Relationship between regional cardiac hyperinnervation and ventricular arrhythmia

Venous endothelin modulates responsiveness of cardiac sympathetic axons to arterial semaphorin

Developing neurons of the peripheral nervous system reach their targets via cues that support directional growth, a process known as axon guidance. In investigating how sympathetic axons reach the heart in mice, we discovered that a combination of guidance cues are employed in sequence to refine axon outgrowth, a process we term second-order guidance. Specifically, endothelin-1 induces sympathetic neurons expressing the receptor Ednra to project to the vena cavae leading to the heart. Endothelin signaling in turn induces expression of the repulsive receptor Plexin-A4, via induction of the transcription factor MEF2C. In the absence of endothelin or plexin signaling, sympathetic neurons misproject to incorrect competing vascular trajectories (the dorsal aorta and intercostal arteries). The same anatomical and physiological consequences occur in Ednra^+/-; Plxna4^+/- double heterozygotes, genetically confirming functional interaction. Second-order axon guidance therefore multiplexes a smaller number of guidance cues in sequential fashion, allowing precise refinement of axon trajectories.

Inhibition of microRNA-155 attenuates sympathetic neural remodeling following myocardial infarction via reducing M1 macrophage polarization and inflammatory responses in mice

Inflammation plays an important role in sympathetic neural remodeling induced by myocardial infarction (MI). MiR-155 is a vital regulator of inflammatory responses, and macrophage-secreted miR-155 promotes cardiac fibrosis and hypertrophy. However, whether miR-155 influences MI-induced sympathetic neural remodeling is not clear. Therefore, we examined the role of miR-155 in MI-induced sympathetic neural remodeling and the related mechanisms in both an mouse model and in lipopolysaccharide (LPS)-stimulated bone marrow-derived macrophages (BMDMs). Our data showed that miR-155 expression was significantly enhanced in the myocardial tissues of MI mice compared to sham mice. Also, MI up-regulated the electrophysiological parameters, M1 macrophage polarization, inflammatory responses, and suppressor of cytokine signaling 1 (SOCS1) expression, which coincided with the increased expression of sympathetic nerve remodeling markers(nerve growth factor, tyrosine hydroxylase and growth-associated protein 43). Except for SOCS1, these proteins were attenuated by miR-155 antagomir. In vitro, LPS-stimulation promoted miR-155 expression in BMDMs. Consistent with the in vivo findings, miR-155 antagomir diminished the LPS-induced M1 macrophage polarization, nuclear factor (NF)-κB activation, and the expression of pro-inflammatory factors and nerve growth factor; but it increased the expression of SOCS1. Inversely, miR-155 agomir significantly potentiated LPS-induced pathophysiological effects in BMDMs. MiR-155 agomir-induced effects were reversed by the NF-κB inhibitor. Mechanistically, treatment with siRNA against SOCS1 augmented the aforementioned LPS-mediated activities, which were antagonized by the addition of miR-155 antagomir. In conclusion, miR-155 inhibition downregulated NGF expression via decreasing M1 macrophage polarization and inflammatory responses dependent on the SOCS1/NF-κB pathway, subsequently diminishing MI-induced sympathetic neural remodeling and ventricular arrhythmias (VAs).

Ageing, the autonomic nervous system and arrhythmia: From brain to heart

An ageing myocardium possesses significant electrophysiological alterations that predisposes the elderly patient to arrhythmic risk. Whilst these alterations are intrinsic to the cardiac myocytes, they are modulated by the cardiac autonomic nervous system (ANS) and consequently, ageing of the cardiac ANS is fundamental to the development of arrhythmias. A systems-based approach that incorporates the influence of the cardiac ANS could lead to better mechanistic understanding of how arrhythmogenic triggers and substrates interact spatially and temporally to produce sustained arrhythmia and why its incidence increases with age. Despite the existence of physiological oscillations of ANS activity on the heart, pathological oscillations can lead to defective activation and recovery properties of the myocardium. Such changes can be attributable to the decrease in functionality and structural alterations to ANS specific receptors in the myocardium with age. These altered ANS adaptive responses can occur either as a normal ageing process or accelerated in the presence of specific cardiac pathologies, such as genetic mutations or neurodegenerative conditions. Targeted intervention that seek to manipulate the ageing ANS influence on the myocardium may prove to be an efficacious approach for the management of arrhythmia in the ageing population.

Update on prevention and treatment of sudden cardiac arrest

Sudden cardiac arrest is the leading cause of cardiovascular mortality, posing a substantial public health burden. The incidence and epidemiology of sudden death are a function of age, with primary arrhythmia syndromes and inherited cardiomyopathies representing the predominant causes in younger patients, while coronary artery disease being the leading etiology in those who are 35 years of age and older. Internal cardioverter defibrillators remain the mainstay of primary and secondary prevention of sudden cardiac arrest. In the acute phase, cardiac chain of survival, early reperfusion, and therapeutic hypothermia are the key steps in improving outcomes. In the chronic settings, ventricular tachycardia ablation has been shown to improve patients' quality of life by reducing frequency of defibrillator shocks. Moreover, recent studies have suggested that it may increase survival. Neuromodulation represents a novel therapeutic modality that has a great potential for improving treatment of ventricular arrhythmias.

Effect of proton pump inhibitors on sympathetic hyperinnervation in infarcted rats: Role of magnesium

The long-term use of proton pump inhibitors (PPIs) has been shown to increase the risk of cardiovascular mortality, however the molecular mechanisms are unknown. Superoxide has been implicated in the regulation of nerve growth factor (NGF), a mediator of sympathetic innervation. The purpose of this study was to determine whether PPIs increase ventricular arrhythmias through magnesium-mediated superoxide production in infarcted rats. Male Wistar rats were randomly assigned to receive vehicle, omeprazole, omeprazole + magnesium sulfate, or famotidine treatment for 4 weeks starting 24 hours after the induction of myocardial infarction by ligating the coronary artery. Increased myocardial superoxide and nitrotyrosine levels were noted post-infarction, in addition to a significant upregulation of NGF expression on mRNA and protein levels. Sympathetic hyperinnervation after infarction was confirmed by measuring myocardial norepinephrine and immunofluorescent analysis. Compared with the vehicle, omeprazole-treated infarcted rats had significantly reduced myocardial magnesium content, increased oxidant production, and increased sympathetic innervation, which in turn increased ventricular arrhythmias. These effects were prevented by the coadministration of magnesium sulfate. In an in vivo study, an omeprazole-induced increase in NGF was associated with a superoxide pathway, which was further confirmed by an ex vivo study showing the attenuation of NGF levels after coadministration of the superoxide scavenger Tiron. Magnesium sulfate did not further attenuate NGF levels compared with omeprazole + Tiron. Our results indicate that the long-term administration of PPIs was associated with reduced tissue magnesium content and increased myocardial superoxide production, which exacerbated ventricular arrhythmias after infarction. Magnesium may be a potential target for PPI-related arrhythmias after infarction.

