Autonomic modulation of electrical restitution, alternans and ventricular fibrillation initiation in the isolated heart

NBQX mediates ventricular fibrillation susceptibility in rat models of anxiety via the Nrf2/HO-1 pathway

Objective

Anxiety disorder (AD) is a common mental disorder related to cardiovascular disease morbidity. Oxidative stress plays a crucial role in the anxiety state and can lead to cardiac remodeling. Over-activation of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) in cardiomyocytes and neurons can cause oxidative stress. Additionally, the AMPAR inhibitor-2,3-dihydroxy-6-nitro-7-sulfamoyl-benzoquinoxaline-2,3-dione (NBQX) plays an important role in ameliorating oxidative stress. This study aimed to explore the anti-arrhythmic effects of NBQX in a rat model of anxiety.

Methods

The AD model was induced using empty bottle stimulation. Male Sprague Dawley rats were randomly divided into four groups: control + saline, control + NBQX, AD + saline, and AD + NBQX. Open field test was conducted to measure anxiety-like behavior. Electrophysiological experiments, histological analysis, biochemical detection and molecular biology were performed to verify the effects of NBQX on the amelioration of electrical remodeling and structural remodeling. Furthermore, the nuclear factor erythroid 2-related factor 2 (Nrf2) inhibitor (ML385) was used in vitro to demonstrate the signaling pathway.

Results

Oxidative stress levels increased with AMPAR over-activation in AD rats, leading to heightened vulnerability to ventricular fibrillation (VF). NBQX reverses anxiety and VF susceptibility. Our results showed that NBQX activated the Nrf2/heme oxygenase-1 (HO-1) pathway, leading to a decline in oxidative stress levels. Connexin 43 and ion channel expression was upregulated. NBQX treatment attenuated fibrosis and apoptosis. This effect was diminished by ML385 treatment in vitro.

Conclusion

NBQX can alleviate VF susceptibility in rat models of anxiety by alleviating electrical remodeling, structural remodeling via regulating the Nrf2/HO-1 pathway to some extent.

Efficacy and safety of transcutaneous auricular vagus nerve stimulation for frequent premature ventricular complexes: rationale and design of the TASC-V trial

BACKGROUND

Premature Ventricular Complexes (PVCs) are very common in clinical practice, with frequent PVCs (more than 30 beats per hour) or polymorphic PVCs significantly increasing the risk of mortality. Previous studies have shown that vagus nerve stimulation improves ventricular arrhythmias. Stimulation of the auricular distribution of the vagus nerve has proven to be a simple, safe, and effective method to activate the vagus nerve. Transcutaneous au ricular vagus nerve stimulation (taVNS) has shown promise in both clinical and experimental setting for PVCs; however, high-quality clinical studies are lacking, resulting in insufficient evidence of efficacy.

METHODS

The study is a prospective, randomized, parallel-controlled trial with a 1:1 ratio between the two groups. Patients will be randomized to either the treatment group (taVNS) or the control group (Sham-taVNS) with a 6-week treatment and a subsequent 12-week follow-up period. The primary outcome is the proportion of patients with a ≥ 50% reduction in the number of PVCs monitored by 24-hour Holter. Secondary outcomes include the proportion of patients with a ≥ 75% reduction in PVCs, as well as the changes in premature ventricular beats, total heartbeats, and supraventricular premature beats recorded by 24-hour Holter. Additional assessments compared score changes in PVCs-related symptoms, as well as the score change of self-rating anxiety scale (SAS), self-rating depression scale (SDS), and 36-item short form health survey (SF-36).

DISCUSSION

The TASC-V trial will help to reveal the efficacy and safety of taVNS for frequent PVCs, offering new clinical evidence for the clinical practice.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT04415203 (Registration Date: May 30, 2020).

Antiarrhythmic Mechanisms of Epidural Blockade After Myocardial Infarction

BACKGROUND

Thoracic epidural anesthesia (TEA) has been shown to reduce the burden of ventricular tachycardia in small case series of patients with refractory ventricular tachyarrhythmias and cardiomyopathy. However, its electrophysiological and autonomic effects in diseased hearts remain unclear, and its use after myocardial infarction is limited by concerns for potential right ventricular dysfunction.

METHODS

Myocardial infarction was created in Yorkshire pigs (N=22) by left anterior descending coronary artery occlusion. Approximately, six weeks after myocardial infarction, an epidural catheter was placed at the C7-T1 vertebral level for injection of 2% lidocaine. Right and left ventricular hemodynamics were recorded using Millar pressure-conductance catheters, and ventricular activation recovery intervals (ARIs), a surrogate of action potential durations, by a 56-electrode sock and 64-electrode basket catheter. Hemodynamics and ARIs, baroreflex sensitivity and intrinsic cardiac neural activity, and ventricular effective refractory periods and slope of restitution (Smax) were assessed before and after TEA. Ventricular tachyarrhythmia inducibility was assessed by programmed electrical stimulation.

RESULTS

TEA reduced inducibility of ventricular tachyarrhythmias by 70%. TEA did not affect right ventricular-systolic pressure or contractility, although left ventricular-systolic pressure and contractility decreased modestly. Global and regional ventricular ARIs increased, including in scar and border zone regions post-TEA. TEA reduced ARI dispersion specifically in border zone regions. Ventricular effective refractory periods prolonged significantly at critical sites of arrhythmogenesis, and Smax was reduced. Interestingly, TEA significantly improved cardiac vagal function, as measured by both baroreflex sensitivity and intrinsic cardiac neural activity.

CONCLUSIONS

TEA does not compromise right ventricular function in infarcted hearts. Its antiarrhythmic mechanisms are mediated by increases in ventricular effective refractory period and ARIs, decreases in Smax, and reductions in border zone electrophysiological heterogeneities. TEA improves parasympathetic function, which may independently underlie some of its observed antiarrhythmic mechanisms. This study provides novel insights into the antiarrhythmic mechanisms of TEA while highlighting its applicability to the clinical setting.

Long-Term Stimulation of the Left Dorsal Branch of the Thoracic Nerve Improves Ventricular Electrical Remodeling in a Canine Model of Chronic Myocardial Infarction

PURPOSE

To evaluate the ventricular electrophysiologic effects of long-term stimulation of the left dorsal branch of thoracic nerve (LDTN) derived from the left stellate ganglion (LSG) in a canine model of chronic myocardial infarction (MI).

METHODS

Seventeen adult male beagles were randomly divided into three groups: the sham group (sham operated, n = 6), the MI group (n = 6), and the MI + LDTN group (MI plus LDTN stimulation, n = 5). The canine model of chronic MI was induced by the occlusion of the left anterior descending artery (LADO). The LDTN was separated and intermittently stimulated immediately after LADO for 2 months. The heart rate variability (HRV) analysis, in vivo electrophysiology, the evaluation of LSG function and neural activity, histological staining, and western blotting (WB) assay were performed to evaluate the effect of LDTN stimulation on the heart.

RESULTS

The canine MI model was successfully established by LADO, and the LDTN was separated and stimulated immediately after LADO. The HRV analysis showed that LDTN stimulation reversed the increased LF value and LF/HF ratio of the MI group. LDTN stimulation prolonged the shortening ERP and APD90, decreased the dispersion of ERP and APD90, and increased the VFT. Additionally, LDTN stimulation inhibits the LSG function and neural activity. Furthermore, LDTN stimulation suppressed the activation of Wnt/β-catenin signaling, which contributed to the LSG neuronal apoptosis by upregulation of pro-apoptotic Bax and downregulation of anti-apoptotic Bcl-2.

CONCLUSION

LDTN stimulation could attenuate cardiac sympathetic remodeling and improve ventricular electrical remodeling, which may be mediated by suppressing the activated Wnt/β-catenin signaling pathway and then promoting the LSG neuronal apoptosis.

Neuropsychobiology of fear-induced bradycardia in humans: progress and pitfalls

In the last century, the paradigm of fear conditioning has greatly evolved in a variety of scientific fields. The techniques, protocols, and analysis methods now most used have undergone a progressive development, theoretical and technological, improving the quality of scientific productions. Fear-induced bradycardia is among these techniques and represents the temporary deceleration of heart beats in response to negative outcomes. However, it has often been used as a secondary measure to assess defensive responding to threat, along other more popular techniques. In this review, we aim at paving the road for its employment as an additional tool in fear conditioning experiments in humans. After an overview of the studies carried out throughout the last century, we describe more recent evidence up to the most contemporary research insights. Lastly, we provide some guidelines concerning the best practices to adopt in human fear conditioning studies which aim to investigate fear-induced bradycardia.

Chronic nicotine exposure is associated with electrophysiological and sympathetic remodeling in the intact rabbit heart

Nicotine is the primary addictive component of tobacco products. Through its actions on the heart and autonomic nervous system, nicotine exposure is associated with electrophysiological changes and increased arrhythmia susceptibility. To assess the underlying mechanisms, we treated rabbits with transdermal nicotine (NIC, 21 mg/day) or control (CT) patches for 28 days before performing dual optical mapping of transmembrane potential (RH237) and intracellular Ca2+ (Rhod-2 AM) in isolated hearts with intact sympathetic innervation. Sympathetic nerve stimulation (SNS) was performed at the first to third thoracic vertebrae, and β-adrenergic responsiveness was additionally evaluated following norepinephrine (NE) perfusion. Baseline ex vivo heart rate (HR) and SNS stimulation threshold were higher in NIC versus CT (P = 0.004 and P = 0.003, respectively). Action potential duration alternans emerged at longer pacing cycle lengths (PCL) in NIC versus CT at baseline (P = 0.002) and during SNS (P = 0.0003), with similar results obtained for Ca2+ transient alternans. SNS shortened the PCL at which alternans emerged in CT but not in NIC hearts. NIC-exposed hearts tended to have slower and reduced HR responses to NE perfusion, but ventricular responses to NE were comparable between groups. Although fibrosis was unaltered, NIC hearts had lower sympathetic nerve density (P = 0.03) but no difference in NE content versus CT. These results suggest both sympathetic hypoinnervation of the myocardium and regional differences in β-adrenergic responsiveness with NIC. This autonomic remodeling may contribute to the increased risk of arrhythmias associated with nicotine exposure, which may be further exacerbated with long-term use.NEW & NOTEWORTHY Here, we show that chronic nicotine exposure was associated with increased heart rate, increased susceptibility to alternans, and reduced sympathetic electrophysiological responses in the intact rabbit heart. We suggest that this was due to sympathetic hypoinnervation of the myocardium and diminished β-adrenergic responsiveness of the sinoatrial node following nicotine treatment. Though these differences did not result in increased arrhythmia propensity in our study, we hypothesize that prolonged nicotine exposure may exacerbate this proarrhythmic remodeling.

