Adaptations of the left ventricle to chronic pressure overload

The fate and role of the pericytes in myocardial diseases

The adult mammalian heart contains a large population of pericytes that play important roles in homeostasis and disease. In the normal heart, pericytes regulate microvascular permeability and flow. Myocardial diseases are associated with marked alterations in pericyte phenotype and function. This review manuscript discusses the role of pericytes in cardiac homeostasis and disease. Following myocardial infarction (MI), cardiac pericytes participate in all phases of cardiac repair. During the inflammatory phase, pericytes may secrete cytokines and chemokines and may regulate leukocyte trafficking, through formation of intercellular gaps that serve as exit points for inflammatory cells. Moreover, pericyte contraction induces microvascular constriction, contributing to the pathogenesis of 'no-reflow' in ischemia and reperfusion. During the proliferative phase, pericytes are activated by growth factors, such as transforming growth factor (TGF)-β and contribute to fibrosis, predominantly through secretion of fibrogenic mediators. A fraction of pericytes acquires fibroblast identity but contributes only to a small percentage of infarct fibroblasts and myofibroblasts. As the scar matures, pericytes form a coat around infarct neovessels, promoting stabilization of the vasculature. Pericytes may also be involved in the pathogenesis of chronic heart failure, by regulating inflammation, fibrosis, angiogenesis and myocardial perfusion. Pericytes are also important targets of viral infections (such as SARS-CoV2) and may be implicated in the pathogenesis of cardiac complications of COVID19. Considering their role in myocardial inflammation, fibrosis and angiogenesis, pericytes may be promising therapeutic targets in myocardial disease.

Soft robotic platform for progressive and reversible aortic constriction in a small-animal model

Our understanding of cardiac remodeling processes due to left ventricular pressure overload derives largely from animal models of aortic banding. However, these studies fail to enable control over both disease progression and reversal, hindering their clinical relevance. Here, we describe a method for progressive and reversible aortic banding based on an implantable expandable actuator that can be finely tuned to modulate aortic banding and debanding in a rat model. Through catheterization, imaging, and histologic studies, we demonstrate that our platform can recapitulate the hemodynamic and structural changes associated with pressure overload in a controllable manner. We leveraged soft robotics to enable noninvasive aortic debanding, demonstrating that these changes can be partly reversed because of cessation of the biomechanical stimulus. By recapitulating longitudinal disease progression and reversibility, this animal model could elucidate fundamental mechanisms of cardiac remodeling and optimize timing of intervention for pressure overload.

Large animal models to study effectiveness of therapy devices in the treatment of heart failure with preserved ejection fraction (HFpEF)

Our understanding of the complex pathophysiology of Heart failure with preserved ejection fraction (HFpEF) is limited by the lack of a robust in vivo model. Existing in-vivo models attempt to reproduce the four main phenotypes of HFpEF; ageing, obesity, diabetes mellitus and hypertension. To date, there is no in vivo model that represents all the haemodynamic characteristics of HFpEF, and only a few have proven to be reliable for the preclinical evaluation of potentially new therapeutic targets. HFpEF accounts for 50% of all the heart failure cases and its incidence is on the rise, posing a huge economic burden on the health system. Patients with HFpEF have limited therapeutic options available. The inadequate effectiveness of current pharmaceutical therapeutics for HFpEF has prompted the development of device-based treatments that target the hemodynamic changes to reduce the symptoms of HFpEF. However, despite the potential of device-based solutions to treat HFpEF, most of these therapies are still in the developmental stage and a relevant HFpEF in vivo model will surely expedite their development process. This review article outlines the major limitations of the current large in-vivo models in use while discussing how these designs have helped in the development of therapy devices for the treatment of HFpEF.

Correlation between artificial intelligence-enabled electrocardiogram and echocardiographic features in aortic stenosis

Aims

An artificial intelligence-enabled electrocardiogram (AI-ECG) is a promising tool to detect patients with aortic stenosis (AS) before developing symptoms. However, functional, structural, or haemodynamic components reflected in AI-ECG responsible for its detection are unknown.

Methods and results

The AI-ECG model that was developed at Mayo Clinic using a convolutional neural network to identify patients with moderate-severe AS was applied. In patients used as the testing group, the correlation between the AI-ECG probability of AS and echocardiographic parameters was investigated. This study included 102 926 patients (63.0 ± 16.3 years, 52% male), and 28 464 (27.7%) were identified as AS positive by AI-ECG. Older age, atrial fibrillation, hypertension, diabetes, coronary artery disease, and heart failure were more common in the positive AI-ECG group than in the negative group (P < 0.001). The AI-ECG was correlated with aortic valve area (ρ = -0.48, R² = 0.20), peak velocity (ρ = 0.22, R² = 0.08), and mean pressure gradient (ρ = 0.35, R² = 0.08). The AI-ECG also correlated with left ventricular (LV) mass index (ρ = 0.36, R² = 0.13), E/e' (ρ = 0.36, R² = 0.12), and left atrium volume index (ρ = 0.42, R² = 0.12). Neither LV ejection fraction nor stroke volume index had a significant correlation with the AI-ECG. Age correlated with the AI-ECG (ρ = 0.46, R² = 0.22) and its correlation with echocardiography parameters was similar to that of the AI-ECG.

Conclusion

A combination of AS severity, diastolic dysfunction, and LV hypertrophy is reflected in the AI-ECG to detect AS. There seems to be a gradation of the cardiac anatomical/functional features in the model and its identification process of AS is multifactorial.

Acute Decompensated Aortic Stenosis: State of the Art Review

Aortic stenosis (AS) is a progressive disease that carries a poor prognosis. Patients are managed conservatively until satisfying an indication for transcatheter aortic valve implantation (TAVI) or surgical aortic valve replacement (SAVR) based on AS severity and the presence of symptoms or adverse impact on the myocardium. Up to 1 in 3 TAVIs are performed for patients with acute symptoms of dyspnoea at rest, angina, and/or syncope - termed acute decompensated aortic stenosis (ADAS) and require urgent aortic valve replacement. These patients have longer hospital length of stay, undergo physical deconditioning, have a higher rate of acute kidney injury and mortality compared to stable patients with less severe symptoms. There is an urgent need to prevent ADAS and to deliver pathways to manage and improve ADAS-related outcomes. We provide here a contemporary review on epidemiological and pathophysiological aspects of ADAS, with a focus on the impact of ADAS from clinical and economic perspectives. We will offer also a global overview of the available evidence for treatment of ADAS and with priorities suggested for addressing current gaps in the literature and unmet clinical needs to improve outcomes for AS patients.