Association of Arrhythmia in Patients with Cervical Spondylosis: A Nationwide Population-Based Cohort Study

BACKGROUND

Sympathetic activity, including cervical ganglia, is involved in the development of cardiac arrhythmias.

OBJECTIVE

The present study investigated the association between cervical spondylosis and arrhythmia, which has never been reported before.

METHODS

Patients newly diagnosed with cervical spondylosis (CS) with an index date between 2000 and 2011 were identified from the National Health Insurance Research Database. We performed a 1:1 case-control matched analysis. Cases were matched to controls according to their estimated propensity scores, based on demographics and existing risk factors. Cox proportional hazard models were applied to assess the association between CS and arrhythmia.

RESULTS

The CS cohort comprised 22,236 patients (males, 42.6%; mean age, 54.4 years) and non-CS cohort comprised 22,236 matched controls. There were 1441 events of arrhythmia in CS cohort and 537 events of arrhythmia in non-CS cohort, which 252 and 127 events of atrial fibrillation in CS and non-CS cohort, 33 and 12 events of ventricular tachycardia in CS cohort and non-CS cohort, 78 and 35 events of supraventricular tachycardia in CS cohort and non-CS cohort. The CS cohort had an arrhythmia incidence of 11.1 per 1000 person-years and a higher risk [adjusted hazard ratio (aHR) = 3.10, 95% confidence interval (CI) = 2.80⁻3.42] of arrhythmia, 2.54-fold aHR of ventricular tachycardia (95% CI = 1.70⁻3.79), and 2.22-fold aHR of atrial fibrillation (95% CI = 1.79⁻2.76) compared with non-CS cohort.

CONCLUSIONS

Cervical spondylosis is associated with a higher risk of arrhythmia.

Substrates and potential therapeutics of ventricular arrhythmias in heart failure

Heart failure (HF) is a clinical syndrome characterized by ventricular contractile dysfunction. About 50% of death in patients with HF are due to fetal ventricular arrhythmias including ventricular tachycardia and ventricular fibrillation. Understanding ventricular arrhythmic substrates and discovering effective antiarrhythmic interventions are extremely important for improving the prognosis of patients with HF and reducing its mortality. In this review, we discussed ventricular arrhythmic substrates and current clinical therapeutics for ventricular arrhythmias in HF. Base on the fact that classic antiarrhythmic drugs have the limited efficacy, side effects, and proarrhythmic potentials, we also updated some therapeutic strategies for the development of potential new antiarrhythmic interventions for patients with HF.

A brain within the heart: A review on the intracardiac nervous system

Cardiac function is under the control of the autonomic nervous system, composed by the parasympathetic and sympathetic divisions, which are finely tuned at different hierarchical levels. While a complex regulation occurs in the central nervous system involving the insular cortex, the amygdala and the hypothalamus, a local cardiac regulation also takes place within the heart, driven by an intracardiac nervous system. This complex system consists of a network of ganglionic plexuses and interconnecting ganglions and axons. Each ganglionic plexus contains numerous intracardiac ganglia that operate as local integration centres, modulating the intricate autonomic interactions between the extrinsic and intracardiac nervous systems. Herein, we summarize the current understanding on the intracardiac nervous system, and acknowledge its role in the pathophysiology of cardiovascular diseases.

Risk factors and prognostic role of an electrical storm in patients after myocardial infarction with an implanted ICD for secondary prevention

INTRODUCTION

The aim of our study was to determine the risk factors for electrical storm (ES) and to assess the impact of ES on the long-term prognosis in patients after myocardial infarction (MI) with an implantable cardioverter-defibrillator (ICD) for secondary prevention of sudden cardiac death (SCD).

MATERIAL AND METHODS

We retrospectively analyzed 416 patients with coronary artery disease after MI who had an implanted ICD for secondary prevention of SCD. Fifty (12%) patients had one or more incidents of an electrical storm - the ES (+) group. We matched the reference group of 47 patients from 366 ES (-) patients.

RESULTS

We analyzed 3,408 episodes of ventricular arrhythmias: 3,148 ventricular tachyarrhythmic episodes in the ES (+) group (including 187 episodes of ES) and 260 in the ES (-) group. Multivariate logistic regression showed that inferior wall MI (RR = 3.98, 95% CI: 1.52-10.41) and the absence of coronary revascularization (RR = 2.92, 95% CI: 1.18-7.21) were independent predictors of ES (p = 0.0014). During 6-year observation of 97 patients, there were 39 (40%) deaths: 25 (50%) subjects in the ES (+) group and 14 (30%) in the ES (-) group (p = 0.036). Independent predictors of death were: the occurrence of ES (HR = 1.93), older age (HR = 1.06), and lower left ventricular ejection fraction (HR = 0.95) (for all p < 0.001).

CONCLUSIONS

Electrical storm in patients after MI with ICD for secondary prevention is a relatively common phenomenon and has a negative prognostic significance. Myocardial infarction of the inferior wall and the absence of coronary revascularization are predisposing factors for the occurrence of an ES.

Activin A inhibition attenuates sympathetic neural remodeling following myocardial infarction in rats

Inflammation serves a critical role in driving sympathetic neural remodeling following myocardial infarction (MI), and activin A has been implicated as an important mediator of the inflammatory response post-MI. However, whether activin A impacts sympathetic neural remodeling post-MI remains unclear. In the present study, the authors assessed the effects of activin A on sympathetic neural remodeling in a rat model of MI. Rats were randomly divided into sham, MI, and MI + follistatin-300 (FS, activin A inhibitor) groups. Cardiac tissues from the peri-infarct zone were assessed for expression of sympathetic neural remodeling and inflammatory factors in rats 4 weeks post-MI by western blotting and immunohistochemical methods. Heart function was assessed by echocardiography. It is demonstrated that FS administration significantly reduced post-MI upregulation of activin A, nerve growth factor protein lever, and the density of nerve fibers with positive and protein expression of sympathetic neural remodeling markers in nerve fibers, which included growth associated protein 43 and tyrosine hydroxylase. In addition, inhibition of activin A reduced cardiac inflammation post-MI based on the reduction of i) interleukin-1 and tumor necrosis factor-α protein expression, ii) numbers and/or proportional area of infiltrating macrophages and myofibroblasts and iii) phosphorylated levels of p65 and IκBα. Furthermore, activin A inhibition lessened heart dysfunction post-MI. These results suggested that activin A inhibition reduced sympathetic neural remodeling post-MI in part through inhibition of the inflammatory response. The current study implicates activin A as a potential therapeutic target to circumvent sympathetic neural remodeling post-MI.

