Catheter stimulation of cardiac parasympathetic nerves in humans: a novel approach to the cardiac autonomic nervous system

Ischemia-induced ventricular proarrhythmia and cardiovascular autonomic dysreflexia after cardioneuroablation

BACKGROUND

Cardioneuroablation (CNA) is an attractive treatment of vasovagal syncope. Its long-term efficacy and safety remain unknown.

OBJECTIVE

The purpose of this study was to develop a chronic porcine model of CNA to examine the susceptibility to ventricular tachyarrhythmia (ventricular tachycardia/ventricular fibrillation [VT/VF]) and cardiac autonomic function after CNA.

METHODS

A percutaneous CNA model was developed by ablation of left- and right-sided ganglionated plexi (n = 5), confirmed by histology. Reproducible bilateral vagal denervation was confirmed after CNA by extracardiac vagal nerve stimulation (VNS) and histology. Chronic studies included 16 pigs randomized to CNA (n = 8) and sham ablation (n = 8, Control). After 6 weeks, animals underwent hemodynamic studies, assessment of cardiac sympathetic and parasympathetic function using sympathetic chain stimulation and direct VNS, respectively, and proarrhythmic potential after left anterior descending (LAD) coronary artery ligation.

RESULTS

After CNA, extracardiac VNS responses remained abolished for 6 weeks despite ganglia remaining in ablated ganglionated plexi. In the CNA group, direct VNS resulted in paradoxical increases in blood pressure, but not in sham-ablated animals (CNA group vs sham group: 8.36% ± 7.0% vs -4.83% ± 8.7%, respectively; P = .009). Left sympathetic chain stimulation (8 Hz) induced significant corrected QT interval prolongation in the CNA group vs the sham group (11.23% ± 4.0% vs 1.49% ± 4.0%, respectively; P < .001). VT/VF after LAD ligation was more prevalent and occurred earlier in the CNA group than in the control group (61.44 ± 73.7 seconds vs 245.11 ± 104.0 seconds, respectively; P = .002).

CONCLUSION

Cardiac vagal denervation is maintained long-term after CNA in a porcine model. However, chronic CNA was associated with cardiovascular dysreflexia, diminished cardioprotective effects of cardiac vagal tone, and increased susceptibility to VT/VF in ischemia. These potential long-term negative effects of CNA suggest the need for rigorous clinical studies on CNA.

β-Adrenergic stimulation induces pro-arrhythmic activity in the caval vein myocardial tissue

Electrical activity of the right superior vena cava (SVC) is considered as a source of the atrial fibrillation. We have shown that bioelectrical properties of the SVC myocardium differ from those of the working atrial myocardium. Electrically evoked action potential duration in SVC is significantly shorter, the resting membrane potential in both stimulated and quiescent SVC preparations is significantly more positive than in atria. Activation of β-adrenoreceptors in SVC myocardium leads to a series of action potentials, and this process depends on protein kinase A. Probably, β-adrenergic stimulation enhances SVC arrhythmogenesis in vivo.

Intravenous electrical vagal nerve stimulation prior to coronary reperfusion in a canine ischemia-reperfusion model markedly reduces infarct size and prevents subsequent heart failure

BACKGROUND

Reducing myocardial damage is a prerequisite to prevent chronic heart failure after acute myocardial infarction (AMI). Although vagal nerve stimulation (VNS) has been repeatedly demonstrated to have potent anti-infarct effect, technical difficulties have precluded its clinical application. We developed a novel therapeutic strategy of intravenous VNS (iVNS) and examined whether iVNS administered prior to coronary reperfusion in a canine AMI model reduces infarct size and prevents heart failure.

