Cardiac Sympathoexcitation Research Articles

Abstract 17051: Oxytocin Receptor in the Spinal Neuraxial Modulation of Ventricular Excitability

Introduction: Cardiac sympathoexcitation is a major contributor to the pathogenesis of ventricular tachyarrhymias (VTs) during ischemia reperfusion (I/R) and chronic myocardial infarction (MI). Afferent network connections in the intermediolateral cell column (IML) and dorsal horn (DH) control sympathetic output to the heart. Our team reported spinal cord stimulation (SCS), decreased cardiac sympathoexcitation and reduced VTs during ischemia. Oxytocin (OXT) is a known neuromodulator; however, whether OXT signaling can modulate the cardiospinal neural network is unknown. Hypothesis: SCS neuromodulation is reducing sympathoexcitation and VTs through OXT signaling pathways. Methods: Two models of cardiac ischemia were used in Yorkshire domestic swine. In acute I/R, a suture was placed around the left anterior descending (LAD) coronary artery, after sternotomy. Chronic infarction (MI) was created by accessing the femoral with fluoroscopy guidance. Polystyrene microspheres (1ml) were injected via a 3mm angioplasty balloon catheter to the LAD. Animals then recovered post-MI for 6-8wk. SCS treatment was delivered through a four-pole lead which was inserted in the epidural space (T1-T4)(50Hz, 0.4ms pulse duration). T2-T4 spinal cord was collected postmortem for molecular analysis. Fluorescence in situ hybridization (FISH) protocol for RNAscope Fluorescent v2 Assay (ACD) was followed. Cell counts represented as 3 puncta or more centered around DAPI. Results: We report that OXT receptor positive cells significantly decreased as a result of I/R and MI (p<0.001, two-way ANOVA n=4-5 animals, average of 2-3 slices per animal). Within the DH the majority of OXT positive cells were inhibitory GABAergic neurons. Within the IML, a majority of the cells regulated by I/R and MI were microglia, and both an inhibitory and excitatory population contributed to the onset of ischemia. SCS treatment after I/R and MI resulted in the recovery of this OXT receptor cell population. Conclusions: By evaluating the role of OXT in reducing cardiac sympathoexcitation at the level of the spinal cord, we provide new insights into optimizing current neuromodulation approaches and developing new pharmacologic therapies.

Spinal neuromodulation mitigates myocardial ischemia-induced sympathoexcitation by suppressing the intermediolateral nucleus hyperactivity and spinal neural synchrony.

Myocardial ischemia disrupts the cardio-spinal neural network that controls the cardiac sympathetic preganglionic neurons, leading to sympathoexcitation and ventricular tachyarrhythmias (VTs). Spinal cord stimulation (SCS) is capable of suppressing the sympathoexcitation caused by myocardial ischemia. However, how SCS modulates the spinal neural network is not fully known. In this pre-clinical study, we investigated the impact of SCS on the spinal neural network in mitigating myocardial ischemia-induced sympathoexcitation and arrhythmogenicity. Ten Yorkshire pigs with left circumflex coronary artery (LCX) occlusion-induced chronic myocardial infarction (MI) were anesthetized and underwent laminectomy and a sternotomy at 4-5 weeks post-MI. The activation recovery interval (ARI) and dispersion of repolarization (DOR) were analyzed to evaluate the extent of sympathoexcitation and arrhythmogenicity during the left anterior descending coronary artery (LAD) ischemia. Extracellular in vivo and in situ spinal dorsal horn (DH) and intermediolateral column (IML) neural recordings were performed using a multichannel microelectrode array inserted at the T2-T3 segment of the spinal cord. SCS was performed for 30 min at 1 kHz, 0.03 ms, 90% motor threshold. LAD ischemia was induced pre- and 1 min post-SCS to investigate how SCS modulates spinal neural network processing of myocardial ischemia. DH and IML neural interactions, including neuronal synchrony as well as cardiac sympathoexcitation and arrhythmogenicity markers were evaluated during myocardial ischemia pre- vs. post-SCS. ARI shortening in the ischemic region and global DOR augmentation due to LAD ischemia was mitigated by SCS. Neural firing response of ischemia-sensitive neurons during LAD ischemia and reperfusion was blunted by SCS. Further, SCS showed a similar effect in suppressing the firing response of IML and DH neurons during LAD ischemia. SCS exhibited a similar suppressive impact on the mechanical, nociceptive and multimodal ischemia sensitive neurons. The LAD ischemia and reperfusion-induced augmentation in neuronal synchrony between DH-DH and DH-IML pairs of neurons were mitigated by the SCS. These results suggest that SCS is decreasing the sympathoexcitation and arrhythmogenicity by suppressing the interactions between the spinal DH and IML neurons and activity of IML preganglionic sympathetic neurons.

