Increase In Left Ventricular Wall Stress Research Articles

Influence of verapamil on pressure overload-induced ventricular arrhythmias by regulating gene-expression profiles.

Life-threatening ventricular arrhythmias can lead to sudden cardiac death in patients. This study aimed to investigate the changes in gene profiles involved when verapamil (VRP) affects increased wall stress (pressure overload)-induced ventricular arrhythmias, thus revealing the potential causative molecular mechanisms and therapeutic targets through gene-expression identification and functional analysis. Animal models with wall stress-induced ventricular arrhythmias were established. Low (0.5 mg/kg) and high (1 mg/kg) doses of VRP were administered intravenously 10 minutes before transverse aortic constriction, and average ventricular arrhythmia scores were calculated. Next, we evaluated the molecular role of VRP by characterising differential gene-expression profiles between VRP-pretreated (1 mg/kg) and control groups using RNA-sequencing technology. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to reveal molecular function. A protein-protein interaction (PPI) network was then developed. VRP exerted its anti-arrhythmic effects in response to increases in left ventricular (LV) afterload. We detected differentially expressed genes (DEGs), of which 36 were upregulated and 1 397 downregulated, between the VRP-pretreated and model groups during acute increases in LV wall stress. GO analysis demonstrated that the DEGs were associated with cytoskeletal protein binding. KEGG analysis showed that enriched pathways were mainly distributed in adherens junctions, actin cytoskeleton regulation and the MAPK signalling pathway. Centralities analysis of the PPI identified Rac1, Grb2, Rbm8a and Mapk1 as hub genes. VRP prevented acute pressure overload-induced ventricular arrhythmias, possibly through the hub genes Rac1, Grb2, Rbm8a and Mapk1 as potential targets of VRP.

Inhibition of Lysyl Oxidase Activity Prevents Volume Overload Diastolic and Systolic Dysfunction

The cardiac extracellular matrix (ECM) is a structural framework which bridges cardiomyocytes to the cystoskeletal myofibril, preserving alignment, while providing tensile strength to the myocardium. Abnormalities in the architectural scaffolding of the ECM have been noted during various cardiac pathologies. The major structural components of the cardiac ECM are collagens, which are produced by fibroblasts. The relative expression of collagens and the degree of cross‐linking dictate the passive mechanical properties of the heart. Lysyl oxidase (LOX) is a copper‐dependent amine oxidase that plays a critical role in covalently cross‐linking fibrillar collagens, which determines the insolubility, stiffness and resistance to degradation of the resulting collagen fibrils. In our previous studies we have shown marked increases in LOX expression and activity in failing hearts relative to compensated and unstressed hearts. Our goal of this study was to determine whether LOX inhibition, initiated during the early stages of cardiac remodeling, could attenuate fibrosis and cardiac dysfunction.We used the aortocaval fistula (ACF) surgical model on Sprague‐Dawley rats to induce biventricular volume overload (VO). Two weeks after surgery, both sham‐operated and VO rats were treated with the LOX inhibitor, beta‐aminoproprionitrile (BAPN; 100 mg/kg/d), for 12 weeks. BAPN was administered via an osmotic pump surgically inserted into the abdominal cavity. After a total of 14 weeks of VO, left ventricular (LV) pressure‐volume catheterization was used to assess alterations in cardiac function. Western blot protein analyses were performed to assess alterations in LOX, collagens I and III, matrix metalloproteinases (MMPs), and their inhibitors (TIMPs). Further, LV strain and stiffness were calculated to determine alterations in diastolic function.Our data demonstrate that chronic VO caused a significant increase in LV wall stress at both diastole and systole, and produced significant LV hypertrophy (183%, 60%, and 92% increase, respectively vs. control; p<0.05). Further, VO induced significant increases in LV strain and stiffness (126% and 77% increase, respectively vs. control), as well as significant increases in the expression of fibrotic proteins including LOX, collagen I, collagen III, MMP2, and TIMP1 (135%, 58.4%, 26.7%, 39%, and 63% increase, respectively vs. control; p<0.05). Finally, VO also caused systolic dysfunction, as evident by decreases in cardiac contractility and ejection fraction (51% and 26% decrease, respectively vs. control; p<0.05). Further, our data highlight the cardioprotective role of LOX inhibition against adverse cardiac remodeling due to VO. LOX inhibition completely prevented VO‐induced increases in LV wall stress and ventricular hypertrophy. Further, LOX inhibition prevented VO‐induced fibrosis and diastolic dysfunction, as evident by normalized levels of collagens, LOX, MMPs, TIMPs, and LV stiffness. Finally, LOX inhibition prevented the VO‐induced decline in cardiac contractility. Overall, our data indicate that LOX inhibition prevented adverse ECM remodeling and cardiac dysfunction in the volume overloaded heart.Support or Funding InformationSupport for this project provided by the American Heart Association Southeast Affiliate and the NIH Heart, Lung and Blood Institute: Grant‐in‐Aid (#16GRNT30440008‐JDG), AHA Predoctoral Fellowship (# 16PRE29150010‐EEH), and F31 (#1F31HL134263‐ 01A1‐EEH).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Estrogen receptor antagonism exacerbates cardiac structural and functional remodeling in female rats.