METHODS AND RESULTS

In 35 mongrel dogs, we induced ischemia by ligating the left anterior descending coronary artery and then reperfused 3h later (I/R). We transvenously placed a catheter electrode in the superior vena cava and adjusted the stimulation intensity to a level that induced bradycardia but maintained stable hemodynamics (continuous, 5.1±2.1V, 10Hz). We administered iVNS from onset (iVNS-0, n=7) or 90min after onset (iVNS-90, n=7) of ischemia until one hour after reperfusion. Four weeks after ischemia-reperfusion, iVNS markedly reduced infarct size (iVNS-0: 2.4±2.1%, p<0.05 and iVNS-90: 4.5±4.5%, p<0.05) compared with I/R control (I/R: 13.3±2.5%), and improved cardiac performance and hemodynamics. Atrial pacing (n=7) to abolish iVNS-induced bradycardia significantly attenuated the beneficial effects of iVNS.

CONCLUSIONS

Short-term iVNS delivered prior to coronary reperfusion markedly reduced infarct size and preserved cardiac function one month after AMI. The bradycardic effect plays an important role in the beneficial effect of iVNS. How other mechanisms contribute to the reduction of infarct size remains to be studied.

Left atrial anatomy relevant to catheter ablation

The rapid development of interventional procedures for the treatment of arrhythmias in humans, especially the use of catheter ablation techniques, has renewed interest in cardiac anatomy. Although the substrates of atrial fibrillation (AF), its initiation and maintenance, remain to be fully elucidated, catheter ablation in the left atrium (LA) has become a common therapeutic option for patients with this arrhythmia. Using ablation catheters, various isolation lines and focal targets are created, the majority of which are based on gross anatomical, electroanatomical, and myoarchitectual patterns of the left atrial wall. Our aim was therefore to review the gross morphological and architectural features of the LA and their relations to extracardiac structures. The latter have also become relevant because extracardiac complications of AF ablation can occur, due to injuries to the phrenic and vagal plexus nerves, adjacent coronary arteries, or the esophageal wall causing devastating consequences.

Computational modeling of an endovascular approach to deep brain stimulation

OBJECTIVE

Deep brain stimulation (DBS) therapy currently relies on a transcranial neurosurgical technique to implant one or more electrode leads into the brain parenchyma. In this study, we used computational modeling to investigate the feasibility of using an endovascular approach to target DBS therapy.

APPROACH

Image-based anatomical reconstructions of the human brain and vasculature were used to identify 17 established and hypothesized anatomical targets of DBS, of which five were found adjacent to a vein or artery with intraluminal diameter ≥1 mm. Two of these targets, the fornix and subgenual cingulate white matter (SgCwm) tracts, were further investigated using a computational modeling framework that combined segmented volumes of the vascularized brain, finite element models of the tissue voltage during DBS, and multi-compartment axon models to predict the direct electrophysiological effects of endovascular DBS.

MAIN RESULTS

The models showed that: (1) a ring-electrode conforming to the vessel wall was more efficient at neural activation than a guidewire design, (2) increasing the length of a ring-electrode had minimal effect on neural activation thresholds, (3) large variability in neural activation occurred with suboptimal placement of a ring-electrode along the targeted vessel, and (4) activation thresholds for the fornix and SgCwm tracts were comparable for endovascular and stereotactic DBS, though endovascular DBS was able to produce significantly larger contralateral activation for a unilateral implantation.

SIGNIFICANCE

Together, these results suggest that endovascular DBS can serve as a complementary approach to stereotactic DBS in select cases.

Dual atrioventricular nodal pathways physiology: a review of relevant anatomy, electrophysiology, and electrocardiographic manifestations

More than half a century has passed since the concept of dual atrioventricular (AV) nodal pathways physiology was conceived. Dual AV nodal pathways have been shown to be responsible for many clinical arrhythmia syndromes, most notably AV nodal reentrant tachycardia. Although there has been a considerable amount of research on this topic, the subject of dual AV nodal pathways physiology remains heavily debated and discussed. Despite advances in understanding arrhythmia mechanisms and the widespread use of invasive electrophysiologic studies, there is still disagreement on the anatomy and physiology of the AV node that is the basis of discontinuous antegrade AV conduction. The purpose of this paper is to review the concept of dual AV nodal pathways physiology and its varied electrocardiographic manifestations.

