Augmentation of left ventricular contractility by cardiac sympathetic neural stimulation

Topographical Association Between Left Ventricular Strain and Brain Lesions in Patients With Acute Ischemic Stroke and Normal Cardiac Function

Background Although it is well known that the disordered brain provokes cardiac autonomic dysfunction, the detailed location of brain lesions related to cardiac function warrants further investigation. We aimed to elucidate the brain lesions topographically associated with left ventricular (LV) systolic function measured by myocardial strain in patients with acute ischemic stroke without preexisting primary cardiac dysfunction by using support vector regression lesion-symptom mapping. Methods and Results Subjects were those with LV ejection fraction of 50% or more among patients with acute ischemic stroke registered in the Samsung Medical Center stroke registry between 2016 and 2017. To evaluate LV systolic performance and contractility, we measured LV ejection fraction and LV global and regional longitudinal strain using 2-dimensional speckle-tracking echocardiography. The association between stroke lesion location and cardiac strain was assessed using support vector regression lesion-symptom mapping. Of a total of 776 patients, 286 subjects (mean age of 67.0 years, 65.4% men) were finally enrolled in this study. The mean global longitudinal strain was -17.0±3.4%, and the mean LV ejection fraction was 64.7±5.7%. The support vector regression lesion-symptom mapping analysis revealed that the right insula and peri-insular regions and left parietal cortex were associated with impaired LV global longitudinal strain in patients with acute ischemic stroke. In addition, impaired regional longitudinal strain showed topographical associations with these regions. Conclusions This study suggests that brain lesions in the right insula and peri-insular regions and left parietal cortex are topographically associated with impaired LV strain in patients with acute ischemic stroke without preexisting cardiac dysfunction.

Left atrial function evaluation by 2D speckle-tracking echocardiography in patients with vasovagal syncope

OBJECTIVES

Evidence indicates left atrial (LA) involvement in vasovagal syncope (VVS). The LA regulates left ventricular filling during the cardiac cycle. We aimed to assess LA function in patients with VVS by 2D speckle-tracking echocardiography.

METHODS

Sixty-nine consecutive patients with VVS were recruited. Based on the head-up tilt test (HUTT) results, the study population was divided into two groups: HUTT+ (n = 45) and HUTT- (n = 24). Fifty-one consecutive subjects were enrolled as the control group. LA myocardial deformation parameters were measured by 2D speckle-tracking echocardiography to evaluate LA function.

RESULTS

Maximal, minimal, and pre-P LA volumes were lower in patients with VVS. Strain and strain rate during reservoir, conduit, and contraction phases in VVS patients with HUTT+ or HUTT- were not statistically significantly different from those in the control group. Additionally, the volumetric parameters of LA function showed no difference in statistical significance between the three study groups.

CONCLUSIONS

While LA phasic function was not different between the two groups of VVS patients with HUTT+ or HUTT- and the control group, LA size during the three LA phases was smaller in patients with VVS.

Acute Modulation of Left Ventricular Control by Selective Intracardiac Sympathetic Denervation

BACKGROUND

The sympathetic nervous system plays an integral role in cardiac physiology. Nerve fibers innervating the left ventricle are amenable to transvenous catheter stimulation along the coronary sinus (CS).

OBJECTIVES

The aim of the present study was to modulate left ventricular control by selective intracardiac sympathetic denervation.

METHODS

First, the impact of epicardial CS ablation on cardiac electrophysiology was studied in a Langendorff model of decentralized murine hearts (n = 10 each, ablation and control groups). Second, the impact of transvenous, anatomically driven axotomy by catheter-based radiofrequency ablation via the CS was evaluated in healthy sheep (n = 8) before and during stellate ganglion stimulation.

RESULTS

CS ablation prolonged epicardial ventricular refractory period without (41.8 ± 8.4 ms vs 53.0 ± 13.5 ms; P = 0.049) and with β_1-2-adrenergic receptor blockade (47.8 ± 7.8 ms vs 73.1 ± 13.2 ms; P < 0.001) in mice. Supported by neuromorphological studies illustrating a circumferential CS neural network, intracardiac axotomy by catheter ablation via the CS in healthy sheep diminished the blood pressure increase during stellate ganglion stimulation (Δ systolic blood pressure 21.9 ± 10.9 mm Hg vs 10.5 ± 12.0 mm Hg; P = 0.023; Δ diastolic blood pressure 9.0 ± 5.5 mm Hg vs 3.0 ± 3.5 mm Hg; P = 0.039).

CONCLUSIONS

Transvenous, anatomically driven axotomy targeting nerve fibers along the CS enables acute modulation of left ventricular control by selective intracardiac sympathetic denervation.

Research Opportunities in Autonomic Neural Mechanisms of Cardiopulmonary Regulation: A Report From the National Heart, Lung, and Blood Institute and the National Institutes of Health Office of the Director Workshop

This virtual workshop was convened by the National Heart, Lung, and Blood Institute, in partnership with the Office of Strategic Coordination of the Office of the National Institutes of Health Director, and held September 2 to 3, 2020. The intent was to assemble a multidisciplinary group of experts in basic, translational, and clinical research in neuroscience and cardiopulmonary disorders to identify knowledge gaps, guide future research efforts, and foster multidisciplinary collaborations pertaining to autonomic neural mechanisms of cardiopulmonary regulation. The group critically evaluated the current state of knowledge of the roles that the autonomic nervous system plays in regulation of cardiopulmonary function in health and in pathophysiology of arrhythmias, heart failure, sleep and circadian dysfunction, and breathing disorders. Opportunities to leverage the Common Fund's SPARC (Stimulating Peripheral Activity to Relieve Conditions) program were characterized as related to nonpharmacologic neuromodulation and device-based therapies. Common themes discussed include knowledge gaps, research priorities, and approaches to develop novel predictive markers of autonomic dysfunction. Approaches to precisely target neural pathophysiological mechanisms to herald new therapies for arrhythmias, heart failure, sleep and circadian rhythm physiology, and breathing disorders were also detailed.

Cardiac Responses to Submaximal Isometric Contraction and Aerobic Exercise in Healthy Pregnancy

PURPOSE

The increased physiological demand of pregnancy results in the profound adaptation of the maternal cardiovascular system, reflected by greater resting cardiac output and left ventricular (LV) deformation. Whether the increased resting demand alters acute cardiac responses to exercise in healthy pregnant women is not well understood.

METHODS

Healthy nonpregnant (n = 18), pregnant (n = 14, 22-26 wk gestation), and postpartum women (n = 13, 12-16 wk postdelivery) underwent assessments of cardiac function and LV mechanics at rest, during a sustained isometric forearm contraction (30% maximum), and during low-intensity (LOW) and moderate-intensity (MOD) dynamic cycling exercise (25% and 50% peak power output). Significant differences (α = 0.05) were determined using ANCOVA and general linear model (resting value included as covariate).