MP-453081-9 CARDIAC SYMPATHOEXCITATION MONITORING DURING PULMONARY VEIN ISOLATION BY PSYCHOGENIC SWEATING: POSSIBILITY OF REPRESENTING CARDIAC SYMPATHETIC NEUROMODULATION

Vagal responses during pulmonary vein isolation (PVI) have been reported, suggesting cardiac neuromodulation in atrial fibrillation (AF) patients. The cardiac sympathetic nervous system also innervates the left atrium (LA) and its nerve fibers are reported to be greatly distributed around the PV antrum. However, the sympathetic nervous system’s response during PVI is unclear and the precise method to evaluate the cardiac sympathetic reflex is still not established. Psychogenic sweating (skin potential response; SPR) occurs during sympathetic excitation and may be useful to represent cardiac sympathoexcitation during PVI. We investigated whether the SPR could represent a cardiac sympathetic response during a balloon-based PVI and considered its clinical implications in persistent AF patients. Eighty persistent AF patients (Hot-balloon;45pt, Cryoballoon;35pt) were enrolled and the SPR was monitored during balloon-based ablation of each PV. The SPR was measured by the difference in two skin potentials recorded from skin electrodes (Figure top row). The reduction in the activation recovery interval (ARI), suggesting sympathetic excitation, was examined from the ventricle unipolar electrogram of the great cardiac vein recorded from an electrode catheter placed inside the coronal sinus (Figure bottom row). An ROC analysis was used to determine a valid reduction in the SPR, with a reduction cut-off value of 3.5mV in the heart rate (HR) increase due to sympathoexcitation (sensitivity 73%, specificity 97%). SPRs occurred in 41% of the PVs (LSPV=41%, RSPV=38%, LIPV=28%, RIPV=20%). The SPR was related to a significant increase in the blood pressure and HR, and a reduction in the ARI (p<0.01, Table). A total of 18 patients (20%) had AF recurrences within the 1-year follow-up. The number of SPRs within the 4PVs was 1.08PV in non-recurrence patients and 1.83PV in AF recurrent patients (p=0.07). The patients that had early recurrences but recovered sinus rhythm (SR) within 3 months, had more frequent SPRs than the other recurrent patients (2.80 vs. 0.63PV, p<0.01). The SPR was strongly related to cardiac sympathoexcitation during PVI. The SPR was suggested to represent the cardiac sympathetic reflex during PV antrum ablation, which may lead to an investigation of the cardiac sympathetic neuromodulation during PVI. Frequent SPRs were related to SR recovery after early AF recurrences and a cardiac sympathetic response may have an important role in the outcome of the PVI.

GABAergic Signaling during Spinal Cord Stimulation Reduces Cardiac Arrhythmias in a Porcine Model.

Neuraxial modulation, including spinal cord stimulation, reduces cardiac sympathoexcitation and ventricular arrhythmogenesis. There is an incomplete understanding of the molecular mechanisms through which spinal cord stimulation modulates cardiospinal neural pathways. The authors hypothesize that spinal cord stimulation reduces myocardial ischemia-reperfusion-induced sympathetic excitation and ventricular arrhythmias through γ-aminobutyric acid (GABA)-mediated pathways in the thoracic spinal cord. Yorkshire pigs were randomized to control (n = 11), ischemia-reperfusion (n = 16), ischemia-reperfusion plus spinal cord stimulation (n = 17), ischemia-reperfusion plus spinal cord stimulation plus γ-aminobutyric acid type A (GABAA) or γ-aminobutyric acid type B (GABAB) receptor antagonist (GABAA, n = 8; GABAB, n = 8), and ischemia-reperfusion plus GABA transaminase inhibitor (GABAculine, n = 8). A four-pole spinal cord stimulation lead was placed epidurally (T1 to T4). GABA modulating pharmacologic agents were administered intrathecally. Spinal cord stimulation at 50 Hz was applied 30 min before ischemia. A 56-electrode epicardial mesh was used for high-resolution electrophysiologic recordings, including activation recovery intervals and ventricular arrhythmia scores. Immunohistochemistry and Western blots were performed to measure GABA receptor expression in the thoracic spinal cord. Cardiac ischemia led to myocardial sympathoexcitation with reduction in activation recovery interval (mean ± SD, -42 ± 11%), which was attenuated by spinal cord stimulation (-21 ± 17%, P = 0.001). GABAA and GABAB receptor antagonists abolished spinal cord stimulation attenuation of sympathoexcitation (GABAA, -9.7 ± 9.7%, P = 0.043 vs. ischemia-reperfusion plus spinal cord stimulation; GABAB, -13 ± 14%, P = 0.012 vs. ischemia-reperfusion plus spinal cord stimulation), while GABAculine alone caused a therapeutic effect similar to spinal cord stimulation (-4.1 ± 3.7%, P = 0.038 vs. ischemia-reperfusion). The ventricular arrhythmia score supported these findings. Spinal cord stimulation during ischemia-reperfusion increased GABAA receptor expression with no change in GABAB receptor expression. Thoracic spinal cord stimulation reduces ischemia-reperfusion-induced sympathoexcitation and ventricular arrhythmias through activation of GABA signaling pathways. These data support the hypothesis that spinal cord stimulation-induced release of GABA activates inhibitory interneurons to decrease primary afferent signaling from superficial dorsal horn to sympathetic output neurons in the intermediolateral nucleus.