Ventricular rate control of atrial fibrillation in heart failure

In the last few years, there has been a major shift in the treatment of atrial fibrillation (AF) in the setting of hear failure (HF), from rhythm to ventricular rate control in most patients with both conditions. In this article, the authors focus on ventricular rate control and discuss the indications; the optimal ventricular rate-control target, including detailed results of the Rate Control Efficacy in Permanent Atrial Fibrillation: a Comparison Between Lenient versus Strict Rate Control II (RACE II) study; and the pharmacologic and nonpharmacologic options to control the ventricular rate during AF in the setting of HF.

Atrial fibrillation in heart failure: The sword of Damocles revisited

Heart failure (HF) and atrial fibrillation (AF) frequently coexist and have emerged as major cardiovascular epidemics. There is growing evidence that AF is an independent prognostic marker in HF and affects patients with both reduced as well as preserved LV systolic function. There has been a general move in clinical practice from a rhythm control to a rate control strategy in HF patients with AF, although recent data suggests that rhythm control strategies may provide better outcomes in selected subgroups of HF patients. Furthermore, various therapeutic modalities including pace and ablate strategies with cardiac resynchronisation or radiofrequency ablation have become increasingly adopted, although their role in the management of AF in patients with HF remains uncertain. This article presents an overview of the multidimensional impact of AF in patients with HF. Relevant literature is highlighted and the effect of various therapeutic modalities on prognosis is discussed. Finally, while novel anticoagulants usher in a new era in thromboprophylaxis, research continues in a variety of new pathways including selective atrial anti-arrhythmic agents and genomic polymorphisms in AF with HF.

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.

Intravascular parasympathetic cardiac nerve stimulation prevents ventricular arrhythmias during acute myocardial ischemia

Although previous animal studies clearly demonstrated antiarrhythmic effects of vagal stimulation during acute myocardial ischemia, highly invasive nature of vagal stimulation limited its clinical use. Recently, intravascular parasympathetic cardiac nerve stimulation (IPS) has emerged as a novel approach to the cardiac autonomic nervous system. We hypothesized that IPS might prevent ventricular arrhythmias during acute myocardial ischemia.

METHODS

The IPS (36 V, 10 Hz) was performed in superior vena cava using an expandable electrode-basket catheter. In 18 open-chest dogs, left anterior descending coronary artery ligation was performed without IPS (control group, n= 6), with IPS (IPS group, n= 6) and with IPS and right atrial pacing at 180/min (IPS+P group, n=6). The ECGs were monitored for 60 min. The incidence and severity of ventricular arrhythmias were analyzed.

RESULTS

The IPS significantly decreased the frequency of premature ventricular contractions (control group: 9.1 &#177; 4.6/min, IPS group: 0.2 &#177; 0.4 /min, IPS+P group: 10.6 &#177; 4.2 / min; p&lt;0.05). The frequency of ventricular tachycardia was lower in IPS group (0 &#177; 0 /min) than in control group (0.15 &#177; 0.18 /min, p&lt;0.05) and than in IPS+P group (0.17 &#177; 0.12 /min, p<0.05). The incidence of ventricular fibrillation was lower in IPS group (0%) than in control group (33.3%) and than in IPS+P group (33.3%).

CONCLUSIONS

The IPS suppressed ventricular arrhythmias during acute ischemia mainly through its bradycardiac effect.

