C-Type Natriuretic Peptide Improves Left Ventricular Functional Performance at Rest and Restores Normal Exercise Responses after Heart Failure.

In heart failure (HF), the impaired left ventricular (LV) arterial coupling and diastolic dysfunction present at rest are exacerbated during exercise. C-type natriuretic peptide (CNP) is elevated in HF; however, its functional effects are unclear. We tested the hypotheses that CNP with vasodilating, natriuretic, and positive inotropic and lusitropic actions may prevent this abnormal exercise response after HF. We determined the effects of CNP (2 µg/kg plus 0.4 µg/kg per minute, i.v., 20 minutes) on plasma levels of cGMP before and after HF and assessed LV dynamics during exercise in 10 chronically instrumented dogs with pacing-induced HF. Compared with the levels before HF, CNP infusion caused significantly greater increases in cGMP levels after HF. After HF, at rest, CNP administration significantly reduced LV end-systolic pressure (PES), arterial elastance (EA), and end-diastolic pressure. The peak mitral flow (dV/dtmax) was also increased owing to decreased minimum LVP (LVPmin) and the time constant of LV relaxation (τ) (P < 0.05). In addition, LV contractility (EES) was increased. The LV-arterial coupling (EES/EA) was improved. The beneficial effects persisted during exercise. Compared with exercise in HF preparation, treatment with CNP caused significantly less important increases in PES but significantly decreased τ (34.2 vs. 42.6 ms) and minimum left ventricular pressure with further augmented dV/dtmax Both EES, EES/EA (0.87 vs. 0.32) were increased. LV mechanical efficiency improved from 0.38 to 0.57 (P < 0.05). After HF, exogenous CNP produces arterial vasodilatation and augments LV contraction, relaxation, diastolic filling, and LV arterial coupling, thus improving LV performance at rest and restoring normal exercise responses after HF.

Presence and Implication of Temporal Nonuniformity of Early Diastolic Left Ventricular Wall Expansion in Patients With Heart Failure.

BACKGROUND: Early-diastolic left ventricular (LV) longitudinal expansion is delayed with diastolic dysfunction. We hypothesized that, in patients with heart failure (HF), regardless of LV ejection fraction (EF), there is diastolic temporal nonuniformity with a delay of longitudinal relative to circumferential expansion. METHODS AND RESULTS: Echocardiography was performed in 143 HF patients-50 with preserved EF (HFpEF) and 93 with reduced EF (HFrEF)-as well as 31 normal control subjects. The delay of early-diastolic mitral annular velocity from the mitral Doppler E (TE-e') was measured as a parameter of the longitudinal expansion delay. The delay of the longitudinal early-diastolic global strain rate (SRE) relative to circumferential SRE (DelayC-L) was calculated as a parameter of temporal nonuniformity. Intra-LV pressure difference (IVPD) was estimated with the use of color M-mode Doppler data as a parameter of LV diastolic suction. Although normal control subjects had symmetric LV expansion in early diastole, TE-e' and DelayC-L were significantly prolonged in HF regardless of EF (P < .01 vs control for all). Multivariate analysis revealed that DelayC-L was the independent determinant of IVPD among the parameters of LV geometry and contraction (ß = -0.21; P < .05). CONCLUSION: An abnormal temporal nonuniformity of early-diastolic expansion is present in HF regardless of EF, which was associated with reduced LV suction.

Mechanism of decreased sensitivity of dobutamine associated left ventricular wall motion analyses for appreciating inducible ischemia in older adults.