RESULTS

When accounting for higher resting cardiac output in pregnant women, pregnant women had greater cardiac output during isometric contraction (2.0 ± 0.3 L·min-1·m-1.83; nonpregnant, 1.3 ± 0.2 L·min-1·m-1.83; postpartum, 1.5 ± 0.5 L·min-1·m-1.83; P = 0.02) but similar values during dynamic cycling exercise (pregnant, LOW = 2.8 ± 0.4 L·min-1·m-1.83, MOD = 3.4 ± 0.7 L·min-1·m-1.83; nonpregnant, LOW = 2.4 ± 0.3 L·min-1·m-1.83, MOD = 3.0 ± 0.3 L·min-1·m-1.83; postpartum, LOW = 2.3 ± 0.4 L·min-1·m-1.83, MOD = 3.0 ± 0.5 L·min-1·m-1.83; P = 0.96). Basal circumferential strain was higher in pregnant women at rest, during the sustained isometric forearm contraction (-23.5% ± 1.2%; nonpregnant, -14.6% ± 1.4%; P = 0.001), and during dynamic cycling exercise (LOW = -27.0% ± 4.9%, MOD = -27.4% ± 4.6%; nonpregnant, LOW = -15.8% ± 4.5%, MOD = -15.2% ± 6.7%; P = 0.012); however, other parameters of LV mechanics were not different between groups.

CONCLUSION

The results support that the maternal heart can appropriately respond to additional cardiac demand and altered loading experienced during acute isometric and dynamic exercise, although subtle differences in responses to these challenges were observed. In addition, the LV mechanics that underpin global cardiac function are greater in pregnant women during exercise, leading to the speculation that the hormonal milieu of pregnancy influences regional deformation.

Cardiac glial cells release neurotrophic S100B upon catheter-based treatment of atrial fibrillation

Atrial fibrillation (AF), the most common sustained heart rhythm disorder worldwide, is linked to dysfunction of the intrinsic cardiac autonomic nervous system (ICNS). The role of ICNS damage occurring during catheter-based treatment of AF, which is the therapy of choice for many patients, remains controversial. We show here that the neuronal injury marker S100B is expressed in cardiac glia throughout the ICNS and is released specifically upon catheter ablation of AF. Patients with higher S100B release were more likely to be AF free during follow-up. Subsequent in vitro studies revealed that murine intracardiac neurons react to S100B with diminished action potential firing and increased neurite growth. This suggests that release of S100B from cardiac glia upon catheter-based treatment of AF is a hallmark of acute neural damage that contributes to nerve sprouting and can be used to assess ICNS damage.

Cardiac adaptation to exercise training in health and disease

The heart is the primary pump that circulates blood through the entire cardiovascular system, serving many important functions in the body. Exercise training provides favorable anatomical and physiological changes that reduce the risk of heart disease and failure. Compared with pathological cardiac hypertrophy, exercise-induced physiological cardiac hypertrophy leads to an improvement in heart function. Exercise-induced cardiac remodeling is associated with gene regulatory mechanisms and cellular signaling pathways underlying cellular, molecular, and metabolic adaptations. Exercise training also promotes mitochondrial biogenesis and oxidative capacity leading to a decrease in cardiovascular disease. In this review, we summarized the exercise-induced adaptation in cardiac structure and function to understand cellular and molecular signaling pathways and mechanisms in preclinical and clinical trials.

Respiratory sinus arrhythmia is reduced after pulmonary vein isolation in patients with paroxysmal atrial fibrillation

INTRODUCTION

Respiratory sinus arrhythmia (RSA) describes heart rate (HR) changes in synchrony with respiration. It is relevant for exercise capacity and mechanistically linked with the cardiac autonomic nervous system. After pulmonary vein isolation (PVI), the current therapy of choice for patients with paroxysmal atrial fibrillation (AF), the cardiac vagal tone is often diminished. We hypothesized that RSA is modulated by PVI in patients with paroxysmal AF.

MATERIAL AND METHODS

Respiratory sinus arrhythmia, measured by using a deep breathing test and heart rate variability parameters, was studied in 10 patients (64 ±3 years) with paroxysmal AF presenting in stable sinus rhythm for their first catheter-based PVI. Additionally, heart rate dynamics before and after PVI were studied during sympathetic/parasympathetic coactivation by using a cold-face test. All tests were performed within 24 h before and 48 h after PVI.

RESULTS

After PVI RSA (E/I difference: 7.9 ±1.0 vs. 3.5 ±0.6 bpm, p = 0.006; E/I ratio: 1.14 ±0.02 vs. 1.05 ±0.01, p = 0.003), heart rate variability (SDNN: 31 ±3 vs. 14 ±3 ms, p = 0.006; RMSSD: 17 ±2 vs. 8 ±2 ms, p = 0.002) and the HR response to sympathetic/parasympathetic coactivation (10.2 ±0.7% vs. 5.7 ±1.1%, p = 0.014) were diminished. The PVI-related changes in RSA correlated with the heart rate change during sympathetic/parasympathetic coactivation before vs. after PVI (E/I difference: r = 0.849, p = 0.002; E/I ratio: r = 0.786, p = 0.007). One patient with vagal driven arrhythmia experienced AF recurrence during follow-up (mean: 6.5 ±0.6 months).

CONCLUSIONS

Respiratory sinus arrhythmia is reduced after PVI in patients with paroxysmal AF. Our findings suggest that this is related to a decrease in cardiac vagal tone. Whether and how this affects the clinical outcome including exercise capacity need to be determined.

Sympathetic and Parasympathetic Coactivation Induces Perturbed Heart Rate Dynamics in Patients with Paroxysmal Atrial Fibrillation

Background

Recent evidence indicates that sympathetic/parasympathetic coactivation (CoA) is causally linked to changes in heart rate (HR) dynamics. Whether this is relevant for patients with atrial fibrillation (AF) is unknown.

Material/Methods

In patients with paroxysmal AF (n=26) and age-matched controls, (n=10) we investigated basal autonomic outflow and HR dynamics during separate sympathetic (cold hand immersion) and parasympathetic activation (O₂-inhalation), as well as during CoA (cold face test). In an additional cohort (n=7), HR response was assessed before and after catheter-based pulmonary vein isolation (PVI). Ultra-high-density endocardial mapping was performed in patients (n=6) before and after CoA.

Results

Sympathetic activation increased (control: 74±3 vs. 77±3 bpm, p=0.0098; AF: 60±2 vs. 64±2 bpm, p=0.0076) and parasympathetic activation decreased HR (control: 71±3 vs. 69±3 bpm, p=0.0547; AF: 60±1 vs. 58±2 bpm, p<0.0009), while CoA induced a paradoxical HR increase in patients with AF (control: 73±3 vs. 71±3 bpm, p=0.084; AF: 59±2 vs. 61±2 bpm, p=0.0006), which was abolished after PVI. Non-linear parameters of HR variability (SD1) were impaired during coactivation in patients with AF (control: 61±7 vs. 69±6 ms, p=0.042, AF: 44±32 vs. 32±5 ms, p=0.3929). CoA was associated with a shift of the earliest activation site (18±4 mm) of the sinoatrial nodal region, as documented by ultra-high-density mapping (3442±343 points per map).

