Is remodeling the dominant compensatory mechanism in both chronic heart failure with preserved and reduced left ventricular ejection fraction?

Left ventricular contractance: A new measure of contractile function

AIMS

Myocardial contractility is poorly defined and difficult to compare between studies. Contractance or myocardial active strain energy density (MASED) measures the mechanical work done per unit volume (with units of kJ/m³) by any cardiac tissue during contraction. Contractance is an ideal candidate for measuring contractile function as it combines information from both stress and strain.

METHODS AND RESULTS

Data obtained from three previously published experimental studies using trabecular tissue was used to provide contemporaneous nominal stress and strain data in 18 different scenarios with different loading conditions. Contractance varied in the differing loading conditions with values of 1.16 (low preload), 2.02 (high afterload) and 3.76 kJ/m³ (normal). Contractance varied between 0 with isometric loading and 2.14 kJ/m³ with an isotonic and moderate afterload. Increasing inotropy increased contractance to 4.7 kJ/m³.

CONCLUSION

We showed that calculating MASED was feasible and provided a measure of energy production (work done) per unit volume of myocardium during contraction. The new term for contractile function, contractance, can be defined and quantified by MASED. Contractance measures contractile function in differing preload, afterload and inotropic settings. The method of measuring contractance is transferable to the assessment of global and regional systolic function.

Left ventricular active strain energy density is a promising new measure of systolic function

The left ventricular ejection fraction does not accurately predict exercise capacity or symptom severity and has a limited role in predicting prognosis in heart failure. A better method of assessing ventricular performance is needed to aid understanding of the pathophysiological mechanisms and guide management in conditions such as heart failure. In this study, we propose two novel measures to quantify myocardial performance, the global longitudinal active strain energy (GLASE) and its density (GLASED) and compare them to existing measures in normal and diseased left ventricles. GLASED calculates the work done per unit volume of muscle (energy density) by combining information from myocardial strain and wall stress (contractile force per unit cross sectional area). Magnetic resonance images were obtained from 183 individuals forming four cohorts (normal, hypertension, dilated cardiomyopathy, and cardiac amyloidosis). GLASE and GLASED were compared with the standard ejection fraction, the corrected ejection fraction, myocardial strains, stroke work and myocardial forces. Myocardial shortening was decreased in all disease cohorts. Longitudinal stress was normal in hypertension, increased in dilated cardiomyopathy and severely decreased in amyloid heart disease. GLASE was increased in hypertension. GLASED was mildly reduced in hypertension (1.39 ± 0.65 kJ/m3), moderately reduced in dilated cardiomyopathy (0.86 ± 0.45 kJ/m3) and severely reduced in amyloid heart disease (0.42 ± 0.28 kJ/m3) compared to the control cohort (1.94 ± 0.49 kJ/m3). GLASED progressively decreased in the hypertension, dilated cardiomyopathy and cardiac amyloid cohorts indicating that mechanical work done and systolic performance is severely reduced in cardiac amyloid despite the relatively preserved ejection fraction. GLASED provides a new technique for assessing left ventricular myocardial health and contractile function.

Ability of soluble ST2 to predict left ventricular remodeling in patients with acute coronary syndrome