Cardiomyocyte Proliferation from Fetal- to Adult- and from Normal- to Hypertrophy and Failing Hearts

Simple Summary

Death from injury to the heart from a variety of causes remains a major cause of mortality worldwide. The cardiomyocyte, the major contracting cell of the heart, is responsible for pumping blood to the rest of the body. During fetal development, these immature cardiomyocytes are small and rapidly divide to complete development of the heart by birth when they develop structural and functional characteristics of mature cells which prevent further division. All further growth of the heart after birth is due to an increase in the size of cardiomyocytes, hypertrophy. Following the loss of functional cardiomyocytes due to coronary artery occlusion or other causes, the heart is unable to replace the lost cells. One of the significant research goals has been to induce adult cardiomyocytes to reactivate the cell cycle and repair cardiac injury. This review explores the developmental, structural, and functional changes of the growing cardiomyocyte, and particularly the sarcomere, responsible for force generation, from the early fetal period of reproductive cell growth through the neonatal period and on to adulthood, as well as during pathological response to different forms of myocardial diseases or injury. Multiple issues relative to cardiomyocyte cell-cycle regulation in normal or diseased conditions are discussed.

Abstract

The cardiomyocyte undergoes dramatic changes in structure, metabolism, and function from the early fetal stage of hyperplastic cell growth, through birth and the conversion to hypertrophic cell growth, continuing to the adult stage and responding to various forms of stress on the myocardium, often leading to myocardial failure. The fetal cell with incompletely formed sarcomeres and other cellular and extracellular components is actively undergoing mitosis, organelle dispersion, and formation of daughter cells. In the first few days of neonatal life, the heart is able to repair fully from injury, but not after conversion to hypertrophic growth. Structural and metabolic changes occur following conversion to hypertrophic growth which forms a barrier to further cardiomyocyte division, though interstitial components continue dividing to keep pace with cardiac growth. Both intra- and extracellular structural changes occur in the stressed myocardium which together with hemodynamic alterations lead to metabolic and functional alterations of myocardial failure. This review probes some of the questions regarding conditions that regulate normal and pathologic growth of the heart.

Early Protective Role of Inflammation in Cardiac Remodeling and Heart Failure: Focus on TNFα and Resident Macrophages

Cardiac hypertrophy, initiated by a variety of physiological or pathological stimuli (hemodynamic or hormonal stimulation or infarction), is a critical early adaptive compensatory response of the heart. The structural basis of the progression from compensated hypertrophy to pathological hypertrophy and heart failure is still largely unknown. In most cases, early activation of an inflammatory program reflects a reparative or protective response to other primary injurious processes. Later on, regardless of the underlying etiology, heart failure is always associated with both local and systemic activation of inflammatory signaling cascades. Cardiac macrophages are nodal regulators of inflammation. Resident macrophages mostly attenuate cardiac injury by secreting cytoprotective factors (cytokines, chemokines, and growth factors), scavenging damaged cells or mitochondrial debris, and regulating cardiac conduction, angiogenesis, lymphangiogenesis, and fibrosis. In contrast, excessive recruitment of monocyte-derived inflammatory macrophages largely contributes to the transition to heart failure. The current review examines the ambivalent role of inflammation (mainly TNFα-related) and cardiac macrophages (Mφ) in pathophysiologies from non-infarction origin, focusing on the protective signaling processes. Our objective is to illustrate how harnessing this knowledge could pave the way for innovative therapeutics in patients with heart failure.

Transforming growth factor-β in myocardial disease

Transforming growth factor-β (TGFβ) isoforms are upregulated and activated in myocardial diseases and have an important role in cardiac repair and remodelling, regulating the phenotype and function of cardiomyocytes, fibroblasts, immune cells and vascular cells. Cardiac injury triggers the generation of bioactive TGFβ from latent stores, through mechanisms involving proteases, integrins and specialized extracellular matrix (ECM) proteins. Activated TGFβ signals through the SMAD intracellular effectors or through non-SMAD cascades. In the infarcted heart, the anti-inflammatory and fibroblast-activating actions of TGFβ have an important role in repair; however, excessive or prolonged TGFβ signalling accentuates adverse remodelling, contributing to cardiac dysfunction. Cardiac pressure overload also activates TGFβ cascades, which initially can have a protective role, promoting an ECM-preserving phenotype in fibroblasts and preventing the generation of injurious, pro-inflammatory ECM fragments. However, prolonged and overactive TGFβ signalling in pressure-overloaded cardiomyocytes and fibroblasts can promote cardiac fibrosis and dysfunction. In the atria, TGFβ-mediated fibrosis can contribute to the pathogenic substrate for atrial fibrillation. Overactive or dysregulated TGFβ responses have also been implicated in cardiac ageing and in the pathogenesis of diabetic, genetic and inflammatory cardiomyopathies. This Review summarizes the current evidence on the role of TGFβ signalling in myocardial diseases, focusing on cellular targets and molecular mechanisms, and discussing challenges and opportunities for therapeutic translation.

A rapid electromechanical model to predict reverse remodeling following cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is an effective therapy for patients who suffer from heart failure and ventricular dyssynchrony such as left bundle branch block (LBBB). When it works, it reverses adverse left ventricular (LV) remodeling and the progression of heart failure. However, CRT response rate is currently as low as 50-65%. In theory, CRT outcome could be improved by allowing clinicians to tailor the therapy through patient-specific lead locations, timing, and/or pacing protocol. However, this also presents a dilemma: there are far too many possible strategies to test during the implantation surgery. Computational models could address this dilemma by predicting remodeling outcomes for each patient before the surgery takes place. Therefore, the goal of this study was to develop a rapid computational model to predict reverse LV remodeling following CRT. We adapted our recently developed computational model of LV remodeling to simulate the mechanics of ventricular dyssynchrony and added a rapid electrical model to predict electrical activation timing. The model was calibrated to quantitatively match changes in hemodynamics and global and local LV wall mass from a canine study of LBBB and CRT. The calibrated model was used to investigate the influence of LV lead location and ischemia on CRT remodeling outcome. Our model results suggest that remodeling outcome varies with both lead location and ischemia location, and does not always correlate with short-term improvement in QRS duration. The results and time frame required to customize and run this model suggest promise for this approach in a clinical setting.