Conclusions

CoA perturbs HR dynamics and shifts the site of earliest endocardial activation in patients with paroxysmal AF. This effect is abolished by PVI, supporting the value of emerging methods targeting the intrinsic cardiac autonomic nervous system to treat AF. CoA might be a valuable tool to assess cardiac autonomic function in a clinical setting.

Stimulation of Epicardial Sympathetic Nerves at Different Sites Induces Cardiac Electrical Instability to Various Degrees

The cardiac sympathetic nerves distribute across cardiac tissues with uneven density. Yet, to what extent this anatomical heterogeneity affects electrical activity of the left ventricle is largely unknown. Dogs were randomized into non-stimulation control (NC), posterior basal-stimulation (PB), anterior superior-stimulation (AS), apical part-stimulation (AP) group. The epicardial sympathetic nerves at different sites along their distribution were with electrical stimulation (ES) for 4 hours except in the NC group. The myocardial effective refractory period (ERP), ventricular fibrillation threshold (VFT) and density of sympathetic nerves were recorded. Compared with ES at other places, the stimulation at PB site significantly shortened ERP (left ventricular anterior and posterior walls; PB group, 118 ± 4 ms, 106 ± 2 ms; Versus NC group, 155 ± 3.5 ms, 160 ± 3 ms; p < 0.01) and VFT (PB group, 11.5 ± 1.5 V; Versus NC group, 20.5 ± 0.9 V; p < 0.01), and induced remarkable regeneration of the cardiac sympathetic nerves, hence influencing electrical activity of the left ventricle to the most extent. Our study demonstrates that the degree of induced ventricular electrical instability is correlated tightly with the density of sympathetic nerves around ES site, and PB site is a potential target for modulating ventricular electrical activity to the maximal extent.

Development of nonfibrotic left ventricular hypertrophy in an ANG II-induced chronic ovine hypertension model

Hypertension is a major risk factor for many cardiovascular diseases and leads to subsequent concomitant pathologies such as left ventricular hypertrophy (LVH). Translational approaches using large animals get more important as they allow the use of standard clinical procedures in an experimental setting. Therefore, the aim of this study was to establish a minimally invasive ovine hypertension model using chronic angiotensin II (ANG II) treatment and to characterize its effects on cardiac remodeling after 8 weeks. Sheep were implanted with osmotic minipumps filled with either vehicle control (n = 7) or ANG II (n = 9) for 8 weeks. Mean arterial blood pressure in the ANG II‐treated group increased from 87.4 ± 5.3 to 111.8 ± 6.9 mmHg (P = 0.00013). Cardiovascular magnetic resonance imaging showed an increase in left ventricular mass from 112 ± 12.6 g to 131 ± 18.7 g after 7 weeks (P = 0.0017). This was confirmed by postmortem measurement of left ventricular wall thickness which was higher in ANG II‐treated animals compared to the control group (18 ± 4 mm vs. 13 ± 2 mm, respectively, P = 0.002). However, ANG II‐treated sheep did not reveal any signs of fibrosis or inflammatory infiltrates as defined by picrosirius red and H&E staining on myocardial full thickness paraffin sections of both atria and ventricles. Measurements of plasma high‐sensitivity C‐reactive protein and urinary 8‐iso‐prostaglandin F_2α were inconspicuous in all animals. Furthermore, multielectrode surface mapping of the heart did not show any differences in epicardial conduction velocity and heterogeneity. These data demonstrate that chronic ANG II treatment using osmotic minipumps presents a reliable, minimally invasive approach to establish hypertension and nonfibrotic LVH in sheep.

Disruption of cardiac cholinergic neurons enhances susceptibility to ventricular arrhythmias

The parasympathetic nervous system plays an important role in the pathophysiology of atrial fibrillation. Catheter ablation, a minimally invasive procedure deactivating abnormal firing cardiac tissue, is increasingly becoming the therapy of choice for atrial fibrillation. This is inevitably associated with the obliteration of cardiac cholinergic neurons. However, the impact on ventricular electrophysiology is unclear. Here we show that cardiac cholinergic neurons modulate ventricular electrophysiology. Mechanical disruption or pharmacological blockade of parasympathetic innervation shortens ventricular refractory periods, increases the incidence of ventricular arrhythmia and decreases ventricular cAMP levels in murine hearts. Immunohistochemistry confirmed ventricular cholinergic innervation, revealing parasympathetic fibres running from the atria to the ventricles parallel to sympathetic fibres. In humans, catheter ablation of atrial fibrillation, which is accompanied by accidental parasympathetic and concomitant sympathetic denervation, raises the burden of premature ventricular complexes. In summary, our results demonstrate an influence of cardiac cholinergic neurons on the regulation of ventricular function and arrhythmogenesis.

Catheter ablation is a common therapy for atrial fibrillation but disrupts cardiac cholinergic neurons. Here the authors report that cholinergic neurons innervate heart ventricles and show that their ablation leads to increased susceptibility to ventricular arrhythmias in mouse models and in patients.

Low Intensity Epicardial Pacing During the Absolute Refractory Period Augments Left Ventricular Function Mediated by Local Catecholamine Release

BACKGROUND

Biventricular epicardial (Epi) pacing can augment left ventricular (LV) function in heart failure. We postulated that these effects might involve catecholamine release from local autonomic nerve activation. To evaluate this hypothesis we applied low intensity Epi electrical stimuli during the absolute refractory period (ARP), thus avoiding altered activation sequence.

METHODS

Anesthetized pigs (n = 6) were instrumented with an LV pressure (LVP) transducer, left atrial (LA) and LV Epi pacing electrodes, and sonomicrometer segment length (SL) gauges placed proximal and remote to the LV stimulation site. A catheter was placed into the great cardiac vein adjacent to the LV pacing site for norepinephrine (NE) analysis. During LA pacing at constant rate, 3 pulses (0.8 milliseconds, 2-3x threshold) were applied to the LV Epi electrodes during the ARP. An experimental run consisted of baseline, stimulation (10 minutes), and recovery (5 minutes), repeated 3 times before and after β1 - receptor blockade (BB, metoprolol).

RESULTS

ARP stimulation produced significant increases in cardiac function reflected by elevated LVP, LV, dP/dtmax , and reduced time to LV dP/dtmax . This was accompanied by increased coronary NE levels and increases in LVP versus SL loop area in the remote myocardial segment. In contrast, the proximal segment exhibited early shortening and decreased loop area. BB abolished the changes in SL and LV function despite continued NE release.

CONCLUSION

These results demonstrate that ARP EPI stimulation induces NE release mediating augmented global LV function. This effect may contribute to the beneficial effect of biventricular Epi pacing in heart failure in some patients.

