augmented afterload-induced upward shift of filling pressures (7.9 ± 3.7 vs. 3.0 ± 1.5; P < 0.01). The normal human response to even markedly increased systolic pressures is no slowing of relaxation and preservation of normal filling pressures. When cardiac function deteriorates, the LV becomes less tolerant, responding with slowed relaxation and increased filling pressures. This increase is exacerbated by volume loading.

Increased cardiovascular risk in rats with primary renal dysfunction; mediating role for vascular endothelial function

Primary chronic kidney disease is associated with high cardiovascular risk. However, the exact mechanisms behind this cardiorenal interaction remain unclear. We investigated the interaction between heart and kidneys in novel animal model for cardiorenal interaction. Normal Wistar rats and Munich Wistar Fromter rats, spontaneously developing renal dysfunction, were subjected to experimental myocardial infarction to induce cardiac dysfunction (CD) and combined cardiorenal dysfunction (CRD), respectively (N = 5–10). Twelve weeks later, cardiac- and renal parameters were evaluated. Cardiac, but not renal dysfunction was exaggerated in CRD. Accelerated cardiac dysfunction in CRD was indicated by decreased cardiac output (CD 109 ± 10 vs. CRD 79 ± 8 ml/min), diastolic dysfunction (E/e′) (CD 26 ± 2 vs. CRD 50 ± 5) and left ventricular overload (LVEDP CD 10.8 ± 2.8 vs. CRD 21.6 ± 1.7 mmHg). Congestion in CRD was confirmed by increased lung and atrial weights, as well as exaggerated right ventricular hypertrophy. Absence of accelerated renal dysfunction, measured by increased proteinuria, was supported by absence of additional focal glomerulosclerosis or further decline of renal blood flow in CRD. Only advanced peripheral endothelial dysfunction, as found in CRD, appeared to correlate with both renal and cardiac dysfunction parameters. Thus, proteinuric rats with myocardial infarction showed accelerated cardiac but not renal dysfunction. As parameters mimic the cardiorenal syndrome, these rats may provide a clinically relevant model to study increased cardiovascular risk due to renal dysfunction. Peripheral endothelial dysfunction was the only parameter that correlated with both renal and cardiac dysfunction, which may indicate a mediating role in cardiorenal interaction.

K201 (JTV-519) alters the spatiotemporal properties of diastolic Ca(2+) release and the associated diastolic contraction during β-adrenergic stimulation in rat ventricular cardiomyocytes

K201 has previously been shown to reduce diastolic contractions in vivo during β-adrenergic stimulation and elevated extracellular calcium concentration ([Ca²⁺]_o). The present study characterised the effect of K201 on electrically stimulated and spontaneous diastolic sarcoplasmic reticulum (SR)-mediated Ca²⁺ release and contractile events in isolated rat cardiomyocytes during β-adrenergic stimulation and elevated [Ca²⁺]_o. Parallel experiments using confocal microscopy examined spontaneous diastolic Ca²⁺ release events at an enhanced spatiotemporal resolution. 1.0 μmol/L K201 in the presence of 150 nmol/L isoproterenol (ISO) and 4.75 mmol/L [Ca²⁺]_o significantly decreased the amplitude of diastolic contractions to ~16% of control levels. The stimulated free Ca²⁺ transient amplitude was significantly reduced, but stimulated cell shortening was not significantly altered. When intracellular buffering was taken into account, K201 led to an increase in action potential-induced SR Ca²⁺ release. Myofilament sensitivity to Ca²⁺ was not changed by K201. Confocal microscopy revealed diastolic events composed of multiple Ca²⁺ waves (2–3) originating at various points along the cardiomyocyte length during each diastolic period. 1.0 μmol/L K201 significantly reduced the (a) frequency of diastolic events and (b) initiation points/diastolic interval in the remaining diastolic events to 61% and 71% of control levels respectively. 1.0 μmol/L K201 can reduce the probability of spontaneous diastolic Ca²⁺ release and their associated contractions which may limit the propensity for the contractile dysfunction observed in vivo.