Thoracic dorsal root ganglion stimulation reduces acute myocardial ischemia induced ventricular arrhythmias.

Dorsal root ganglion stimulation (DRGS) may serve as a novel neuromodulation strategy to reduce cardiac sympathoexcitation and ventricular excitability. In this pre-clinical study, we investigated the effectiveness of DRGS on reducing ventricular arrhythmias and modulating cardiac sympathetic hyperactivity caused by myocardial ischemia. Twenty-three Yorkshire pigs were randomized to two groups, which was control LAD ischemia-reperfusion (CONTROL) or LAD ischemia-reperfusion + DRGS (DRGS) group. In the DRGS group (n = 10), high-frequency stimulation (1 kHz) at the second thoracic level (T2) was initiated 30 min before ischemia and continued throughout 1 h of ischemia and 2 h of reperfusion. Cardiac electrophysiological mapping and Ventricular Arrhythmia Score (VAS) were assessed, along with evaluation of cFos expression and apoptosis in the T2 spinal cord and DRG. DRGS decreased the magnitude of activation recovery interval (ARI) shortening in the ischemic region (CONTROL: -201 ± 9.8 ms, DRGS: -170 ± 9.4 ms, p = 0.0373) and decreased global dispersion of repolarization (DOR) at 30 min of myocardial ischemia (CONTROL: 9546 ± 763 ms2, DRGS: 6491 ± 636 ms2, p = 0.0076). DRGS also decreased ventricular arrhythmias (VAS-CONTROL: 8.9 ± 1.1, DRGS: 6.3 ± 1.0, p = 0.038). Immunohistochemistry studies showed that DRGS decreased % cFos with NeuN expression in the T2 spinal cord (p = 0.048) and the number of apoptotic cells in the DRG (p = 0.0084). DRGS reduced the burden of myocardial ischemia-induced cardiac sympathoexcitation and has a potential to be a novel treatment option to reduce arrhythmogenesis.

Enhanced Peripheral Chemoreflex Drive Is Associated with Cardiorespiratory Disorders in Mice with Coronary Heart Disease.

Coronary heart disease (CHD) is a prevalent cardiovascular disease characterized by coronary artery blood flow reductions caused by lipid deposition and oxidation within the coronary arteries. Dyslipidemia is associated with local tissue damage by oxidative stress/inflammation and carotid bodies (CB) peripheral chemoreceptors are heavily modulated by both reactive oxygen species and pro-inflammatory molecules (i.e., cytokines). Despitethis,it is not know whether CB-mediated chemoreflex drive may be affected in CHD. In the present study, we evaluated peripheral CB-mediated chemoreflex drive, cardiac autonomic function, and the incidence of breathing disorders in a murine model of CHD. Compared to age-matched control mice, CHD mice showed enhanced CB-chemoreflex drive (twofold increase in the hypoxic ventilatory response), cardiac sympathoexcitation, and irregular breathing disorders. Remarkably, all these were closely linked to the enhanced CB-mediated chemoreflex drive. Our results showed that mice with CHD displayed an enhanced CB chemoreflex, sympathoexcitation, and disordered breathing and suggest that CBs may be involved in chronic cardiorespiratory alterations in the setting of CHD.

Abstract 11617: Chronic Spinal Cord Stimulation Mitigates Cardiac Sympathoexcitation and Reduces Ventricular Arrhythmias Induced by Myocardial Infarction

Introduction: Spinal cord stimulation (SCS) is effective neuromodulation therapy for pain, but little is known about the effectiveness of SCS for arrhythmia prevention in chronic myocardial infarction (MI). Hypothesis: Chronic SCS reduces MI-induced cardiac sympathoexcitation and reduces ventricular arrhythmias. Methods: Yorkshire pigs were randomized to chronic left circumflex coronary artery MI alone (n=11) or MI + chronic SCS (n=9). Epidural SCS lead was placed percutaneously T1-T4 of the spinal cord and reactive SCS was performed at 10 kHz, 0.03ms, and 2.5mA after MI. Holter ECG was recorded for heart rate variability (HRV) analysis, performed throughout 4-5 weeks post-MI. To create acute stress in chronic MI, epicardial extraventricular programmed stimulus (S1/S2 pacing), and acute left anterior descending coronary artery (LAD) ischemia(1h)+reperfusion(2h) (I/R) injury were conducted during terminal experiment. SCS was continued throughout terminal experiment. Cardiac electrophysiological data (activation recovery interval (ARI) and dispersion of repolarization (DOR)), as well as ventricular arrhythmia quantification were measured by placing a 56-electrode mesh sock over the heart . Data is shown as mean±SEM. Results: 1 week after MI, 30min HRV showed a higher high-frequency band and lower very-low and low-frequency band with SCS (%HF: MI 25±4 vs SCS 51±4, p=0.0028. %VLF: 50±4 vs 30±3, p=0.0015. %LF: 22±2 vs 14±2, p=0.047). In the terminal experiment, SCS reduced the maximum slope (Smax) of the electrical restitution curve described by S1/S2 pacing (Smax: MI 0.6±0.03 vs SCS 0.4±0.05, p=0.023). After acute LAD ischemia, SCS reduced global %ARI change (MI -19±3% vs SCS -11±1%, p=0.019), specifically in the ischemic region (MI -31±4% vs SCS -16±3%, p=0.008), and global %DOR (MI 1513±288% vs SCS 595±144%, p=0.011). Chronic SCS also reduced ventricular tachycardia and ventricular fibrillation during acute I/R (MI 15±3 vs SCS 5±0.8, p=0.014). Conclusions: Reactive SCS therapy mitigates cardiac autonomic imbalance in chronic MI and protects from new acute ischemia induced cardiac sympathoexcitation and ventricular arrhythmias.