Mismatch Between Cardiac Perfusion, Sympathetic Innervation, and Left Ventricular Electroanatomical Map in a Patient with Recurrent Ventricular Tachycardia

BACKGROUND

Regional cardiac sympathetic denervation causes electrophysiological heterogeneity and has been found to be a predictor of potentially lethal VT.

CASE REPORT

We present the case of 69-year-old patient admitted with recurrent ventricular tachycardia and a history of anterior myocardial infarction. In line with Tc-99m-MIBI-SPECT perfusion imaging, electroanatomical mapping revealed extensive LV anterior scarring as detected by low-voltage areas. Surprisingly, I-123-MIBG-SPECT showed an extensive deficit of sympathetic innervation inferior (mismatch) and anterolateral (match).

CONCLUSIONS

Combination of electroanatomical mapping with tomographic imaging of innervation and perfusion might improve our understanding of the neural trigger of VT after myocardial infarction or substrate-based catheter ablation.

Left Atrial Appendage Closure Guided by Integrated Echocardiography and Fluoroscopy Imaging Reduces Radiation Exposure

Aims

To investigate whether percutaneous left atrial appendage (LAA) closure guided by automated real-time integration of 2D-/3D-transesophageal echocardiography (TEE) and fluoroscopy imaging results in decreased radiation exposure.

Methods and Results

In this open-label single-center study LAA closure (Amplatzer^TM Cardiac Plug) was performed in 34 consecutive patients (8 women; 73.1±8.5 years) with (n = 17, EN+) or without (n = 17, EN-) integrated echocardiography/fluoroscopy imaging guidance (EchoNavigator^® [EN]; Philips Healthcare). There were no significant differences in baseline characteristics between both groups. Successful LAA closure was documented in all patients. Radiation dose was reduced in the EN+ group about 52% (EN+: 48.5±30.7 vs. EN-: 93.9±64.4 Gy/cm²; p = 0.01). Corresponding to the radiation dose fluoroscopy time was reduced (EN+: 16.7±7 vs. EN-: 24.0±11.4 min; p = 0.035). These advantages were not at the cost of increased procedure time (89.6±28.8 vs. 90.1±30.2 min; p = 0.96) or periprocedural complications. Contrast media amount was comparable between both groups (172.3±92.7 vs. 197.5±127.8 ml; p = 0.53). During short-term follow-up of at least 3 months (mean: 8.1±5.9 months) no device-related events occurred.

Conclusions

Automated real-time integration of echocardiography and fluoroscopy can be incorporated into procedural work-flow of percutaneous left atrial appendage closure without prolonging procedure time. This approach results in a relevant reduction of radiation exposure.

Trial Registration

ClinicalTrials.gov NCT01262508

POTS following traumatic stress: interacting central and intracardiac neural control?

Cardiovascular autonomic dysfunction is one of the most overlooked complications in patients with diabetes. We report the case of a 19-year-old woman with a 4-year history of diabetes referred due to palpitations and light-headedness following traumatic stress. Rise of heart rate and blood pressure during tilt table testing indicated hyperadrenergic postural orthstatic tachycardia syndrome (POTS). Elevated blood pressure variability, an indirect parameter of increased sympathetic activity, remained almost stable during orthostatic stress. Short-term treatment with ivabradine in combination with psychosocial support alleviated POTS-related symptoms. Our findings suggest that traumatic stress in patients with type 1 diabetes mellitus might translate into disturbed neural heart rate control due to a central, ephemeral alteration in autonomic balance.

Augmentation of cardiac sympathetic tone by percutaneous low-level stellate ganglion stimulation in humans: a feasibility study

Modulation of human cardiac mechanical and electrophysiologic function by direct stellate ganglion stimulation has not been performed. Our aim was to assess the effect of low-level left stellate ganglion (LSG) stimulation (SGS) on arrhythmias, hemodynamic, and cardiac electrophysiological indices. Patients undergoing ablation procedures for arrhythmias were recruited for SGS. A stimulating electrode was placed next to the LSG under fluoroscopy and ultrasound imaging; and SGS (5-10 Hz, 10-20 mA) was performed. We measured hemodynamic, intracardiac and ECG parameters, and activation recovery intervals (ARIs) (surrogate for action potential duration) from a duodecapolar catheter in the right ventricular outflow tract. Five patients underwent SGS (3 males, 45 ± 20 years). Stimulating catheter placement was successful, and without complication in all patients. SGS did not change heart rate, but increased mean arterial blood pressure (78 ± 3 mmHg to 98 ± 5 mmHg, P < 0.001) and dP/dt max (1148 ± 244 mmHg/sec to 1645 ± 493 mmHg/sec, P = 0.03). SGS shortened mean ARI from 304 ± 23 msec to 283 ± 17 msec (P < 0.001), although one patient required parasympathetic blockade. Dispersion of repolarization (DOR) increased in four patients and decreased in one, consistent with animal models. QT interval, T-wave duration and amplitude at baseline and with SGS were 415 ± 15 msec versus 399 ± 15 msec (P < 0.001); 201 ± 12 msec versus 230 ± 28 msec; and 0.2 ± 0.09 mV versus 0.22 ± 0.08 mV, respectively. At the level of SGS performed, no increase in arrhythmias was seen. Percutaneous low-level SGS shortens ARI in the RVOT, and increases blood pressure and LV contractility. These observations demonstrate feasibility of percutaneous SGS in humans.

Non-excitatory electrical stimulation attenuates myocardial infarction via homeostasis of calcitonin gene-related peptide in myocardium

Electrical stimulation has been shown protection of brain, retina, optic nerves and pancreatic β-cells but the effect on cardio-protection is still unknown. Calcitonin gene-related peptide (CGRP) participates in the pathology of injury and protection of myocardium but whether or not electrical stimulation modulates endogenous CGRP is not clear. Male Sprague-Dawley rats were divided into 4 groups: (1) control group, without any treatment. (2) I/R group, animals were subjected to 30 min of myocardial ischemia followed by 60 min reperfusion. (3) NES+I/R group, non-excitatory electrical stimulation (NES) was commenced from 15 min before coronary artery occlusion till the end of reperfusion. (4) I/R+CGRP8-37 group, animals were given with CGRP8-37 (an antagonist of CGRP receptor, 10(-7) mol/L, 0.3 ml, i.v.) at 5 min before reperfusion without any electrical stimulation. The hemodynamics and electrocardiogram were monitored and recorded. Infarct size and troponin I were examined and CGRP expression in the myocardium and serum was analyzed. It was found that the infarct size and TnI were significantly reduced in NES+I/R group, by 45% and 58% respectively, accompanied by an obvious fall back of CGRP in myocardium, compared to I/R group (all p<0.05). Treatment with CGRP8-37 resulted in the same protection on myocardium as NES did. No significant difference in hemodynamics or ventricular tachycardia was detected among the groups (all p>0.05). It can be concluded that NES reduced the infarction size after acute myocardial ischemia and reperfusion, for which the underlying mechanism may be associated with modulation of endogenous CGRP in myocardium.

