The neurohormonal network in the RAAS can bend before breaking

Mechanisms for the development of heart failure and improvement of cardiac function by angiotensin-converting enzyme inhibitors

Angiotensin-converting enzyme (ACE) inhibitors, which prevent the conversion of angiotensin I to angiotensin II, are well-known for the treatments of cardiovascular diseases, such as heart failure, hypertension and acute coronary syndrome. Several of these inhibitors including captopril, enalapril, ramipril, zofenopril and imidapril attenuate vasoconstriction, cardiac hypertrophy and adverse cardiac remodeling, improve clinical outcomes in patients with cardiac dysfunction and decrease mortality. Extensive experimental and clinical research over the past 35 years has revealed that the beneficial effects of ACE inhibitors in heart failure are associated with full or partial prevention of adverse cardiac remodeling. Since cardiac function is mainly determined by coordinated activities of different subcellular organelles, including sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils, for regulating the intracellular concentration of Ca2+ and myocardial metabolism, there is ample evidence to suggest that adverse cardiac remodelling and cardiac dysfunction in the failing heart are the consequence of subcellular defects. In fact, the improvement of cardiac function by different ACE inhibitors has been demonstrated to be related to the attenuation of abnormalities in subcellular organelles for Ca2+-handling, metabolic alterations, signal transduction defects and gene expression changes in failing cardiomyocytes. Various ACE inhibitors have also been shown to delay the progression of heart failure by reducing the formation of angiotensin II, the development of oxidative stress, the level of inflammatory cytokines and the occurrence of subcellular defects. These observations support the view that ACE inhibitors improve cardiac function in the failing heart by multiple mechanisms including the reduction of oxidative stress, myocardial inflammation and Ca2+-handling abnormalities in cardiomyocytes.

Progression of Myocardial Fibrosis in Nonischemic DCM and Association With Mortality and Heart Failure Outcomes

OBJECTIVES

The purpose of this study was to assess whether the presence and extent of fibrosis changes over time in patients with nonischemic, dilated cardiomyopathy (DCM) receiving optimal medical therapy and the implications of any such changes on left ventricular ejection fraction (LVEF) and clinical outcomes.

BACKGROUND

Myocardial fibrosis on cardiovascular magnetic resonance (CMR) imaging has emerged as important risk marker in patients with DCM.

METHODS

In total, 85 patients (age 56 ± 15 years, 45% women) with DCM underwent serial CMR (median interval 1.5 years) for assessment of LVEF and fibrosis. The primary outcome was all-cause mortality; the secondary outcome was a composite of heart failure hospitalization, aborted sudden cardiac death, left ventricular (LV) assist device implantation, or heart transplant.

RESULTS

On CMR-1, fibrosis (median 0.0 [interquartile range: 0% to 2.6%]) of LV mass was noted in 34 (40%) patients. On CMR-2, regression of fibrosis was not seen in any patient. Fibrosis findings were stable in 70 (82%) patients. Fibrosis progression (increase >1.8% of LV mass or new fibrosis) was seen in 15 patients (18%); 46% of these patients had no fibrosis on CMR-1. Although fibrosis progression was on aggregate associated with adverse LV remodeling and decreasing LVEF (40 ± 7% to 34 ± 10%; p < 0.01), in 60% of these cases the change in LVEF was minimal (<5%). Fibrosis progression was associated with increased hazards for all-cause mortality (hazard ratio: 3.4 [95% confidence interval: 1.5 to 7.9]; p < 0.01) and heart failure-related complications (hazard ratio: 3.5 [95% confidence interval: 1.5 to 8.1]; p < 0.01) after adjustment for clinical covariates including LVEF.

CONCLUSIONS

Once myocardial replacement fibrosis in DCM is present on CMR, it does not regress in size or resolve over time. Progressive fibrosis is often associated with minimal change in LVEF and identifies a high-risk cohort.