BACKGROUND: Dobutamine associated left ventricular (LV) wall motion analyses exhibit reduced sensitivity for detecting inducible ischemia in individuals with increased LV wall thickness. This study was performed to better understand the mechanism of this reduced sensitivity in the elderly who often manifest increased LV wall thickness and risk factors for coronary artery disease. METHODS: During dobutamine cardiovascular magnetic resonance (DCMR) stress testing, we assessed rate pressure product (RPP), aortic pulse wave velocity (PWV), LV myocardial oxygen demand (pressure volume area, PVA, mass, volumes, concentricity, and the presence of wall motion abnormalities (WMA) and first pass gadolinium enhanced perfusion defects (PDs) indicative of ischemia in 278 consecutively recruited individuals aged 69 ± 8 years with pre-existing or known risk factors for coronary artery disease. Each variable was assessed independently by personnel blinded to participant identifiers and analyses of other DCMR or hemodynamic variables. RESULTS: Participants were 80% white, 90% hypertensive, 43% diabetic and 55% men. With dobutamine, 60% of the participants who exhibited PDs had no inducible WMA. Among these participants, myocardial oxygen demand was lower than that observed in those who had both wall motion and perfusion abnormalities suggestive of ischemia (p = 0.03). Relative to those with PDs and inducible WMAs, myocardial oxygen demand remained different in these individuals with PDs without an inducible WMA after accounting for LV afterload and contractility (p = 0.02 and 0.03 respectively), but not after accounting for either LV stress related end diastolic volume index (LV preload) or resting concentricity (p = 0.31-0.71). CONCLUSIONS: During dobutamine stress testing, elderly patients experience increased LV concentricity and declines in LV preload and myocardial oxygen demand, all of which are associated with an absence of inducible LV WMAs indicative of myocardial ischemia. These findings provide insight as to why dobutamine associated wall motion analyses exhibit reduced sensitivity for identifying inducible ischemia in elderly. TRIAL REGISTRATION: This study was registered with Clinicaltrials.gov (NCT00542503).

ß3-Adrenergic receptor antagonist improves exercise performance in pacing-induced heart failure.

In heart failure (HF), the impaired left ventricular (LV) arterial coupling and diastolic dysfunction present at rest are exacerbated during exercise. We have previously shown that in HF at rest stimulation of ß3-adrenergic receptors by endogenous catecholamine depresses LV contraction and relaxation. ß3-Adrenergic receptors are activated at higher concentrations of catecholamine. Thus exercise may cause increased stimulation of cardiac ß3-adrenergic receptors and contribute to this abnormal response. We assessed the effect of L-748,337 (50 µg/kg iv), a selective ß3-adrenergic receptor antagonist (ß3-ANT), on LV dynamics during exercise in 12 chronically instrumented dogs with pacing-induced HF. Compared with HF at rest, exercise increased LV end-systolic pressure (PES), minimum LV pressure (LVPmin), and the time constant of LV relaxation (τ) with an upward shift of early diastolic portion of LV pressure-volume loop. LV contractility decreased and arterial elastance (EA) increased. LV arterial coupling (EES/EA) (0.40 vs. 0.51) was impaired. Compared with exercise in HF preparation, exercise after ß3-ANT caused similar increases in heart rate and PES but significantly decreased τ (34.9 vs. 38.3 ms) and LVPmin with a downward shift of the early diastolic portion of LV pressure-volume loop and further augmented dV/dtmax. Both EES and EES/EA (0.68 vs. 0.40) were increased. LV mechanical efficiency improved from 0.39 to 0.53. In conclusion, after HF, ß3-ANT improves LV diastolic filling; increases LV contractility, LV arterial coupling, and mechanical efficiency; and improves exercise performance.

Left ventricular vortex formation is unaffected by diastolic impairment.

Normal left ventricular (LV) filling occurs rapidly early in diastole caused by a progressive pressure gradient within the ventricle and with a low left atrial pressure. This normal diastolic function is altered in patients with heart failure. Such impairment of diastolic filling is manifested as an abrupt deceleration of the early filling wave velocity. Although variations within the early filling wave have been observed previously, the underlying hydrodynamic mechanisms are not well understood. Previously, it was proposed that the mitral annulus vortex ring formation time was the total duration of early diastolic filling and provided a measure of the efficiency of diastolic filling. However, we found that the favorable LV pressure difference driving early diastolic filling becomes zero simultaneously with the deceleration of the early filling wave propagation velocity and pinch-off of the LV vortex ring. Thus we calculated the vortex ring formation time using the duration of the early diastolic filling wave from its initiation to the time of the early filling wave propagation velocity deceleration when pinch-off occurs. This formation time does not vary with decreasing intraventricular pressure difference or with degree of diastolic dysfunction. Thus we conclude the vortex ring pinch-off occurs before the completion of early diastole, and its formation time remains invariant to changes of diastolic function.