Wearable sensors in syncope management

Syncope is a common disorder with a lifetime prevalence of about 40%. Implantable cardiac electronic devices, including implantable loop recorders (ILR) and implantable cardioverter-defibrillators (ICD), are well established in syncope management. However, despite the successful use of ILR and ICD, diagnosis and therapy still remain challenging in many patients due to the complex hemodynamic interplay of cardiac and vascular adaptations during impending syncopes. Wearable sensors might overcome some limitations, including misdiagnosis and inappropriate defibrillator shocks, because a variety of physiological measures can now be easily acquired by a single non-invasive device at high signal quality. In neurally-mediated syncope (NMS), which is the most common cause of syncope, advanced signal processing methodologies paved the way to develop devices for early syncope detection. In contrast to the relatively benign NMS, in arrhythmia-related syncopes immediate therapeutical intervention, predominantly by electrical defibrillation, is often mandatory. However, in patients with a transient risk of arrhythmia-related syncope, limitations of ICD therapy might outweigh their potential therapeutic benefits. In this context the wearable cardioverter-defibrillator offers alternative therapeutical options for some high-risk patients. Herein, we review recent evidence demonstrating that wearable sensors might be useful to overcome some limitations of implantable devices in syncope management.

Effect of mental challenge induced by movie clips on action potential duration in normal human subjects independent of heart rate

BACKGROUND

Mental stress and emotion have long been associated with ventricular arrhythmias and sudden death in animal models and humans. The effect of mental challenge on ventricular action potential duration (APD) in conscious healthy humans has not been reported.

METHODS AND RESULTS

Activation recovery intervals measured from unipolar electrograms as a surrogate for APD (n=19) were recorded from right and left ventricular endocardium during steady-state pacing, whilst subjects watched an emotionally charged film clip. To assess the possible modulating role of altered respiration on APD, the subjects then repeated the same breathing pattern they had during the stress, but without the movie clip. Hemodynamic parameters (mean, systolic, and diastolic blood pressure, and rate of pressure increase) and respiration rate increased during the stressful part of the film clip (P=0.001). APD decreased during the stressful parts of the film clip, for example, for global right ventricular activation recovery interval at end of film clip 193.8 ms (SD, 14) versus 198.0 ms (SD, 13) during the matched breathing control (end film left ventricle 199.8 ms [SD, 16] versus control 201.6 ms [SD, 15]; P=0.004). Respiration rate increased during the stressful part of the film clip (by 2 breaths per minute) and was well matched in the respective control period without any hemodynamic or activation recovery interval changes.

CONCLUSIONS

Our results document for the first time direct recordings of the effect of a mental challenge protocol on ventricular APD in conscious humans. The effect of mental challenge on APD was not secondary to emotionally induced altered respiration or heart rate.

Effect of head-up tilt-table testing on left ventricular longitudinal strain in patients with neurocardiogenic syncope

Recent studies have shown conflicting data regarding left ventricular (LV) function in patients with neurocardiogenic syncope, with some investigators reporting a marked decrease in LV end-systolic wall stress and stress-corrected fractional shortening. We sought to determine the characteristics of resting LV deformation in patients with neurocardiogenic syncope by selective motion tracking of subendocardial and subepicardial regions using speckle tracking echocardiography. We assessed resting LV function in 82 patients undergoing head-up tilt-table (HUTT) testing. Patients were divided into 3 groups based on a positive HUTT test with associated co-morbid conditions (n = 30), no associated co-morbid conditions (n = 30), or negative HUTT results (n = 22). LV longitudinal, circumferential, and radial strains were obtained by speckle tracking echocardiography of subendocardial and subepicardial regions in each group and compared with resting LV deformation in 20 healthy control subjects. Compared with endocardial longitudinal strain in control subjects, that in patients with positive HUTT results was attenuated, irrespective of co-morbid conditions (p <0.05). Circumferential and radial strains did not differ among groups. On multivariate logistic regression analysis, endocardial longitudinal strain was an independent predictor (odds ratio, 1.16; p = 0.01) of positive HUTT test results. In conclusion, resting LV longitudinal strain is attenuated in patients with positive HUTT test results. Overall, these results may suggest that an increase in resting LV contractility is not a prerequisite for development of neurocardiogenic syncope.

Video-assisted pericardioscopic surgery for epimyocardial lead implantation

PURPOSE

Video-assisted pericardioscopic surgery (VAPS) for epimyocardial lead implantation has demonstrated positive acute results concerning the safety and degree of freedom inside the pericardium. We evaluated the employment of a newly developed trocar for pericardioscopy with regard to long-term effects and feasibility of reoperation.

DESCRIPTION

Eight adult sheep were divided into three groups. In two animals, VAPS was used exclusively. All other animals received four small-caliber epicardial leads through VAPS. After 6 and 12 months (n = 3 each), reoperation was conducted for reevaluation of entry site, intrapericardial adhesions, lead position, and morphology of the implantation site.

EVALUATION

Reentry close to the previous entry site proves unproblematic. Adhesions were mild to moderate in the immediate area of the implanted leads. Throughout the follow-up, pacing parameters were satisfactory. Lead dislodgement occurred in 1 of 24 leads. The deployment of small-caliber flexible endoscopes through the new trocar provided sufficient navigation, stability, and maneuverability.

CONCLUSIONS

Reoperation from the same subxiphoid approach proved feasible. Lead removal and reimplantation were feasible at both 6 months and 12 months after initial implantation. The intrapericardial adhesions caused by VAPS alone are mild.

Effects of percutaneous stimulation of both sympathetic and parasympathetic cardiac autonomic nerves on cardiac function in dogs

OBJECTIVE

Augmentation of left ventricular (LV) contractility and heart rate (HR) by sympathetic nerve stimulation and amelioration of heart failure by vagal nerve stimulation has been reported. However, the effects of concomitant electrical stimulation of both sympathetic and parasympathetic cardiac nerves in tissues such as those of the cardiac plexus remain unclear. This study sought to assess acute changes in cardiac function and hemodynamics in response to endovascular cardiac plexus stimulation (CPS).

METHODS

Twelve dogs received endovascular CPS via a bipolar catheter within the right pulmonary artery. Stimulation frequency (20 Hz) and pulse width (4 milliseconds) were fixed; voltage varied (range, 15-60 V).

RESULTS

Results fell into three categories: 1, no response (n = 4); 2, an increase in systemic arterial pressure that was dependent on electrode placement (n = 4); and 3, a very reproducible and stable increase in aortic pressure (n = 4). In the third group, mean systolic aortic pressures, maximum value of the first derivative of LV pressure, and LV stroke work increased with stimulation (P < 0.02 for all parameters) as did cardiac output, end-systolic elastance, and preload recruitable stroke work (P = 0.03). Systemic and pulmonary vascular resistance, central venous pressure, pulmonary arterial pressure, and HR remained unchanged (P > 0.05).