Large animal models of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is characterized by diastolic dysfunction and multiple comorbidities. The number of patients is continuously increasing, with no improvement in its unfavorable prognosis, and there is a strong need for novel treatments. New devices and drugs are difficult to assess at the translational preclinical step due to the lack of high-fidelity large animal models of HFpEF. In this review, we describe the summary of historical and evolving techniques for developing large animal models. The representative methods are pressure overload models, including (1) aortic banding, (2) aortic stent, (3) renal hypertension, and (4) mineralocorticoid-induced hypertension. Diet-induced metabolic syndromes are also used. A new technique with an inflatable balloon inside the left ventricle can be used during acute/chronic in vivo surgeries to simulate HFpEF-like hemodynamics for pump-based therapies. Canines and porcine are most widely used, but other non-rodent animals (sheep, non-human primates, felines, or calves) have been used. Feline models present the most well-simulated HFpEF pathology, but small size is a concern, and the information is still very limited. The rapid and reliable establishment of large animal models for HFpEF, and novel methodology based on the past experimental attempts with large animals, are needed.

The canine chronic atrioventricular block model in cardiovascular preclinical drug research

Ventricular cardiac arrhythmia is a life threating condition arising from abnormal functioning of many factors in concert. Animal models mirroring human electrophysiology are essential to predict and understand the rare pro- and anti-arrhythmic effects of drugs. This is very well accomplished by the canine chronic atrioventricular block (CAVB) model. Here we summarize canine models for cardiovascular research, and describe the development of the CAVB model from its beginning. Understanding of the structural, contractile and electrical remodelling processes following atrioventricular (AV) block provides insight in the many factors contributing to drug-induced arrhythmia. We also review all safety pharmacology studies, efficacy and mechanistic studies on anti-arrhythmic drugs in CAVB dogs. Finally, we compare pros and cons with other in vivo preclinical animal models. In view of the tremendous amount of data obtained over the last 100 years from the CAVB dog model, it can be considered as man's best friend in preclinical drug research.

Left Ventricular Remodeling in Degenerative Aortic Valve Stenosis

Aortic stenosis was once considered a pure isolated valve obstacle challenging left ventricle driving force of contraction and flow generation. Left ventricular (LV) adaptation was merely interpreted as a uniform hypertrophic response to increased afterload. However, in these last 2 decades cardiac imaging research and some histopathology correlation studies brought insight towards the complex interaction between the vasculature, the valve and the myocardium. Verily, LV remodeling in this setting is a complex multidetermined process that goes further beyond myocardial hypertrophy. Ultrastructural changes involving both diffuse and replacement fibrosis of the myocardium take part and might explain the transition of clinical phenotypes with distinct prognosis, from compensated hypertrophy to LV maladaptive dysfunction and heart failure. Presently, the combined appropriate use of echocardiography and cardiac magnetic resonance may better assess the global LV afterload, hypertrophy and geometric remodeling, global and regional LV function, beyond ejection fraction, and structural changes that include the fibrotic burden of the myocardium. As a whole these may not only better stratify individual risk of disease progression but also identify patients benefiting from earlier valve intervention. In this paper, we review the maladaptive response of the LV to chronic pressure overload, describing the different signaling pathways and mechanisms that underly both hypertrophy and remodeling. Histomorphology changes in this setting are described and we try to make sense of the use of new imaging tools for LV characterization.

Acute effects of transcatheter aortic valve replacement on the ventricular-aortic interaction

Transcatheter aortic valve replacement (TAVR) is linked with an immediate increase in aortic systolic blood pressure and maximal flow, as well as steeper aortic pressure and flow wave upstrokes. After TAVR, the forward wave pumped by the heart is enhanced. Although the arterial properties remain unchanged, the central augmentation index (AIx) is markedly decreased after TAVR. This challenges the interpretation of AIx as a solely vascular measure in patients with aortic valve stenosis.

Prognostic value of the H2 FPEF score in patients undergoing transcatheter aortic valve implantation

Aims

The aim of this study was to assess the prognostic value of the H₂FPEF score in patients undergoing transcatheter aortic valve implantation (TAVI) for severe aortic stenosis (AS) and preserved left ventricular ejection fraction (EF).

Methods and results

In this multicentre study, a total of 832 patients from two German high‐volume centres, who received TAVI for severe AS and preserved EF (≥50%), were identified for calculation of the H₂FPEF score. Patients were dichotomized according to low (0–5 points; n = 570) and high (6–9 points; n = 262) H₂FPEF scores. Kaplan–Meier and Cox regression analyses were applied to assess the prognostic impact of the H₂FPEF score. We observed a decrease in stroke volume index (−2.04 mL/m²/point) and mean transvalvular gradients (−1.14 mmHg/point) with increasing H₂FPEF score translating into a higher prevalence of paradoxical low‐flow, low‐gradient AS among patients with high H₂FPEF score. One year after TAVI, the rates of all‐cause (low vs. high H₂FPEF score: 8.0% vs. 19.4%, P < 0.0001) and cardiovascular (CV) mortality (1.9% vs. 9.0%, P < 0.0001) as well as the rate of CV mortality or rehospitalization for congestive heart failure (6.4% vs. 23.2%, P < 0.0001) were higher in patients with high H₂FPEF score compared with those with low H₂FPEF score. After multivariable analysis, a high H₂FPEF score remained independently predictive of all‐cause mortality [hazard ratio 1.59 (1.28–2.35), P = 0.018] and CV mortality or rehospitalization for congestive heart failure [hazard ratio 2.92 (1.65–5.15), P < 0.001]. Among the H₂FPEF score variables, atrial fibrillation, pulmonary hypertension, and elevated left ventricular filling pressure were the strongest outcome predictors.

Conclusions

The H₂FPEF score serves as an independent predictor of adverse CV and heart failure outcome among TAVI patients with preserved EF. A high H₂FPEF score is associated with the presence of paradoxical low‐flow, low‐gradient AS, the HFpEF in patients with AS. By identifying patients in advanced stages of HFpEF, the H₂FPEF score might be useful as a risk prediction tool in patients with preserved EF scheduled for TAVI.

Large Animal Models of Heart Failure: A Translational Bridge to Clinical Success

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Preclinical large animal models play a critical and expanding role in translating basic science findings to the development and clinical approval of novel cardiovascular therapeutics.