Artificial intelligence for ventricular arrhythmia capability using ambulatory electrocardiograms

Aims

European and American clinical guidelines for implantable cardioverter defibrillators are insufficiently accurate for ventricular arrhythmia (VA) risk stratification, leading to significant morbidity and mortality. Artificial intelligence offers a novel risk stratification lens through which VA capability can be determined from the electrocardiogram (ECG) in normal cardiac rhythm. The aim of this study was to develop and test a deep neural network for VA risk stratification using routinely collected ambulatory ECGs.

Methods and results

A multicentre case-control study was undertaken to assess VA-ResNet-50, our open source ResNet-50-based deep neural network. VA-ResNet-50 was designed to read pyramid samples of three-lead 24 h ambulatory ECGs to decide whether a heart is capable of VA based on the ECG alone. Consecutive adults with VA from East Midlands, UK, who had ambulatory ECGs as part of their NHS care between 2014 and 2022 were recruited and compared with all comer ambulatory electrograms without VA. Of 270 patients, 159 heterogeneous patients had a composite VA outcome. The mean time difference between the ECG and VA was 1.6 years (⅓ ambulatory ECG before VA). The deep neural network was able to classify ECGs for VA capability with an accuracy of 0.76 (95% confidence interval 0.66-0.87), F1 score of 0.79 (0.67-0.90), area under the receiver operator curve of 0.8 (0.67-0.91), and relative risk of 2.87 (1.41-5.81).

Conclusion

Ambulatory ECGs confer risk signals for VA risk stratification when analysed using VA-ResNet-50. Pyramid sampling from the ambulatory ECGs is hypothesized to capture autonomic activity. We encourage groups to build on this open-source model.

Question

Can artificial intelligence (AI) be used to predict whether a person is at risk of a lethal heart rhythm, based solely on an electrocardiogram (an electrical heart tracing)?

Findings

In a study of 270 adults (of which 159 had lethal arrhythmias), the AI was correct in 4 out of every 5 cases. If the AI said a person was at risk, the risk of lethal event was three times higher than normal adults.

Meaning

In this study, the AI performed better than current medical guidelines. The AI was able to accurately determine the risk of lethal arrhythmia from standard heart tracings for 80% of cases over a year away-a conceptual shift in what an AI model can see and predict. This method shows promise in better allocating implantable shock box pacemakers (implantable cardioverter defibrillators) that save lives.

Thoracic epidural blockade after myocardial infarction benefits from anti-arrhythmic pathways mediated in part by parasympathetic modulation

Background

Thoracic epidural anesthesia (TEA) has been shown to reduce the burden of ventricular tachyarrhythmias (VT) in small case-series of patients with refractory VT and cardiomyopathy. However, its electrophysiological and autonomic effects in diseased hearts remain unclear and its use after myocardial infarction (MI) is limited by concerns for potential RV dysfunction.

Methods

MI was created in Yorkshire pigs ( N =22) by LAD occlusion. Six weeks post-MI, an epidural catheter was placed at the C7-T1 vertebral level for injection of 2% lidocaine. RV and LV hemodynamics were recorded using Millar pressure-conductance catheters, and ventricular activation-recovery intervals (ARIs), a surrogate of action potential durations, by a 56-electrode sock and 64-electrode basket catheter. Hemodynamics and ARIs, baroreflex sensitivity (BRS) and intrinsic cardiac neural activity, and ventricular effective refractory periods (ERP) and slope of restitution (S max ) were assessed before and after TEA. VT/VF inducibility was assessed by programmed electrical stimulation.

Results

TEA reduced inducibility of VT/VF by 70%. TEA did not affect RV-systolic pressure or contractility, although LV-systolic pressure and contractility decreased modestly. Global and regional ventricular ARIs increased, including in scar and border zone regions post-TEA. TEA reduced ARI dispersion specifically in border zone regions. Ventricular ERPs prolonged significantly at critical sites of arrhythmogenesis, and S max was reduced. Interestingly, TEA significantly improved cardiac vagal function, as measured by both BRS and intrinsic cardiac neural activity.

Conclusion

TEA does not compromise RV function in infarcted hearts. Its anti-arrhythmic mechanisms are mediated by increases in ventricular ERP and ARIs, decreases in S max , and reductions in border zone heterogeneity. TEA improves parasympathetic function, which may independently underlie some of its observed anti-arrhythmic mechanisms. This study provides novel insights into the anti-arrhythmic mechanisms of TEA, while highlighting its applicability to the clinical setting.

Abstract Illustration

Myocardial infarction is known to cause cardiac autonomic dysfunction characterized by sympathoexcitation coupled with reduced vagal tone. This pathological remodeling collectively predisposes to ventricular arrhythmia. Thoracic epidural anesthesia not only blocks central efferent sympathetic outflow, but by also blocking ascending projections of sympathetic afferents, relieving central inhibition of vagal function. These complementary autonomic effects of thoracic epidural anesthesia may thus restore autonomic balance, thereby improving ventricular electrical stability and suppressing arrhythmogenesis. DRG=dorsal root ganglion, SG=stellate ganglion.

Psychological stress, the central nervous system and arrhythmias

This review highlights the links between psychological stress and the neurocircuitry of cardiac-brain interactions leading to arrhythmias. The role of efferent and afferent connections in the heart-brain axis is considered, with the mechanisms by which emotional responses promote arrhythmias illustrated by inherited cardiac conditions. Novel therapeutic targets for intervention in the autonomic nervous system are considered.

Chronic nicotine exposure is associated with electrophysiological and sympathetic remodeling in the intact rabbit heart

Nicotine is the primary addictive component in tobacco products. Through its actions on the heart and autonomic nervous system, nicotine exposure is associated with electrophysiological changes and increased arrhythmia susceptibility. However, the underlying mechanisms are unclear. To address this, we treated rabbits with transdermal nicotine (NIC, 21 mg/day) or control (CT) patches for 28 days prior to performing dual optical mapping of transmembrane potential (RH237) and intracellular Ca 2+ (Rhod-2 AM) in isolated hearts with intact sympathetic innervation. Sympathetic nerve stimulation (SNS) was performed at the 1 st - 3 rd thoracic vertebrae, and β-adrenergic responsiveness was additionally evaluated as changes in heart rate (HR) following norepinephrine (NE) perfusion. Baseline ex vivo HR and SNS stimulation threshold were increased in NIC vs. CT ( P = 0.004 and P = 0.003 respectively). Action potential duration alternans emerged at longer pacing cycle lengths (PCL) in NIC vs. CT at baseline ( P = 0.002) and during SNS ( P = 0.0003), with similar results obtained for Ca 2+ transient alternans. SNS reduced the PCL at which alternans emerged in CT but not NIC hearts. NIC exposed hearts also tended to have slower and reduced HR responses to NE perfusion. While fibrosis was unaltered, NIC hearts had lower sympathetic nerve density ( P = 0.03) but no difference in NE content vs. CT. These results suggest both sympathetic hypo-innervation of the myocardium and diminished β-adrenergic responsiveness with NIC. This autonomic remodeling may underlie the increased risk of arrhythmias associated with nicotine exposure, which may be further exacerbated with continued long-term usage.

NEW & NOTEWORTHY

Here we show that chronic nicotine exposure was associated with increased heart rate, lower threshold for alternans and reduced sympathetic electrophysiological responses in the intact rabbit heart. We suggest that this was due to the sympathetic hypo-innervation of the myocardium and diminished β- adrenergic responsiveness observed following nicotine treatment. Though these differences did not result in increased arrhythmia propensity in our study, we hypothesize that prolonged nicotine exposure may exacerbate this pro-arrhythmic remodeling.

Optical mapping of cardiac electromechanics in beating in vivo hearts

Optical mapping has been widely used in the study of cardiac electrophysiology in motion-arrested, ex vivo heart preparations. Recent developments in motion artifact mitigation techniques have made it possible to optically map beating ex vivo hearts, enabling the study of cardiac electromechanics using optical mapping. However, the ex vivo setting imposes limitations on optical mapping such as altered metabolic states, oversimplified mechanical loads, and the absence of neurohormonal regulation. In this study, we demonstrate optical electromechanical mapping in an in vivo heart preparation. Swine hearts were exposed via median sternotomy. Voltage-sensitive dye, either di-4-ANEQ(F)PTEA or di-5-ANEQ(F)PTEA, was injected into the left anterior descending artery. Fluorescence was excited by alternating green and amber light for excitation ratiometry. Cardiac motion during sinus and paced rhythm was tracked using a marker-based method. Motion tracking and excitation ratiometry successfully corrected most motion artifact in the membrane potential signal. Marker-based motion tracking also allowed simultaneous measurement of epicardial deformation. Reconstructed membrane potential and mechanical deformation measurements were validated using monophasic action potentials and sonomicrometry, respectively. Di-5-ANEQ(F)PTEA produced longer working time and higher signal/noise ratio than di-4-ANEQ(F)PTEA. In addition, we demonstrate potential applications of the new optical mapping system including electromechanical mapping during vagal nerve stimulation, fibrillation/defibrillation. and acute regional ischemia. In conclusion, although some technical limitations remain, optical mapping experiments that simultaneously image electrical and mechanical function can be conducted in beating, in vivo hearts.