Pulmonary hypertension in heart failure with preserved left ventricular ejection fraction: diagnosis and management.

PURPOSE OF REVIEW: To clarify the importance of pulmonary hypertension in the diagnosis and treatment of heart failure with preserved ejection fraction (HFpEF). RECENT FINDINGS: Pulmonary hypertension is frequently present in HFpEF because of both elevated pulmonary venous pressure and some element of pulmonary vasoconstriction. HFpEF may be the most common cause of pulmonary hypertension in the elderly. The noninvasive detection of pulmonary hypertension can distinguish patients with HFpEF from those with diastolic dysfunction without heart failure. Pulmonary hypertension may be an important target for treatment of HFpEF. Phosphodiesterase-5 inhibitors are a promising method to treat pulmonary hypertension because of HFpEF. SUMMARY: Pulmonary hypertension is an important contributor to the pathophysiology of HFpEF, can be used to recognize HFpEF and may be an important target for therapy.

Fibronectin forms the most extensible biological fibers displaying switchable force-exposed cryptic binding sites.

Rather than maximizing toughness, as needed for silk and muscle titin fibers to withstand external impact, the much softer extracellular matrix fibers made from fibronectin (Fn) can be stretched by cell generated forces and display extraordinary extensibility. We show that Fn fibers can be extended more than 8-fold (>700% strain) before 50% of the fibers break. The Young's modulus of single fibers, given by the highly nonlinear slope of the stress-strain curve, changes orders of magnitude, up to MPa. Although many other materials plastically deform before they rupture, evidence is provided that the reversible breakage of force-bearing backbone hydrogen bonds enables the large strain. When tension is released, the nano-sized Fn domains first contract in the crowded environment of fibers within seconds into random coil conformations (molten globule states), before the force-bearing hydrogen bond networks that stabilize the domain's secondary structures are reestablished within minutes (double exponential). The exposure of cryptic binding sites on Fn type III modules increases steeply upon stretching. Thus fiber extension steadily up-regulates fiber rigidity and cryptic epitope exposure, both of which are known to differentially alter cell behavior. Finally, since stress-strain relationships cannot directly be measured in native extracellular matrix (ECM), the stress-strain curves were correlated with stretch-induced alterations of intramolecular fluorescence resonance energy transfer (FRET) obtained from trace amounts of Fn probes (mechanical strain sensors) that can be incorporated into native ECM. Physiological implications of the extraordinary extensibility of Fn fibers and contraction kinetics are discussed.

Mode of death in patients with heart failure and a preserved ejection fraction: results from the Irbesartan in Heart Failure With Preserved Ejection Fraction Study (I-Preserve) trial.

BACKGROUND: The mode of death has been well characterized in patients with heart failure and a reduced ejection fraction; however, less is known about the mode of death in patients with heart failure and a preserved ejection fraction (HFPEF). The purpose of this study was to examine the mode of death in patients with HFPEF enrolled in the Irbesartan in Heart Failure With Preserved Ejection Fraction Study (I-Preserve) trial and to determine whether irbesartan altered the distribution of mode of death in HFPEF. METHODS AND RESULTS: All deaths were reviewed by a clinical end-point committee, and the mode of death was assigned by consensus of the members. The annual mortality rate was 5.2% in the I-Preserve trial. There were no significant differences in mortality rate between the placebo and irbesartan groups. The mode of death was cardiovascular in 60% (including 26% sudden, 14% heart failure, 5% myocardial infarction, and 9% stroke), noncardiovascular in 30%, and unknown in 10%. There were no differences in the distribution of mode-specific mortality rates between placebo and irbesartan. CONCLUSIONS: Sixty percent of the deaths in patients with HFPEF were cardiovascular, with sudden death and heart failure death being the most common. Treatment with irbesartan did not affect overall mortality or the distribution of mode-specific mortality rates. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00095238.

Levosimendan restores the positive force-frequency relation in heart failure.