Catheter Ablation of Ventricular Tachycardia in Structural Heart Disease: Indications, Strategies, and Outcomes-Part II

In contrast to ventricular tachycardia (VT) that occurs in the setting of a structurally normal heart, VT that occurs in patients with structural heart disease carries an elevated risk for sudden cardiac death (SCD), and implantable cardioverter-defibrillators (ICDs) are the mainstay of therapy. In these individuals, catheter ablation may be used as adjunctive therapy to treat or prevent repetitive ICD therapies when antiarrhythmic drugs are ineffective or not desired. However, certain patients with frequent premature ventricular contractions (PVCs) or VT and tachycardiomyopathy should be considered for ablation before ICD implantation because left ventricular function may improve, consequently decreasing the risk of SCD and obviating the need for an ICD. The goal of this paper is to review the pathophysiology, mechanism, and management of VT in the setting of structural heart disease and discuss the evolving role of catheter ablation in decreasing ventricular arrhythmia recurrence.

Cardiac Innervation and the Autonomic Nervous System in Sudden Cardiac Death

Neural remodeling in the autonomic nervous system contributes to sudden cardiac death. The fabric of cardiac excitability and propagation is controlled by autonomic innervation. Heart disease predisposes to malignant ventricular arrhythmias by causing neural remodeling at the level of the myocardium, the intrinsic cardiac ganglia, extracardiac intrathoracic sympathetic ganglia, extrathoracic ganglia, spinal cord, and the brainstem, as well as the higher centers and the cortex. Therapeutic strategies at each of these levels aim to restore the balance between the sympathetic and parasympathetic branches. Understanding this complex neural network will provide important therapeutic insights into the treatment of sudden cardiac death.

Cardiac autonomic innervation

The autonomic nervous system plays a key role in regulating changes in the cardiovascular system and its adaptation to various human body functions. The sympathetic arm of the autonomic nervous system is associated with the fight and flight response, while the parasympathetic division is responsible for the restorative effects on heart rate, blood pressure, and contractility. Disorders involving these two divisions can lead to, and are seen as, a manifestation of most common cardiovascular disorders. Over the last few decades, extensive research has been performed establishing imaging techniques to quantify the autonomic dysfunction associated with various cardiovascular disorders. Additionally, several techniques have been tested with variable success in modulating the cardiac autonomic nervous system as treatment for these disorders. In this review, we summarize basic anatomy, physiology, and pathophysiology of the cardiac autonomic nervous system including adrenergic receptors. We have also discussed several imaging modalities available to aid in diagnosis of cardiac autonomic dysfunction and autonomic modulation techniques, including pharmacologic and device-based therapies, that have been or are being tested currently.

Sudden death mechanisms in nonischemic cardiomyopathies: Insights gleaned from clinical implantable cardioverter-defibrillator trials

Sudden cardiac death (SCD) represents a major cause of death among patients with heart failure. Although scar-based, macroreentrant ventricular tachycardia/ventricular fibrillation is the primary etiology for SCD among patients with ischemic cardiomyopathy, a more diverse set of mechanisms and substrates is likely at play for the diverse group of patients characterized by nonischemic dilated cardiomyopathy (NICM). These causes may include scar-based reentry, but also neurohormonal stimulation (sympathetic, parasympathetic, renin-angiotensin-aldosterone), inflammation, and nonarrhythmic processes occurring in the context of a genetic predisposition. In addition to basic and translational science, observations from large randomized clinical trials of implantable cardioverter-defibrillators (ICDs) can also offer insight and support for specific mechanisms of SCD in these patients. This review will discuss the background of SCD in NICM, its potential mechanisms based on experimental and theoretical models, and the evidence for these mechanisms that can be derived from clinical trials of ICD therapy.

Alteration of Cholinergic Anti-Inflammatory Pathway in Rat With Ischemic Cardiomyopathy-Modified Electrophysiological Function of Heart

BACKGROUND

With chronic ischemia after myocardial infarction, the resulting scar tissue result in electrical and structural remodeling vulnerable to an arrhythmogenic substrate. The cholinergic anti-inflammatory pathway elicited by vagal nerve via α7 nicotinic acetylcholine receptors (α7-nAChR) can modulate local and systemic inflammatory responses. Here, we aimed to clarify a novel mechanism for the antiarrhythmogenic properties of vagal nerve during the ischemic cardiomyopathy (ICM).

METHODS AND RESULTS

Left anterior descending artery of adult male Sprague-Dawley rats was ligated for 4 weeks to develop ICM. Western blot revealed that eliciting the cholinergic anti-inflammatory pathway by nicotine treatment showed a significant reduction in the amounts of collagens, cytokines, and other inflammatory mediators in the left ventricular infarcted border zone via inhibited NF-κB activation, whereas it increased the phosphorylated connexin 43. Vagotomy inhibited the anti-inflammatory, anti-fibrosis, and anti-arrhythmogenic effect of nicotine administration. And immunohistochemistry confirmed that the nicotine administration-induced increase of connexin 43 was located in intercellular junctions. Furthermore nicotine treatment suppressed NF-κB activation in lipopolysaccharide-stimulated RAW264.7 cells, and α-bungarotoxin (an α7-nAChR selective antagonist) partly inhibited the nicotine-treatment effect. In addition, 4-week nicotine administration slightly improved the cardiac function, increased cardiac parasympathetic tone, decreased the prolonged QTc, and decreased the arrhythmia score of programmed electric stimulation-induced ventricular arrhythmia.

CONCLUSIONS

Eliciting the cholinergic anti-inflammatory pathway exerts anti-arrhythmogenic effects against ICM-induced ventricular arrhythmia accompanied by downregulation of cytokines, downgenerating of collagens, decrease in sympathetic/parasympathetic ratio, and prevention of the loss of phosphorylated connexin 43 during ICM. Our findings may suggest a promising therapy for the generation of ICM-induced ventricular arrhythmia by eliciting the cholinergic anti-inflammatory pathway.