Autonomic neuro-cardiac profile of electrical, structural and neuronal remodeling in myocardial infarction-induced heart failure

Aims

Heart failure is a clinical syndrome typified by abnormal autonomic tone, impaired ventricular function, and increased arrhythmic vulnerability. This study aims to examine electrophysiological, structural and neuronal remodeling following myocardial infarction in a rabbit heart failure model to establish its neuro-cardiac profile.

Methods and results

Weight-matched adult male New Zealand White rabbits (3.2 ± 0.1 kg, n = 25) were randomized to have coronary ligation surgeries (HF group, n = 13) or sham procedures (SHM group, n = 12). Transthoracic echocardiography was performed six weeks post-operatively. On week 8, dual-innervated Langendorff-perfused heart preparations were set up for terminal experiments. Seventeen hearts (HF group, n = 10) underwent ex-vivo cardiac MRI. Twenty-two hearts (HF group, n = 7) were examined histologically. Electrical remodeling and abnormal autonomic profile were evident in HF rabbits with exaggerated sympathetic and attenuated vagal effect on ventricular fibrillation threshold, ventricular refractoriness and restitution curves, in addition to increased spatial restitution dispersion. Histologically, there was significant neuronal enlargement at the heart hila and conus arteriosus in HF. Structural remodeling was characterized by quantifiable myocardial scarring, enlarged left ventricles, altered ventricular geometry and impaired contractility.

Conclusion

In an infarct-induced rabbit heart failure model, extensive structural, neuronal and electrophysiological remodeling in conjunction with abnormal autonomic profile provide substrates for ventricular arrhythmias.

Phloretin ameliorates heart function after myocardial infarction via NLRP3/Caspase-1/IL-1β signaling

OBJECTIVES/AIMS

Inflammation is crucial in structural and electrical remodeling after myocardial infarction (MI), affecting cardiac pump function and conduction pathways. Phloretin possesses an anti-inflammation role by inhibiting the NLRP3/Caspase-1/IL-1β pathway. However, the effects of Phloretin on cardiac contractile and electrical conduction function after MI remained unclear. Therefore, we aimed to investigate the potential role of Phloretin in a rat model of MI.

METHODS

Rats were assigned into four groups: Sham, Sham+Phloretin, MI and MI+Phloretin, with ad libitum food and water. In the MI and MI+Phloretin groups, the left anterior descending coronary artery was occluded for 4 weeks, while the Sham and Sham+Phloretin groups received sham operation. The Sham+Phloretin group and the MI+Phloretin group received oral administration of Phloretin. In vitro, H9c2 cells were subjected to hypoxic conditions to simulate an MI model, with Phloretin for 24 h. Cardiac electrophysiological properties were assessed following MI, including the effective refractory period (ERP), action potential duration (APD)90 and ventricular fibrillation (VF) incidence. Echocardiography evaluated left ventricular ejection fraction (LVEF), left ventricular fraction shortening (LVFS), left ventricular internal diameter at end-diastole (LVIDd), left ventricular internal diameter at end-systole (LVIDs), left ventricular end-systolic volume (LVESV) and left ventricular end-diastolic volume (LVEDV) to assess cardiac function. Serum type B natriuretic peptide (BNP) level was applied to evaluate the degree of Heart failure (HF). The fibrosis area and severity were assessed by Masson staining and protein expression levels of collagen 3, collagen 1, TGF-β and α-SMA. Western blot analysis estimated the protein expression levels of NLRP3, Pro Caspase-1, Caspase-1, ASC, IL-18, IL-1β, pp38, p38, and Connexin43(Cx43) to elucidate the influence of inflammation on electrical remodeling after MI.

RESULTS

Our findings demonstrate that Phloretin inhibits the NLRP3/Caspase-1/IL-1β pathway, leading to the upregulation of Cx43 by limiting p38 phosphorylation, which further decreases susceptibility to ventricular arrhythmias (VAs). Additionally, Phloretin attenuated fibrosis by inhibiting inflammation to prevent HF. In vitro experiments also provided strong evidence supporting the inhibitory effects of Phloretin on the NLRP3/Caspase-1/IL-1β pathway.

CONCLUSION

Our results suggest that Phloretin could suppress the NLRP3/Caspase-1/IL-1β pathway to reverse structural and electrical remodeling after MI to prevent the occurrence of VAs and HF.

Renal denervation reverses ventricular structural and functional remodeling in failing rabbit hearts

Renal denervation (RDN) suppresses the activity of the renin-angiotensin-aldosterone system and inflammatory cytokines, leading to the prevention of cardiac remodeling. Limited studies have reported the effects of renal denervation on ventricular electrophysiology. We aimed to use optical mapping to evaluate the effect of RDN on ventricular structural and electrical remodeling in a tachycardia-induced cardiomyopathy rabbit model. Eighteen rabbits were randomized into 4 groups: sham control group (n = 5), renal denervation group receiving RDN (n = 5), heart failure group receiving rapid ventricular pacing for 1 month (n = 4), and RDN-heart failure group (n = 4). Rabbit hearts were harvested for optical mapping. Different cycle lengths were paced (400, 300, 250, 200, and 150 ms), and the results were analyzed. In optical mapping, the heart failure group had a significantly slower epicardial ventricular conduction velocity than the other three groups. The RDN-heart failure, sham control, and RDN groups had similar velocities. We then analyzed the 80% action potential duration at different pacing cycle lengths, which showed a shorter action potential duration as cycle length decreased (P for trend < 0.01), which was consistent across all groups. The heart failure group had a significantly longer action potential duration than the sham control and RDN groups. Action potential duration was shorter in the RDN-heart failure group than the heart failure group (P < 0.05). Reduction of conduction velocity and prolongation of action potential duration are significant hallmarks of heart failure, and RDN reverses these remodeling processes.

Catheter Ablation of Ventricular Fibrillation

Ventricular fibrillation (VF) is a common cause of sudden cardiac death (SCD) and is unfortunately without a cure. Current therapies focus on prevention of SCD, such as implantable cardioverter-defibrillator (ICD) implantation and anti-arrhythmic agents. Significant progress has been made in improving our understanding and ability to target the triggers of VF, via advanced mapping and ablation techniques, as well as with autonomic modulation. However, the critical substrate for VF maintenance remains incompletely defined. In this review, we discuss the evidence behind the basic mechanisms of VF and review the current role of catheter ablation in patients with VF.

Repolarization indicates electrical instability in ventricular arrhythmia originating from papillary muscle

AIMS

Cardiac arrhythmia originating from the papillary muscle (PM) can trigger ventricular fibrillation (VF) and cause sudden cardiac death even in the absence of structural heart disease. Most premature ventricular contractions, however, are benign and hitherto difficult to distinguish from a potentially fatal arrhythmia. Altered repolarization characteristics are associated with electrical instability, but electrophysiological changes which precede degeneration into VF are still not fully understood.

METHODS AND RESULTS

Ventricular arrhythmia (VA) was induced by aconitine injection into PMs of healthy sheep. To investigate mechanisms of degeneration of stable VA into VF in structurally healthy hearts, endocardial high-density and epicardial mapping was performed during sinus rhythm (SR) and VA. The electrical restitution curve, modelling the relation of diastolic interval and activation recovery interval (a surrogate parameter for action potential duration), is steeper in VA than in non-arrhythmia (ventricular pacing and SR). Steeper restitution curves reflect electrical instability and propensity to degenerate into VF. Importantly, we find the parameter repolarization time in relation to cycle length (RT/CL) to differentiate self-limiting from degenerating arrhythmia with high specificity and sensitivity.

CONCLUSION

RT/CL may serve as a simple index to aid differentiation between self-limiting and electrically instable arrhythmia with the propensity to degenerate to VF. RT/CL is independent of cycle length and could easily be measured to identify electrical instability in patients.

The Effects of Vagus Nerve Stimulation on Ventricular Electrophysiology and Nitric Oxide Release in the Rabbit Heart

Background: Abnormal autonomic activity including impaired parasympathetic control is a known hallmark of heart failure (HF). Vagus nerve stimulation (VNS) has been shown to reduce the susceptibility of the heart to ventricular fibrillation, however the precise underlying mechanisms are not well understood and the detailed stimulation parameters needed to improve patient outcomes clinically are currently inconclusive.

Objective: To investigate NO release and cardiac electrophysiological effects of electrical stimulation of the vagus nerve at varying parameters using the isolated innervated rabbit heart preparation.

Methods: The right cervical vagus nerve was electrically stimulated in the innervated isolated rabbit heart preparation (n = 30). Heart rate (HR), effective refractory period (ERP), ventricular fibrillation threshold (VFT) and electrical restitution were measured as well as NO release from the left ventricle.

Results: High voltage with low frequency VNS resulted in the most significant reduction in HR (by −20.6 ± 3.3%, −25.7 ± 3.0% and −30.5 ± 3.0% at 0.1, 1 and 2 ms pulse widths, with minimal increase in NO release. Low voltage and high frequency VNS significantly altered NO release in the left ventricle, whilst significantly flattening the slope of restitution and significantly increasing VFT. HR changes however using low voltage, high frequency VNS were minimal at 20Hz (to 138.5 ± 7.7 bpm (−7.3 ± 2.0%) at 1 ms pulse width and 141.1 ± 6.6 bpm (−4.4 ± 1.1%) at 2 ms pulse width).

Conclusion: The protective effects of the VNS are independent of HR reductions demonstrating the likelihood of such effects being as a result of the modulation of more than one molecular pathway. Altering the parameters of VNS impacts neural fibre recruitment in the ventricle; influencing changes in ventricular electrophysiology, the protective effect of VNS against VF and the release of NO from the left ventricle.