The association of the soluble suppression of tumorigenicity 2 (sST2) and the prognosis of heart failure have been well evaluated. However, little is known about the prediction of sST2 for left ventricular (LV) remodeling in acute coronary syndrome (ACS). We investigated the ability of sST2 to predict LV remodeling following the revascularization of ACS. From May 2019 to December 2020, 95 patients with LV ejection fraction (EF) < 50% who underwent coronary revascularization for ACS (unstable angina, non-ST-elevation myocardial infarction, ST-elevation myocardial infarction) were enrolled. Echocardiography and sST2 were performed at baseline and at a 3-month follow-up. The association between LV remodeling, using the end-diastolic volume index, and sST2 at baseline and at the 3-month follow-up, and the difference between each value was explored. During follow-up, 41 patients showed LV adverse remodeling. The baseline sST2 increased in patients without adverse remodeling (32.05 ng/mL vs. 23.5 ng/mL, p < 0.001), although clinical characteristics were similar between the two groups. During the mean follow-up of 3 months, a significant correlation was found in the changes between sST2 and LV end-diastolic/systolic volume index (r = 0.649; p < 0.001, r = 0.618; p < 0.001, respectively), but not in the changes of LVEF (r = - 0.132, p = 0.204). The use of angiotensin-converting enzyme 2 inhibitors/receptor blockers was higher (90.7% vs. 53.7%, p < 0.001) and sST2 decreased more predominantly in patients without adverse remodeling (23.18 ng/mL vs 26.40 ng/mL, p = 0.003). However, the changes in sST2 and LV volume were not different according to the ACS types (p > 0.05, for all). Estimates of the odds ratio (OR) for remodeling according to the sST2 difference increased substantially with a negative increase in the sST2 difference. Multivariable analysis found that, the difference between the baseline and 3-month sST2 was the most important determinant of LV remodeling following the revascularization of ACS (OR 1.24; 95% confidence interval: 1.09 to 1.41; p = 0.001). In conclusion, an increase in sST2 during follow-up was a useful predictor of LV remodeling.

The end of the unique myocardial band: Part II. Clinical and functional considerations

Two of the leading concepts of mural ventricular architecture are the unique myocardial band and the myocardial mesh model. We have described, in an accompanying article published in this journal, how the anatomical, histological and high-resolution computed tomographic studies strongly favour the latter concept. We now extend the argument to describe the linkage between mural architecture and ventricular function in both health and disease. We show that clinical imaging by echocardiography and magnetic resonance imaging, and electrophysiological studies, all support the myocardial mesh model. We also provide evidence that the unique myocardial band model is not compatible with much of scientific research.

The Relationship Between Left Ventricular Wall Thickness, Myocardial Shortening, and Ejection Fraction in Hypertensive Heart Disease: Insights From Cardiac Magnetic Resonance Imaging

Hypertensive heart disease is often associated with a preserved left ventricular ejection fraction despite impaired myocardial shortening. The authors investigated this paradox in 55 hypertensive patients (52±13 years, 58% male) and 32 age- and sex-matched normotensive control patients (49±11 years, 56% male) who underwent cardiac magnetic resonance imaging at 1.5T. Long-axis shortening (R=0.62), midwall fractional shortening (R=0.68), and radial strain (R=0.48) all decreased (P<.001) as end-diastolic wall thickness increased. However, absolute wall thickening (defined as end-systolic minus end-diastolic wall thickness) was maintained, despite the reduced myocardial shortening. Absolute wall thickening correlated with ejection fraction (R=0.70, P<.0001). In multiple linear regression analysis, increasing wall thickness by 1 mm independently increased ejection fraction by 3.43 percentage points (adjusted β-coefficient: 3.43 [2.60-4.26], P<.0001). Increasing end-diastolic wall thickness augments ejection fraction through preservation of absolute wall thickening. Left ventricular ejection fraction should not be used in patients with hypertensive heart disease without correction for degree of hypertrophy.

Physiological mechanisms of pulmonary hypertension

Pulmonary hypertension is usually related to obstruction of pulmonary blood flow at the level of the pulmonary arteries (eg, pulmonary embolus), pulmonary arterioles (idiopathic pulmonary hypertension), pulmonary veins (pulmonary venoocclusive disease) or mitral valve (mitral stenosis and regurgitation). Pulmonary hypertension is also observed in heart failure due to left ventricle myocardial diseases regardless of the ejection fraction. Pulmonary hypertension is often regarded as a passive response to the obstruction to pulmonary flow. We review established fluid dynamics and physiology and discuss the mechanisms underlying pulmonary hypertension. The important role that the right ventricle plays in the development and maintenance of pulmonary hypertension is discussed. We use principles of thermodynamics and discuss a potential common mechanism for a number of disease states, including pulmonary edema, through adding pressure energy to the pulmonary circulation.