Short‑term vagus nerve stimulation reduces myocardial apoptosis by downregulating microRNA‑205 in rats with chronic heart failure

Previous studies have reported that short-term vagus nerve stimulation (VNS) improves cardiac function in rats with chronic heart failure (CHF). The molecular mechanisms are unclear. The potential effect of microRNA (miR)-205 in apoptosis of short-term VNS was examined. A total of 3 weeks after inducing CHF, the rats were divided into three groups: Sham stimulation in sham operated rats, sham stimulation in CHF rats (CHF-SS), and treated with VNS in CHF rats (CHF-VNS). The right vagus nerve of the neck was stimulated for 72 h in CHF rats with rectangular pulses of 40 msec duration at 1 Hz and 5 V. miR-205 was focused on, which exhibited differential expression in the miRNA microarray analysis of CHF rats, and the effects of VNS on apoptosis were examined. It was verified that the expression level of miR-205 in the CHF-SS group was increased, and the expression was reduced in the CHF-VNS group. Furthermore, mimics or inhibitor of miR-205 was transfected into H9c2 to investigate its function on apoptosis. Baculoviral IAP repeat-containing protein 2 (Birc2) was confirmed a target of miR-205 through a dual luciferase reporter assay and western blotting. It was demonstrated that downregulated miR-205 decreased apoptosis in H9c2 cells. The apoptosis-associated proteins were further detected in H9c2 cells and rat tissue. The mRNA and protein expression levels of caspase-3 and Bcl-2-associated X protein were decreased in the CHF-VNS group, the expression of Birc2 and B-cell lymphoma 2 were increased. The results were consistent with the in vitro study in the miR-205 inhibitor group. The present study demonstrated that short-term VNS decreased apoptosis by downregulating miR-205 in rats with CHF. Therefore, the results of the present study provide basic evidence for short-term VNS in the clinical treatment of CHF.

Parasympathetic dysfunction and antiarrhythmic effect of vagal nerve stimulation following myocardial infarction

Myocardial infarction causes sympathetic activation and parasympathetic dysfunction, which increase risk of sudden death due to ventricular arrhythmias. Mechanisms underlying parasympathetic dysfunction are unclear. The aim of this study was to delineate consequences of myocardial infarction on parasympathetic myocardial neurotransmitter levels and the function of parasympathetic cardiac ganglia neurons, and to assess electrophysiological effects of vagal nerve stimulation on ventricular arrhythmias in a chronic porcine infarct model. While norepinephrine levels decreased, cardiac acetylcholine levels remained preserved in border zones and viable myocardium of infarcted hearts. In vivo neuronal recordings demonstrated abnormalities in firing frequency of parasympathetic neurons of infarcted animals. Neurons that were activated by parasympathetic stimulation had low basal firing frequency, while neurons that were suppressed by left vagal nerve stimulation had abnormally high basal activity. Myocardial infarction increased sympathetic inputs to parasympathetic convergent neurons. However, the underlying parasympathetic cardiac neuronal network remained intact. Augmenting parasympathetic drive with vagal nerve stimulation reduced ventricular arrhythmia inducibility by decreasing ventricular excitability and heterogeneity of repolarization of infarct border zones, an area with known proarrhythmic potential. Preserved acetylcholine levels and intact parasympathetic neuronal pathways can explain the electrical stabilization of infarct border zones with vagal nerve stimulation, providing insight into its antiarrhythmic benefit.

Quantification of sympathetic hyperinnervation and denervation after myocardial infarction by three-dimensional assessment of the cardiac sympathetic network in cleared transparent murine hearts

Background

The sympathetic nervous system is critical in maintaining the normal physiological function of the heart. Its dysfunction in pathological states may exacerbate the substrate for arrhythmias. Obviously, knowledge of its three-dimensional (3D) structure is important, however, it has been revealed by conventional methods only to a limited extent. In this study, a new method of tissue clearance in combination with immunostaining unravels the 3D structure of the sympathetic cardiac network as well as its changes after myocardial infarction.

Methods and results

Hearts isolated from adult male mice were optically cleared using the CUBIC-perfusion protocol. After making the hearts transparent, sympathetic nerves and coronary vessels were immunofluorescently labeled, and then images were acquired. The spatial distribution of sympathetic nerves was visualized not only along the epicardial surface, but also transmurally. They were distributed over the epicardial surface and penetrated into the myocardium to twist around coronary vessels, but also independent from the coronary vasculature. At 2 weeks after myocardial infarction, we were able to quantify both denervation distal from the site of infarction and nerve sprouting (hyperinnervation) at the ischemic border zone of the hearts in a 3D manner. The nerve density at the ischemic border zone was more than doubled in hearts with myocardial infarction compared to intact mice hearts (3D analyses; n = 5, p<0.05).

Conclusions

There is both sympathetic hyperinnervation and denervation after myocardial infarction. Both can be visualized and quantified by a new imaging technique in transparent hearts and thereby become a useful tool in elucidating the role of the sympathetic nervous system in arrhythmias associated with myocardial infarction.

Effects of local cardiac denervation on cardiac innervation and ventricular arrhythmia after chronic myocardial infarction

Background

Modulation of the autonomic nervous system (ANS) has already been demonstrated to display antiarrhythmic effects in patients and animals with MI. In this study, we investigated whether local cardiac denervation has any beneficial effects on ventricular electrical stability and cardiac function in the chronic phase of MI.

Methods

Twenty-one anesthetized dogs were randomly assigned into the sham-operated, MI and MI-ablation groups, respectively. Four weeks after local cardiac denervation, LSG stimulation was used to induce VPCs and VAs. The ventricular fibrillation threshold (VFT) and the incidence of inducible VPCs were measured with electrophysiological protocol. Cardiac innervation was determined with immunohistochemical staining of growth associated protein-43 (GAP43) and tyrosine hydroxylase (TH). The global cardiac and regional ventricular function was evaluated with doppler echocardiography in this study.

Results

Four weeks after operation, the incidence of inducible VPC and VF in MI-ablation group were significantly reduced compared to the MI dogs (p<0.05). Moreover, local cardiac denervation significantly improved VFT in the infarcted border zone (p<0.05). The densities of GAP43 and TH-positive nerve fibers in the infarcted border zone in the MI-ablation group were lower than those in the MI group (p<0.05). However, the local cardiac denervation did not significantly improve cardiac function in the chronic phase of MI, determined by the left ventricle diameter (LV), left atrial diameter (LA), ejection fraction (EF).

Conclusions

Summarily, in the chronic phase of MI, local cardiac denervation reduces the ventricular electrical instability, and attenuates spatial heterogeneity of sympathetic nerve reconstruction. Our study suggests that this methodology might decrease malignant ventricular arrhythmia in chronic MI, and has a great potential for clinical application.