Abstract 9479: Defined Subsets of Sympathetic Neurons Innervate the Heart and Differentially Respond to Cardiac Pathology

Introduction: Sympathetic regulatory aspect of cardiac functions is governed by neural circuit originating from postganglionic sympathetic neurons (PGNs) that primarily reside in stellate ganglia. PGNs is comprised of a diversified neuronal population that innervate heart and other tissue beds. Hypothesis: We hypothesize that cardiac innervating stellate ganglionic neurons (SGNs) exhibit diversity and distinction from those innervating other organs. In the settings of cardiac pathology, distribution of cardiac neuronal subtypes is altered, yielding a dominant neuronal subtype. Methods: We utilized method of retrograde axonal transport from heart and paw using adeno-associated virus (AAV-GFP/tdTomato, 1+e12 gc/ml, 10μl) followed by single cell RNA sequencing (scRNAseq) to identify and resolve transcriptomic profiles of SGNs in normal (n=8) and heart-failure mice (n=4). Using NPY-hrGFP mice, we characterized membrane excitability for NPY high and NPY low neurons (n=11). We delineated impact of NPY on cardiac sympathoexcitation by injecting AAV5-Flex-taCasp3 in NPY-Cre mice (n=8) and afterwards electrically stimulating right stellate ganglia (RSG). Results: In our scRNAseq study, we identified 3 adrenergic neuronal subtypes (NA1a, NA1b, and NA3) innervate heart. These subtypes differentiated as NPY high (NA1a) and NPY low (NA1b and NA3) subpopulations. NPY high (4.250±0.90) showed higher number of action potentials compared to NPY low (1.818±0.18). Cardiac sympathoexcitation was diminished in NPY-ablated mice compared to controls in response to escalating intensities (1, 5, 10, 15, &amp; 20 Hz). Maximal heart-rate change was detected at 10 Hz (p = 0.0240) for NPY-ablated mice (91.061±12.62 bpm) vs. controls (27.017±11.88). Across mice, ~70% of cardiac neurons are NPY+. In dilated cardiomyopathy mice, NA1b is a predominant subtype, consists of increased expression of Kcnq2 (M-current) and significant enriched pathways neurodegenerative disorders and neurotrophic signaling. Conclusion: These findings provide novel insights into the unique properties of neurons responsible for cardiac sympathetic regulation, with implications for novel strategies to target specific neuronal subtypes for sympathetic blockade in cardiac disease.

O109 / #501 CESSATION OF TRADITIONAL LOW-FREQUENCY THORACIC SPINAL CORD STIMULATION CAUSES EXCITATORY SPINAL NEURAL RESPONSE IN SUBJECTS WITH CHRONIC MYOCARDIAL INFARCTION: TRACK 4: CARDIOVASCULAR DISORDERS / NEURAL ENGINEERING

Myocardial infarction (MI) causes neural remodeling in the cardio-spinal network leading to sudden cardiac death. Spinal cord stimulation (SCS), as a novel therapy for cardiac disease, reduces such cardiac sympathoexcitation. In this study, we evaluated the consequence of the cessation of conventional low frequency vs. high-frequency SCS on the cardio-spinal neural network.

Catecholaminergic RVLM C1 neurons mediates heart failure decompensation and mortality during salt loading