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This state-of-the-art review outlines existing methodologies and physiological phenotypes of several HF models developed in large animals. A comprehensive list of porcine, ovine, and canine models of disease are presented, and the translational importance of these studies to clinical success is highlighted through a brief overview of recent devices approved by the FDA alongside associated clinical trials and preclinical animal reports.

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Increasing the use of large animal models of HF holds significant potential for identifying new mechanisms underlying this disease and providing valuable information regarding the safety and efficacy of new therapies, thus, improving physiological and economical translation of animal research to the successful treatment of human HF.

Preclinical large animal models of heart failure (HF) play a critical and expanding role in translating basic science findings to the development and clinical approval of novel therapeutics and devices. The complex combination of cardiovascular events and risk factors leading to HF has proved challenging for the development of new treatments for these patients. This state-of-the-art review presents historical and recent studies in porcine, ovine, and canine models of HF and outlines existing methodologies and physiological phenotypes. The translational importance of large animal studies to clinical success is also highlighted with an overview of recent devices approved by the Food and Drug Administration, together with preclinical HF animal studies used to aid both development and safety and/or efficacy testing. Increasing the use of large animal models of HF holds significant potential for identifying the novel mechanisms underlying the clinical condition and to improving physiological and economical translation of animal research to successfully treat human HF.

Left Ventricular Global Longitudinal Strain Is Associated With Long-Term Outcomes in Moderate Aortic Stenosis

Background:

Left ventricular global longitudinal strain (GLS) is associated with long-term outcomes of patients with severe aortic stenosis. However, its prognostic value in patients with moderate aortic stenosis remains unknown.

Methods:

Patients diagnosed with moderate aortic stenosis (1.0< aortic valve area ≤1.5 cm 2 ) and left ventricular ejection fraction ≥50% were identified. GLS was assessed by 2-dimensional strain imaging using speckle-tracking method. All-cause mortality was assessed according to the median GLS value.

Results:

Two hundred eighty-seven patients were included (median age 76 years; 47% male). Mean aortic valve area was 1.25 cm 2 , left ventricular ejection fraction 62%, and median GLS −15.2%. During a median follow-up of 3.9 years, there were 103 deaths (36%). Mortality was higher in patients with GLS>−15.2% (hazard ratio 2.62 [95% CI 1.69–4.06]) compared with patients with GLS ≤−15.2% even after adjusting for confounders. Mortality rates at 1, 3, 5 years were 21%, 35%, 48%, respectively, in patients with GLS >−15.2%, and 6%, 15%, 19% in those with GLS ≤−15.2%. Even among those with left ventricular ejection fraction ≥60%, GLS discriminated higher-risk patients ( P =0.0003). During follow-up, 106 (37%) patients underwent aortic valve replacement with median waiting-time of 2.4 years, and their survival was better than patients without aortic valve replacement. Among those patients undergoing aortic valve replacement, prognosis was still worse in patients with GLS >−15.2% ( P =0.04). Mortality rates at 1, 3, 5 years were 2%, 10%, 20%, respectively, in patients with GLS >-15.2% and 2%, 5%, 6% in those with GLS ≤−15.2%.

Conclusions:

Impaired GLS in moderate aortic stenosis patients is associated with higher mortality rates even among those undergoing aortic valve replacement.

Heart Plasticity in Response to Pressure- and Volume-Overload: A Review of Findings in Compensated and Decompensated Phenotypes

The adult human heart has an exceptional ability to alter its phenotype to adapt to changes in environmental demand. This response involves metabolic, mechanical, electrical, and structural alterations, and is known as cardiac plasticity. Understanding the drivers of cardiac plasticity is essential for development of therapeutic agents. This is particularly important in contemporary cardiology, which uses treatments with peripheral effects (e.g., on kidneys, adrenal glands). This review focuses on the effects of different hemodynamic loads on myocardial phenotype. We examine mechanical scenarios of pressure- and volume overload, from the initial insult, to compensated, and ultimately decompensated stage. We discuss how different hemodynamic conditions occur and are underlined by distinct phenotypic and molecular changes. We complete the review by exploring how current basic cardiac research should leverage available cardiac models to study mechanical load in its different presentations.

Predictions of hypertrophy and its regression in response to pressure overload

Mechanics-based cardiac growth models can now predict changes in mass, chamber size, and wall thickness in response to perturbations such as pressure overload (PO), volume overload, and myocardial infarction with a single set of growth parameters. As these models move toward clinical applications, many of the most interesting applications involve predictions of whether or how a patient's heart will reverse its growth after an intervention. In the case of PO, significant regression in wall thickness is observed both experimentally and clinically following relief of overload, for example following replacement of a stenotic aortic valve. Therefore, the objective of this work was to evaluate the ability of a published cardiac growth model that captures forward growth in multiple situations to predict growth reversal following relief of PO. Using a finite element model of a beating canine heart coupled to a circuit model of the circulation, we quantitatively matched hemodynamic data from a canine study of aortic banding followed by unbanding. Surprisingly, although the growth model correctly predicted the time course of PO-induced hypertrophy, it predicted only limited growth reversal given the measured unbanding hemodynamics, contradicting experimental and clinical observations. We were able to resolve this discrepancy only by incorporating an evolving homeostatic setpoint for the governing growth equations. Furthermore, our analysis suggests that many strain- and stress-based growth laws using the traditional volumetric growth framework will have similar difficulties capturing regression following the relief of PO unless growth setpoints are allowed to evolve.

Using machine learning to characterize heart failure across the scales

Heart failure is a progressive chronic condition in which the heart undergoes detrimental changes in structure and function across multiple scales in time and space. Multiscale models of cardiac growth can provide a patient-specific window into the progression of heart failure and guide personalized treatment planning. Yet, the predictive potential of cardiac growth models remains poorly understood. Here, we quantify predictive power of a stretch-driven growth model using a chronic porcine heart failure model, subject-specific multiscale simulation, and machine learning techniques. We combine hierarchical modeling, Bayesian inference, and Gaussian process regression to quantify the uncertainty of our experimental measurements during an 8-week long study of volume overload in six pigs. We then propagate the experimental uncertainties from the organ scale through our computational growth model and quantify the agreement between experimentally measured and computationally predicted alterations on the cellular scale. Our study suggests that stretch is the major stimulus for myocyte lengthening and demonstrates that a stretch-driven growth model alone can explain [Formula: see text] of the observed changes in myocyte morphology. We anticipate that our approach will allow us to design, calibrate, and validate a new generation of multiscale cardiac growth models to explore the interplay of various subcellular-, cellular-, and organ-level contributors to heart failure. Using machine learning in heart failure research has the potential to combine information from different sources, subjects, and scales to provide a more holistic picture of the failing heart and point toward new treatment strategies.