Cardiac electrophysiology in mice: a matter of size

Over the last decade, mouse models have become a popular instrument for studying cardiac arrhythmias. This review assesses in which respects a mouse heart is a miniature human heart, a suitable model for studying mechanisms of cardiac arrhythmias in humans and in which respects human and murine hearts differ. Section I considers the issue of scaling of mammalian cardiac (electro) physiology to body mass. Then, we summarize differences between mice and humans in cardiac activation (section II) and the currents underlying the action potential in the murine working myocardium (section III). Changes in cardiac electrophysiology in mouse models of heart disease are briefly outlined in section IV, while section V discusses technical considerations pertaining to recording cardiac electrical activity in mice. Finally, section VI offers general considerations on the influence of cardiac size on the mechanisms of tachy-arrhythmias.

Therapeutic effects of selective atrioventricular node vagal stimulation in atrial fibrillation and heart failure

INTRODUCTION

Atrial fibrillation (AF) and heart failure (HF) frequently coexist. We have previously demonstrated that selective atrioventricular node (AVN) vagal stimulation (AVN-VS) can be used to control ventricular rate during AF. Due to withdrawal of vagal activity in HF, the therapeutic effects of AVN-VS may be compromised in the combined condition of AF and HF. Accordingly, this study was designed to evaluate the therapeutic effects of AVN-VS to control ventricular rate in AF and HF.

METHODS AND RESULTS

A combined model of AF and HF was created by implanting a dual chamber pacemaker in 24 dogs. A newly designed bipolar electrode was inserted into the ganglionic AVN fat pad and connected to a nerve stimulator for delivering AVN-VS. In all dogs, HF was induced by high rate ventricular pacing at 220 bpm for 4 weeks. AF was then induced and maintained by rapid atrial pacing at 600 bpm after discontinuation of ventricular pacing. These HF + AF dogs were randomized into control (n = 9) and AVN-VS (n = 15) groups. In the latter group, vagal stimulation (310 μs, 20 Hz, 3-7 mA) was delivered continuously for 6 months. Compared with the control, AVN-VS had a consistent effect on ventricular rate slowing (by >50 bpm, all P < 0.001) during the entire 6-month observation period that was associated with left ventricular functional improvement. Moreover, AVN-VS was well tolerated by the treated animals.

CONCLUSIONS

AVN-VS achieved consistent rate slowing, which was associated with improved ventricular function in a canine AF and HF model. Thus, AVN-VS may be a novel, effective therapeutic option in the combined condition of AF and HF.

Epicardial ganglionated plexus stimulation decreases postoperative inflammatory response in humans

BACKGROUND

Surgical cardiac revascularization produces a high degree of systemic inflammation and the secretion of several cytokines. Intensive postoperative inflammation may increase the incidence of postoperative atrial fibrillation and favor organ dysfunctions. No data documenting the anti-inflammatory properties of epicardial vagal ganglionated plexus stimulation are available.

OBJECTIVE

To verify the feasibility and safety of postoperative inferior vena cava-inferior atrial ganglionated plexus (IVC-IAGP) burst stimulation and the effectiveness of this approach in reducing serum levels of inflammatory cytokines.

METHODS

In 27 patients who were candidates for off-pump surgical revascularization, the IVC-IAGP was located during surgery, a temporary wire was inserted, and a negative atrioventricular node dromotropic effect was obtained in 20 patients on applying high-frequency burst stimulation. In 5 patients atrial fibrillation or phrenic nerve stimulation was induced, and the remaining 15 patients served as the experimental group. Twenty additional patients underwent off-pump surgical revascularization without IVC-IAGP stimulation and served as the control group. On arrival in the intensive care unit, the experimental group underwent IVC-IAGP stimulation for 6 hours. Blood samples were collected at different times.

RESULTS

The serum levels of cytokines were not statistically different at baseline and on arrival in the intensive care unit between the groups, while they proved statistically different after 6 hours of stimulation: interleukin-6 (EG: 121 ± 71 pg/mL vs CG: 280 ± 194 pg/mL; P = .004), tumor necrosis factor-α (EG: 2.68 ± 1.81 pg/mL vs CG: 5.87 ± 3.48 pg/mL; P = .003), vascular endothelial growth factor (EG: 93 ± 43 pg/mL vs CG: 177 ± 86 pg/mL; P = .002), and epidermal growth factor (EG: 79 ± 48 pg/mL vs CG: 138 ± 76 pg/mL; P = .012).