Left ventricular ejection fraction is determined by both global myocardial strain and wall thickness

Objectives

The purpose of this study was to determine the mathematical relationship between left ventricular ejection fraction and global myocardial strain. A reduction in myocardial strain would be expected to cause a fall in ejection fraction. However, there is abundant evidence that abnormalities of myocardial strain can occur with a normal ejection fraction. Explanations such as a compensatory increase in radial or circumferential strain are not supported by clinical studies. We set out to determine the biomechanical relationship between ejection fraction, wall thickness and global myocardial strain.

Methods

The study used an established abstract model of left ventricular contraction to examine the effect of global myocardial strain and wall thickness on ejection fraction. Equations for the relationship between ejection fraction, wall thickness and myocardial strain were obtained using curve fitting methods.

Results

The mathematical relationship between ejection fraction, ventricular wall thickness and myocardial strain was derived as follows: φ = e^{(0.14Ln(ε) + 0.06)ω + (0.9Ln(ε) + 1.2)}, where φ is ejection fraction (%), ω is wall thickness (cm) and ε is myocardial strain (−%).

Conclusion

The findings of this study explain the coexistence of reduced global myocardial strain and normal ejection fraction seen in clinical observational studies. Our understanding of the pathophysiological processes in heart failure and associated conditions is substantially enhanced. These results provide a much better insight into the biophysical inter-relationship between myocardial strain and ejection fraction. This improved understanding provides an essential foundation for the design and interpretation of future clinical mechanistic and prognostic studies.

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Ejection fraction has a limited value in predicting mortality and functional capacity.

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Myocardial mechanics including the relationship between myocardial strain and ejection fraction are currently poorly understood.

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We showed that there is biophysical relationship between end-diastolic wall thickness, myocardial strain and ejection fraction.

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Such a relationship explains the poor correlation of ejection fraction with prognosis and functional capacity.

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The study provides the foundation for determining the relationship between ventricular hypertrophy, ejection fraction and prognosis.

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words

Abnormal calcium homeostasis in heart failure with preserved ejection fraction is related to both reduced contractile function and incomplete relaxation: an electromechanically detailed biophysical modeling study

Heart failure with preserved ejection fraction (HFpEF) accounts for about 50% of heart failure cases. It has features of incomplete relaxation and increased stiffness of the left ventricle. Studies from clinical electrophysiology and animal experiments have found that HFpEF is associated with impaired calcium homeostasis, ion channel remodeling and concentric left ventricle hypertrophy (LVH). However, it is still unclear how the abnormal calcium homeostasis, ion channel and structural remodeling affect the electro-mechanical dynamics of the ventricles. In this study we have developed multiscale models of the human left ventricle from single cells to the 3D organ, which take into consideration HFpEF-induced changes in calcium handling, ion channel remodeling and concentric LVH. Our simulation results suggest that at the cellular level, HFpEF reduces the systolic calcium level resulting in a reduced systolic contractile force, but elevates the diastolic calcium level resulting in an abnormal residual diastolic force. In our simulations, these abnormal electro-mechanical features of the ventricular cells became more pronounced with the increase of the heart rate. However, at the 3D organ level, the ejection fraction of the left ventricle was maintained due to the concentric LVH. The simulation results of this study mirror clinically observed features of HFpEF and provide new insights toward the understanding of the cellular bases of impaired cardiac electromechanical functions in heart failure.

Swimming-induced pulmonary oedema in two triathletes: a novel pathophysiological explanation

Swimming-induced pulmonary oedema/edema (SIPO/SIPE) is likely to become commoner with increasing popularity of endurance sports meaning an increased awareness by participants, organisers and medical personnel is important, especially as individuals are at increased risk of future life threatening episodes and drowning if an accurate diagnosis and appropriate advice are not given. The most important risk factors we identified are a highly trained individual, competitive exercise, hypertension and cold environment.