Heart failure (HF) is a complex clinical syndrome affecting over 37 million people worldwide. Although advances in medical therapy have significantly improve HF condition, morbidity and mortality rate are still high and global prevalence is continuously rising. Common clinical features of HF include cardiac sympathoexcitation and disordered breathing, which are strongly associated with poor survival of HF patients. Importantly, we have previously shown that brainstem pre‐sympathetic neurons (C1) from the rostral ventrolateral medulla (RVLM), play a key role in sympathetic regulation in HF. However, the role played by RVLM‐C1 neurons during heart failure decompensation is totally unknown. Accordingly, we aimed to determine the contribution of RVLM‐C1 neurons on survival during HF decompensation. Adult male Sprague‐Dawley rats underwent volume overload induce non‐ischemic HF. After two weeks, anti‐dopamine β‐hydroxylase‐saporin toxin (DβH‐SAP: 2.5ng/150nl; or saline) was bilaterally injected into RVLM to ablate C1 neurons. Animals were then expose to high salt diet (3% Na+ in food and 2% Na+ in water) for 3 weeks to induce transition from compensated to decompensated HF state. At 6 weeks post‐HF induction, echocardiography, cardiac autonomic function, breathing function, blood pressure, and mortality were assessed. Compared to normal chow fed HF animals, HF+Na+ rats displayed an increased cardiac index (15.1 ± 0.6 vs. 18.5 ± 1.3 ml/min/100cm2, HF vs. HF+Na+, respectively) and cardiac sympathetic tone (∆HR to propranolol: 8.7 ± 3.1 vs. 23.4 ± 2.5 bpm, HF vs. HF+Na+, respectively). Furthermore, HF+Na+ animals showed a further increase in the incidence of breathing disorders compared to HF (apnea‐hypopnea index: 8.1 ± 0.6 vs. 12.5 ± 2.1 events/hr, HF vs. HF+Na+, respectively). Lastly, salt loading results in marked decompensation in HF rats being the outcome a significant increase in mortality risk (survival: 100% vs. 10% HF vs. HF+Na+, respectively). We found that partial ablation of RVLM C1 neurons in HF+Na+ prevented further deterioration in cardiac autonomic function and breathing disorders and markedly improved survival in HF rats that underwent salt loading (survival: 10% vs. 75% HF+Na+ vs. HF+DβH‐SAP+Na+, respectively). Our results strongly support the role for RVLM C1 neurons in HF decompensation during salt loading and suggest that RVLM C1 may act as a key nodal point mediating salt induced cardiorespiratory distress, decompensation and mortality in HF.

Activation of satellite glia in stellate ganglia from chronic heart failure rats

Cardiac sympathetic overactivation is linked to ventricular arrhythmogenesis and is associated with mortality in patients with chronic heart failure (CHF). However, the sites and mechanisms responsible for increased cardiac sympathetic activity are still poorly understood. Our previous studies showed that CHF‐elevated proinflammatory cytokine levels and macrophage expansion in stellate ganglia are critical factors for cardiac sympathoexcitation. Here we tested if activation of satellite glial cells (SGCs) contributes to macrophage expansion in stellate ganglia from CHF rats.Rat CHF was induced by surgical ligation of the left anterior descending coronary artery. SGCs and postsynaptic sympathetic neurons were respectively identified by anti‐S100B and anti‐tyrosine hydroxylase (TH) antibodies with immunofluorescence staining. As a marker of SGC activation, glial fibrillary acidic protein (GFAP) was measured by immunofluorescence double staining and Western blot analysis.Sympathetic neurons in stellate ganglia from both sham and CHF rats were totally surrounded by S100B‐positive SGCs. However, However, a few GFAP‐postive SGCs covered sympathetic neurons in sham stellate ganglia, whereas more GFAP‐positive SGCs surrounded sympathetic neurons in CHF stellate ganglia. Western blot data showed that GFAP was elevated in stellate ganglia from CHF rats, compared to sham rats.From these results, we conclude that activation of SGCs in stellate ganglia is higher in CHF rats than that in sham rats, which might contribute to the neuroinflammation and sympathoexcitation in stellate ganglia.

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 (Smax), 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 Smax (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.

Spinal Cord Stimulation Reduces Ventricular Arrhythmias by Attenuating Reactive Gliosis and Activation of Spinal Interneurons.

This study investigated spinal cord neuronal and glial cell activation during cardiac ischemia-reperfusion (IR)-triggered ventricular arrhythmias and neuromodulation therapy by spinal cord stimulation (SCS). Myocardial ischemia induces changes in cardiospinal neural networks leading to sudden cardiac death. Neuromodulation with SCS decreases cardiac sympathoexcitation; however, the molecular mechanisms remain unknown. Yorkshire pigs (n=16) were randomized to Control, IR, or IR+SCS groups. A 4-pole SCS lead was placed in the T1-T4 epidural space with stimulation for 30minutes before IR (50Hz, 0.4-ms duration, 90% motor threshold). Cardiac electrophysiological mapping and Ventricular Arrhythmia Score (VAS) were recorded. Immunohistochemistry of thoracic spinal sections was used to map and identify Fos-positive neuronal and glial cell types during IR with and without SCS. IR increased cardiac sympathoexcitation and arrhythmias (VAS=6.2 ± 0.9) that were attenuated in IR+ SCS (VAS=2.8 ± 0.5; P=0.017). IR increased spinal cellular Fos expression (#Fos+ cells Control=23 ± 2 vs IR=88 ± 5; P< 0.0001) in T1-T4, with the greatest increase localized to T3, and the greatest %Fos+ cells being microglia and astrocytes. Fos expression was attenuated by IR+ SCS (62 ± 4; P< 0.01), primarily though a reduction in Fos+ microglia and astrocytes, as SCS also led to increase in Fos+ neurons in deep dorsal laminae. In a porcine model, cardiac IR was associated with astrocyte and microglial cell activation. Our results suggest that preemptive thoracic SCS decreased IR-induced cardiac sympathoexcitation and ventricular arrhythmias through attenuation of reactive gliosis and activation of inhibitory interneurons in the dorsal horn of spinal cord.