The Extracellular Matrix in Ischemic and Nonischemic Heart Failure

The ECM (extracellular matrix) network plays a crucial role in cardiac homeostasis, not only by providing structural support, but also by facilitating force transmission, and by transducing key signals to cardiomyocytes, vascular cells, and interstitial cells. Changes in the profile and biochemistry of the ECM may be critically implicated in the pathogenesis of both heart failure with reduced ejection fraction and heart failure with preserved ejection fraction. The patterns of molecular and biochemical ECM alterations in failing hearts are dependent on the type of underlying injury. Pressure overload triggers early activation of a matrix-synthetic program in cardiac fibroblasts, inducing myofibroblast conversion, and stimulating synthesis of both structural and matricellular ECM proteins. Expansion of the cardiac ECM may increase myocardial stiffness promoting diastolic dysfunction. Cardiomyocytes, vascular cells and immune cells, activated through mechanosensitive pathways or neurohumoral mediators may play a critical role in fibroblast activation through secretion of cytokines and growth factors. Sustained pressure overload leads to dilative remodeling and systolic dysfunction that may be mediated by changes in the interstitial protease/antiprotease balance. On the other hand, ischemic injury causes dynamic changes in the cardiac ECM that contribute to regulation of inflammation and repair and may mediate adverse cardiac remodeling. In other pathophysiologic conditions, such as volume overload, diabetes mellitus, and obesity, the cell biological effectors mediating ECM remodeling are poorly understood and the molecular links between the primary insult and the changes in the matrix environment are unknown. This review article discusses the role of ECM macromolecules in heart failure, focusing on both structural ECM proteins (such as fibrillar and nonfibrillar collagens), and specialized injury-associated matrix macromolecules (such as fibronectin and matricellular proteins). Understanding the role of the ECM in heart failure may identify therapeutic targets to reduce geometric remodeling, to attenuate cardiomyocyte dysfunction, and even to promote myocardial regeneration.

Can the echocardiographic LV mass equation reliably demonstrate stable LV mass following acute change in LV load?

Background

Limited data are available on performance of the left ventricular (LV) mass equation when there is a dynamic change to LV load. We aimed to test this equation in the immediate post-operative period following aortic valve replacement (AVR) for aortic regurgitation (AR) to see if it would reliably demonstrate stable LV mass before and after surgery. Since LV mass would be unlikely to change in the immediate postoperative period, we hypothesized that a decrease in LV diameter postoperatively would be accompanied by concomitant increases in LV wall thickness as predicted by the LV mass equation.

Methods

We reviewed echocardiograms of adult patients with AR who underwent AVR from 2007-2017 at Montefiore Medical Center (n=28). Three independent readers performed septal wall thickness (SWT), posterior wall thickness (PWT) and left ventricular internal diameter (LVID) measurements on pre-operative and post-operative echocardiograms. LV masses were calculated using the American Society of Echocardiography (ASE) equation.

Results

Post-operatively, LVID decreased from 5.7±1.2 to 4.9±1.0 cm, P<0.001. SWT was noted to increase from 1.08±0.20 to 1.18±0.27 cm, P=0.03, but PWT was unchanged, 1.11±0.21 to 1.16±0.27 cm, P=0.21. Accordingly, the LV mass equation calculated a decrease in LV mass from 266±126 to 232±99 gm, P=0.01. A control group of coronary artery bypass grafting alone (n=14) did not demonstrate any significant change in SWT, LVID, PWT and LV mass measurements. Similar findings were found for all three readers.

Conclusions

Following aortic valve replacement for regurgitation, the LV mass equation calculated a reduction in LV mass in the immediate postoperative period. Since an immediate change in LV mass after AVR is unlikely, we feel that these results highlight an important limitation of the mass equation, when used with acutely changing loading conditions.

New classification of geometric ventricular patterns in severe aortic stenosis: Could it be clinically useful?

BACKGROUND

In severe aortic stenosis, different left ventricle (LV) remodeling patterns as a response to pressure overload have distinct hemodynamic profiles, cardiac function, and outcomes. The most common classification considers LV relative wall thickness and LV mass index to create 4 different groups. A new classification including also end-diastolic volume index has been recently proposed.

AIM

To describe the prevalence of the newly identified remodeling patterns in patients with severe aortic stenosis and to evaluate their clinical relevance according to symptoms.

METHODS

We analyzed 286 consecutive patients with isolated severe aortic stenosis. Current guidelines were used for echocardiographic evaluation. Symptoms were defined as the presence of angina, syncope, or NYHA class III-IV.

RESULTS

The mean age was 75 ± 9 years, 156 patients (54%) were men, while 158 (55%) were symptomatic. According to the new classification, the most frequent remodeling pattern was concentric hypertrophy (57.3%), followed by mixed (18.9%) and dilated hypertrophy (8.4%). There were no patients with eccentric remodeling; only 4 patients had a normalLV geometry. Symptomatic patients showed significantly more mixed hypertrophy (P < .05), while the difference regarding the prevalence of the other patterns was not statistically significant. When we analyzed the distribution of the classic 4 patterns stratified by the presence of symptoms, however, we did not find a significant difference (P = .157).

CONCLUSIONS

The new classification had refined the description of different cardiac geometric phenotypes that develop as a response to pressure overload. It might be superior to the classic 4 patterns in terms of association with symptoms.

Predicting the Time Course of Ventricular Dilation and Thickening Using a Rapid Compartmental Model

The ability to predict long-term growth and remodeling of the heart in individual patients could have important clinical implications, but the time to customize and run current models makes them impractical for routine clinical use. Therefore, we adapted a published growth relation for use in a compartmental model of the left ventricle (LV). The model was coupled to a circuit model of the circulation to simulate hemodynamic overload in dogs. We automatically tuned control and acute model parameters based on experimentally reported hemodynamic data and fit growth parameters to changes in LV dimensions from two experimental overload studies (one pressure, one volume). The fitted model successfully predicted the reported time course of LV dilation and thickening not only in independent studies of pressure and volume overload but also following myocardial infarction. Implemented in MATLAB on a desktop PC, the model required just 6 min to simulate 3 months of growth.