Regulation of heart rate in vertebrates during hypoxia: A comparative overview

Acute exposure to low oxygen (hypoxia) places conflicting demands on the heart. Whilst an increase in heart rate (tachycardia) may compensate systemic oxygen delivery as arterial oxygenation falls, the heart itself is an energetically expensive organ that may benefit from slowing (bradycardia) to reduce work when oxygen is limited. Both strategies are apparent in vertebrates, with tetrapods (mammals, birds, reptiles, and amphibians) classically exhibiting hypoxic tachycardia and fishes displaying characteristic hypoxic bradycardia. With a richer understanding of the ontogeny and evolution of the responses, however, we see similarities in the underlying mechanisms between vertebrate groups. For example, in adult mammals, primary bradycardia results from the hypoxic stimulation of carotid body chemoreceptors that are overwhelmed by mechano-sensory feedback from the lung associated with hyperpnoea. Fish-like bradycardia prevails in the mammalian foetus (which, at this stage, is incapable of pulmonary ventilation), and in fish and foetus alike, the bradycardia ensues despite an elevation of circulating catecholamines. In both cases, the reduced heart rate may primarily serve to protect the heart. Thus, the comparative perspective offers fundamental insight into how and why different vertebrates regulate heart rate in different ways during periods of hypoxia.

High-resolution structure-function mapping of intact hearts reveals altered sympathetic control of infarct border zones

Remodeling of injured sympathetic nerves on the heart after myocardial infarction (MI) contributes to adverse outcomes such as sudden arrhythmic death, yet the underlying structural mechanisms are poorly understood. We sought to examine microstructural changes on the heart after MI and to directly link these changes with electrical dysfunction. We developed a high-resolution pipeline for anatomically precise alignment of electrical maps with structural myofiber and nerve-fiber maps created by customized computer vision algorithms. Using this integrative approach in a mouse model, we identified distinct structure-function correlates to objectively delineate the infarct border zone, a known source of arrhythmias after MI. During tyramine-induced sympathetic nerve activation, we demonstrated regional patterns of altered electrical conduction aligned directly with altered neuroeffector junction distribution, pointing to potential neural substrates for cardiac arrhythmia. This study establishes a synergistic framework for examining structure-function relationships after MI with microscopic precision that has potential to advance understanding of arrhythmogenic mechanisms.

The short-chain fatty acid propionate improved ventricular electrical remodeling in a rat model with myocardial infarction

The short-chain fatty acid (SCFA) propionate (C3), a microorganism metabolite produced by gut microbial fermentation, has parasympathetic-activation effects. The cardiac autonomic rebalancing strategy is considered as an important therapeutic approach to myocardial infarction (MI)-produced ventricular arrhythmias (VAs). Thus, our research was designed to clarify the potential functions of the SCFA propionate in VAs and cardiac electrophysiology in MI rats. A hundred adult Sprague-Dawley rats were allocated to four groups: the sham group (200 mM sodium chloride), the sham + C3 group (200 mM propionate), the MI group (200 mM sodium chloride) and the MI + C3 group (200 mM propionate). In comparison with the sham group, propionate significantly increased the parasympathetic components heart rate variability (HRV) and acetylcholine levels, prolonged cardiac repolarization, induced STAT3 phosphorylation and up-regulated the c-fos expression in nodose ganglia and solitary nucleus. Propionate intake reduced the susceptibility to VAs. MI induced by coronary ligation caused a significant increase in the sympathetic components HRV, abnormal repolarization, global repolarization dispersion, norepinephrine and inflammatory cytokines, reduction and redistribution of Connexin 43 in the infarcted border zone, and activation of NFκB, which were attenuated in the MI + C3 group. Oral propionate supplementation, as a nutritional intervention, protected the heart against MI-induced VAs and cardiac electrophysiology instability partly by parasympathetic activation based on the gut-brain axis.

Autonomic modulation of ventricular electrical activity: recent developments and clinical implications

PURPOSE

This review aimed to provide a complete overview of the current stance and recent developments in antiarrhythmic neuromodulatory interventions, focusing on lifethreatening vetricular arrhythmias.

METHODS

Both preclinical studies and clinical studies were assessed to highlight the gaps in knowledge that remain to be answered and the necessary steps required to properly translate these strategies to the clinical setting.

RESULTS

Cardiac autonomic imbalance, characterized by chronic sympathoexcitation and parasympathetic withdrawal, destabilizes cardiac electrophysiology and promotes ventricular arrhythmogenesis. Therefore, neuromodulatory interventions that target the sympatho-vagal imbalance have emerged as promising antiarrhythmic strategies. These strategies are aimed at different parts of the cardiac neuraxis and directly or indirectly restore cardiac autonomic tone. These interventions include pharmacological blockade of sympathetic neurotransmitters and neuropeptides, cardiac sympathetic denervation, thoracic epidural anesthesia, and spinal cord and vagal nerve stimulation.

CONCLUSION

Neuromodulatory strategies have repeatedly been demonstrated to be highly effective and very promising anti-arrhythmic therapies. Nevertheless, there is still much room to gain in our understanding of neurocardiac physiology, refining the current neuromodulatory strategic options and elucidating the chronic effects of many of these strategic options.

Autonomic Modulation of Cardiac Arrhythmias: Methods to Assess Treatment and Outcomes

The autonomic nervous system plays a central role in the pathogenesis of multiple cardiac arrhythmias, including atrial fibrillation and ventricular tachycardia. As such, autonomic modulation represents an attractive therapeutic approach in these conditions. Notably, autonomic modulation exploits the plasticity of the neural tissue to induce neural remodeling and thus obtain therapeutic benefit. Different forms of autonomic modulation include vagus nerve stimulation, tragus stimulation, renal denervation, baroreceptor activation therapy, and cardiac sympathetic denervation. This review seeks to highlight these autonomic modulation therapeutic modalities, which have shown promise in early preclinical and clinical trials and represent exciting alternatives to standard arrhythmia treatment. We also present an overview of the various methods used to assess autonomic tone, including heart rate variability, skin sympathetic nerve activity, and alternans, which can be used as surrogate markers and predictors of the treatment effect. Although the use of autonomic modulation to treat cardiac arrhythmias is supported by strong preclinical data and preliminary studies in humans, in light of the disappointing results of a number of recent randomized clinical trials of autonomic modulation therapies in heart failure, the need for optimization of the stimulation parameters and rigorous patient selection based on appropriate biomarkers cannot be overemphasized.

Non-invasive detection of exercise-induced cardiac conduction abnormalities in sudden cardiac death survivors in the inherited cardiac conditions

AIMS

Rate adaptation of the action potential ensures spatial heterogeneities in conduction across the myocardium are minimized at different heart rates providing a protective mechanism against ventricular fibrillation (VF) and sudden cardiac death (SCD), which can be quantified by the ventricular conduction stability (V-CoS) test previously described. We tested the hypothesis that patients with a history of aborted SCD due to an underlying channelopathy or cardiomyopathy have a reduced capacity to maintain uniform activation following exercise.

METHODS AND RESULTS

Sixty individuals, with (n = 28) and without (n = 32) previous aborted-SCD event underwent electro-cardiographic imaging recordings following exercise treadmill test. These included 25 Brugada syndrome, 13 hypertrophic cardiomyopathy, 12 idiopathic VF, and 10 healthy controls. Data were inputted into the V-CoS programme to calculate a V-CoS score that indicate the percentage of ventricle that showed no significant change in ventricular activation, with a lower score indicating the development of greater conduction heterogeneity. The SCD group, compared to those without, had a lower median (interquartile range) V-CoS score at peak exertion [92.8% (89.8-96.3%) vs. 97.3% (94.9-99.1%); P < 0.01] and 2 min into recovery [95.2% (91.1-97.2%) vs. 98.9% (96.9-99.5%); P < 0.01]. No significant difference was observable later into recovery at 5 or 10 min. Using the lowest median V-CoS scores obtained during the entire recovery period post-exertion, SCD survivors had a significantly lower score than those without for each of the different underlying aetiologies.

CONCLUSION

Data from this pilot study demonstrate the potential use of this technique in risk stratification for the inherited cardiac conditions.

Microvolt T-Wave Alternans Is Modulated by Acute Low-Level Tragus Stimulation in Patients With Ischemic Cardiomyopathy and Heart Failure

Aims: Microvolt T-wave alternans (TWA), an oscillation in T-wave morphology of the electrocardiogram (ECG), has been associated with increased susceptibility to ventricular tachy-arrhythmias, while vagus nerve stimulation has shown promising anti-arrhythmic effects in in vivo and ex vivo animal studies. We aimed to examine the effect of non-invasive, acute low-level tragus stimulation (LLTS) on TWA in patients with ischemic cardiomyopathy and heart failure.

Methods: 26 patients with ischemic cardiomyopathy (left ventricular ejection fraction <35%) and chronic stable heart failure, previously implanted with an automatic implantable cardioverter defibrillator (ICD) device with an atrial lead (dual chamber ICD or cardiac resynchronization therapy defibrillator), were enrolled in the study. Each patient sequentially received, (1) Sham LLTS (electrode on tragus, but no stimulation delivered) for 5 min; (2) Active LLTS at two different frequencies (5 and 20 Hz, 15 min each); and (3) Active LLTS, during concomitant atrial pacing at 100 bpm at two different frequencies (5 and 20 Hz, 15 min each). LLTS was delivered through a transcutaneous electrical nerve stimulation device (pulse width 200 μs, frequency 5/20 Hz, amplitude 1 mA lower than the discomfort threshold). TWA burden was assessed using continuous ECG monitoring during sham and active LLTS in sinus rhythm, as well as during atrial pacing.