Systems biology and biomechanical model of heart failure

Heart failure is seen as a complex disease caused by a combination of a mechanical disorder, cardiac remodeling and neurohormonal activation. To define heart failure the systems biology approach integrates genes and molecules, interprets the relationship of the molecular networks with modular functional units, and explains the interaction between mechanical dysfunction and cardiac remodeling. The biomechanical model of heart failure explains satisfactorily the progression of myocardial dysfunction and the development of clinical phenotypes. The earliest mechanical changes and stresses applied in myocardial cells and/or myocardial loss or dysfunction activate left ventricular cavity remodeling and other neurohormonal regulatory mechanisms such as early release of natriuretic peptides followed by SAS and RAAS mobilization. Eventually the neurohormonal activation and the left ventricular remodeling process are leading to clinical deterioration of heart failure towards a multi-organic damage. It is hypothesized that approaching heart failure with the methodology of systems biology we promote the elucidation of its complex pathophysiology and most probably we can invent new therapeutic strategies.

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.

A general theory of acute and chronic heart failure

Current concepts of heart failure propose multiple heterogeneous pathophysiological mechanisms. Recently a theoretical framework for understanding chronic heart failure was suggested. This paper develops this framework to include acute heart failure syndromes. We propose that all acute heart failure syndromes may be understood in terms of a relative fall in left ventricular stroke volume. The initial compensatory mechanism is frequently a tachycardia often resulting in a near normal cardiac output. In more severe forms a fall in cardiac output causes hypotension or cardiogenic shock. In chronic heart failure the stroke volume and cardiac output is returned to normal predominantly through ventricular remodeling or dilatation. Ejection fraction is simply the ratio of stroke volume and end-diastolic volume. The resting stroke volume is predetermined by the tissue's needs; therefore, if the ejection fraction changes, the end-diastolic volume must change in a reciprocal manner. The potential role of the right heart in influencing the presentation of left heart disease is examined. We propose that acute pulmonary edema occurs when the right ventricular stroke volume exceeds left ventricular stroke volume leading to fluid accumulation in the alveoli. The possible role of the right heart in determining pulmonary hypertension and raised filling pressures in left-sided heart disease are discussed. Different clinical scenarios are presented to help clarify these proposed mechanisms and the clinical implications of these theories are discussed. Finally an alternative definition of heart failure is proposed.

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.

The TIR/BB-loop mimetic AS-1 prevents cardiac hypertrophy by inhibiting IL-1R-mediated MyD88-dependent signaling

Activation of NF-κB contributes to cardiac hypertrophy and the interleukin-1 receptor (IL-1R)-mediated MyD88-dependent signaling pathway predominately activates NF-κB. Recent studies have shown that the TIR/BB-Loop mimetic (AS-1) disrupted the interaction of MyD88 with the IL-1R, resulting in blunting of NF-κB activation. We have examined the effects of AS-1 on the IL-1β-induced hypertrophic response using cultured neonatal cardiac myocytes in vitro and transverse aortic constriction (TAC) pressure overload-induced cardiac hypertrophy in vivo. Neonatal cardiac myocytes were treated with AS-1 15 min prior to IL-1β stimulation for 24 h. AS-1 treatment significantly attenuated IL-1β-induced hypertrophic responses of cardiac myocytes. In vivo experiments showed that AS-1 administration prevented cardiac hypertrophy and dysfunction induced by pressure overload. AS-1 administration disrupted the interaction of IL-1R with MyD88 in the pressure overloaded hearts and prevented activation of NF-κB. In addition, AS-1 prevented increases in activation of the MAPK pathway (p38 and p-ERK) in TAC-induced hypertrophic hearts. Our data suggest that the IL-1R-mediated MyD88-dependent signaling pathway plays a role in the development of cardiac hypertrophy and AS-1 attenuation of cardiac hypertrophy is mediated by blocking the interaction between IL-1R and MyD88, resulting in decreased NF-κB binding activity and decreased MAPK activation.