Frequency potentiation of contractile function is a major mechanism of the increase in myocardial performance during exercise. In heart failure (HF), this positive force-frequency relation is impaired, and the abnormal left ventricular (LV)-arterial coupling is exacerbated by tachycardia. A myofilament Ca(2+) sensitizer, levosimendan, has been shown to improve exercise tolerance in HF. This may be due to its beneficial actions on the force-frequency relation and LV-arterial coupling (end-systolic elastance/arterial elastance, E(ES)/E(A)). We assessed the effects of therapeutic doses of levosimendan on the force-frequency relation and E(ES)/E(A) in nine conscious dogs after pacing-induced HF using pressure-volume analysis. Before HF, pacing tachycardia increased E(ES), shortened τ, and did not impair E(ES)/E(A) and mechanical efficiency (stroke work/pressure-volume area, SW/PVA). In contrast, after HF, pacing at 140, 160, 180, and 200 beat/min (bpm) produced smaller a increase of E(ES) or less shortening of τ, whereas E(ES)/E(A) (from 0.56 at baseline to 0.42 at 200 bpm) and SW/PVA (from 0.52 at baseline to 0.43 at 200 bpm) progressively decreased. With levosimendan, basal E(ES) increased 27% (6.2 mmHg/ml), τ decreased 11% (40.8 ms), E(ES)/E(A) increased 34% (0.75), and SW/PVA improved by 15% (0.60). During tachycardia, E(ES) further increased by 23%, 37%, 68%, and 89%; τ decreased by 9%, 12%, 15%, and 17%; and E(ES)/E(A) was augmented by 11%, 16%, 31%, and 33%, incrementally, with pacing rate. SW/PVA was improved (0.61 to 0.64). In conclusion, in HF, treatment with levosimendan restores the normal positive LV systolic and diastolic force-frequency relation and prevents tachycardia-induced adverse effect on LV-arterial coupling and mechanical efficiency.

Chronic baroreflex activation: a potential therapeutic approach to heart failure with preserved ejection fraction.

Heart failure with preserved ejection fraction (HFpEF) is a substantial public health issue, equal in magnitude to heart failure with reduced ejection fraction. Clinical outcomes of HFpEF patients are generally poor, related annual accrual of health care expenses amount to billions of dollars, and no therapy has been shown to be effective in randomized clinical trials. Baroreflex activation therapy (BAT) produced by stimulating the carotid sinuses using an implanted device (Rheos) is being studied for the treatment of hypertension, the primary comorbidity of HFpEF. Other potential benefits include regression of left ventricular hypertrophy, normalization of the sympathovagal balance, inhibition of the renin-angiotensin-aldosterone system, arterio- and venodilation, and preservation of renal function. This paper reviews the evidence suggesting that BAT may be a promising therapy for HFpEF and introduces the HOPE4HF trial (ClinicalTrials.gov Identifier: NCT00957073), a randomized outcomes trial designed to evaluate the clinical safety and efficacy of BAT in the HFpEF population.

Assessment of left ventricular diastolic function using 4-dimensional phase-contrast cardiac magnetic resonance.

OBJECTIVES: Phase-contrast magnetic resonance imaging can potentially assess the dynamics of left ventricular (LV) early diastolic filling. METHODS: Fifteen participants underwent phase-contrast magnetic resonance imaging on a 1.5-T whole-body Avanto scanner (Siemens Healthcare, Erlangen, Germany). Left ventricular intracavitary velocities were measured in 3 orthogonal directions. Imaging parameters included a repetition time of 92.45 milliseconds, an echo time of 2.88 milliseconds, a flip angle of 30 degrees, and a velocity-encoding range of 100 to 150 cm/s. RESULTS: The color vector analysis provided a visual assessment of LV diastolic flow. In normal subjects, there was rapid organized early diastolic flow that extended from the mitral valve to the LV apex. In patients with LV diastolic dysfunction, organized high-velocity flow stopped in the mid-left ventricle. CONCLUSIONS: Four-dimensional phase-contrast cardiovascular magnetic resonance can differentiate between normal and abnormal diastolic flow propagation within the left ventricle.

Evolving focus on diastolic dysfunction in patients with coronary artery disease.