Results: Right atrial pacing at 100 bpm led to significantly heightened TWA burden compared to sinus rhythm, with or without LLTS. Acute LLTS at both 5 and 20 Hz, during sinus rhythm led to a significant rise in TWA burden in the precordial leads (p < 0.05).

Conclusion: Acute LLTS results in a heart-rate dependent increase in TWA burden.

Pulmonary vein isolation in a real-world population does not influence QTc interval

AIMS

We aimed to examine whether routine pulmonary vein isolation (PVI) induces significant ventricular repolarization changes as suggested earlier.

METHODS AND RESULTS

Five-minute electrocardiograms were recorded at hospital's admission (T-1d), 1 day after the PVI-procedure (T+1d) and at 3 months post-procedure (T+3m) from a registry of consecutive atrial fibrillation (AF) patients scheduled for routine PVI with different PVI modalities (radiofrequency, cryo-ablation, and hybrid). Only patients who were in sinus rhythm at all three recordings (n = 117) were included. QT-intervals and QT-dispersion were evaluated with custom-made software and QTc was calculated using Bazett's, Fridericia's, Framingham's, and Hodges' formulas. Both QT- and RR-intervals were significantly shorter at T+1d (399 ± 37 and 870 ± 141 ms) and T+3m (407 ± 36 and 950 ± 140 ms) compared with baseline (417 ± 36 and 1025 ± 164 ms). There was no statistically significant within-subject difference in QTc Fridericia (T-1d 416 ± 28 ms, T+1d 419 ± 33 ms, and T+3m 414 ± 25 ms) and QT-dispersion (T-1d 18 ± 12 ms, T+1d 21 ± 19 ms, and T+3m 17 ± 12 ms) between the recordings. A multiple linear regression model with age, sex, AF type, ablation technique, first/re-do ablation, and AF recurrence to predict the change in QTc at T+3m with respect to QTc at T-1d did not reach significance which indicates that the change in QTc does not differ between all subgroups (age, sex, AF type, ablation technique, first/re-do ablation, and AF recurrence).

CONCLUSION

Based on our data a routine PVI does not result in a prolongation of QTc in a real-world population. These findings, therefore, suggest that there is no need to intensify post-PVI QT-interval monitoring.

Utility of Zebrafish Models of Acquired and Inherited Long QT Syndrome

Long-QT Syndrome (LQTS) is a cardiac electrical disorder, distinguished by irregular heart rates and sudden death. Accounting for ∼40% of cases, LQTS Type 2 (LQTS2), is caused by defects in the Kv11.1 (hERG) potassium channel that is critical for cardiac repolarization. Drug block of hERG channels or dysfunctional channel variants can result in acquired or inherited LQTS2, respectively, which are typified by delayed repolarization and predisposition to lethal arrhythmia. As such, there is significant interest in clear identification of drugs and channel variants that produce clinically meaningful perturbation of hERG channel function. While toxicological screening of hERG channels, and phenotypic assessment of inherited channel variants in heterologous systems is now commonplace, affordable, efficient, and insightful whole organ models for acquired and inherited LQTS2 are lacking. Recent work has shown that zebrafish provide a viable in vivo or whole organ model of cardiac electrophysiology. Characterization of cardiac ion currents and toxicological screening work in intact embryos, as well as adult whole hearts, has demonstrated the utility of the zebrafish model to contribute to the development of therapeutics that lack hERG-blocking off-target effects. Moreover, forward and reverse genetic approaches show zebrafish as a tractable model in which LQTS2 can be studied. With the development of new tools and technologies, zebrafish lines carrying precise channel variants associated with LQTS2 have recently begun to be generated and explored. In this review, we discuss the present knowledge and questions raised related to the use of zebrafish as models of acquired and inherited LQTS2. We focus discussion, in particular, on developments in precise gene-editing approaches in zebrafish to create whole heart inherited LQTS2 models and evidence that zebrafish hearts can be used to study arrhythmogenicity and to identify potential anti-arrhythmic compounds.

Application of two novel electrical restitution-based ECG markers of ventricular arrhythmia to patients with nonischemic cardiomyopathy

INTRODUCTION

Sudden cardiac death (SCD) risk assessment is limited, particularly in patients with nonischemic cardiomyopathies. This is the first application, in patients with cardiomyopathies, of two novel risk markers, regional restitution instability index (R2I2) and peak electrocardiogram restitution slope (PERS), which have been shown to be predictive of ventricular arrhythmias (VA) or death in ischemic heart disease patients.

METHODS

Blinded retrospective study of 50 patients: 33 dilated cardiomyopathy and 17 other; undergoing electrophysiological study (EPS) for SCD risk stratification, and 29 controls with structurally normal hearts undergoing EPS. R2I2 was calculated from an EPS using electrocardiogram surrogates for action potential duration and diastolic interval. Cut-offs for high and low R2I2/PERS were predefined.

RESULTS

R2I2 was significantly higher in study than control patients (0.99 ± 0.05 vs. 0.63 ± 0.04, p < .001). PERS showed a trend to higher values in the study group (1.18[0.63] vs. 1.09[0.54], p = .07). During median follow up of 5.6 years [interquartile range 1.9 years], nine study patients reached the endpoint of VA/death. Patients who experienced VA/death showed trends to higher mean R2I2 (1.14 ± 0.07 vs.0.95 ± 0.05, p = .12) and PERS (1.46[0.49] vs. 1.13[0.62], p = .22). A Cox proportional hazards model using grouped markers: R2I2 < 1.03 + PERS < 1.21/either R2I2 ≥ 1.03 or PERS ≥ 1.21/R2I2 ≥ 1.03 + PERS ≥ 1.21; significantly predicted VA/death (p = .02) with a hazard ratio per positive component of 3.2 (95% confidence interval 1.2-8.8).

CONCLUSION

R2I2≥ 1.03 + PERS ≥ 1.21 may predict VA/death in patients with cardiomyopathies. R2I2 ≥ 1.03 + PERS ≥ 1.21 have the potential to play an important role in SCD risk stratification in cardiomyopathies but their validity should be confirmed in a larger study.

Neuromodulation With Thoracic Dorsal Root Ganglion Stimulation Reduces Ventricular Arrhythmogenicity

Introduction: Sympathetic hyperactivity is strongly associated with ventricular arrhythmias and sudden cardiac death. Neuromodulation provides therapeutic options for ventricular arrhythmias by modulating cardiospinal reflexes and reducing sympathetic output at the level of the spinal cord. Dorsal root ganglion stimulation (DRGS) is a recent neuromodulatory approach; however, its role in reducing ventricular arrhythmias has not been evaluated. The aim of this study was to determine if DRGS can reduce cardiac sympathoexcitation and the indices for ventricular arrhythmogenicity induced by programmed ventricular extrastimulation. We evaluated the efficacy of thoracic DRGS at both low (20 Hz) and high (1 kHz) stimulation frequencies. Methods: Cardiac sympathoexcitation was induced in Yorkshire pigs (n = 8) with ventricular extrastimulation (S1/S2 pacing), before and after DRGS. A DRG-stimulating catheter was placed at the left T2 spinal level, and animals were randomized to receive low-frequency (20 Hz and 0.4 ms) or high-frequency (1 kHz and 0.03 ms) DRGS for 30 min. High-fidelity cardiac electrophysiological recordings were performed with an epicardial electrode array measuring the indices of ventricular arrhythmogenicity-activation recovery intervals (ARIs), electrical restitution curve (S_max), and Tpeak-Tend interval (Tp-Te interval). Results: Dorsal root ganglion stimulation, at both 20 Hz and 1 kHz, decreased S1/S2 pacing-induced ARI shortening (20 Hz DRGS -21±7 ms, Control -50±9 ms, P = 0.007; 1 kHz DRGS -13 ± 2 ms, Control -46 ± 8 ms, P = 0.001). DRGS also reduced arrhythmogenicity as measured by a decrease in S_max (20 Hz DRGS 0.5 ± 0.07, Control 0.7 ± 0.04, P = 0.006; 1 kHz DRGS 0.5 ± 0.04, Control 0.7 ± 0.03, P = 0.007), and a decrease in Tp-Te interval/QTc (20 Hz DRGS 2.7 ± 0.13, Control 3.3 ± 0.12, P = 0.001; 1 kHz DRGS 2.8 ± 0.08, Control; 3.1 ± 0.03, P = 0.007). Conclusions: In a porcine model, we show that thoracic DRGS decreased cardiac sympathoexcitation and indices associated with ventricular arrhythmogenicity during programmed ventricular extrastimulation. In addition, we demonstrate that both low-frequency and high-frequency DRGS can be effective neuromodulatory approaches for reducing cardiac excitability during sympathetic hyperactivity.

Role of defective calcium regulation in cardiorespiratory dysfunction in Huntington's disease

Huntington’s disease (HD) is a progressive, autosomal dominant neurodegenerative disorder affecting striatal neurons beginning in young adults with loss of muscle coordination and cognitive decline. Less appreciated is the fact that patients with HD also exhibit cardiac and respiratory dysfunction, including pulmonary insufficiency and cardiac arrhythmias. The underlying mechanism for these symptoms is poorly understood. In the present study we provide insight into the cause of cardiorespiratory dysfunction in HD and identify a potentially novel therapeutic target. We now show that intracellular calcium (Ca²⁺) leak via posttranslationally modified ryanodine receptor/intracellular calcium release (RyR) channels plays an important role in HD pathology. RyR channels were oxidized, PKA phosphorylated, and leaky in brain, heart, and diaphragm both in patients with HD and in a murine model of HD (Q175). HD mice (Q175) with endoplasmic reticulum Ca²⁺ leak exhibited cognitive dysfunction, decreased parasympathetic tone associated with cardiac arrhythmias, and reduced diaphragmatic contractile function resulting in impaired respiratory function. Defects in cognitive, motor, and respiratory functions were ameliorated by treatment with a novel Rycal small-molecule drug (S107) that fixes leaky RyR. Thus, leaky RyRs likely play a role in neuronal, cardiac, and diaphragmatic pathophysiology in HD, and RyRs are a potential novel therapeutic target.