CONCLUSIONS

In contrast to conventional inotropic agents, endovascular CPS induced significant and selective increases in LV contractility without increasing HR. Efforts to optimize electrode placement and fixation will improve the reproducibility of endovascular CPS treatment.

Cardiac autonomic nerve stimulation in the treatment of heart failure

Research on the therapeutic modulation of cardiac autonomic tone by electrical stimulation has yielded encouraging early clinical results. Vagus nerve stimulation has reduced the rates of morbidity and sudden death from heart failure, but therapeutic vagus nerve stimulation is limited by side effects of hypotension and bradycardia. Sympathetic nerve stimulation that has been implemented in the experiment may exacerbate the sympathetic-dominated autonomic imbalance. In contrast, concurrent stimulation of both sympathetic and parasympathetic cardiac nerves increases myocardial contractility without increasing heart rate. This review assesses the current state of electrical stimulation of the cardiac autonomic nervous system to treat heart failure.

Effect of stellate ganglia stimulation on global and regional left ventricular function as assessed by speckle tracking echocardiography

Left ventricular (LV) twist mechanics and regional strain during cardiac sympathetic efferent activation are poorly understood. The purpose of this study was to compare the effects of left stellate ganglia (LSG) and right stellate ganglia (RSG) stimulation on cardiac twist/untiwst mechanics and regional strain. In nine pigs, echocardiographic imaging and LV pressure-volume measurements were performed before and during unilateral and bilateral stellate ganglion stimulation. LSG and RSG stimulation significantly augmented LV end-systolic pressure by 24% and 22% (P < 0.01), maximal rate of LV pressure change by 167% and 165% (P < 0.01), and time constant of LV relaxation by 20% and 12% (P < 0.01), respectively. RSG stimulation resulted in a greater chronotropic response than LSG stimulation (RSG: 68% vs. LSG: 12%, P < 0.01). Both LSG and RSG stimulation significantly increased global epicardial and endocardial LV rotation and diastolic untwisting rate and reduced the time to peak rotation (P < 0.05). However, LSG stimulation predominantly increased radial and circumferential strain in the LV inferoseptal, inferior, posterior, and lateral regions, whereas RSG stimulation primarily increased radial and circumferential strain in the anteroseptal, anterior, and lateral LV regions. Stimulation of both stellate ganglia led to a uniform increase in all LV segments. Our data suggest that LSG and RSG stimulation lead to a global increase in LV twist, driven by distinct regional strain heterogeneity that may result from myocardial innervation from the LSG and RSG. These findings provide a better understanding of the global and regional functional consequences of regional myocardial innervation from the LSG and RSG.

Functional and topographic concordance of right atrial neural structures inducing sinus tachycardia

Cardiorespiratory autonomic control is in tight interaction with an intracardiac neural network modulating sinus node function. To gain novel mechanistical insights and to investigate possible novel targets concerning the treatment of inadequate sinus tachycardia, we aimed to characterize functionally and topographically the right atrial neural network modulating sinus node function. In 16 sheep 3-dimensional electro-anatomical mapping of the right atrium was performed. In five animals additionally magnetically steered remote navigation was used. Selective stimulation of nerve fibers was conducted by applying high frequency (200 Hz) electrical impulses within the atrial refractory period. Histological analysis of whole heart preparations by acetylcholinesterase staining was performed and compared to the acquired neuroanatomical mapping.We found that neural stimulation in the cranial part of the right atrium, within a perimeter around the sinus node area, elicited predominantly shortening of the sinus cycle length of -20.3 ± 10.1 % (n = 80, P < 0.05). Along the course of the crista terminalis atrial premature beats (n = 117) and atrial fibrillation (n = 123) could be induced. Catheter stability was excellent during remote catheter navigation. Histological work-up (n = 4) was in accord with the distribution of neurostimulation sites. Ganglions were mainly innervated by the dorsal right-atrial subplexus, with substantial additional input from the ventral right atrial subplexus. In conclusion, our findings suggest a functional and topographic concordance of right atrial neural structures inducing sinus tachycardia. This might open up new avenues in the treatment of heart rate related disorders.

Effect of epivascular cardiac autonomic nerve stimulation on cardiac function

BACKGROUND

The cardiac plexus contains sympathetic and parasympathetic cardiac nerves. Our goal was to assess the hemodynamic and functional effects of stimulating the cardiac autonomic nervous system (CANS) at the epivascular surfaces of the cardiac plexus. Although CANS therapy to modulate cardiovascular function has drawn widespread interest, research has focused only on stimulating parasympathetic or sympathetic nerves, not both at once.

METHODS

Using general anesthesia and an open-chest surgical procedure, 12 dogs received epivascular stimulation of the cardiac plexus. A bipolar electrode was placed between the right pulmonary artery (PA) and the ascending aorta, with the stimulation frequency/pulse width held constant (20 Hz/4 ms) and the voltage varied (10-50 V). Left ventricular (LV) pressure-volume loops and hemodynamic data were recorded with and without stimulation.

RESULTS

In all dogs, aortic and LV systolic pressures, maximum rate of change of LV pressure, and LV stroke work increased (p<0.0001), as did cardiac output (2.9±1.0-0.4±1.0 L/min; p=0.001), end-systolic elastance (1.2±0.4-1.5±0.5 mm Hg/mL; p=0.0001), preload recruitable stroke work (30.1±11.0-39.3±7.8 mm Hg; p=0.003), and LV ejection fraction (p=0.012). Systemic vascular resistance increased slightly (p=0.04), and pulmonary vascular resistance decreased (p=0.01). Mean heart rate and pulmonary arterial, central venous, and left atrial pressures remained unchanged (p>0.1).

CONCLUSIONS

In contrast to inotropic drugs, epivascular CANS stimulation induced a significant and selective increase in LV contractility with no increase in heart rate.

Cardiac contractility modulation for heart failure: a meta-analysis of randomized controlled trials

BACKGROUND

Cardiac contractility modulation (CCM) emerges as a promising device treatment for heart failure (HF). This meta-analysis aimed to systematically review the latest available randomized evidence on the effectiveness and safety of CCM in HF.

METHODS

The Cochrane Central Register of Controlled Trials, MEDLINE, and EMBASE were searched in November 2011 to identify eligible randomized controlled trials comparing CCM with sham treatment or usual care. Primary outcomes of interest were all-cause mortality, all-cause hospitalizations, and adverse effects. Risk ratios (RRs) and 95% confidence intervals (CIs) were calculated for dichotomous data using a random-effects model.

RESULTS

Three studies enrolling 641 participants were included. Pooled analysis showed that, compared to control, CCM did not significantly improve all-cause mortality (n = 629, RR 1.19, 95% CI 0.50-2.86, P = 0.69), nor was there a favorable effect in all-cause hospitalizations. No increase in adverse effects with CCM was observed.