A Comparison of Phenomenologic Growth Laws for Myocardial Hypertrophy

The heart grows in response to changes in hemodynamic loading during normal development and in response to valve disease, hypertension, and other pathologies. In general, a left ventricle subjected to increased afterload (pressure overloading) exhibits concentric growth characterized by thickening of individual myocytes and the heart wall, while one experiencing increased preload (volume overloading) exhibits eccentric growth characterized by lengthening of myocytes and dilation of the cavity. Predictive models of cardiac growth could be important tools in evaluating treatments, guiding clinical decision making, and designing novel therapies for a range of diseases. Thus, in the past 20 years there has been considerable effort to simulate growth within the left ventricle. While a number of published equations or systems of equations (often termed "growth laws") can capture some aspects of experimentally observed growth patterns, no direct comparisons of the various published models have been performed. Here we examine eight of these laws and compare them in a simple test-bed in which we imposed stretches measured during in vivo pressure and volume overload. Laws were compared based on their ability to predict experimentally measured patterns of growth in the myocardial fiber and radial directions as well as the ratio of fiber-to-radial growth. Three of the eight laws were able to reproduce most key aspects of growth following both pressure and volume overload. Although these three growth laws utilized different approaches to predict hypertrophy, they all employed multiple inputs that were weakly correlated during in vivo overload and therefore provided independent information about mechanics.

Relation of Left Ventricular Mass to Prognosis in Initially Asymptomatic Mild to Moderate Aortic Valve Stenosis

The prognostic importance of left ventricular (LV) mass in nonsevere asymptomatic aortic stenosis has not been documented in a large prospective study.

The left ventricle in aortic stenosis--imaging assessment and clinical implications

Aortic stenosis has an increasing prevalence in the context of aging population. In these patients non-invasive imaging allows not only the grading of valve stenosis severity, but also the assessment of left ventricular function. These two goals play a key role in clinical decision-making. Although left ventricular ejection fraction is currently the only left ventricular function parameter that guides intervention, current imaging techniques are able to detect early changes in LV structure and function even in asymptomatic patients with significant aortic stenosis and preserved ejection fraction. Moreover, new imaging parameters emerged as predictors of disease progression in patients with aortic stenosis. Although proper standardization and confirmatory data from large prospective studies are needed, these novel parameters have the potential of becoming useful tools in guiding intervention in asymptomatic patients with aortic stenosis and stratify risk in symptomatic patients undergoing aortic valve replacement.

This review focuses on the mechanisms of transition from compensatory left ventricular hypertrophy to left ventricular dysfunction and heart failure in aortic stenosis and the role of non-invasive imaging assessment of the left ventricular geometry and function in these patients.

Selecting oversized donor cardiac allografts for patients with pulmonary hypertension may be unnecessary

INTRODUCTION

There is a tendency to favor oversized donor hearts for heart transplant candidates affected by mild to moderate pulmonary hypertension (PHTN). We hypothesize that both undersized and oversized donor hearts fare equally well in this setting.

METHODS

A total of 107 cases from 2003 to 2008 were retrospectively reviewed and subsequently divided into those receiving organs from undersized donors (group 1: donor weight/recipient weight ≤ 0.90, n = 37) and oversized donors (group 2: donor weight/recipient weight ≥ 1.2, n = 70). PHTN was identified in the perioperative period in those patients with systolic pulmonary artery pressure (SPAP) ≥ 40 mm Hg. Endpoints of mortality and hemodynamic data were investigated.

RESULTS

Of 107 patients, 37 received undersized donor allografts, with a mean donor-to-recipient weight ratio of 0.8, and 70 received oversized donors allografts, with a mean donor-to-recipient ratio of 1.4. Perioperative PAH was diagnosed in 20 of the 37 (54%) patients from the undersized group (mean SPAP = 45.9 mm Hg) and 41 of 70 (59%) patients from the oversized group (mean SPAP = 46.5 mm Hg). There was no significant difference in right ventricular function at 1 week, 1 month, or 6 months. Left ventricular function was similar between both groups at 6 months (P = .22). The mean SPAP in the undersized group was 45.9, 33.4, 31.8, and 23.1 mm Hg at the perioperative, 1 week, 1 month, and 6 month time points, respectively. Corresponding mean SPAP for the oversized group was 46.5, 35.0, 29.4, and 26.1 mm Hg. The 1 month, 1 year, and 3 year survivals were similar in both groups.

CONCLUSIONS

Oversized and undersized donor hearts fared equally well in the setting of mild to moderate perioperative PAH. This in addition to the propensity for resolution of pulmonary hypertension over time suggests that the current practice of favoring oversized donor hearts for patients with pre-transplantation PAH may be unwarranted.

[Asymptomatic severe aortic stenosis: a reopened debate]

Aortic stenosis is a complex disease. About 2-7% of the population over 65 years of age is affected by its degenerative form. In patients with severe aortic stenosis presenting with symptoms or left ventricle ejection fraction (LVEF)<.50, aortic valve replacement is indicated. Management and timing of surgery in asymptomatic patients with preserved LVEF is still a matter of debate. Recent published data show that about one third of these patients present with low left ventricle stroke volume, which may affect survival. For this reason, and considering that aortic valve replacement is in most cases a low risk procedure, early surgery in this subgroup is a strategy that deserves to be taken into account. In this review we report on these recent findings, which allow understanding why patients with asymptomatic severe aortic stenosis should not be considered and treated as a homogenous population.

Left ventricular remodelling in aortic stenosis

Aortic stenosis (AS) is a progressive condition associated with high mortality if not treated. The hemodynamic effects of AS have serious implications for the left ventricle. In this review, we describe the responses of the left ventricle to AS by highlighting the process of adaptive remodelling, which begins as a beneficial compensatory mechanism but ultimately transitions to a maladaptive process with potentially irreversible consequences. We discuss the impact of left ventricular (LV) remodelling on diastolic and systolic function and on the development of symptoms. In addition, we review the adverse consequences of maladaptive LV remodelling on clinical outcomes before and after aortic valve replacement. The relative irreversibility of maladaptive remodelling and the clear relationship between its progression and clinical outcomes suggest a need to incorporate measures of LV performance beyond simply systolic function when deciding on the timing of valve replacement.