We assessed the estrogen receptor (ER) dependence of female-specific cardioprotection using a rat model of chronic volume-overload stress. ER antagonism worsened ventricular wall stress, ventricular dilation, and cardiac dysfunction induced by volume overload. Further, blocking ERs resulted in cardiac remodeling and functional changes similar to that previously found in ovariectomized rats.

Titin Isoforms, Extracellular Matrix, and Global Chamber Remodeling in Experimental Dilated Cardiomyopathy

Background— Altered titin isoforms may modify cardiac function in heart failure (HF), but the nature of isoform switches and associated functional implications are not well defined. Limited studies have reported an increased compliant isoform (N2BA) expression in human systolic HF. Titin may also modulate stretch-regulated responses such as myocardial natriuretic peptide production. Methods and Results— We characterized titin isoform expression and extracellular matrix in all 4 cardiac chambers and the left ventricular (LV) epicardium and endocardium in normal dogs (n=6) and those with HF (n=6) due to tachypacing and characterized functional implications at the LV myofiber and chamber level. Recognizing the potential for uncoupling of the extracellular matrix and cardiomyocyte in tachypacing, myocardial natriuretic peptide production, a molecular marker of stretch-regulated responses, was also assessed. All chambers were dilated in HF, but the extracellular matrix was not increased. HF dogs had markedly lower N2BA in the atria and right ventricle. In failing LVs, N2BA was decreased only in the epicardium, where myofiber passive stiffness was increased. However, LV chamber mechanics were driven by the marked LV dilatation, with no increase in LV diastolic stiffness. Natriuretic peptide concentrations increased markedly in the endocardium in relation to increases in LV wall stress. Conclusions— Tachypacing HF is characterized by decreases in compliant titin isoform expression in the atria, right ventricle, and LV epicardium. However, LV chamber mechanics are principally determined by geometric and extracellular matrix changes rather than titin-based myofiber stiffness in this model. Stretch-regulated myocardial responses (natriuretic peptide production) appeared intact, suggesting that the mechanotransduction role of titin was not impaired in HF.

Effect of aging on peak systolic left ventricular wall stress in normal subjects

Studies of cardiac mechanics in compensated heart muscle suggest that muscle hypertrophy is stimulated by long-term increases in peak myocardial wall stress. 1–6 Conditions leading to either chronic left ventricular (LV) pressure or volume overload generally result in an increase in LV wall stress (expressed as force per unit area). Increased systolic stress results in decreased LV performance unless compensatory hypertrophy develops to normalize systolic wall stress. Measurements of LV wall stress in patients with chronic LV volume or pressure overload should provide an excellent index of cardiac compensation that could be followed serially to permit detection of early myocardial decompensation such as an abnormal increase in wall stress due to inadequate hypertrophy. 4–6 The objectives of this study were to examine the relation of LV peak systolic wall stress to age and body surface area in normal subjects and to establish the normal range of values for LV peak systolic stress, taking age and body surface area into account. We have shown that in normal subjects, LV wall thickness increases with increasing age and body surface area, while LV internal dimensions decrease slightly with aging, but increase with increasing body surface area. 7–9 To determine the effect of age and body surface area on LV peak systolic (meridional) wall stress, we analyzed M-mode echocardiographic data previously recorded in an adult population without evidence of cardiovascular disease. 7–9