CONCLUSIONS

Meta-analysis of data from small randomized trials suggests that CCM, although with no clear benefits in improving clinical outcomes, is not associated with worsening prognosis. Large, well-designed trials are needed to confirm its role in HF patients for whom cardiac resynchronization therapy is contraindicated or unsuccessful.

Age-related regional differences in cardiac nerve growth factor expression

Age has been identified as an independent risk factor for cardiovascular diseases. A shift of the cardiac autonomic nervous system towards an increase in sympathetic tone has been reported in the elderly. Nerve growth factor (NGF) is the main neurotrophic factor that increases the sympathetic activity of the heart. If there is a shift of NGF expression in old compared to young cardiomyocytes and whether there are regional differences in the heart still remain unclear. Therefore, we chose a rat model of different-aged rats (3-4 days = neonatal, 6-8 weeks = young, 20-24 months = old), and isolated cardiomyocytes from the left and the right atrium (LA, RA), as well as from the left and the right ventricle (LV, RV), were used to determine NGF expression on mRNA and protein levels. In neonatal, young, and old rats, NGF amount in LA and RA was significantly lower as compared to LV and RV. In young and old rats, we found significant higher NGF protein levels in LA compared to RA. In addition, both atria showed an increase in NGF expression between age groups neonatal, young, and old. In both ventricles, we observed a significant decrease in NGF expression from neonatal to young rats and a significant increase from young to old rats. The highest NGF amount in LV and RV was observed in neonatal rats. Regarding tyrosine kinase A receptor (TrkA) expression, the main receptor for NGF signaling, both atria showed the largest expression in old rats; while in LV and RV, TrkA was expressed mainly in young rats. These results point to a contribution of nerve growth factors to the change of autonomic tone observed in elderly patients.

Acute initial haemodynamic changes in a rat isoprenaline model of cardiotoxicity

The synthetic catecholamine isoprenaline (ISO) has been used as an inductor in the acute myocardial infarction model for more than a half century. Despite the fact that many articles were published on this topic, precise early haemodynamic pathology remains unknown. Acute haemodynamic changes were measured in rats; first, in preliminary experiments by the thermodilution method; and second, in main experiments continuously for 2 h using a Millar catheter. Animals received saline or ISO in the cardiotoxic dose (100 mg/kg, subcutaneously). Also, additional experiments were performed with salbutamol in order to evaluate the role of β2-receptors. ISO caused a rapid, within 1 min, approximately 40% decrease in arterial blood pressures, 30% increase in the heart rate, and 30% decrease in the stroke volume. Within the first 2 min, the changes were followed by decreases in afterload (−40%), preload (−10%), diastolic relaxation (−50%), diastolic filling (−40%), and a marked, but short-term, increase in the left ventricle contractility (+100%). Ejection fraction did not significantly change, suggesting diastolic dysfunction. Salbutamol, with the exception of diastolic pressure and afterload, did not substantially influence other parameters. In conclusion, this study demonstrated that diastolic dysfunction precedes systolic dysfunction and β2-receptor stimulation alone is not sufficient for an early induction of diastolic dysfunction.

Electrical modalities beyond pacing for the treatment of heart failure

In this review, we report on electrical modalities, which do not fit the definition of pacemaker, but increase cardiac performance either by direct application to the heart (e.g., post-extrasystolic potentiation or non-excitatory stimulation) or indirectly through activation of the nervous system (e.g., vagal or sympathetic activation). The physiological background of the possible mechanisms of these electrical modalities and their potential application to treat heart failure are discussed.

Chronic Electrical Neuronal Stimulation Increases Cardiac Parasympathetic Tone by Eliciting Neurotrophic Effects

Rationale:

Recently, we provided a technique of chronic high-frequency electric stimulation (HFES) of the right inferior ganglionated plexus for ventricular rate control during atrial fibrillation in dogs and humans. In these experiments, we observed a decrease of the intrinsic ventricular rate during the first 4 to 5 months when HFES was intermittently shut off.

Objective:

We thus hypothesized that HFES might elicit trophic effects on cardiac neurons, which in turn increase baseline parasympathetic tone of the atrioventricular node.

Methods and Results:

In mongrel dogs atrial fibrillation was induced by rapid atrial pacing. Endocardial HFES of the right inferior ganglionated plexus, which contains abundant fibers to the atrioventricular node, was performed for 2 years. Sham-operated nonstimulated dogs served as control. In chronic neurostimulated dogs, we found an increased neuronal cell size accompanied by an increase of choline acetyltransferase and unchanged tyrosine hydroxylase protein expression as compared with unstimulated dogs. Moreover, β-nerve growth factor (NGF) and neurotrophin (NT)-3 were upregulated in chronically neurostimulated dogs. In vitro, HFES of cultured neurons of interatrial ganglionated plexus from adult rats increased neuronal growth accompanied by upregulation of NGF, NT-3, glial-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) expression. NGF was identified as the main growth-inducing factor, whereas NT-3 did not affect HFES-induced growth. However, NT-3 could be identified as an important acetylcholine-upregulating factor.

Conclusions:

HFES of cardiac neurons in vivo and in vitro causes neuronal cellular hypertrophy, which is mediated by NGF and boosters cellular function by NT-3–mediated acetylcholine upregulation. This knowledge may contribute to develop HFES techniques to augment cardiac parasympathetic tone.

The acute inotropic effects of cardiac contractility modulation (CCM) are associated with action potential duration shortening and mediated by β1-adrenoceptor signalling

Despite promising results in clinical trials conducted to date, little is known about how cardiac contractile modulation (CCM) mediated inotropic enhancement occurs and how CCM affects the electrophysiological characteristics of the heart. The aims of the present study were to 1) investigate how the stimulation parameters of the CCM signal and the location of stimulus delivery influence the contractile response, 2) characterise the effect of CCM on ventricular electrophysiology, and 3) investigate the potential physiological mechanisms underlying these acute inotropic and electrophysiological effects. Experiments were conducted in isolated rabbit hearts with simultaneous measurement of ventricular contractility and monophasic action potential duration (MAPD). Biphasic square wave pulses were applied to the left ventricle, timed to coincide with the absolute refractory period. CCM mediated responses were assessed over a range of signal amplitudes (2–30 mA), durations (2–15 ms) and delays from the activation of the locally recorded monophasic action potential (0–30 ms). Responses were assessed during perfusion with the β1-adrenoceptor antagonist metoprolol (1.8 μM) and HMR 1556 (500 nM), an inhibitor of the slow delayed rectifying potassium current. Norepinephrine content was collected and assessed by ELISA from samples of coronary effluent collected during CCM. CCM induced a significant increase in left ventricular pressure (LVP) in a manner dependent upon the amplitude and duration of the CCM signal but independent of the delay of the stimulus within the action potential plateau and was associated with an increase in norepinephrine in coronary effluent (Mean: 46 ± 9 pg/ml). CCM promoted a shortening of MAPD-90% close to the site of stimulation (− 19 ± 3%) but had no effect on those recorded at distant sites (0 ± 1%). The increase in LVP (4.7 ± 1.8 vs. 0.7 ± 0.9%, P < 0.01) and shortening of local MAPD-90% (− 15 ± 3 vs. 1 ± 1%, P < 0.01) was abolished with metoprolol. Perfusion with HMR 1556 caused a significant inhibition of local MAPD shortening (− 27 ± 2 vs. − 21 ± 3 ms, P < 0.05). CCM is associated with a shortening of ventricular MAPD in a manner dependent upon β-adrenoceptor stimulation resulting from catecholamine release, a finding which may be of clinical significance in regard to the development of malignant ventricular arrhythmias. This article is part of a Special Issue entitled Possible Editorial.