Cardiac myosin activators for heart failure therapy: focus on omecamtiv mecarbil

Heart failure continues to be a major global health problem with a pronounced impact on morbidity and mortality and very limited drug treatment options especially with regard to inotropic therapy. Omecamtiv mecarbil is a first-in-class cardiac myosin activator, which increases the proportion of myosin heads that are tightly bound to actin and creates a force-producing state that is not associated with cytosolic calcium accumulation. Phase I and phase II studies have shown that it is safe and well tolerated. It produces dose-dependent increases in systolic ejection time (SET), stroke volume (SV), left ventricular ejection fraction (LVEF), and fractional shortening. In the ATOMIC-AHF trial, intravenous (IV) omecamtiv mecarbil did not improve dyspnoea overall but may have improved it in a high-dose group of acute heart failure patients. It did, however, increase SET, decrease left ventricular end-systolic diameter, and was well tolerated. The COSMIC-HF trial showed that a pharmacokinetic-based dose-titration strategy of oral omecamtiv mecarbil improved cardiac function and reduced ventricular diameters compared to placebo and had a similar safety profile. It also significantly reduced plasma N-terminal-pro B-type natriuretic peptide compared with placebo. The GALACTIC-HF trial is now underway and will compare omecamtiv mecarbil with placebo when added to current heart failure standard treatment in patients with chronic heart failure and reduced LVEF. It is expected to be completed in January 2021. The ongoing range of preclinical and clinical research on omecamtiv mecarbil will further elucidate its full range of pharmacological effects and its clinical usefulness in heart failure.

Fibrosis and heart failure

The extracellular matrix (ECM) is a living network of proteins that maintains the structural integrity of the myocardium and allows the transmission of electrical and mechanical forces between the myocytes for systole and diastole. During ventricular remodeling, as a result of iterations in the hemodynamic workload, collagen, the main component of the ECM, increases and occupies the areas between the myocytes and the vessels. The resultant fibrosis (reparative fibrosis) is initially a compensatory mechanism and may progress adversely influencing tissue stiffness and ventricular function. Replacement fibrosis appears at sites of previous cardiomyocyte necrosis to preserve the structural integrity of the myocardium, but with the subsequent formation of scar tissue and widespread distribution, it has adverse functional consequences. Continued accumulation of collagen impairs diastolic function and compromises systolic mechanics. Nevertheless, the development of fibrosis is a dynamic process wherein myofibroblasts, the principal cellular elements of fibrosis, are not only metabolically active and capable of the production and upregulation of cytokines but also have contractile properties. During the process of reverse remodeling with left ventricular assist device unloading, cellular, structural, and functional improvements are observed in terminal heart failure patients. With the advent of anti-fibrotic pharmacologic therapies, cellular therapy, and ventricular support devices, fibrosis has become an important therapeutic target in heart failure patients. Herein, we review the current concepts of fibrosis as a main component of ventricular remodeling in heart failure patients. Our aim is to integrate the histopathologic process of fibrosis with the neurohormonal, cytochemical, and molecular changes that lead to ventricular remodeling and its physiologic consequences in patients. The concept of fibrosis as living scar allows us to envision targeting this scar as a means of improving ventricular function in heart failure patients.

Alpha-1 adrenoceptor-angiotensin II type 1 receptor cross-talk and its relevance in clinical medicine

The two most relevant clinical trials investigating the efficacy of multiple neurohormonal drug combinations in the treatment of chronic congestive heart failure are the Valsartan Heart Failure Trial and the Candesartan in Heart Failure Assessment of Reduction in Mortality and Morbidity-added studies. The Valsartan Heart Failure Trial study randomized patients with congestive heart failure to the angiotensin receptor blocker (ARB) valsartan versus placebo, in addition to baseline angiotensin-converting enzyme inhibitor (ACE-I) therapy. Overall, valsartan was found to significantly reduce the combined morbidity and mortality end point compared with placebo, mainly due to a reduction in heart failure admissions. However, a subgroup analysis showed that patients receiving triple therapy with valsartan, an ACE-I and a β-adrenoceptor blocker, appeared to do worse. These findings led to speculation that "triple therapy" with ARB, ACE-I, and nonselective β-blocker might be harmful, possibly due to excessive neurohormonal inhibition. In contrast, in the Candesartan in Heart Failure Assessment of Reduction in Mortality and Morbidity-added study, the "triple therapy" combination of ARB, ACE-I, and β-adrenoceptor blocker was proven safe and beneficial. We propose that the discrepancy in outcomes observed in these two trials is related to the interaction between the α1-adrenoceptor and the angiotensin II type-1 receptor, and it is not just an inherent adverse event related to "triple therapy."