This study explores the role of ryanodine receptor calcium channels in the brain, the heart, and the diaphragm and central versus peripheral pathophysiological mechanisms in Huntington’s disease.

Vagal Stimulation and Arrhythmias

I mbalance of the sympathetic and parasympathetic nervous systems is probably the most prevalent autonomic mechanism underlying many a rrhythmias . Recently, vagus nerve stimulation ( VNS has emerged as a novel therapeutic modality to treat arrhythmias through its anti adrenergic and anti inflammatory actions . C linical trials applying VNS to the cervical vagus nerve in heart failure pati en ts yielded conflicting results, possibly due to limited understanding of the optimal stimulation parameters for the targeted cardiovascular diseases. Transcutaneous VNS by stimulating the auricular branch of the vagus nerve, has attracted great attention d ue to its noninvasiveness. In this r eview, we summarize current knowledge about the complex relationship between VNS and cardiac arrhythmias and discuss recent advances in using VNS , particularly transcutaneous VNS , to treat arrhythmias.

The hERG channel activator, RPR260243, enhances protective IKr current early in the refractory period reducing arrhythmogenicity in zebrafish hearts

Human ether-à-go-go related gene (hERG) K⁺ channels are important in cardiac repolarization, and their dysfunction causes prolongation of the ventricular action potential, long QT syndrome, and arrhythmia. As such, approaches to augment hERG channel function, such as activator compounds, have been of significant interest due to their marked therapeutic potential. Activator compounds that hinder channel inactivation abbreviate action potential duration (APD) but carry risk of overcorrection leading to short QT syndrome. Enhanced risk by overcorrection of the APD may be tempered by activator-induced increased refractoriness; however, investigation of the cumulative effect of hERG activator compounds on the balance of these effects in whole organ systems is lacking. Here, we have investigated the antiarrhythmic capability of a hERG activator, RPR260243, which primarily augments channel function by slowing deactivation kinetics in ex vivo zebrafish whole hearts. We show that RPR260243 abbreviates the ventricular APD, reduces triangulation, and steepens the slope of the electrical restitution curve. In addition, RPR260243 increases the post-repolarization refractory period. We provide evidence that this latter effect arises from RPR260243-induced enhancement of hERG channel-protective currents flowing early in the refractory period. Finally, the cumulative effect of RPR260243 on arrhythmogenicity in whole organ zebrafish hearts is demonstrated by the restoration of normal rhythm in hearts presenting dofetilide-induced arrhythmia. These findings in a whole organ model demonstrate the antiarrhythmic benefit of hERG activator compounds that modify both APD and refractoriness. Furthermore, our results demonstrate that targeted slowing of hERG channel deactivation and enhancement of protective currents may provide an effective antiarrhythmic approach.NEW & NOTEWORTHY hERG channel dysfunction causes long QT syndrome and arrhythmia. Activator compounds have been of significant interest due to their therapeutic potential. We used the whole organ zebrafish heart model to demonstrate the antiarrhythmic benefit of the hERG activator, RPR260243. The activator abbreviated APD and increased refractoriness, the combined effect of which rescued induced ventricular arrhythmia. Our findings show that the targeted slowing of hERG channel deactivation and enhancement of protective currents caused by the RPR260243 activator may provide an effective antiarrhythmic approach.

Cardiac innervation in acute myocardial ischaemia/reperfusion injury and cardioprotection

Acute myocardial infarction (AMI) and the heart failure (HF) that often complicates this condition, are among the leading causes of death and disability worldwide. To reduce myocardial infarct (MI) size and prevent heart failure, novel therapies are required to protect the heart against the detrimental effects of acute ischaemia/reperfusion injury (IRI). In this regard, targeting cardiac innervation may provide a novel therapeutic strategy for cardioprotection. A number of cardiac neural pathways mediate the beneficial effects of cardioprotective strategies such as ischaemic preconditioning and remote ischaemic conditioning, and nerve stimulation may therefore provide a novel therapeutic strategy for cardioprotection. In this article, we provide an overview of cardiac innervation and its impact on acute myocardial IRI, the role of extrinsic and intrinsic cardiac neural pathways in cardioprotection, and highlight peripheral and central nerve stimulation as a cardioprotective strategy with therapeutic potential for reducing MI size and preventing HF following AMI. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Adrenoceptor Responses in Human Embryonic Stem Cell-Derived Cardiomyocytes: a Special Focus on Electrophysiological Property

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) have become a promising cell source for cardiovascular research. The electrophysiological characteristic of hESC-CMs has been generally studied, but little is known about electrophysiological response to adrenergic receptor (AR) activation. This study aims to characterize electrophysiological response of hESC-CMs to adrenergic stimulation in terms of the conduction velocity (CV) and action potential (AP) shape. The H9 hESC-CMs were acquired by a classic differentiation protocol and cultured to achieve confluent cell monolayers. The AP shape and CV among the monolayers were recorded using optical mapping during electrophysiological and pharmacological stimulation experiments. Quantitative real-time polymerase chain reaction and Western blot were adopted to determine the expression levels of Connexin and ion channel gene and protein. Chronic β-AR stimulation by isoproterenol for 24 hours in hESC-CM monolayers increased CV by approximately 50%, whereas α-AR or acute β-AR stimulation had no significant effect; chronic β-AR stimulation resulted in a significant Connexin (Cx) 43 and Na_v1.5 upregulation at both protein and mRNA level. Isoproterenol-induced CV accelerating and Cx43 and Na_v1.5 upregulation in hESC-CMs, which was attenuated by selective β1-adrenoceptor antagonist CGP 20712A but not selective β2-antagonist ICI 118551. Moreover, pretreatment with protein kinase A (PKA) inhibitor H89, mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (MEK) inhibitor SB203580, and MAPK inhibitor PD98059 suppressed the isoproterenol-induced CV accelerating and Cx43 upregulation, whereas it had no significant effect on Na_v1.5 upregulation. The AP shape in hESC-CM monolayers was less susceptible by either β-AR or α-AR stimulation. It was β1-AR not β2-AR contributing to the modification of conduction velocity among hESC-CM monolayers. Chronic β1-AR stimulation accelerates CV by upregulating Cx43 via PKA/MEK/MAPK pathway. SIGNIFICANCE STATEMENT: These data provide new insight into the electrophysiological characteristics of human embryonic stem cell-derived cardiomyocytes (hESC-CMs) and depict a concise signaling pathway in the adrenergic receptor (AR) regulation of action potential shape and electrical propagation across hESC-CM monolayer. It is β1-AR not β2-AR contributing to the modification of conduction velocity in hESC-CMs and accelerating conduction velocity by upregulating Connexin 43 via protein kinase A/ mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase/MAPK pathway.

Ablation of Neuroaxial in Patients with Ventricular Tachycardia

Ventricular tachycardia (VT) remains a common cause of sudden cardiac death. It is widely accepted that VTs are strongly associated with autonomic imbalance with reduced vagal and increased sympathetic activities. Pharmacologic therapy remains the first-line therapy, but antiarrhythmic agents may not be effective or carry significant side effects. Sympathetic denervation is an emerging therapy to prevent or treat VTs by rebalancing the sympathetic and parasympathetic activity. This article focuses on the role of sympathetic activation in VT, and the mapping and ablation of sympathetic nervous system in patients with VT.

The autonomic nervous system and ventricular arrhythmias in myocardial infarction and heart failure

Ventricular arrhythmias (VA) can range in presentation from asymptomatic to cardiac arrest and sudden cardiac death (SCD). Sustained ventricular tachycardias/ventricular fibrillation (VT/VF) are a common cause of SCD in the setting of myocardial infarction (MI) and heart failure. A particularly arrhythmogenic cardiac syncytia in these conditions can be attributed to both sympathetic activation and parasympathetic dysfunction, while appropriate neuromodulation has the potential to reduce occurrence of VT/VF. In this review, we outline the components of the autonomic nervous system that play an important role in normal cardiac electrophysiology and function. In addition, we discuss changes that occur in the setting of cardiac disease including adverse neural remodeling and neurohormonal activation which significantly contribute to propensity for VT/VF. Finally, we review neuromodulation strategies to mitigate VT/VF which predominantly rely on increasing parasympathetic drive and blockade of sympathetic neurotransmission.

Renal denervation ameliorates the risk of ventricular fibrillation in overweight and heart failure

Aims

Both obesity and heart failure (HF) are associated with sudden cardiac death. The current study aimed to investigate the effects of overweight and HF on the substrate for ventricular fibrillation (VF), and whether renal denervation (RDN) can protect the heart from sympathetic activation and cardiac remodelling in HF rabbits fed with high-fat diet (HFD).

Methods and results

Twenty-four rabbits randomized into control group fed with regular diet (Control), HFD, HFD-HF, and HFD-HF-RDN groups. Rapid ventricular pacing of 400 b.p.m. for 4 weeks was applied in HFD-HF and HFD-HF-RDN. Surgical and chemical RDNs were approached through bilateral retroperitoneal flank incisions in HFD-HF-RDN. All rabbits received electrophysiological study and a VF inducibility test. The ventricular myocardium was harvested for trichrome stain. After 3 months, mean body weight was heavier in HFD, compared with control (3.5 ± 0.1 kg vs. 2.6 ± 0.1 kg, P &lt; 0.01). No differences in body weight among the three groups fed with HFD were observed. The ventricular refractory periods were longer in HFD-HF and HFD-HF-RDN than in control. An extension of ventricular fibrosis was observed in HFD and HFD-HF compared with control, and the degree of ventricular fibrosis was suppressed in HFD-HF-RDN compared with HFD-HF. The level of tyrosine hydroxylase staining was reduced in HFD-HF-RDN compared with HFD and HFD-HF. Importantly, VF inducibility was lower in HFD-RDN-HF (10 ± 4%), when compared with those in HFD-HF (58 ± 10%, P &lt; 0.01) and HFD (42 ± 5%, P &lt; 0.05), respectively.