Macrophage depletion in stellate ganglia alleviates cardiac sympathetic overactivation and ventricular arrhythmogenesis by attenuating neuroinflammation in heart failure

Cardiac sympathetic overactivation is involved in arrhythmogenesis in patients with chronic heart failure (CHF). Inflammatory infiltration in the stellate ganglion (SG) is a critical factor for cardiac sympathoexcitation in patients with ventricular arrhythmias. This study aims to investigate if macrophage depletion in SGs decreases cardiac sympathetic overactivation and ventricular arrhythmogenesis in CHF. Surgical ligation of the coronary artery was used for induction of CHF. Clodronate liposomes were microinjected into bilateral SGs of CHF rats for macrophage depletion. Using cytokine array, immunofluorescence staining, and Western blot analysis, we found that macrophage expansion and expression of TNFα and IL-1β in SGs were markedly increased in CHF rats. Flow cytometry data confirmed that the percentage of macrophages in SGs was higher in CHF rats than that in sham rats. Clodronate liposomes significantly reduced CHF-elevated proinflammatory cytokine levels and macrophage expansion in SGs. Clodronate liposomes also reduced CHF-increased N-type Ca2+ currents and excitability of cardiac sympathetic postganglionic neurons and inhibited CHF-enhanced cardiac sympathetic nerve activity. ECG data from 24-h, continuous telemetry recording in conscious rats demonstrated that clodronate liposomes not only restored CHF-induced heterogeneity of ventricular electrical activities, but also decreased the incidence and duration of ventricular tachycardia/fibrillation in CHF. Macrophage depletion with clodronate liposomes attenuated CHF-induced cardiac sympathetic overactivation and ventricular arrhythmias through reduction of macrophage expansion and neuroinflammation in SGs.

Spinal Anesthesia Reduces Myocardial Ischemia-triggered Ventricular Arrhythmias by Suppressing Spinal Cord Neuronal Network Interactions in Pigs.

Cardiac sympathoexcitation leads to ventricular arrhythmias. Spinal anesthesia modulates sympathetic output and can be cardioprotective. However, its effect on the cardio-spinal reflexes and network interactions in the dorsal horn cardiac afferent neurons and the intermediolateral nucleus sympathetic neurons that regulate sympathetic output is not known. The authors hypothesize that spinal bupivacaine reduces cardiac neuronal firing and network interactions in the dorsal horn-dorsal horn and dorsal horn-intermediolateral nucleus that produce sympathoexcitation during myocardial ischemia, attenuating ventricular arrhythmogenesis. Extracellular neuronal signals from the dorsal horn and intermediolateral nucleus neurons were simultaneously recorded in Yorkshire pigs (n = 9) using a 64-channel high-density penetrating microarray electrode inserted at the T2 spinal cord. Dorsal horn and intermediolateral nucleus neural interactions and known markers of cardiac arrhythmogenesis were evaluated during myocardial ischemia and cardiac load-dependent perturbations with intrathecal bupivacaine. Cardiac spinal neurons were identified based on their response to myocardial ischemia and cardiac load-dependent perturbations. Spinal bupivacaine did not change the basal activity of cardiac neurons in the dorsal horn or intermediolateral nucleus. After bupivacaine administration, the percentage of cardiac neurons that increased their activity in response to myocardial ischemia was decreased. Myocardial ischemia and cardiac load-dependent stress increased the short-term interactions between the dorsal horn and dorsal horn (324 to 931 correlated pairs out of 1,189 pairs, P < 0.0001), and dorsal horn and intermediolateral nucleus neurons (11 to 69 correlated pairs out of 1,135 pairs, P < 0.0001). Bupivacaine reduced this network response and augmentation in the interactions between dorsal horn-dorsal horn (931 to 38 correlated pairs out of 1,189 pairs, P < 0.0001) and intermediolateral nucleus-dorsal horn neurons (69 to 1 correlated pairs out of 1,135 pairs, P < 0.0001). Spinal bupivacaine reduced shortening of ventricular activation recovery interval and dispersion of repolarization, with decreased ventricular arrhythmogenesis during acute ischemia. Spinal anesthesia reduces network interactions between dorsal horn-dorsal horn and dorsal horn-intermediolateral nucleus cardiac neurons in the spinal cord during myocardial ischemia. Blocking short-term coordination between local afferent-efferent cardiac neurons in the spinal cord contributes to a decrease in cardiac sympathoexcitation and reduction of ventricular arrhythmogenesis.