[Electrical therapy for heart failure. Perspectives for 2011]

Implantable defibrillators (ICDs) and cardiac resynchronization therapy (CRT) represent established treatments for heart failure with positive results from clinical trials. However, for daily practice, several questions on the optimal use remain (e.g., patient selection, imaging, pacing sites). In addition, new treatment options which attempt to improve heart failure by modulating cellular calcium handling and autonomic dysbalance have recently been developed. For cardiac contractility modulation, initial results from randomized trials have been published. At present, the use of vagal stimulation is also being studied in clinical trials in Germany. New approaches refer to stimulation of sympathetic ganglia in the coronary sinus and left ventricular multisite pacing by ultrasound, but are still in the stage of acute testing.

Modulation of peripheral chemoreflex by neurohumoral adaptations after kidney transplantation

BACKGROUND

Peripheral chemoreceptors residing predominantly in the carotid body monitor changes in arterial blood oxygen and are mechanistically linked to the cardiorespiratory control by the autonomic nervous system. Enhanced sympathetic activation is common in end-stage renal disease and kidney transplantation has been shown to improve cardiorespiratory reflex measures of autonomic function.

OBJECTIVE

The aim of the present study was to test whether improvement in renal function following kidney transplantation is related to an improvement in chemosensory function.

METHODS AND RESULTS

We compared hyperoxic chemoreflex sensitivity (CHRS) in patients after renal transplantation (RTX) to that in patients on maintenance hemodialysis (HD), and that of age- and gender-matched healthy controls. In addition, we investigated the impact of common confounding factors including pharmacological neurohumoral modulation and diabetes mellitus. The difference in the R-R intervals divided by the difference in the oxygen pressures before and after deactivation of the chemoreceptors by 5-min inhalation of 7 L oxygen was calculated as the hyperoxic CHRS. Autonomic activity was characterized by 24-h time-domain heart rate variability (HRV) parameters. CHRS was improved in RTX patients as compared to HD patients being related to HRV. CHRS was related to the concomitant presence of diabetes and medication with cyclosporine.

CONCLUSION

Our findings indicate that chemosensory activity following kidney transplantation is related to cardiac autonomic control, but functional testing might only be useful to characterize the time course and extent of sympathetic activation in selected patients due to existing co-morbidities and immunosuppressive medication in this population.

Peripheral chemosensor function is blunted in moderate to severe chronic kidney disease

BACKGROUND

Cardiovascular mortality is markedly increased in chronic kidney disease (CKD) and may be explained in part by sympathetic hyperactivity. Impaired hyperoxic chemoreflex sensitivity (CHRS) has been attributed to an increased sympathetic tone. The aim of the present study was to examine whether chemosensor function is altered in patients with CKD.

METHODS AND RESULTS

We assessed CHRS in 20 patients with stage 3 CKD [glomerular filtration rate (GFR) 30-59 ml/min/1.73 m(2)], in 15 patients with stage 4 CKD [GFR 15-29 ml/min/1.73 m(2)], as well as in 35 age and gender matched patients without any evidence of CKD. The difference in the R-R intervals divided by the difference in the oxygen pressures before and after deactivation of the chemoreceptors by inhalation of pure oxygen was calculated as the CHRS. A CHRS below 3.0 ms/mmHg was defined as pathological. CHRS was significantly depressed in patients with stage 3 CKD (2.9 ± 0.9 ms/mmHg, P=0.005) and in patients with stage 4 CKD (2.1 ± 0.6 ms/mmHg, P<0.001), as compared with patients without CKD (6.7 ± 0.9 ms/mmHg). There was a negative correlation between serum creatinine and CHRS (r=-0.51; P<0.001). In patients with CKD, chemosensor deactivation decreased mean arterial pressure from 91 ± 4 mmHg to 87 ± 3 mmHg (P=0.03). Multivariate analysis showed that GFR (P=0.001) was the only independent predictor of a pathological CHRS.

CONCLUSION

Using a relatively non-invasive bedside test we provide evidence for a blunted peripheral chemosensor function in chronic kidney disease. We thereby lay the basis for interventional studies assessing chemosensor function in chronic kidney disease.

Sympathetic neurons express and secrete MMP-2 and MT1-MMP to control nerve sprouting via pro-NGF conversion

Recently, we have shown that high frequency electrical field stimulation (HFES) of sympathetic neurons (SN) induces nerve sprouting by up-regulation of nerve growth factor (NGF) which targets the tyrosine kinase A receptor (TrkA) in an autocrine/paracrine manner. There is increasing evidence that matrix metalloproteinase-2 (MMP-2) is not only involved in extracellular matrix (ECM) turnover but may also exert beneficial effects during neuronal growth. Therefore, this study aimed to investigate the regulation and function of MMP-2 and its major activator membrane type 1-matrix metalloproteinase (MT1-MMP) as well its inhibitor TIMP-1 in SN under conditions of HFES. Moreover, we analyzed molecular mechanisms of the beneficial effect of losartan, an angiotensin II type I receptor (AT-1)blocker on HFES-induced nerve sprouting. Cell cultures of SN from the superior cervical ganglia (SCG) of neonatal rats were electrically stimulated for 48 h with a frequency of 5 or 50 Hz. HFES increased MMP-2 and MT1-MMP mRNA and protein expression, whereas TIMP-1 expression remained unchanged. Under conditions of HFES, we observed a shift from pro- to active-MMP-2 indicating an increase in MMP-2 enzyme activity. Specific pharmacological MMP-2 inhibition contributed to an increase in pro-NGF amount in the cell culture supernatant and significantly reduced HFES-induced neurite outgrowth. Losartan abolished HFES-induced nerve sprouting in a significant manner by preventing HFES-induced NGF, MMP-2, and MT1-MMP up-regulation. In summary, specific MMP-2 blockade prevents sympathetic nerve sprouting (SNS) by inhibition of pro-NGF conversion while losartan abolishes HFES-induced SNS by reducing total NGF, MMP-2 and MT1-MMP expression.