Intermedin improves cardiac function and sympathetic neural remodeling in a rat model of post myocardial infarction heart failure

Emerging evidence has suggested that intermedin (IMD), a novel member of the calcitonin gene-related peptide (CGRP) family, has a wide range of cardioprotective effects. The present study investigated the effects of long-term administration of IMD on cardiac function and sympathetic neural remodeling in heart failure (HF) rats, and studied potential underlying mechanism. HF was induced in rats by myocardial infarction (MI). Male Sprague Dawley rats were randomly assigned to either saline or IMD (0.6 µg/kg/h) treatment groups for 4 weeks post-MI. Another group of sham-operated rats served as controls. Cardiac function was assessed by echocardiography, cardiac catheterization and plasma level of B-type natriuretic peptide (BNP). Cardiac sympathetic neural remodeling was assessed by immunohistochemistical study of tyrosine hydroxylase (TH) and growth associated protein 43 (GAP43) immunoreactive nerve fibers. The protein expression levels of nerve growth factor (NGF), TH and GAP43 in the ventricular myocardium were studied by western blotting. Ventricular fibrillation threshold (VFT) was determined to evaluate the incidence of ventricular arrhythmia. Oxidative stress was assessed by detecting the activity of superoxide dismutase and the level of malondialdehyde. Compared with rats administrated with saline, IMD significantly improved cardiac function, decreased the plasma BNP level, attenuated sympathetic neural remodeling, increased VFT and suppressed oxidative stress. In conclusion, these results indicated that IMD prevents ventricle remodeling and improves the performance of a failing heart. In addition, IMD attenuated sympathetic neural remodeling and reduced the incidence of ventricular arrhythmia, which may contribute to its anti-oxidative property. These results implicate IMD as a potential therapeutic agent for the treatment of HF.

The role of the autonomic nervous system in arrhythmias and sudden cardiac death

The autonomic nervous system (ANS) is complex and plays an important role in cardiac arrhythmia pathogenesis. A deeper understanding of the anatomy and development of the ANS has shed light on its involvement in cardiac arrhythmias. Alterations in levels of Sema-3a and NGF, both growth factors involved in innervation patterning during development of the ANS, leads to cardiac arrhythmias. Dysregulation of the ANS, including polymorphisms in genes involved in ANS development, have been implicated in sudden infant death syndrome. Disruptions in the sympathetic and/or parasympathetic systems of the ANS can lead to cardiac arrhythmias and can vary depending on the type of arrhythmia. Simultaneous stimulation of both the sympathetic and parasympathetic systems is thought to lead to atrial fibrillation whereas increased sympathetic stimulation is thought to lead to ventricular fibrillation or ventricular tachycardia. In inherited arrhythmia syndromes, such as Long QT and Catecholaminergic Polymorphic Ventricular Tachycardia, sympathetic system stimulation is thought to lead to ventricular tachycardia, subsequent arrhythmias, and in severe cases, cardiac death. On the other hand, arrhythmic events in Brugada Syndrome have been associated with periods of high parasympathetic tone. Increasing evidence suggests that modulation of the ANS as a therapeutic strategy in the treatment of cardiac arrhythmias is safe and effective. Further studies investigating the involvement of the ANS in arrhythmia pathogenesis and its modulation for the treatment of cardiac arrhythmias is warranted.

Management of Arrhythmias in Heart Failure

Heart failure patients are predisposed to develop arrhythmias. Supraventricular arrhythmias can exacerbate the heart failure symptoms by decreasing the effective cardiac output and their control require pharmacological, electrical, or catheter-based intervention. In the setting of atrial flutter or atrial fibrillation, anticoagulation becomes paramount to prevent systemic or cerebral embolism. Patients with heart failure are also prone to develop ventricular arrhythmias that can present a challenge to the managing clinician. The management strategy depends on the type of arrhythmia, the underlying structural heart disease, the severity of heart failure, and the range from optimization of heart failure therapy to catheter ablation. Patients with heart failure, irrespective of ejection fraction are at high risk for developing sudden cardiac death, however risk stratification is a clinical challenge and requires a multiparametric evaluation for identification of patients who should undergo implantation of a cardioverter defibrillator. Finally, patients with heart failure can also develop symptomatic bradycardia, caused by sinus node dysfunction or atrio-ventricular block. The treatment of bradycardia in these patients with pacing is usually straightforward but needs some specific issue.

Targeting the pathway of GSK-3β/nerve growth factor to attenuate post-infarction arrhythmias by preconditioned adipose-derived stem cells

Adipose-derived stem cell (ADSC) transplantation is a promising new therapy to improve cardiac function after myocardial infarction. However, its low efficacy of transdifferentiation hampers its usefulness. Glycogen synthase kinase-3β (GSK-3β) signal has been shown to play a role in preconditioning-induced cardioprotection. We assessed whether n-butylidenephthalide (BP) primed ADSCs can attenuate arrhythmias by a GSK-3β-dependent pathway after myocardial infarction. Male Wistar rats after coronary ligation was randomly allocated to receive intramyocardial injection of vehicle, ADSCs, BP-preconditioned ADSCs, (BP+lithium)-preconditioned ADSCs, (BP+SB216763)-preconditioned ADSCs, and (BP+LY294002)-preconditioned ADSCs. ADSCs were primed for 16h before implantation. After 4weeks of implantation, ADSCs were retained in myocardium, reduced fibrosis and improved cardiac function. Sympathetic hyperinnervation was blunted after administering ADSCs, assessed by immunofluorescent analysis, and Western blotting and real-time quantitative RT-PCR of nerve growth factor. Arrhythmic scores during programmed stimulation in the ADSC-treated infarcted rats were significantly lower than vehicle. BP-preconditioned ADSCs had superior cardioprotection, greater ADSC engraftment and transdifferentiation, and antiarrhythmic effects compared with ADSCs alone. Simultaneously, BP increased the levels of phospho-Akt and down-regulated GSK-3β activity. The effects of BP against sympathetic hyperinnervation were blocked by LY294002, a PI3K inhibitor. Addition of either lithium or SB216763 did not have additional effects compared with BP alone. Compared with ADSC alone, BP-primed ADSC implantation improved stem cell engraftment and attenuated sympathetic hyperinnervation and arrhythmias through a PI3K/Akt/GSK-3β-dependent pathway, suggesting that a synergic action was achieved between BP pretreatment and ADSCs.