L‐Menthol Inhibits Cardiac Sympathoexcitation Caused by Inhaled Irritants in the Spontaneously Hypertensive Rat

Inhalation of irritants (e.g. particulate matter and ozone) triggers various efferent responses through activation of transient receptor potential ankyrin 1 (TRPA1) and TRP vanilloid 1 (TRPV1) channels expressed on airway vagal afferent nerves. In the airways they cause cough and mucus secretion and in conscious, healthy animals parasympathetic‐mediated reflexes include bradycardia and atrioventricular block. However, inhalation of air pollutants including particulate matter and ozone evokes sympathoexcitation (tachycardia, hypertension) in patients with cardiovascular disease. Interestingly, selective activation of airway vagal afferent nerves in spontaneously hypertensive (SH) rats via inhalation of the TRPA1‐specific agonist allyl isothiocyanate (AITC) evoked sympathetic‐mediated tachycardia and premature ventricular contractions (PVCs) consistent with reflexes evoked by inhaled pollution in patients with cardiovascular disease.Airway reflexes such as cough have been shown to be inhibited by nasal stimulation with L‐menthol via activation of cold‐sensitive trigeminal pathways which regulate brainstem respiratory networks. Here, we investigated the cardiac reflexes evoked by inhalation of L‐menthol (150mg/ml) alone and in combination with AITC (4.7mg/ml) in conscious SH rats. L‐menthol inhalation alone had no effect on heart rate, but, when inhaled during AITC inhalation, L‐menthol selectively inhibited the AITC‐evoked tachyarrhythmia. Inhibition of the AITC‐evoked sympathoexcitatory reflexes was not seen in identical studies performed with inactive D‐menthol (150mg/ml). Therefore, we conclude that pulmonary‐cardiac reflex tachyarrhythmia are reduced by activation of nasal menthol‐sensitive pathways. This data supports the potential for prevention of aberrant irritant‐evoked pulmonary‐cardiac reflexes by nasal menthol treatment.Support or Funding InformationNIH r56

Neurocognitive Disorders in Heart Failure: Novel Pathophysiological Mechanisms Underpinning Memory Loss and Learning Impairment.

Heart failure (HF) is a major public health issue affecting more than 26 million people worldwide. HF is the most common cardiovascular disease in elder population; and it is associated with neurocognitive function decline, which represent underlying brain pathology diminishing learning and memory faculties. Both HF and neurocognitive impairment are associated with recurrent hospitalization episodes and increased mortality rate in older people, but particularly when they occur simultaneously. Overall, the published studies seem to confirm that HF patients display functional impairments relating to attention, memory, concentration, learning, and executive functioning compared with age-matched controls. However, little is known about the molecular mechanisms underpinning neurocognitive decline in HF. The present review round step recent evidence related to the possible molecular mechanism involved in the establishment of neurocognitive disorders during HF. We will make a special focus on cerebral ischemia, neuroinflammation and oxidative stress, Wnt signaling, and mitochondrial DNA alterations as possible mechanisms associated with cognitive decline in HF. Also, we provide an integrative mechanism linking pathophysiological hallmarks of altered cardiorespiratory control and the development of cognitive dysfunction in HF patients. Graphical Abstract Main molecular mechanisms involved in the establishment of cognitive impairment during heart failure. Heart failure is characterized by chronic activation of brain areas responsible for increasing cardiac sympathetic load. In addition, HF patients also show neurocognitive impairment, suggesting that the overall mechanisms that underpin cardiac sympathoexcitation may be related to the development of cognitive disorders in HF. In low cardiac output, HF cerebral infarction due to cardiac mural emboli and cerebral ischemia due to chronic or intermittent cerebral hypoperfusion has been described as a major mechanism related to the development of CI. In addition, while acute norepinephrine (NE) release may be relevant to induce neural plasticity in the hippocampus, chronic or tonic release of NE may exert the opposite effects due to desensitization of the adrenergic signaling pathway due to receptor internalization. Enhanced chemoreflex drive is a major source of sympathoexcitation in HF, and this phenomenon elevates brain ROS levels and induces neuroinflammation through breathing instability. Importantly, both oxidative stress and neuroinflammation can induce mitochondrial dysfunction and vice versa. Then, this ROS inflammatory pathway may propagate within the brain and potentially contribute to the development of cognitive impairment in HF through the activation/inhibition of key molecular pathways involved in neurocognitive decline such as the Wnt signaling pathway.

Spinal cord stimulation reduces ventricular arrhythmias during acute ischemia by attenuation of regional myocardial excitability.

Myocardial ischemia creates autonomic nervous system imbalance and can trigger cardiac arrhythmias. We hypothesized that neuromodulation by spinal cord stimulation (SCS) will attenuate local cardiac sympathoexcitation from ischemia-induced increases in afferent signaling, reduce ventricular arrhythmias, and improve myocardial function during acute ischemia. Yorkshire pigs (n = 20) were randomized to SCS (50 Hz at 200-μs duration, current 90% motor threshold) or sham operation (sham) for 30 min before ischemia. A four-pole SCS lead was placed percutaneously in the epidural space (T1-T4), and a 56-electrode mesh was placed over the heart for high-resolution electrophysiological recordings, including activation recovery intervals (ARIs), activation time, repolarization time, and dispersion of repolarization. Electrophysiological and hemodynamic measures were recorded at baseline, after SCS/sham, during acute ischemia (300-s coronary artery ligation), and throughout reperfusion. SCS 1) reduced sympathoexcitation-induced ARI and repolarization time shortening in the ischemic myocardium; 2) attenuated increases in the dispersion of repolarization; 3) reduced ventricular tachyarrythmias [nonsustained ventricular tachycardias: 24 events (3 sham animals) vs. 1 event (1 SCS animal), P < 0.001]; and 4) improved myocardial function (dP/dt from baseline to ischemia: 1,814 ± 213 to 1,596 ± 282 mmHg/s in sham vs. 1,422 ± 299 to 1,380 ± 299 mmHg/s in SCS, P < 0.01). There was no change in ventricular electrophysiology during baseline conditions without myocardial stress or in the nonischemic myocardium. In conclusion, in a porcine model of acute ventricular ischemia, SCS reduced regional myocardial sympathoexcitation, decreased ventricular arrhythmias, and improved myocardial function. SCS decreased sympathetic nerve activation locally in the ischemic myocardium with no effect observed in the normal myocardium, thus providing mechanistic insights into the antiarrhythmic and myocardial protective effects of SCS.NEW & NOTEWORTHY In a porcine model of ventricular ischemia, spinal cord stimulation decreased sympathetic nerve activation regionally in ischemic myocardium with no effect on normal myocardium, demonstrating that the antiarrhythmic effects of spinal cord stimulation are likely due to attenuation of local sympathoexcitation in the ischemic myocardium and not changes in global myocardial electrophysiology.