CONCLUSIONS

Prolonged burst IVC-IAGP stimulation after surgical revascularization appears to be feasible and safe and significantly reduces inflammatory cytokines in the postoperative period.

Shift in the pattern of autonomic atrial innervation in subjects with persistent atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is a multifactorial disease of the atria.

OBJECTIVE

We studied the differences in the atrial autonomic innervation pattern in subjects with AF compared with sinus rhythm (SR).

METHODS

Preparation of postmortem isolated hearts of subjects with documented persistent AF (group A) and SR (group B) included: (1) histological sectioning of predefined areas and quantification of nerve density, and (2) differentiation using immunohistochemistry in adrenergic (sympathetic, tyrosine-hydroxylase antibody), cholinergic (parasympathetic, choline-acetyltransferase antibody) and mixed (adrenergic and cholinergic staining) nerves.

RESULTS

Characteristics of subjects in group A (N = 15) and group B (N = 24) did not differ. The mean overall nerve density was similar between groups (A: 0.31 ± 0.25/mm(2); B: 0.35 ± 0.25/mm(2); P = .87). Nerve density appeared higher in the region of the pulmonary vein ostia and antrum (group A: 0.38 ± 0.21/mm(2); group B: 0.32 ± 0.19/mm(2),) compared with other locations of the right and left atrium. A total of 2,224 (group A: 685; group B: 1539) nerves were differentiated using immunohistochemistry. There was a high degree of colocalization of adrenergic and cholinergic nerves (group A: 80% mixed staining, group B: 69% mixed staining). In group A hearts there was a significantly lower density of predominantly cholinergic nerves (0.025 ± 0.052/mm(2) vs. 0.058 ± 0.099/mm(2); P = .008) and a higher density of nerves containing adrenergic components (0.24 ± 0.18/mm(2) vs. 0.18 ± 0.17/mm(2), P = .046).

CONCLUSION

Overall autonomic nerve density did not differ between atria with persistent AF compared with SR. On a morphological level, we detected a shift toward a lower density of cholinergic nerves and a higher density of nerves containing adrenergic components in AF subjects.

Endocardial vagal atrioventricular node stimulation in humans: reproducibility on 18-month follow-up

AIMS

Control of atrioventricular (AV) node conduction by means of high-frequency stimulation (HFS) of efferent AV node vagal stimulation (AVNS) fibres enables the ventricular rate (VR) to be modulated during atrial fibrillation (AF). The aims of this study were to verify, on 18-month follow-up, the reproducibility of the dromotropic effect obtained on implantation and the long-term reliability of the system in patients who received an implantable cardioverter-defibrillator (ICD) with a standard atrial lead positioned at a location suitable for AVNS.

METHODS AND RESULTS

We enrolled 12 patients with paroxysmal or persistent AF who were candidates for ICD. The right atrium was mapped to locate the pacing site, and a transvenous screw-in lead was implanted in that region. The voltages required for VR modulation (25% VR reduction) and complete AV block at different pulse durations (from 0.1 to 0.5 ms) were recorded. Eleven out of 12 patients underwent 18-month follow-up examination. Atrial pacing parameters were adequate and did not differ from the baseline values (all P > 0.05): pacing threshold 0.9 ± 0.5 V (0.5 ms pulse duration) and impedance 556 ± 121 Ω, with P-wave amplitude of 1.6 ± 0.7 mV. High-frequency stimulation induced VR modulation in nine patients and complete AV block in eight patients at pulse durations ≥0.3 ms. No differences were observed in the voltages for VR modulation and complete AV block between implantation and 18-month examination (all P > 0.100).