PURPOSE OF REVIEW: The purpose of this review is to summarize recent studies of coronary artery disease (CAD) and diastolic dysfunction. RECENT FINDINGS: Myocardial ischemia slows ventricular relaxation and can impair ventricular distensibility resulting in diastolic dysfunction apparent as abnormal left ventricular (LV) filling dynamics that can be recognized noninvasively. As such, the development of diastolic dysfunction during stress testing may improve the recognition of CAD. The noninvasive recognition of diastolic dysfunction indicates a poor prognosis in patients with an acute coronary syndrome and chronic CAD. Patients with heart failure with preserved ejection fraction (HFpEF) frequently have CAD, and it may contribute to the heart failure. SUMMARY: Myocardial ischemia produces diastolic dysfunction. The evaluation of diastolic dysfunction has diagnostic and prognostic roles in the management of CAD. CAD is a frequent and important comorbidity of HFpEF.

Force-induced unfolding of fibronectin in the extracellular matrix of living cells.

Whether mechanically unfolded fibronectin (Fn) is present within native extracellular matrix fibrils is controversial. Fn extensibility under the influence of cell traction forces has been proposed to originate either from the force-induced lengthening of an initially compact, folded quaternary structure as is found in solution (quaternary structure model, where the dimeric arms of Fn cross each other), or from the force-induced unfolding of type III modules (unfolding model). Clarification of this issue is central to our understanding of the structural arrangement of Fn within fibrils, the mechanism of fibrillogenesis, and whether cryptic sites, which are exposed by partial protein unfolding, can be exposed by cell-derived force. In order to differentiate between these two models, two fluorescence resonance energy transfer schemes to label plasma Fn were applied, with sensitivity to either compact-to-extended conformation (arm separation) without loss of secondary structure or compact-to-unfolded conformation. Fluorescence resonance energy transfer studies revealed that a significant fraction of fibrillar Fn within a three-dimensional human fibroblast matrix is partially unfolded. Complete relaxation of Fn fibrils led to a refolding of Fn. The compactly folded quaternary structure with crossed Fn arms, however, was never detected within extracellular matrix fibrils. We conclude that the resting state of Fn fibrils does not contain Fn molecules with crossed-over arms, and that the several-fold extensibility of Fn fibrils involves the unfolding of type III modules. This could imply that Fn might play a significant role in mechanotransduction processes.

Up-regulation and functional effect of cardiac ß3-adrenoreceptors in alcoholic monkeys.

BACKGROUND: Recent studies link altered cardiac beta-adrenergic receptor (AR) signaling to the pathology of alcoholic cardiomyopathy (ACM). However, the alteration and functional effect of beta(3)-AR activation in ACM are unknown. We tested the hypothesis that chronic alcohol intake causes an up-regulation of cardiac beta(3)-AR, which exacerbates myocyte dysfunction and impairs calcium regulation, thereby directly contributing to the progression of ACM. METHODS: We compared myocyte beta(3)- and beta(1)-AR expression and myocyte contractile ([Ca(2+)](i)), transient ([Ca(2+)](iT)), and Ca(2+) current (I(Ca,L)) responses to beta- and beta(3)-AR stimulation in myocytes obtained from left ventricle (LV) tissue samples obtained from 10 normal control (C) and 16 monkeys with self-administered alcohol for 12 months prior to necropsy: 6 moderate (M) and 10 heavy (H) drinkers with group average alcohol intakes of 1.5 +/- 0.2 and 3.3 +/- 0.2 g/kg/d, respectively. RESULTS: Compared with control myocytes (C), in alcoholic cardiomyocytes, basal cell contraction (dL/dt(max), -39%, H: 69.8 vs. C: 114.6 microm/s), relaxation (dR/dt(max), -37%, 58.2 vs. 92.9 microm/s), [Ca(2+)](iT) (-34%, 0.23 vs. 0.35), and I(Ca,L) (-25%, 4.8 vs. 6.4pA/pF) were all significantly reduced. Compared with controls, in moderate and heavy drinkers, beta(1)-AR protein levels decreased by 23% and 42%, but beta(3)-AR protein increased by 46% and 85%, respectively. These changes were associated with altered myocyte functional responses to beta-AR agonist, isoproterenol (ISO), and beta(3)-AR agonist, BRL-37344 (BRL). Compared with controls, in alcoholic myocytes, ISO (10(-8) M) produced significantly smaller increases in dL/dt(max) (H: 40% vs. C: 71%), dR/dt(max) (37% vs. 52%), [Ca(2+)](iT) (17% vs. 37%), and I(Ca,L) (17% vs. 27%), but BRL (10(-8) M) produced a significantly greater decrease in dL/dt(max) (H: -23% vs. C: -11%), [Ca(2+)](iT) (-30% vs. -11%), and I(Ca,L) (-28% vs. -17%). CONCLUSIONS: Chronic alcohol consumption down-regulates cardiac beta(1)- and up-regulates beta(3)-ARs, contributing to the abnormal response to catecholamines in ACM. The up-regulation of cardiac beta(3)-AR signaling enhances inhibition of LV myocyte contraction and relaxation and exacerbates the dysfunctional [Ca(2+)](i) regulation and, thus, may precede the development of ACM.