Evolving approaches to the management of heart failure with preserved ejection fraction in patients with coronary artery disease

OPINION STATEMENT

Coronary artery disease (CAD) is a major cause of heart failure with preserved ejection fraction (HFpEF). In studies of HFpEF, the reported prevalence of CAD varies widely, which may be the result of inconsistent definitions of CAD, geographic and ethnic differences in CAD burden, varying definitions of HFpEF (including different cutoffs for "preserved ejection fraction"), and differences in study design. Despite these limitations, pooled analysis of prospective HFpEF studies demonstrates that CAD is common in HFpEF, with an estimated prevalence of approximately 50%. Based on available data, patients with signs and symptoms of heart failure who have preserved left ventricular ejection fraction and evidence of CAD (HFpEF-CAD) most likely comprise a distinct etiologic and pathophysiologic subset of HFpEF. Therefore, future clinical trials in HFpEF should a priori stratify by CAD or specifically target patients with CAD, strategies that may improve the disappointing track record of therapies tested in HFpEF. The combination of systematic evaluation and management of CAD in HFpEF, along with promising future therapies for HFpEF-CAD, may lead to improved outcomes for this challenging clinical syndrome.

Improvement of left ventricular diastolic function induced by β-blockade: a comparison between nebivolol and metoprolol

OBJECTIVES

Enhanced adrenergic drive is involved in the development of left ventricular (LV) diastolic dysfunction observed in metabolic syndrome (MS). Thus, β-blockers might improve LV dysfunction observed in MS, but whether this occurs is unknown.

METHODS

We assessed in Zucker fa/fa rats the effects of short- (5 days) and long-term (90 days) metoprolol ('pure' β-blockade; 80 mg/kg/day) or nebivolol (β-blocker with vasodilating properties; 5mg/kg/day) treatment on LV hemodynamics and remodeling, as well as the long-term effects on coronary and peripheral endothelial dysfunction.

RESULTS

At identical degree of β(1)-receptor blockade, metoprolol and nebivolol decreased heart rate to the same extent and preserved cardiac output via increased stroke volume. None of the β-blockers, either after long- or short-term administration, modified LV end-systolic pressure-volume relation. Both β-blockers reduced, after long-term administration, LV end-diastolic pressure, Tau and end-diastolic pressure-volume relation, and this was associated with reduced LV collagen density, but not heart weight. Similar hemodynamic effects were also observed after short-term nebivolol, but not short-term metoprolol. These short-term effects of nebivolol were abolished by NO synthase inhibition. At the vascular level, nebivolol, and to a lesser extend metoprolol, improved NO dependent coronary vasorelaxation, which was abolished by NO synthase inhibition.

CONCLUSIONS

In a model of MS, the β-blockers metoprolol and nebivolol improve to the same extent LV hemodynamics, remodeling and diastolic function, but nebivolol prevent more markedly endothelium dependent vasorelaxation involving a more marked enhancement of NO bio-availability.

Heart failure with preserved ejection fraction: pathophysiology, diagnosis, and treatment

Half of patients with heart failure (HF) have a preserved left ventricular ejection fraction (HFpEF). Morbidity and mortality in HFpEF are similar to values observed in patients with HF and reduced EF, yet no effective treatment has been identified. While early research focused on the importance of diastolic dysfunction in the pathophysiology of HFpEF, recent studies have revealed that multiple non-diastolic abnormalities in cardiovascular function also contribute. Diagnosis of HFpEF is frequently challenging and relies upon careful clinical evaluation, echo-Doppler cardiography, and invasive haemodynamic assessment. In this review, the principal mechanisms, diagnostic approaches, and clinical trials are reviewed, along with a discussion of novel treatment strategies that are currently under investigation or hold promise for the future.

Clopidogrel improves endothelial function and NO bioavailability by sensitizing adenylyl cyclase in rats with congestive heart failure

Clopidogrel treatment in patients with coronary artery disease not only inhibits platelet activation but also improves endothelial function and nitric oxide (NO) bioavailability. Congestive heart failure (CHF) is associated with endothelial dysfunction and increased platelet activation. In rats with CHF following myocardial infarction (MI), we investigated whether treatment with clopidogrel modifies endothelial function. Eight weeks after coronary artery ligation, rats with CHF were randomized to placebo or the P2Y(12) receptor antagonist clopidogrel (5 mg/kg twice daily, given by gavage) for another 2 weeks. Afterwards, endothelial function was assessed in isolated aortic rings in organ bath experiments. Acetylcholine-induced, endothelium-dependent, nitric oxide-mediated vasorelaxation was significantly attenuated in CHF rats compared to sham-operated animals, and was significantly improved by treatment with clopidogrel. Adenosine-induced vasorelaxation via adenylyl cyclase stimulation was attenuated in CHF and significantly improved by clopidogrel. Increased vasoconstriction to phenylephrine was observed in CHF, particularly evident under cyclooxygenase inhibition, but prevented by clopidogrel treatment. Vasoconstriction by the P2Y(12) activator 2MeS-ADP was increased in CHF. Clopidogrel-treated CHF animals displayed enhanced phosphorylation of AKT and eNOS. In conclusion, clopidogrel improved endothelial function and NO bioavailability in heart failure. During CHF, sensitivity to P2Y(12) signaling was increased leading to impaired adenylyl cyclase-mediated signaling. Chronic P2Y(12)-blockade with clopidogrel improved adenylyl cyclase-mediated signaling including increased AKT- and eNOS-phosphorylation contributing to improved NO-mediated vasorelaxation.