Conclusion

Our results suggest that overweight and HF increase sympathetic activity, structural remodelling, and VF inducibility, but RDN prevents them.

Effects of sympatho-vagal interaction on ventricular electrophysiology and their modulation during beta-blockade

AIMS

The effects of sympatho-vagal interaction on heart rate (HR) changes are characterized by vagal dominance resulting in accentuated antagonism. Complex autonomic modulation of ventricular electrophysiology may exert prognostic arrhythmic impact. We examined the effects of concurrent sympathetic (SNS) and vagus (VNS) nerve stimulation on ventricular fibrillation threshold (VFT) and standard restitution (RT) in an isolated rabbit heart preparation with intact dual autonomic innervation, with and without beta-blockade.

METHODS AND RESULTS

Monophasic action potentials were recorded from left ventricular epicardial surface of dual-innervated isolated heart preparations from New Zealand white rabbits (n = 18). HR, VFT and RT were measured during different stimulation protocols (Protocol 1: VNS-SNS; Protocol 2: SNS-VNS) involving low- and high-frequency stimulations. A sub-study of Protocol 2 was performed in the presence of metoprolol tartrate. In both protocols, HR changes were characterized by vagal-dominant bradycardic component, affirming accentuated antagonism. During concurrent high-frequency VNS (HV), SNS prevails in lowering VFT in a frequency-sensitive manner during low (LS) or high (HS)-frequency stimulations (HV-LS: -2.8 ± 0.8 mA; HV-HS: -4.0 ± 0.9 mA, p < .05 vs. HV), with accompanying steepening of relative RT slope gradients (HV-LS: 223.54 ± 37.41%; HV-HS: 295.20 ± 60.86%, p < .05 vs. HV). In protocol 2, low (LV) and high (HV) vagal stimulations during concurrent HS raised VFT (HS-LV: 1.0 ± 0.4 mA; HS-HV: 3.0 ± 0.6 mA, p < .05 vs HS) with associated flattening of RT slopes (HS-LV: 32.40 ± 4.97%;HS-HV: 38.07 ± 6.37%; p < .05 vs HS). Metoprolol abolished accentuated antagonism in HR changes, reduced VFT and flattened RT globally during SNS-VNS.

CONCLUSIONS

Accentuated antagonism is absent in ventricular electrophysiological changes during sympatho-vagal interaction with sympathetic effect prevailing, suggesting a different mechanism at the ventricular level from heart rate effects. Metoprolol nullified accentuated antagonism with additional anti-fibrillatory effect beyond adrenergic blockade during sympatho-vagal stimulations.

Cardiac Dysfunction in Neurocritical Care: An Autonomic Perspective

A number of neurologic disorders can cause cardiac dysfunction by involving the conductive system and contractile apparatus of the heart. This is especially prominent in the neurocritical care setting where the spectrum of cardiac dysfunction due to acute neurologic injury ranges from trivial and isolated electrocardiographic changes to malignant arrhythmias and sudden death (Table 1). The mechanism of these cardiac complications is complex and not fully understood. An understanding of the neuroanatomical structures and pathways is of immense importance to comprehend the underlying pathophysiology that culminates as cardiac damage and dysregulation. Once the process is initiated, it can complicate and adversely affect the outcome of primary neurologic conditions commonly seen in the neurocritical care setting. Not only are these cardiac disorders under-recognized, there is a paucity of data to formulate evidence-based guidelines regarding early detection, acute management, and preventive strategies. However, certain details of clinical features and their course combined with location of primary neurologic lesion on neuroimaging and data obtained from laboratory investigations can be of great value to develop a strategy to appropriately manage these patients and to prevent adverse outcome from these cardiac complications. In this review, we highlight the mechanisms of cardiac dysfunction due to catastrophic neurologic conditions or due to stress of critical illness. We also address various clinical syndromes of cardiac dysfunction that occur as a result of the neurologic illness and in turn may complicate the course of the primary neurologic condition.

Hype or hope: Vagus nerve stimulation against acute myocardial ischemia-reperfusion injury

Acute myocardial infarction (MI) is a major cause of death worldwide. Although timely and successful reperfusion could reduce myocardial ischemia injury, limit infarct size, and improve ventricular dysfunction and reduce acute mortality, restoring blood flow might also lead to unwanted myocardial ischemic-reperfusion (I/R) injury. Pre-clinical studies have demonstrated that multiple approaches are capable of attenuating the myocardial I/R injury. However, there is still no effective therapy for preventing myocardial I/R injury for the clinical setting. It is known that myocardial I/R injury could induce cardiac autonomic imbalance with over-activated sympathetic tone and reduced vagal activity, in turn, contributing to pathogenesis of myocardial I/R injury. Cumulative evidence shows that the enhancement of vagal activity, so called vagus nerve stimulation (VNS), is able to reduce injury and promote recovery of injured myocardium. Therefore, VNS might be a potentially novel strategy choice for preventing/attenuating myocardial I/R injury. In this review, we describe the protective role of VNS in myocardial I/R injury and related potential mechanisms. Then, we discuss the challenge and the opportunity of VNS in the treatment of acute myocardial I/R injury.

Targeted ablation of cardiac sympathetic neurons improves ventricular electrical remodelling in a canine model of chronic myocardial infarction

Aims

The purpose of this study was to evaluate the cardiac electrophysiologic effects of targeted ablation of cardiac sympathetic neurons (TACSN) in a canine model of chronic myocardial infarction (MI).

Methods and results

Thirty-eight anaesthetized dogs were randomly assigned into the sham-operated, MI, and MI-TACSN groups, respectively. Myocardial infarction-targeted ablation of cardiac sympathetic neuron was induced by injecting cholera toxin B subunit-saporin compound in the left stellate ganglion (LSG). Five weeks after surgery, the cardiac function, heart rate variability (HRV), ventricular electrophysiological parameters, LSG function and neural activity, serum norepinephrine (NE), nerve growth factor (NGF), and brain natriuretic peptide (BNP) levels were measured. Cardiac sympathetic innervation was determined with immunofluorescence staining of growth associated protein-43 (GAP43) and tyrosine hydroxylase (TH). Compared with MI group, TACSN significantly improved HRV, attenuated LSG function and activity, prolonged corrected QT interval, decreased Tpeak-Tend interval, prolonged ventricular effective refractory period (ERP), and action potential duration (APD), decreased the slopes of APD restitution curves, suppressed the APD alternans, increased ventricular fibrillation threshold, and reduced serum NE, NGF, and BNP levels. Moreover, the densities of GAP43 and TH-positive nerve fibres in the infarcted border zone in the MI-TACSN group were lower than those in the MI group.

Conclusion

Targeted ablation of cardiac sympathetic neuron attenuates sympathetic remodelling and improves ventricular electrical remodelling in the chronic phase of MI. These data suggest that TACSN may be a novel approach to treating ventricular arrhythmias.

Improved Outcomes of Cardiopulmonary Resuscitation in Rats Treated With Vagus Nerve Stimulation and Its Potential Mechanism

Studies have demonstrated that vagus nerve stimulation (VNS) reduces ischemia/reperfusion injury. In this study, we investigated the protective effects of VNS in a rat model of cardiopulmonary resuscitation (CPR). We further investigated whether the beneficial effects of VNS were dependent on the alpha 7 nicotinic acetylcholine receptor (α7nAChR). Forty animals were randomized into four groups and all underwent CPR (n = 10 each): CPR alone (control); VNS during CPR; α7nAChR antagonist methyllycaconitine citrate (MLA) with VNS; α7nAChR agonist 3-(2, 4-dimethoxybenzylidene) anabaseine (GTS-21 dihydrochloride) without VNS. The right vagus nerve was exteriorized in all animals. Ventricular fibrillation was induced and untreated for 8 min. Defibrillation was attempted after 8 min of CPR. VNS was initiated at the beginning of precordial chest compressions and continued for 4 h after return of spontaneous circulation (ROSC) in both the VNS and MLA groups. Hemodynamic measurements and myocardial function, including ejection fraction and myocardial performance index, were assessed at baseline, 1 and 4 h after ROSC. The neurological deficit score was measured at 24-h intervals for a total of 72 h. The heart rate was reduced in the VNS and MLA groups, while no difference was found in mean arterial pressure between the four groups. Better post-resuscitation myocardial and cerebral function and longer duration of survival were observed in the VNS-treated animals. The protective effects of VNS could be abolished by MLA and imitated by GTS-21. In addition, VNS decreased the number of electrical shocks and the duration of CPR required. VNS improves multiple outcomes after CPR.

The role of low-level vagus nerve stimulation in cardiac therapy

Introduction: Cardiovascular diseases are accompanied by autonomic nervous system (ANS) imbalance which is characterized by decreased vagal tone. Preclinical and clinical studies have revealed that increasing vagal activity via vagus nerve stimulation (VNS) could protect the heart. Based on these studies, VNS has emerged as a potential non-pharmaceutical treatment strategy. Although it's still difficult to find the optimal stimulus parameters, however, in arrhythmia model, it is reported that low-level VNS (LL-VNS) exacts paradoxical effects from the high-level VNS. Thus, the concept of LL-VNS is introduced. Areas covered: Animal and human studies have discussed the safety and efficacy of VNS and LL-VNS, and this review will discuss the research data in cardiovascular diseases, including atrial arrhythmia, ventricular arrhythmia, ischemia/reperfusion injury, heart failure, and hypertension. Expert opinion: In this regard, various clinical studies have been performed to verify the safety and efficacy of VNS. It is shown that VNS is well-tolerated and safe, but the results of its efficacy are conflicting, which may well block the translational process of VNS. The appearance of LL-VNS brings new idea and inspiration, suggesting an important role of subthreshold stimulation. A better understanding of the LL-VNS will contribute to translational research of VNS.