CONCLUSION

Ventricular rate control during AF was obtained under HFS 18 months after implantation in patients with the atrial lead positioned at a location suitable for AVNS. The pacing outputs needed to achieve the dromotropic effect were comparable to those measured on implantation.

Acetylcholine as an age-dependent non-neuronal source in the heart

In the heart, acetylcholine (ACh) slows pacemaker activity, depresses contractility and slows conduction in the atrioventricular node. Beside these cardiovascular effects, ACh has also been associated with an anti-inflammatory and anti-apoptotic pathway. There is no evidence for ACh synthesis and excretion in other cell types than neuronal cells in the heart. Therefore, this study investigates whether cardiomyocytes are able to synthesize, transport and excrete ACh in the heart. We chose a rat model of different aged rats (neonatal, 6-8 week = young, 20-24 month = old). By real-time PCR, Western blot and immunofluorescence experiments we could demonstrate that adult, but not neonatal cardiomyocytes, express the choline acetyltransferase (ChAT). The expression level of ChAT is down-regulated in old cardiomyocytes. Furthermore, we found that young and old cardiomyocytes express the ACh transport proteins choline transporter-1 (CHT-1) and the vesicular acetylcholine transporter (VAChT). The amount of ACh excretion detected by high performance liquid chromatography (HPLC) is significantly down-regulated in old cardiomyocytes. Bromo-acetylcholine (BrACh), a specific ChAT inhibitor, significantly decreased ACh concentrations in cardiomyocyte supernatants demonstrating that ChAT is the main ACh synthesizing enzyme in cardiomyocytes. In conclusion, we could demonstrate that adult, but not neonatal, cardiomyocytes are able to synthesize, transport and excrete ACh in the rat heart. The expression level of ChAT and the ACh excretion amount are significantly down-regulated in old cardiomyocytes. This finding may provide new physiological/pathological aspects in the communication between cardiomyocytes and other cell types in the myocardium, e.g. fibrocytes, neurocytes or endothelial cells.

[Atrial fibrillation. New aspects for diagnosis and follow-up]

Continuous rhythm monitoring is the gold standard of objective rhythm assessment in patients with atrial fibrillation, thus, facilitating accurate detection of symptomatic and asymptomatic atrial fibrillation. This is of scientific and clinical interest for the understanding of this arrhythmia, the establishment of evidence-based therapeutic approaches, the definition of clinically indicated monitoring strategies, and for decision-making about oral anticoagulation. This article illustrates the importance of continuous monitoring of atrial fibrillation and presents developing technologies with their advantages and limitations as well as initial clinical experience.

Epicardial neural ganglionated plexus of ovine heart: anatomic basis for experimental cardiac electrophysiology and nerve protective cardiac surgery

BACKGROUND

Sheep are routinely used in experimental cardiac electrophysiology and surgery.

OBJECTIVE

The purpose of this study was to (1) ascertain the topography and architecture of the ovine epicardial neural plexus (ENP), (2) determine the relationships of ENP with vagal and sympathetic cardiac nerves and ganglia, and (3) evaluate gross anatomic differences and similarities of ENP in humans, sheep, and other species.

METHODS

Ovine ENP and extrinsic sympathetic and vagal nerves were stained histochemically for acetylcholinesterase in whole heart and/or thorax-dissected preparations from 23 newborn lambs, with subsequent examination by stereomicroscope.