Infusion of Losartan into the 4th Ventricle Reduced Cardiac Sympathoexcitation in Heart Failure

Background and AimsA key feature of heart failure (HF) is an increase in cardiac sympathetic nerve activity (CSNA). We have found that the area postrema (AP), a brainstem circumventricular organ, plays an important role in controlling CSNA and in determining the increase in CSNA in heart failure. We hypothesized that in sheep with HF, 4th ventricular infusions of losartan (angiotensin II type 1 receptor antagonist) will reduce CSNA to a greater extent than infusion into the cisterna magna.MethodsIn sheep (n=6), when ejection fraction (EF) had fallen to ~50%, cannulae were implanted for infusion into the 4th ventricle and cisterna magna. Blood pressure, heart rate, CSNA &amp; renal SNA were recorded when EF had fallen to &lt;40%. Losartan (1.0 mg/h) or artificial cerebrospinal fluid (aCSF) (1.0 mL/h) were infused into the 4th ventricle and cisterna magna for 5 h, at two days after nerve recording electrodes were surgically implanted.ResultsIn sheep with HF, there was a significant decrease in EF (from 81 ± 3 % to 37 ± 1 %, P &lt;0.001). During 4th ventricle infusion of losartan, there was a significant decrease in CSNA (89 ± 3 to 48 ± 8 bursts/100 heartbeats, P&lt;0.01). Infusion of losartan into the cisterna magna caused a smaller decrease in CSNA (85 ± 2 to 74 ± 4 bursts/100 heartbeats, P&lt;0.05). Infusion of losartan into the 4th ventricle caused no significant changes in renal SNA or in other parameters. Infusion of aCSF into the 4th ventricle or cistrena magna had no effects.ConclusionsInfusion of losartan into the 4th ventricle reduced the elevated CSNA in sheep with HF. The findings suggest that angiotensin type 1 receptors in the brainstem have an important role in determining the increased CSNA in heart failure.

Abstract 328: Effects of Sympatho-excitation on Directional Anisotropy in Ventricular Myocardium

Introduction: Control of electrical propagation exerted by the sympathetic nervous system is has not been quantified in-depth. Methods: High-resolution mapping (64-electrode plaque, 8x8, 1.96cm 2 ) of the anterior LV myocardium in porcine model (n=6) was performed before &amp; during left stellate ganglion stimulation (LSGS). Activation times (AT), activation recovery intervals (ARIs), conduction velocities (CV), and CV anisotropy were obtained during pacing. Ex vivo diffusion tensor MRI and histology were performed to define myocardial fiber orientation in the mapped regions. Results: LSGS shortened ARI (314.3±7.8ms vs. 287.8±6.6ms, p&lt;0.001). At baseline, longitudinal CV (CV L ) was greater than transverse CV (CV T ) (1.2±0.2m/s vs 0.7±0.1m/s, p&lt;0.001). LSGS did not increase CV L (1.16±0.16m/s vs 1.17±0.15m/s, p=0.2), or CV T (0.67±0.07m/s vs 0.7±0.04m/s, p=0.2). However, CV in the retrograde direction along fiber orientation was significantly increased by LSGS (0.7±0.05m/s vs 0.9±0.06m/s, p&lt;0.01). This resulted in a significant reduction in directional anisotropy (CV antegrade /CV retrograde ) along fiber direction (1.6±0.3 vs 1.3±0.3, p&lt;0.001), but not CV L /CV T (1.78±0.2 vs. 1.66±0.2 for BL and LSGS, respectively, p&gt;0.2). Heterogeneity of activation (AT disp ) was greater in the transverse than longitudinal direction (20±2ms 2 /cm 2 vs. 13±1.5ms 2 /cm 2 , p= 0.022). LSGS decreased transverse AT disp to 18±1.8 ms 2 /cm 2 (p=0.015), but not longitudinal AT disp . Conclusion: Cardiac sympatho-excitation modulates CV and AT disp in a fiber orientation-dependent manner. These uneven changes may contribute to arrhythmogenic mechanisms seen during sympatho-excitation.