Different paths, same destination: divergent action potential responses produce conserved cardiac fight-or-flight response in mouse and rabbit hearts

KEY POINTS

Cardiac electrophysiology and Ca²⁺ handling change rapidly during the fight-or-flight response to meet physiological demands. Despite dramatic differences in cardiac electrophysiology, the cardiac fight-or-flight response is highly conserved across species. In this study, we performed physiological sympathetic nerve stimulation (SNS) while optically mapping cardiac action potentials and intracellular Ca²⁺ transients in innervated mouse and rabbit hearts. Despite similar heart rate and Ca²⁺ handling responses between mouse and rabbit hearts, we found notable species differences in spatio-temporal repolarization dynamics during SNS. Species-specific computational models revealed that these electrophysiological differences allowed for enhanced Ca²⁺ handling (i.e. enhanced inotropy) in each species, suggesting that electrophysiological responses are fine-tuned across species to produce optimal cardiac fight-or-flight responses.

ABSTRACT

Sympathetic activation of the heart results in positive chronotropy and inotropy, which together rapidly increase cardiac output. The precise mechanisms that produce the electrophysiological and Ca²⁺ handling changes underlying chronotropic and inotropic responses have been studied in detail in isolated cardiac myocytes. However, few studies have examined the dynamic effects of physiological sympathetic nerve activation on cardiac action potentials (APs) and intracellular Ca²⁺ transients (CaTs) in the intact heart. Here, we performed bilateral sympathetic nerve stimulation (SNS) in fully innervated, Langendorff-perfused rabbit and mouse hearts. Dual optical mapping with voltage- and Ca²⁺ -sensitive dyes allowed for analysis of spatio-temporal AP and CaT dynamics. The rabbit heart responded to SNS with a monotonic increase in heart rate (HR), monotonic decreases in AP and CaT duration (APD, CaTD), and a monotonic increase in CaT amplitude. The mouse heart had similar HR and CaT responses; however, a pronounced biphasic APD response occurred, with initial prolongation (50.9 ± 5.1 ms at t = 0 s vs. 60.6 ± 4.1 ms at t = 15 s, P < 0.05) followed by shortening (46.5 ± 9.1 ms at t = 60 s, P = NS vs. t = 0). We determined the biphasic APD response in mouse was partly due to dynamic changes in HR during SNS and was exacerbated by β-adrenergic activation. Simulations with species-specific cardiac models revealed that transient APD prolongation in mouse allowed for greater and more rapid CaT responses, suggesting more rapid increases in contractility; conversely, the rabbit heart requires APD shortening to produce optimal inotropic responses. Thus, while the cardiac fight-or-flight response is highly conserved between species, the underlying mechanisms orchestrating these effects differ significantly.

Antiarrhythmic mechanisms of beta blocker therapy

Sympathetic activity plays an important role in modulation of cardiac rhythm. Indeed, while exerting positive tropic effects in response to physiologic and pathologic stressors, β-adrenergic stimulation influences cardiac electrophysiology and can lead to disturbances of the heart rhythm and potentially lethal arrhythmias, particularly in pathological settings. For this reason, β-blockers are widely utilized clinically as antiarrhythmics. In this review, the molecular mechanisms of β-adrenergic action in the heart, the cellular and tissue level cardiac responses to β-adrenergic stimulation, and the clinical use of β-blockers as antiarrhythmic agents are reviewed. We emphasize the complex interaction between cardiomyocyte signaling, contraction, and electrophysiology occurring over multiple time- and spatial-scales during pathophysiological responses to β-adrenergic stimulation. An integrated understanding of this complex system is essential for optimizing therapies aimed at preventing arrhythmias.

Interaction between Endothelin-1 and Left Stellate Ganglion Activation: A Potential Mechanism of Malignant Ventricular Arrhythmia during Myocardial Ischemia

Endothelin-1 (ET-1) is synthesized primarily by endothelial cells. ET-1 administration in vivo enhances the cardiac sympathetic afferent reflex and sympathetic activity. Previous studies have shown that sympathetic hyperactivity promotes malignant ventricular arrhythmia (VA). The aim of this study was to investigate whether ET-1 could activate the left stellate ganglion (LSG) and promote malignant VA. Twelve male beagle dogs who received local microinjections of saline (control, n = 6) and ET-1 into the LSG (n = 6) were included. The ventricular effective refractory period (ERP), LSG function, and LSG activity were measured at different time points. VA was continuously recorded for 1 h after left anterior descending occlusion (LADO), and LSG tissues were then collected for molecular detection. Compared to that of the control group, local ET-1 microinjection significantly decreased the ERP and increased the occurrence of VA. In addition, local microinjection of ET-1 increased the function and activity of the LSG in the normal and ischemic hearts. The expression levels of proinflammatory cytokines and the protein expression of c-fos and nerve growth factor (NGF) in the LSG were also increased. More importantly, endothelin A receptor (ETA-R) expression was found in the LSG, and its signaling was significantly activated in the ET-1 group. LSG activation induced by local ET-1 microinjection aggravates LADO-induced VA. Activated ETA-R signaling and the upregulation of proinflammatory cytokines in the LSG may be responsible for these effects.

Cardiac Sympathetic Afferent Denervation Protects Against Ventricular Arrhythmias by Modulating Cardiac Sympathetic Nerve Activity During Acute Myocardial Infarction

Background

Augmented cardiac sympathetic afferent reflex (CSAR) plays a role in enhanced sympathetic activity. Given that a strategy for abolishing augmented CSAR-induced sympathetic activation may be beneficial for protecting against ventricular arrhythmias (VAs) triggered by acute myocardial infarction (AMI), we investigated whether cardiac sympathetic afferent denervation (CSAD) could protect against VAs by modulating cardiac sympathetic nerve activity in an AMI dog model.

Material/Methods

Twenty-two anesthetized dogs were assigned to the CSAD group (n=9) and the sham group (n=13) randomly. CSAD was produced by epicardial application of resiniferatoxin. Heart rate variability (HRV), ventricular action potential duration (APD), APD dispersion, beat-to-beat variability of repolarization (BVR), effective refractory period (ERP) of ventricles, ERP dispersion, plasma norepinephrine (NE) concentration, and left stellate ganglion (LSG) neural activity were determined at baseline and after CSAD. We designed an AMI model by occluding the left anterior coronary artery, and performed analysis of VAs for 60 minutes using electrocardiography. Then, levels of c-fos and nerve growth factor (NGF) were determined.

Results

Relative to baseline values, CSAD prolonged ERP and APD of ventricles, increased HRV, decreased APD dispersion, BVR, ERP dispersion and serum NE concentration, and attenuated LSG activity in the CSAD group. AMI triggered a remarkable increase in LSG activity and function but decreased the HRV of the sham group animals relative to the CSAD group. Moreover, the CSAD group had higher levels of VAs relative to the sham group. This was accompanied by a corresponding decrease in proteins quantities of NGF and c-fos in the CSAD group in the LSG after AMI compared to the sham group.

Conclusions

CSAD can suppress LSG neural activity, hence enhance the electrophysiological stability and protect the heart from AMI-triggered VAs.

The effects of interleukin 17A on left stellate ganglion remodeling are mediated by neuroimmune communication in normal structural hearts

BACKGROUND

It is reported interleukin (IL)-17A, a classical proinflammatory cytokine, is implicated in neuroimmune-associated remodeling in neural plasticity and pathological conditions. However, the effect of IL-17A on left stellate ganglion (LSG) remodeling remains unclear.

OBJECTIVE

This study was performed to determine whether exogenous IL-17A promotes LSG remodeling and destabilize ventricular electrophysiological properties (EPs) in normal canines.

METHODS

24 beagles were randomly allocated into three groups. In the first group, animals were subjected to 0.1 ml phosphate buffer saline (PBS) microinjection of into LSG (n = 8), an equivalent IL-17A was administrated in the second group (n = 8), and an equivalent anti-IL-17A mAb plus IL-17A was administrated in the third group (n = 8). The ventricular EPs, neural function and activity of the LSG were determined at baseline and 30 min after administration. In the end, LSG tissues were collected.

RESULTS

Compared with the control group, the experimental group had a significantly shorter effective refractory period (ERP) and action potential duration (APD)₉₀, an increased ERP, APD₉₀, S_max dispersion, and APD alternans cycle length; and steepened APD restitution curves. In addition, IL-17A enhanced the neural function and activity of the LSG, upregulated the expressions of neuropeptides and proinflammatory cytokines and cells. And all these effects were attenuated by anti-IL-17A mAb. Importantly, IL-17 receptor A (IL-17R-A) was detected in sympathetic neurons in the LSG.

CONCLUSION

IL-17A promoted LSG remodeling by regulating the neural inflammation response. It did so by binding to IL-17R-A, resulting in unstable ventricular electrophysiology in normal structural hearts.

The Role of Neuropeptide Y in Cardiovascular Health and Disease

Neuropeptide Y (NPY) is an abundant sympathetic co-transmitter, widely found in the central and peripheral nervous systems and with diverse roles in multiple physiological processes. In the cardiovascular system it is found in neurons supplying the vasculature, cardiomyocytes and endocardium, and is involved in physiological processes including vasoconstriction, cardiac remodeling, and angiogenesis. It is increasingly also implicated in cardiovascular disease pathogenesis, including hypertension, atherosclerosis, ischemia/infarction, arrhythmia, and heart failure. This review will focus on the physiological and pathogenic role of NPY in the cardiovascular system. After summarizing the NPY receptors which predominantly mediate cardiovascular actions, along with their signaling pathways, individual disease processes will be considered. A thorough understanding of these roles may allow therapeutic targeting of NPY and its receptors.