The plasticity of cardiac sympathetic nerves and its clinical implication in cardiovascular disease

Comprehensive Insights into Mechanisms for Ventricular Remodeling in Right Heart Failure

Ventricular remodeling in right heart failure is a complex pathological process involving interactions between multiple mechanisms. Overactivation of the neuro-hormonal pathways, activation of the oxidative stress response, expression of cytokines, apoptosis of cardiomyocytes, and alterations of the extracellular matrix (ECM) are among the major mechanisms involved in the development of ventricular remodeling in right heart failure. These mechanisms are involved in ventricular remodeling, such as myocardial hypertrophy and fibrosis, leading to the deterioration of myocardial systolic and diastolic function. A deeper understanding of these mechanisms can help develop more effective therapeutic strategies in patients with right heart failure (RHF) to improve patient survival and quality of life. Despite the importance of ventricular remodeling in RHF, there are a limited number of studies in this field. This article explores in-depth historical and current information about the specific mechanisms in ventricular remodeling in RHF, providing a theoretical rationale for recognizing its importance in health and disease.

Resting heart rate assessed within clinical practice demonstrates no prognostic relevance for defibrillator recipients in the German DEVICE registry

Resting heart rate (RHR) has prognostic implications in heart failure with reduced ejection fraction, where ≤ 70 bpm is targeted. Whether a RHR > 70 bpm assessed within clinical practice goes along with elevated cardiovascular risk in implantable cardioverter-defibrillator (ICD) / cardiac resynchronization therapy-defibrillator (CRT-D) recipients remains incompletely understood. A total of 1589 patients (ICD n = 1172 / CRT-D n = 417, median age 65 years, 22.6% female) undergoing ICD/CRT-D implantation or revision in the prospective German DEVICE multicenter registry were analyzed. RHR was assessed via a 12-channel electrocardiogram at enrollment. 1-year outcomes (all-cause mortality, major cardio- and cerebrovascular events (MACCE), all-cause hospital admission) were compared between patients with a RHR ≤ 70 bpm and > 70 bpm. 733 patients (46.1%) showed a RHR > 70 bpm. Median RHR was 63 (interquartile range 59; 68) bpm (≤ 70 bpm group) and 80 (75; 89) bpm (> 70 bpm group). Heart failure with reduced ejection fraction was present in 76.3%, a prior myocardial infarction in 32.4% and non-ischemic heart disease in 44.9%. One-year all-cause mortality was similar between RHR groups (≤ 70 bpm 5.4% vs. > 70 bpm 5.4%, p = 0.96), and subgroup analysis regarding patient characteristics and comorbidities revealed only a significantly higher rate of patients with dual chamber ICD in the > 70 bpm group (0.8% vs. 9.2%, p = 0.003). MACCE (5.9% vs. 6.1%, p = 0.87) and defibrillator shock rates (9.9% vs. 9.8%, p = 1.0) were similar. Higher all-cause hospital admission rates were observed in patients with > 70 bpm RHR (23.1% vs. 29.0%, p = 0.027) driven by non-cardiovascular events (6.0% vs. 11.7%, p = 0.001). In conclusion, in ICD and CRT-D recipients a RHR at admission > 70 bpm may indicate patients at increased risk of all-cause hospital admission but not of other adverse cardiovascular events or death at 1-year follow-up.

Continuous peripheral electrical nerve stimulation improves cardiac function via autonomic nerve regulation in MI rats

BACKGROUND

Peripheral electrical nerve stimulation (PENS) reportedly improves cardiac function after myocardial ischemia (MI) by rebalancing the cardiac autonomic nervous system. The dynamic and continuous influence of PENS on autonomic and cardiac function based on cardiac self-repair is not well understood.

OBJECTIVES

This study aimed to explore the relationship between autonomic nervous balance and functional cardiac repair after MI and to clarify the optimal acupoint selection and time course for PENS.

METHODS

The activities of the superior cervical cardiac sympathetic nerve and vagus nerve were recorded to evaluate the autonomic tone directly. The pressure-volume loop system was used for left ventricular diastolic and systolic function. Noninvasive continuous electrocardiography and echocardiography were performed to analyze heart rate, heart rate variability, and left ventricular function. The effect of continuous PENS (cPENS) or instant PENS (iPENS) on autonomic and cardiac indications was tested.