Sympathetic modulation of electrical activation in normal and infarcted myocardium: implications for arrhythmogenesis

The influence of cardiac sympathetic innervation on electrical activation in normal and chronically infarcted ventricular myocardium is not understood. Yorkshire pigs with normal hearts (NL, n = 12) or anterior myocardial infarction (MI, n = 9) underwent high-resolution mapping of the anteroapical left ventricle at baseline and during left and right stellate ganglion stimulation (LSGS and RSGS, respectively). Conduction velocity (CV), activation times (ATs), and directionality of propagation were measured. Myocardial fiber orientation was determined using diffusion tensor imaging and histology. Longitudinal CV (CV_L) was increased by RSGS (0.98 ± 0.11 vs. 1.2 ± 0.14m/s, P < 0.001) but not transverse CV (CV_T). This increase was abrogated by β-adrenergic receptor and gap junction (GJ) blockade. Neither CV_L nor CV_T was increased by LSGS. In the peri-infarct region, both RSGS and LSGS shortened ARIs in sinus rhythm (423 ± 37 vs. 322 ± 30 ms, P < 0.001, and 423 ± 36 vs. 398 ± 36 ms, P = 0.035, respectively) and altered activation patterns in all animals. CV, as estimated by mean ATs, increased in a directionally dependent manner by RSGS (14.6 ± 1.2 vs. 17.3 ± 1.6 ms, P = 0.015), associated with GJ lateralization. RSGS and LSGS inhomogeneously modulated AT and induced relative or absolute functional activation delay in parts of the mapped regions in 75 and 67%, respectively, in MI animals, and in 0 and 15%, respectively, in control animals (P < 0.001 for both). In conclusion, sympathoexcitation increases CV in normal myocardium and modulates activation propagation in peri-infarcted ventricular myocardium. These data demonstrate functional control of arrhythmogenic peri-infarct substrates by sympathetic nerves and in part explain the temporal nature of arrhythmogenesis.NEW & NOTEWORTHY This study demonstrates regional control of conduction velocity in normal hearts by sympathetic nerves. In infarcted hearts, however, not only is modulation of propagation heterogeneous, some regions showed paradoxical conduction slowing. Sympathoexcitation altered propagation in all infarcted hearts studied, and we describe the temporal arrhythmogenic potential of these findings.Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/sympathetic-nerves-and-cardiac-propagation/.

Renal denervation in male rats with heart failure improves ventricular sympathetic nerve innervation and function

Heart failure is characterized by the loss of sympathetic innervation to the ventricles, contributing to impaired cardiac function and arrhythmogenesis. We hypothesized that renal denervation (RDx) would reverse this loss. Male Wistar rats underwent myocardial infarction (MI) or sham surgery and progressed into heart failure for 4 wk before receiving bilateral RDx or sham RDx. After additional 3 wk, left ventricular (LV) function was assessed, and ventricular sympathetic nerve fiber density was determined via histology. Post-MI heart failure rats displayed significant reductions in ventricular sympathetic innervation and tissue norepinephrine content (nerve fiber density in the LV of MI+sham RDx hearts was 0.31 ± 0.05% vs. 1.00 ± 0.10% in sham MI+sham RDx group, P < 0.05), and RDx significantly increased ventricular sympathetic innervation (0.76 ± 0.14%, P < 0.05) and tissue norepinephrine content. MI was associated with an increase in fibrosis of the noninfarcted ventricular myocardium, which was attenuated by RDx. RDx improved LV ejection fraction and end-systolic and -diastolic areas when compared with pre-RDx levels. This is the first study to show an interaction between renal nerve activity and cardiac sympathetic nerve innervation in heart failure. Our findings show denervating the renal nerves improves cardiac sympathetic innervation and function in the post-MI failing heart.

The role of nuclear cardiac imaging in risk stratification of sudden cardiac death

Sudden cardiac death (SCD) represents a significant portion of all cardiac deaths. Current guidelines focus mainly on left ventricular ejection fraction (LVEF) as the main criterion for SCD risk stratification and management. However, LVEF alone lacks both sensitivity and specificity in stratifying patients. Recent research has provided interesting data which supports a greater role for advanced cardiac imaging in risk stratification and patient management. In this article, we will focus on nuclear cardiac imaging, including left ventricular function assessment, myocardial perfusion imaging, myocardial blood flow quantification, metabolic imaging, and neurohormonal imaging. We will discuss how these can be used to better understand SCD and better stratify patient with both ischemic and non-ischemic cardiomyopathy.

Clinical neurocardiology defining the value of neuroscience-based cardiovascular therapeutics

The autonomic nervous system regulates all aspects of normal cardiac function, and is recognized to play a critical role in the pathophysiology of many cardiovascular diseases. As such, the value of neuroscience-based cardiovascular therapeutics is increasingly evident. This White Paper reviews the current state of understanding of human cardiac neuroanatomy, neurophysiology, pathophysiology in specific disease conditions, autonomic testing, risk stratification, and neuromodulatory strategies to mitigate the progression of cardiovascular diseases.

Periodic Repolarisation Dynamics: A Natural Probe of the Ventricular Response to Sympathetic Activation

Periodic repolarisation dynamics (PRD) refers to low-frequency (≤0.1Hz) modulations of cardiac repolarisation instability. Spontaneous PRD can be assessed non-invasively from 3D high-resolution resting ECGs. Physiological and experimental studies have indicated that PRD correlates with efferent sympathetic nerve activity, which clusters in low-frequency bursts. PRD is increased by physiological provocations that lead to an enhancement of sympathetic activity, whereas it is suppressed by pharmacological β-blockade. Electrophysiological studies revealed that PRD occurs independently from heart rate variability. Increased PRD under resting conditions is a strong predictor of mortality in post-myocardial infarction (post-MI) patients, yielding independent prognostic value from left-ventricular ejection fraction (LVEF), heart rate variability, the Global Registry of Acute Coronary Events score and other established risk markers. The predictive value of PRD is particularly strong in post-MI patients with preserved LVEF (>35 %) in whom it identifies a new high-risk group of patients. The upcoming Implantable Cardiac Monitors in High-Risk Post-Infarction Patients with Cardiac Autonomic Dysfunction and Moderately Reduced Left Ventricular Ejection Fraction (SMART-MI) trial will test prophylactic strategies in high-risk post-MI patients with LVEF 36-50 % identified by PRD and deceleration capacity of heart rate (NCT02594488).

Molecular and cellular neurocardiology: development, and cellular and molecular adaptations to heart disease

The nervous system and cardiovascular system develop in concert and are functionally interconnected in both health and disease. This white paper focuses on the cellular and molecular mechanisms that underlie neural-cardiac interactions during development, during normal physiological function in the mature system, and during pathological remodelling in cardiovascular disease. The content on each subject was contributed by experts, and we hope that this will provide a useful resource for newcomers to neurocardiology as well as aficionados.

Cardiac sympathetic activity in 22q11.2 deletion syndrome

AIM

22q11.2 deletion syndrome (22q11.2DS) affects catechol-O-methyl-transferase (COMT), which involves the degradation of norepinephrine (NE). Clinically, adults with 22q11.2DS are at increased risk for sudden unexpected death. Although the causes are likely multifactorial, increased cardiac sympathetic activity with subsequent fatal arrhythmia, due to increased levels of NE, should be considered as a possible mechanism predisposing to this premature death. The purpose of this study was to determine whether cardiac sympathetic activity is increased in 22q11.2DS, both at baseline and following an acute NE depletion with alpha-methyl-para-tyrosine (AMPT).