Stretched extracellular matrix proteins turn fouling and are functionally rescued by the chaperones albumin and casein.

While evidence is mounting that cells exploit protein unfolding for mechanochemical signal conversion (mechanotransduction), what mechanisms are in place to deal with the unwanted consequences of exposing hydrophobic residues upon force-induced protein unfolding? Here, we show that mechanical chaperones exist that can transiently bind to hydrophobic residues that are freshly exposed by mechanical force. The stretch-upregulated binding of albumin or casein to fibronectin fibers is reversible and does not inhibit fiber contraction once the tension is released.

Restrictive left ventricular filling pattern does not result from increased left atrial pressure alone.

BACKGROUND: The restrictive filling pattern seen with severe heart failure (HF) may be due to diastolic dysfunction with elevated left ventricular (LV) diastolic pressure or may be merely a manifestation of an overfilled LV as a result of increased left atrial (LA) pressure. We investigated whether the LV restrictive filling pattern is due to elevated LA pressure alone. METHODS AND RESULTS: We studied conscious dogs instrumented to measure LA pressure, LV pressure, and 3 LV diameters. LV filling dynamics were evaluated in 2 situations with similar elevations of LA pressure: in normal animals after rapid volume loading with dextran 500 mL and in animals with pacing-induced HF with restrictive filling. With HF, there was increased LV chamber stiffness and slow relaxation. Volume loading and HF had similar heart rates (129+/-19 versus 131+/-15 bpm) and LA pressure (22.1+/-5.8 versus 22.6+/-3.3 mm Hg). The peak early filling rate (E) was increased with both HF and volume loading. However, in HF, the peak mitral annular velocity (E') was decreased and delayed, and the E deceleration time was shorter. In contrast, with volume loading, E' was increased and not delayed. CONCLUSIONS: The restrictive filling pattern is distinguished from overfilling of a normal ventricle by a reduced and delayed E' and a shortened E deceleration time that reflect slow relaxation and increased LV stiffness.

Development and validation of a risk score for predicting death in Chagas' heart disease.

BACKGROUND: Chagas' disease is an important health problem in Latin America, and cardiac involvement is associated with substantial morbidity and mortality. We developed a model to predict the risk of death in patients with Chagas' heart disease. METHODS: We retrospectively evaluated 424 outpatients from a regional Brazilian cohort. The association of potential risk factors with death was tested by Cox proportional-hazards analysis, and a risk score was created. The model was validated in 153 patients from a separate community hospital. RESULTS: During a mean follow-up of 7.9 years, 130 patients in the development cohort died. Six independent prognostic factors were identified, and each was assigned a number of points proportional to its regression coefficient: New York Heart Association class III or IV (5 points), evidence of cardiomegaly on radiography (5 points), left ventricular systolic dysfunction on echocardiography (3 points), nonsustained ventricular tachycardia on 24-hour Holter monitoring (3 points), low QRS voltage on electrocardiography (2 points), and male sex (2 points). We calculated risk scores for each patient and defined three risk groups: low risk (0 to 6 points), intermediate risk (7 to 11 points), and high risk (12 to 20 points). In the development cohort, the 10-year mortality rates for these three groups were 10 percent, 44 percent, and 84 percent, respectively. In the validation cohort, the corresponding mortality rates were 9 percent, 37 percent, and 85 percent. The C statistic for the point system was 0.84 in the development cohort and 0.81 in the validation cohort. CONCLUSIONS: A simple risk score was developed to predict death in Chagas' heart disease and was validated in an independent cohort.