RESULTS

Sympathetic nerve activity and vagus nerve activity increased as compensatory self-regulation on days 7 and 14 post-MI, followed by an imbalance of autonomic tone and cardiac dysfunction on day 28. cPENS at acupoint PC6 maintained autonomic hyperexcitability, improved myocardial systolic and diastolic abilities, and reduced myocardial fibrosis on day 28 post-MI, whereas cPENS at acupoint ST36 had a limited effect. Both iPENS at PC6 and ST36 improved the autonomic and cardiac function of rats in the cPENS groups.

CONCLUSION

Rats showed autonomic fluctuations and cardiac dysfunction 28 days post-MI. cPENS produced sympathomimetic action to sustain cardiac self-compensation, but with acupoint specificity. On the basis of cPENS, iPENS evoked autonomic regulation and cardiac benefits without acupoint differentiation.

Nrf2-Keap1 in Cardiovascular Disease: Which Is the Cart and Which the Horse?

High levels of oxidant stress in the form of reactive oxidant species are prevalent in the circulation and tissues in various types of cardiovascular disease including heart failure, hypertension, peripheral arterial disease, and stroke. Here we review the role of nuclear factor erythroid 2-related factor 2 (Nrf2), an important and widespread antioxidant and anti-inflammatory transcription factor that may contribute to the pathogenesis and maintenance of cardiovascular diseases. We review studies showing that downregulation of Nrf2 exacerbates heart failure, hypertension, and autonomic function. Finally, we discuss the potential for using Nrf2 modulation as a therapeutic strategy for cardiovascular diseases and autonomic dysfunction.

X-ray Radiotherapy Impacts Cardiac Dysfunction by Modulating the Sympathetic Nervous System and Calcium Transients

Recent epidemiological studies have shown that patients with right-sided breast cancer (RBC) treated with X-ray irradiation (IR) are more susceptible to developing cardiovascular diseases, such as arrhythmias, atrial fibrillation, and conduction disturbances after radiotherapy (RT). Our aim was to investigate the mechanisms induced by low to moderate doses of IR and to evaluate changes in the cardiac sympathetic nervous system (CSNS), atrial remodeling, and calcium homeostasis involved in cardiac rhythm. To mimic the RT of the RBC, female C57Bl/6J mice were exposed to X-ray doses ranging from 0.25 to 2 Gy targeting 40% of the top of the heart. At 60 weeks after RI, Doppler ultrasound showed a significant reduction in myocardial strain, ejection fraction, and atrial function, with a significant accumulation of fibrosis in the epicardial layer and apoptosis at 0.5 mGy. Calcium transient protein expression levels, such as RYR2, NAK, Kir2.1, and SERCA2a, increased in the atrium only at 0.5 Gy and 2 Gy at 24 h, and persisted over time. Interestingly, 3D imaging of the cleaned hearts showed an early reduction of CSNS spines and dendrites in the ventricles and a late reorientation of nerve fibers, combined with a decrease in SEMA3a expression levels. Our results showed that local heart IR from 0.25 Gy induced late cardiac and atrial dysfunction and fibrosis development. After IR, ventricular CSNS and calcium transient protein expression levels were rearranged, which affected cardiac contractility. The results are very promising in terms of identifying pro-arrhythmic mechanisms and preventing arrhythmias during RT treatment in patients with RBC.

Exploring the prospects, advancements, and challenges of in vitro modeling of the heart-brain axis

Research on bidirectional communication between the heart and brain has often relied on studies involving nonhuman animals. Dependance on animal models offer limited applicability to humans and a lack of high-throughput screening. Recently, the field of 3D cell biology, specifically organoid technology, has rapidly emerged as a valuable tool for studying interactions across organ systems, i.e., gut-brain axis. The initial success of organoid models indicates the usefulness of 3D cultures for elucidating the intricate interactivity of the autonomic nervous system and overall health. This perspective aims to explore the potential of advancing in vitro modeling of the heart-brain axis by discussing the benefits, applications, and adaptability of organoid technologies. We closely examine the current state of brain organoids in conjunction with the advancements of cardiac organoids. Moreover, we explore the use of combined organoid systems to investigate pathophysiology and provide a platform for treatment discovery. Finally, we address the challenges that accompany the use of 3D models for studying the heart-brain axis with an emphasis on generating tailored engineering strategies for further refinement of dynamic organ system modeling in vitro.