METHODS

Five adults with 22q11.2DS and five age- and sex-matched healthy controls underwent 2 sessions with either AMPT or placebo administration before (123)I-mIBG scintigraphy. Heart-to-mediastinum ratios (H/M) were determined from the images 15min (early) and 4h (late) after administration of (123)I-mIBG and the washout (WO) was calculated as an indicator of adrenergic drive.

RESULTS

At baseline there were no significant differences in both early and late H/M between 22q11.2DS and controls. However, there was a significant difference in WO between 22q11.2DS and controls (-4.92±2.8 and -10.44±7.2, respectively; p=0.027), but a "negative WO" does not support an increased sympathetic drive. In addition there was a trend towards a higher late H/M after AMPT administration compared to baseline which was more pronounced in 22q11.2DS.

CONCLUSION

This study for the first time suggests normal cardiac sympathetic activity in adults with 22q11.2DS assessed by (123)I-mIBG scintigraphy. Although there is a small difference in adrenergic drive compared to healthy subjects, this most likely does not explain the increased unexpected death rate in the 22q11.2 DS population.

Pathological effects of chronic myocardial infarction on peripheral neurons mediating cardiac neurotransmission

OBJECTIVE

To determine whether chronic myocardial infarction (MI) induces structural and neurochemical changes in neurons within afferent and efferent ganglia mediating cardiac neurotransmission.

METHODS

Neuronal somata in i) right atrial (RAGP) and ii) ventral interventricular ganglionated plexi (VIVGP), iii) stellate ganglia (SG) and iv) T1-2 dorsal root ganglia (DRG) bilaterally derived from normal (n=8) vs. chronic MI (n=8) porcine subjects were studied. We examined whether the morphology and neuronal nitric oxide synthase (nNOS) expression in soma of RAGP, VIVGP, DRG and SG neurons were altered as a consequence of chronic MI. In DRG, we also examined immunoreactivity of calcitonin gene related peptide (CGRP), a marker of afferent neurons. Chronic MI increased neuronal size and nNOS immunoreactivity in VIVGP (but not RAGP), as well as in the SG bilaterally. Across these ganglia, the increase in neuronal size was more pronounced in nNOS immunoreactive neurons. In the DRG, chronic MI also caused neuronal enlargement, and increased CGRP immunoreactivity. Further, DRG neurons expressing both nNOS and CGRP were increased in MI animals compared to controls, and represented a shift from double negative neurons.

CONCLUSIONS

Chronic MI impacts diverse elements within the peripheral cardiac neuraxis. That chronic MI imposes such widespread, diverse remodeling of the peripheral cardiac neuraxis must be taken into consideration when contemplating neuronal regulation of the ischemic heart.

Principles and techniques of imaging in identifying the substrate of ventricular arrhythmia

Life-threatening ventricular arrhythmias (VA) are a major cause of death in patients with cardiomyopathy. To date, impaired left ventricular ejection fraction remains the primary criterion for implantable cardioverter-defibrillator therapy to prevent sudden cardiac death. In recent years, however, advanced imaging techniques such as nuclear imaging, cardiac magnetic resonance imaging, and computed tomography have allowed for a more detailed evaluation of the underlying substrate of VA. These imaging modalities have emerged as a promising approach to assess the risk of sudden cardiac death. In addition, non-invasive identification of the critical sites of arrhythmias may guide ablation therapy. Typical anatomical substrates that can be evaluated by multiple advanced imaging techniques include perfusion abnormalities, scar and its border zone, and sympathetic denervation. Understanding the principles and techniques of different imaging modalities is essential to gain more insight in their role in identifying the arrhythmic substrate. The current review describes the principles of currently available imaging techniques to identify the substrate of VA.

Effects of urate-lowering agents on arrhythmia vulnerability in post-infarcted rat hearts

Hyperuricemia has been shown to be associated with ventricular arrhythmias. However, the mechanisms remained unknown. We assessed whether different urate-lowering agents can attenuate arrhythmias through lowering urate itself or inhibiting xanthenes oxidize (XO) activity in infarcted rats. Male Wistar rats after ligating coronary artery were randomized to either allopurinol, or febuxostat, chemically unrelated inhibitors of XO, benzbromarone or vehicle for 4 weeks. Post-infarction was associated with increased oxidant stress, as measured by myocardial superoxide, isoprostane, XO activity and dihydroethidine fluorescence staining. Measurement of myocardial norepinephrine levels revealed a significant elevation in vehicle-treated infarcted rats compared with sham-operated rats. Sympathetic hyperinnervation was blunted after administering both XO inhibitors, assessed by immunofluorescent analysis, Western blotting and real-time quantitative RT-PCR. Besides, the XO inhibitors-attenuated nerve growth factor levels were reversed in the presence of peroxynitrite generator. Arrhythmic scores in the XO inhibitors-treated infarcted rats were significantly lower than that in vehicle. For similar levels of urate lowering, the uricosuric agent benzbromarone had no beneficial effects on oxidative stress, sympathetic hyperinnervation or arrhythmia vulnerability. Chronic use of XO inhibitors, but not uricosuric agent, down-regulated sympathetic innervation probably through a superoxide-dependent pathway and plays a role in the beneficial effect on arrhythmogenic response.

Swallowing-induced atrial tachycardia: case report

A 53‐year‐old man presented with heart palpitations while swallowing. Electrophysiologic study (EPS) and immunohistochemical results of his esophageal leiomyoma suggested that swallowing‐induced atrial tachycardia is related with neural reflex. S100‐immunopositive nerve fibers are demonstrated sympathetic nerves which possibly explain the mechanism. Metoprolol tartrate tablets are effective in our patient.