Coexisting cardiac diseases and pressure recovery phenomenon contribute to discrepancy between the echocardiographic severity of aortic stenosis and left ventricular hypertrophy

BACKGROUND

Assessing left ventricular (LV) hypertrophy (LVH) is an important step in the echocardiographic diagnosis of aortic stenosis (AS). We aimed to investigate the causes of discrepancies between the degrees of AS and LVH.

METHODS

The study subjects consisted of 149 consecutive patients with AS having aortic valve area <2.0 cm(2) (mean age 72.5 ± 11.9 years, 67 men and 82 women). Coexisting cardiac diseases were determined based on echocardiographic findings and comprehensive clinical judgment. Echocardiographic measurements included LV mass index (LVMI), aortic valve area index (AVAI), transaortic mean pressure gradient (MPG), valvulo-arterial impedance (Zva), energy loss coefficient (ELCo), and energy loss index (ELI).

RESULTS

LVMI was not significantly correlated with AVAI and Zva, and had a weak correlation with MPG (r = 0.305, p = 0.0001). There were 55 patients in group A (non-severe AS without significant LVH), 58 in group B (non-severe AS with significant LVH), 7 in group C (severe AS without significant LVH), and 29 in group D (severe AS with significant LVH). Coexisting cardiac diseases were more frequently observed (p = 0.0003) in group B (50 %) than in group A (18 %). In group C, ELCo and (ELI - AVAI)/ELI were significantly greater than in group D (p = 0.043 and 0.007, respectively).

CONCLUSION

Significant LVH seen in less than moderate AS is often due to coexisting cardiac diseases, and there may be an overestimation of AS severity due to pressure recovery among patients with apparently severe AS who do not have significant LVH.

Congenital valvular aortic stenosis in young adults: predictors for rate of progression of stenosis and aortic dilatation

BACKGROUND

Congenital aortic stenosis (AS) is the most common obstructive left-sided cardiac lesion in young adults, however little is known about the progression in adults. Therefore, we aimed to evaluate the progression rate of AS and aortic dilatation in a large multicenter retrospective cohort of asymptomatic young adults with congenital valvular AS.

METHODS

Data were obtained from chart abstraction. Linear mixed-effects models were used to evaluate the progression of AS and aortic dilatation over time. A joint model combining longitudinal echocardiographic and survival data was used for survival analysis.

RESULTS

A total of 414 patients (age 29 ± 10 years, 68% male) were included. Median follow-up duration was 4.1 (2.5-5.1) years (1587 patient-years). Peak aortic velocity was 3.4 ± 0.7 m/s at baseline and did not change over time in the total patient population (-0.01 ± 0.03 m/s/year). Increased left ventricular mass was significantly associated with faster AS progression (p<0.001). Aortic dilatation was present in 34% at baseline and 48% at follow-up (p<0.001). The aortic diameter linearly increased over time with a rate of 0.7 ± 0.2mm/year. Rate of aortic dissection was 0.06% per patient-year. Seventy patients required an aortic valve intervention (4.4% per patient-year), with AS progression rate as most powerful predictor (HR 5.11 (95% CI 3.47-7.53)).

CONCLUSIONS

In the majority of patients with mild-to-moderate congenital AS, AS severity does not progress over time. However patients with left ventricular hypertrophy are at risk for faster progression and should be monitored carefully. Although aortic dissections rarely occur, aortic dilatation is common and steadily progresses over time, warranting serial aortic imaging.

Follistatin-like 3 mediates paracrine fibroblast activation by cardiomyocytes

Follistatins are extracellular inhibitors of the TGF-β family ligands including activin A, myostatin and bone morphogenetic proteins. Follistatin-like 3 (FSTL3) is a potent inhibitor of activin signalling and antagonises the cardioprotective role of activin A in the heart. FSTL3 expression is elevated in patients with heart failure and is upregulated in cardiomyocytes by hypertrophic stimuli, but its role in cardiac remodelling is largely unknown. Here, we show that the production of FSTL3 by cardiomyocytes contributes to the paracrine activation of cardiac fibroblasts, inducing changes in cell adhesion, promoting proliferation and increasing collagen production. We found that FSTL3 is necessary for this response and for the induction of cardiac fibrosis. However, full activation requires additional factors, and we identify connective tissue growth factor as a FSTL3 binding partner in this process. Together, our data unveil a novel mechanism of paracrine communication between cardiomyocytes and fibroblasts that may provide potential as a therapeutic target in heart remodelling.

A single strain-based growth law predicts concentric and eccentric cardiac growth during pressure and volume overload

Adult cardiac muscle adapts to mechanical changes in the environment by growth and remodeling (G&R) via a variety of mechanisms. Hypertrophy develops when the heart is subjected to chronic mechanical overload. In ventricular pressure overload (e.g. due to aortic stenosis) the heart typically reacts by concentric hypertrophic growth, characterized by wall thickening due to myocyte radial growth when sarcomeres are added in parallel. In ventricular volume overload, an increase in filling pressure (e.g. due to mitral regurgitation) leads to eccentric hypertrophy as myocytes grow axially by adding sarcomeres in series leading to ventricular cavity enlargement that is typically accompanied by some wall thickening. The specific biomechanical stimuli that stimulate different modes of ventricular hypertrophy are still poorly understood. In a recent study, based on in-vitro studies in micropatterned myocyte cell cultures subjected to stretch, we proposed that cardiac myocytes grow longer to maintain a preferred sarcomere length in response to increased fiber strain and grow thicker to maintain interfilament lattice spacing in response to increased cross-fiber strain. Here, we test whether this growth law is able to predict concentric and eccentric hypertrophy in response to aortic stenosis and mitral valve regurgitation, respectively, in a computational model of the adult canine heart coupled to a closed loop model of circulatory hemodynamics. A non-linear finite element model of the beating canine ventricles coupled to the circulation was used. After inducing valve alterations, the ventricles were allowed to adapt in shape in response to mechanical stimuli over time. The proposed growth law was able to reproduce major acute and chronic physiological responses (structural and functional) when integrated with comprehensive models of the pressure-overloaded and volume-overloaded canine heart, coupled to a closed-loop circulation. We conclude that strain-based biomechanical stimuli can drive cardiac growth, including wall thickening during pressure overload.