Loss of developmentally derived Irf8+ macrophages promotes hyperinnervation and arrhythmia in the adult zebrafish heart

Recent developments in cardiac macrophage biology have broadened our understanding of the critical functions of macrophages in the heart. As a result, there is further interest in understanding the independent contributions of distinct subsets of macrophage to cardiac development and function. Here, we demonstrate that genetic loss of interferon regulatory factor 8 (Irf8)-positive embryonic-derived macrophages significantly disrupts cardiac conduction, chamber function, and innervation in adult zebrafish. At 4 months post-fertilization (mpf), homozygous irf8st96/st96 mutants have significantly shortened atrial action potential duration and significant differential expression of genes involved in cardiac contraction. Functional in vivo assessments via electro- and echocardiograms at 12 mpf reveal that irf8 mutants are arrhythmogenic and exhibit diastolic dysfunction and ventricular stiffening. To identify the molecular drivers of the functional disturbances in irf8 null zebrafish, we perform single cell RNA sequencing and immunohistochemistry, which reveal increased leukocyte infiltration, epicardial activation, mesenchymal gene expression, and fibrosis. Irf8 null hearts are also hyperinnervated and have aberrant axonal patterning, a phenotype not previously assessed in the context of cardiac macrophage loss. Gene ontology analysis supports a novel role for activated epicardial-derived cells (EPDCs) in promoting neurogenesis and neuronal remodeling in vivo. Together, these data uncover significant cardiac abnormalities following embryonic macrophage loss and expand our knowledge of critical macrophage functions in heart physiology and governing homeostatic heart health.

The sympathetic nervous system in heart failure revisited

Several attempts have been made, by the scientific community, to develop a unifying hypothesis that explains the clinical syndrome of heart failure (HF). The currently widely accepted neurohormonal model has substituted the cardiorenal and the cardiocirculatory models, which focused on salt-water retention and low cardiac output/peripheral vasoconstriction, respectively. According to the neurohormonal model, HF with eccentric left ventricular (LV) hypertrophy (LVH) (systolic HF or HF with reduced LV ejection fraction [LVEF] or HFrEF) develops and progresses because endogenous neurohormonal systems, predominantly the sympathetic nervous system (SNS) and the renin-angiotensin-aldosterone system (RAAS), exhibit prolonged activation following the initial heart injury exerting deleterious hemodynamic and direct nonhemodynamic cardiovascular effects. However, there is evidence to suggest that SNS overactivity often preexists HF development due to its association with HF risk factors, is also present in HF with preserved LVEF (diastolic HF or HFpEF), and that it is linked to immune/inflammatory factors. Furthermore, SNS activity in HF may be augmented by coexisting noncardiac morbidities and modified by genetic factors and demographics. The purpose of this paper is to provide a contemporary overview of the complex associations between SNS overactivity and the development and progression of HF, summarize the underlying mechanisms, and discuss the clinical implications as they relate to therapeutic interventions mitigating SNS overactivity.

Comparative analysis of intracardiac neural structures in the aged rats with essential hypertension

Persistent arterial hypertension initiates cardiac autonomic imbalance and alters cardiac tissues. Previous studies have shown that neural component contributes to arterial hypertension etiology, maintenance, and progression and leads to brain damage, peripheral neuropathy, and remodeling of intrinsic cardiac neural plexus. Recently, significant structural changes of the intracardiac neural plexus were demonstrated in young prehypertensive and adult hypertensive spontaneously hypertensive rats (SHR), yet structural alterations of intracardiac neural plexus that occur in the aged SHR remain undetermined. Thus, we analyzed the impact of uncontrolled arterial hypertension in old (48-52 weeks) SHR and the age-matched Wistar-Kyoto rats (WKY). Intrinsic cardiac neural plexus was examined using a combination of immunofluorescence confocal microscopy and transmission electron microscopy in cardiac sections and whole-mount preparations. Our findings demonstrate that structural changes of intrinsic cardiac neural plexus caused by arterial hypertension are heterogeneous and may support recent physiological implications about cardiac denervation occurring together with the hyperinnervation of the SHR heart. We conclude that arterial hypertension leads to (i) the decrease of the neuronal body area, the thickness of atrial nerves, the number of myelinated nerve fibers, unmyelinated axon area and cumulative axon area in the nerve, and the density of myocardial nerve fibers, and (ii) the increase in myelinated nerve fiber area and density of neuronal bodies within epicardiac ganglia. Despite neuropathic alterations of myelinated fibers were exposed within intracardiac nerves of both groups, SHR and WKY, we consider that the determined significant changes in structure of intrinsic cardiac neural plexus were predisposed by arterial hypertension.