Sitagliptin decreases ventricular arrhythmias by attenuated glucose-dependent insulinotropic polypeptide (GIP)-dependent resistin signalling in infarcted rats

Myocardial infarction (MI) was associated with insulin resistance, in which resistin acts as a critical mediator. We aimed to determine whether sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, can attenuate arrhythmias by regulating resistin-dependent nerve growth factor (NGF) expression in postinfarcted rats. Normoglycaemic male Wistar rats after ligating coronary artery were randomized to either vehicle or sitagliptin for 4 weeks starting 24 h after operation. Post-infarction was associated with increased myocardial noradrenaline [norepinephrine (NE)] levels and sympathetic hyperinnervation. Compared with vehicle, sympathetic innervation was blunted after administering sitagliptin, as assessed by immunofluorescent analysis of tyrosine hydroxylase, growth-associated factor 43 and neurofilament and western blotting and real-time quantitative RT-PCR of NGF. Arrhythmic scores in the sitagliptin-treated infarcted rats were significantly lower than those in vehicle. Furthermore, sitagliptin was associated with reduced resistin expression and increased Akt activity. Ex vivo studies showed that glucose-dependent insulinotropic polypeptide (GIP) infusion, but not glucagon-like peptide-1 (GLP-1), produced similar reduction in resistin levels to sitagliptin in postinfarcted rats. Furthermore, the attenuated effects of sitagliptin on NGF levels can be reversed by wortmannin (a phosphatidylinositol 3-kinase antagonist) and exogenous resistin infusion. Sitagliptin protects ventricular arrhythmias by attenuating sympathetic innervation in the non-diabetic infarcted rats. Sitagliptin attenuated resistin expression via the GIP-dependent pathway, which inhibited sympathetic innervation through a signalling pathway involving phosphatidylinositol 3-kinase (PI3K) and Akt protein.

The nervous heart

Many cardiac electrophysiological abnormalities are accompanied by autonomic nervous system dysfunction. Here, we review mechanisms by which the cardiac nervous system controls normal and abnormal excitability and may contribute to atrial and ventricular tachyarrhythmias. Moreover, we explore the potential antiarrhythmic and/or arrhythmogenic effects of modulating the autonomic nervous system by several strategies, including ganglionated plexi ablation, vagal and spinal cord stimulations, and renal sympathetic denervation as therapies for atrial and ventricular arrhythmias.

Cardiac Sympathetic Nerve Sprouting and Susceptibility to Ventricular Arrhythmias after Myocardial Infarction

Ventricular arrhythmogenesis is thought to be a common cause of sudden cardiac death following myocardial infarction (MI). Nerve remodeling as a result of MI is known to be an important genesis of life-threatening arrhythmias. It is hypothesized that neural modulation might serve as a therapeutic option of malignant arrhythmias. In fact, left stellectomy or β-blocker therapy is shown to be effective in the prevention of ventricular tachyarrhythmias (VT), ventricular fibrillation (VF), and sudden cardiac death (SCD) after MI both in patients and in animal models. Results from decades of research already evidenced a positive relationship between abnormal nerve density and ventricular arrhythmias after MI. In this review, we summarized the molecular mechanisms involved in cardiac sympathetic rejuvenation and mechanisms related to sympathetic hyperinnervation and arrhythmogenesis after MI and analyzed the potential therapeutic implications of nerve sprouting modification for ventricular arrhythmias and SCD control.

Myocardial infarction induces structural and functional remodelling of the intrinsic cardiac nervous system

KEY POINTS

Intrinsic cardiac (IC) neurons undergo differential morphological and phenotypic remodelling that reflects the site of myocardial infarction (MI). Afferent neural signals from the infarcted region to IC neurons are attenuated, while those from border and remote regions are preserved post-MI, giving rise to a 'neural sensory border zone'. Convergent IC local circuit (processing) neurons have enhanced transduction capacity following MI. Functional network connectivity within the intrinsic cardiac nervous system is reduced post-MI. MI reduces the response and alters the characteristics of IC neurons to ventricular pacing.

ABSTRACT

Autonomic dysregulation following myocardial infarction (MI) is an important pathogenic event. The intrinsic cardiac nervous system (ICNS) is a neural network located on the heart that is critically involved in autonomic regulation. The aims of this study were to characterize structural and functional remodelling of the ICNS post-MI in a porcine model (control (n = 16) vs. healed anteroapical MI (n = 16)). In vivo microelectrode recordings of basal activity, as well as responses to afferent and efferent stimuli, were recorded from intrinsic cardiac neurons. From control 118 neurons and from MI animals 102 neurons were functionally classified as afferent, efferent, or convergent (receiving both afferent and efferent inputs). In control and MI, convergent neurons represented the largest subpopulation (47% and 48%, respectively) and had enhanced transduction capacity following MI. Efferent inputs to neurons were maintained post-MI. Afferent inputs were attenuated from the infarcted region (19% in control vs. 7% in MI; P = 0.03), creating a 'neural sensory border zone', or heterogeneity in afferent information. MI reduced transduction of changes in preload (54% in control vs. 41% in MI; P = 0.05). The overall functional network connectivity, or the ability of neurons to respond to independent pairs of stimuli, within the ICNS was reduced following MI. The neuronal response was differentially decreased to ventricular vs. atrial pacing post-MI (63% in control vs. 44% in MI to ventricular pacing; P < 0.01). MI induced morphological and phenotypic changes within the ICNS. The alteration of afferent neural signals, and remodelling of convergent neurons, represents a 'neural signature' of ischaemic heart disease.

Semaphorin 3a transfection into the left stellate ganglion reduces susceptibility to ventricular arrhythmias after myocardial infarction in rats

AIMS

Myocardial infarction (MI) induces neural remodelling of the left stellate ganglion (LSG), which may contribute to ischaemia-induced arrhythmias. The neural chemorepellent Semaphorin 3a (Sema3a) has been identified as a negative regulator of sympathetic innervation in the LSG and heart. We previously reported that overexpression of Sema3a in the border zone could reduce the arrhythmogenic effects of cardiac sympathetic hyperinnervation post-MI. This study investigated whether Sema3a overexpression within the LSG confers an antiarrhythmic effect after MI through decreasing extra- and intra-cardiac neural remodelling.

METHODS AND RESULTS

Sprague-Dawley rats were subjected to MI, and randomly allocated to intra-LSG microinjection of either phosphate-buffered saline (PBS), adenovirus encoding green fluorescent protein (AdGFP), or adenovirus encoding Sema3a (AdSema3a). Sham-operated rats served as controls. Two weeks after infarction, MI-induced nerve sprouting and sympathetic hyperinnervation in the LSG and myocardium were significantly attenuated by intra-LSG injection with AdSema3a, as assessed by immunohistochemistry and western blot analysis of growth-associated protein 43 and tyrosine hydroxylase. This was also confirmed by sympathetic nerve function changes assessed by cardiac norepinephrine content. Additionally, intra-LSG injection with AdSema3a alleviated MI-induced accumulation of dephosphorylated connexin 43 in the infarct border zone. Furthermore, Sema3a overexpression in the LSG reduced the incidence of inducible ventricular tachyarrhythmia by programmed electrical stimulation post-MI, and arrhythmia scores were significantly lower in the AdSema3a group than in the PBS and AdGFP groups.

CONCLUSION

Semaphorin 3a overexpression in the LSG ameliorates the inducibility of ventricular arrhythmias after MI, mainly through attenuation of neural remodelling within the cardiac-neuraxis.