Diastolic dysfunction and arrhythmias caused by overexpression of CaMKIIδ(C) can be reversed by inhibition of late Na(+) current

Transgenic (TG) Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) δ_C mice develop systolic heart failure (HF). CaMKII regulates intracellular Ca²⁺ handling proteins as well as sarcolemmal Na⁺ channels. We hypothesized that CaMKII also contributes to diastolic dysfunction and arrhythmias via augmentation of the late Na⁺ current (late I_Na) in early HF (8-week-old TG mice). Echocardiography revealed severe diastolic dysfunction in addition to decreased systolic ejection fraction. Premature arrhythmogenic contractions (PACs) in isolated isometrically twitching papillary muscles only occurred in TG preparations (5 vs. 0, P < 0.05) which could be completely terminated when treated with the late I_Na inhibitor ranolazine (Ran, 5 μmol/L). Force–frequency relationships revealed significantly reduced twitch force amplitudes in TG papillary muscles. Most importantly, diastolic tension increased with raising frequencies to a greater extent in TG papillary muscles compared to WT specimen (at 10 Hz: 3.7 ± 0.4 vs. 2.5 ± 0.3 mN/mm²; P < 0.05). Addition of Ran improved diastolic dysfunction to 2.1 ± 0.2 mN/mm² (at 10 Hz; P < 0.05) without negative inotropic effects. Mechanistically, the late I_Na was markedly elevated in myocytes isolated from TG mice and could be completely reversed by Ran. In conclusion, our results show for the first time that TG CaMKIIδ_C overexpression induces diastolic dysfunction and arrhythmogenic triggers possibly via an enhanced late I_Na. Inhibition of elevated late I_Na had beneficial effects on arrhythmias as well as diastolic function in papillary muscles from CaMKIIδ_C TG mice. Thus, late I_Na inhibition appears to be a promising option for diastolic dysfunction and arrhythmias in HF where CaMKII is found to be increased.

Immune-inflammatory dysregulation modulates the incidence of progressive fibrosis and diastolic stiffness in the aging heart

Diastolic dysfunction in the aging heart is a grave condition that challenges the life and lifestyle of a growing segment of our population. This report seeks to examine the role and interrelationship of inflammatory dysregulation in interstitial myocardial fibrosis and progressive diastolic dysfunction in aging mice. We studied a population of C57BL/6 mice that developed progressive diastolic dysfunction over 30 months of life. This progressive dysfunction was associated with increasing infiltration of CD45(+) fibroblasts of myeloid origin. In addition, increased rates of collagen expression as measured by cellular procollagen were apparent in the heart as a function of age. These cellular and functional changes were associated with progressive increases in mRNA for MCP-1 and IL-13, which correlated both temporally and quantitatively with changes in fibrosis and cellular procollagen levels. MCP-1 protein was also increased and found to be primarily in the venular endothelium. Protein assays also demonstrated elevation of IL-4 and IL-13 suggesting a shift to a Th2 phenotype in the aging heart. In vitro studies demonstrated that IL-13 markedly enhanced monocyte-fibroblast transformation. Our results indicate that immunoinflammatory dysregulation in the aging heart induces progressive MCP-1 production and an increased shift to a Th2 phenotype paralleled by an associated increase in myocardial interstitial fibrosis, cellular collagen synthesis, and increased numbers of CD45(+) myeloid-derived fibroblasts that contain procollagen. The temporal association and functional correlations suggest a causative relationship between age-dependent immunoinflammatory dysfunction, fibrosis and diastolic dysfunction.

Current controversies in heart failure with a preserved ejection fraction

Heart failure with a preserved ejection fraction is a fascinating and multifaceted condition that has provoked enormous debate and a wealth of mechanistic studies. Controversies exist with regard to its nomenclature. If its nomenclature is questioned, one can be certain the pathogenesis is ill understood. If the pathogenesis is disputed, the diagnosis becomes difficult and inconsistent. These diagnostic challenges result in inappropriate recruitment to clinical trials. Therefore, the trials may be underpowered and difficult to interpret. This paper examines contemporary theories of heart failure with a preserved ejection fraction, clarifies the controversies and attempts to resolve the divergences of opinion.