Assessment and management of aortic valve disease in patients with left ventricular dysfunction

The onset of symptoms or left ventricular systolic dysfunction heralds a poor prognosis for patients with either aortic stenosis or aortic regurgitation. Echocardiography is the primary imaging modality for assessment of aortic valvular lesions. Cardiac catheterization is indicated to determine the severity of the aortic valve lesion when there is a discrepancy between the clinical findings and the results of echocardiography in patients with either symptoms or left ventricular dysfunction. For patients with low-gradient, low-output aortic stenosis, dobutamine provocation should be used to differentiate truly severe aortic stenosis from patients with a primary cardiomyopathy and low aortic valve area due to low forward flow. Aortic valve surgery improves myocardial performance by relief of ventricular afterload in both patients with severe stenosis and those with severe regurgitation. Surgery should be pursued in both patients with severe aortic stenosis and those with severe regurgitation regardless of the degree of left ventricular dysfunction.

Effects of diabetes mellitus, pressure-overload and their association on myocardial structure and function

BACKGROUND

Structural and functional changes involved in cardiac injury induced by diabetes mellitus, pressure-overload, or both conditions were evaluated.

METHODS

Pressure-overload was established by suprarenal aortic banding in rats. Six weeks later, diabetes was induced by streptozotocin (STZ, 65 mg/kg, intraperitoneally), resulting in four groups: SHAM, banded (BA), diabetic (DM), and diabetic-banded (DM-BA). On the 12th week, left ventricular (LV) structure and function were evaluated. LV function was assessed in vivo with pressure-volume catheters and in vitro by papillary muscles' performance at baseline and in response to isoprenaline (ISO, 10(-8) to 10(-5) M).

RESULTS

Compared to SHAM, we observed a significant increase of type-B natriuretic peptide (BA = 370 +/- 110%; DM-BA = 580 +/- 210%), LV mass (BA = 36.8 +/- 3.6%; DM-BA = 32.1 +/- 3.1%), cardiomyocyte diameter (BA = 19.5 +/- 2.3%; DM = 14.3 +/- 1.9%; DM-BA = 11.4 +/- 2.0%), fibrosis (BA = 85 +/- 14%; DM = 145 +/- 28%; DM-BA = 155 +/- 14%), advanced glycation end-product (AGE) deposition (DM = 141 +/- 29%; DM-BA = 166 +/- 46%), contraction (tAT: DM = 13.7 +/- 2.4%; DM-BA = 26.3 +/- 7.1%); a delayed relaxation (tHR: DM = 13.8 +/- 2.6%; DM-BA = 25.5 +/- 9.2%) and a decrease of collagen type-I/type-III ratio (DM = -66.1 +/- 4.6%; DM-BA = -51.9 +/- 5.5). In SHAM animals, ISO (10(-5) M) increased 86.5 +/- 26.2% active tension, 105.3 +/- 20.2% dT/dt(max), and 166.8 +/- 29.9% dT/dt(min). Similar effects were observed in BA and DM animals, whereas in DM-BA these inotropic and lusitropic responses were blunted. Moreover, at a similar resting muscle length, ISO decreased passive tension by 12 +/- 3% in SHAM and 11 +/- 3% in BA, indicating an increase in myocardial distensibility, an effect that was absent in both diabetic groups.

CONCLUSION

Long-standing pressure-overload increased LV mass, while diabetes promoted AGE and collagen deposition, which might explain the abolition of ISO-induced increased myocardial distensibility. Association of pressure-overload and diabetes completely blunted the inotropic and lusitropic responses to ISO, with no additional structural damages than in pressure-overload or diabetes alone.

CT angiography of the cardiac valves: normal, diseased, and postoperative appearances

Although echocardiography remains the principal imaging technique for assessment of the cardiac valves, contrast material-enhanced electrocardiographically gated computed tomographic (CT) angiography is proving to be an increasingly valuable complementary modality in this setting. CT angiography allows excellent visualization of the morphologic features and function of the normal valves, as well as of a wide range of valve diseases, including congenital and acquired diseases, infectious endocarditis, and complications of valve replacement. The number, thickness, and opening and closing of the valve leaflets, as well as the presence of valve calcification, can be directly observed. CT angiography also permits simultaneous assessment of the valves and coronary arteries, which may prove valuable in presurgical planning. Unlike echocardiography and magnetic resonance imaging, however, CT angiography requires ionizing radiation and does not provide a direct measure of the valvular pressure gradient. Nevertheless, with further development of related imaging techniques, CT angiography can be expected to play an increasingly important role in the evaluation of the cardiac valves. Supplemental material available at http://radiographics.rsna.org/cgi/content/full/29/5/1393/DC1.

Microarray identifies extensive downregulation of noncollagen extracellular matrix and profibrotic growth factor genes in chronic isolated mitral regurgitation in the dog

BACKGROUND

The volume overload of isolated mitral regurgitation (MR) in the dog results in left ventricular (LV) dilatation and interstitial collagen loss. To better understand the mechanism of collagen loss, we performed a gene array and overlaid regulated genes into ingenuity pathway analysis.

METHODS AND RESULTS

Gene arrays from LV tissue were compared in 4 dogs before and 4 months after MR. Cine-magnetic resonance-derived LV end-diastolic volume increased 2-fold (P=0.005), and LV ejection fraction increased from 41% to 53% (P<0.007). LV interstitial collagen decreased 40% (P<0.05) compared with controls, and replacement collagen was in short strands and in disarray. Ingenuity pathway analysis identified Marfan syndrome, aneurysm formation, LV dilatation, and myocardial infarction, all of which have extracellular matrix protein defects and/or degradation. Matrix metalloproteinase-1 and -9 mRNA increased 5- (P=0.01) and 10-fold (P=0.003), whereas collagen I did not change and collagen III mRNA increased 1.5-fold (P=0.02). However, noncollagen genes important in extracellular matrix structure were significantly downregulated, including decorin, fibulin 1, and fibrillin 1. In addition, connective tissue growth factor and plasminogen activator inhibitor were downregulated, along with multiple genes in the transforming growth factor-beta signaling pathway, resulting in decreased LV transforming growth factor-beta1 activity (P=0.03).

CONCLUSIONS

LV collagen loss in isolated, compensated MR is chiefly due to posttranslational processing and degradation. The downregulation of multiple noncollagen genes important in global extracellular matrix structure, coupled with decreased expression of multiple profibrotic factors, explains the failure to replace interstitial collagen in the MR heart.