RESULTS

Intrinsic cardiac nerves extend from the venous part of the ovine heart hilum along the roots of the cranial (superior) caval and left azygos veins to both atria and ventricles via five epicardial routes: dorsal right atrial, middle dorsal, left dorsal, right ventral, and ventral left atrial nerve subplexuses. Intrinsic nerves proceeding from the arterial part of the heart hilum along the roots of the aorta and pulmonary trunk extend exclusively into the ventricles as the right and left coronary subplexuses. The dorsal right atrial, right ventral, and middle dorsal subplexuses receive the main extrinsic neural input from the right cervicothoracic and right thoracic sympathetic T(2) and T(3) ganglia as well as from the right vagal nerve. The left dorsal is supplied by sizeable extrinsic nerves from the left thoracic T(4)-T(6) sympathetic ganglia and the left vagal nerve. Sheep hearts contained an average of 769 +/- 52 epicardial ganglia. Cumulative areas of epicardial ganglia on the root of the cranial vena cava and on the wall of the coronary sinus were the largest of all regions (P <.05).

CONCLUSION

Despite substantial interindividual variability in the morphology of ovine ENP, right-sided epicardial neural subplexuses supplying the sinoatrial and atrioventricular nodes are mostly concentrated at a fat pad between the right pulmonary veins and the cranial vena cava. This finding is in sharp contrast with a solely left lateral neural input to the human atrioventricular node, which extends mainly from the left dorsal and middle dorsal subplexuses. The abundance of epicardial ganglia distributed widely along the ovine ventricular nerves over respectable distances below the coronary groove implies a distinctive neural control of the ventricles in human and sheep hearts.

Chronic augmentation of the parasympathetic tone to the atrioventricular node: a nonthoracotomy neurostimulation technique for ventricular rate control during atrial fibrillation

INTRODUCTION

The right inferior ganglionated plexus (RIGP) selectively innervates the atrioventricular node. Temporary electrical stimulation of this plexus reduces the ventricular rate during atrial fibrillation (AF). We sought to assess the feasibility of chronic parasympathetic stimulation for ventricular rate control during AF with a nonthoracotomy intracardiac neurostimulation approach.

METHODS AND RESULTS

In 9 mongrel dogs, the small endocardial area inside the right atrium, which overlies the RIGP, was identified by 20 Hz stimulation over a guiding catheter with integrated electrodes. Once identified, an active-fixation lead was implanted. The lead was connected to a subcutaneous neurostimulator. An additional dual-chamber pacemaker was implanted for AF induction by rapid atrial pacing and ventricular rate monitoring. Continuous neurostimulation was delivered for 1-2 years to decrease the ventricular rate during AF to a range of 100-140 bpm. Implantation of a neurostimulation lead was achieved within 37 +/- 12 min. The latency of the negative dromotropic response after on/offset or modulation of neurostimulation was <1 s. Continuous neurostimulation was effective and well tolerated during a 1-2 year follow-up with a stimulation voltage <5 V. The neurostimulation effect displayed a chronaxie-rheobase behavior (chronaxie time of 0.07 +/- 0.02 ms for a 50% decrease of the ventricular rate during AF).

CONCLUSION

Chronic parasympathetic stimulation can be achieved via a cardiac neurostimulator. The approach is safe, effective, and well tolerated in the long term. The atrioventricular nodal selectivity and the opportunity to adjust the negative dromotropic effect within seconds may represent an advantage over pharmacological rate control.

Vagal nerve stimulation prevents reperfusion injury through inhibition of opening of mitochondrial permeability transition pore independent of the bradycardiac effect

BACKGROUND

In spite of recent advances in coronary interventional therapy, reperfusion injury is still considered to be a major problem in patients undergoing surgical procedures, such as bypass grafting. Here we demonstrate a novel therapeutic strategy against ischemia-reperfusion injury: vagally mediated prevention of reperfusion-induced opening of mitochondrial permeability transition pore.

METHODS

We investigated the effects of efferent vagal stimulation on myocardial reperfusion injury with ex vivo and in vitro rat models. In the ex vivo model the hearts were perfused with intact vagal innervation, which allowed us to study the effects of the vagal nerve on the heart without other systemic effects.

RESULTS

Compared with sham stimulation, vagal stimulation exerted a marked anti-infarct effect irrespective of the heart rate (34% +/- 6% vs 85% +/- 9% at a heart rate of 300 beats/min, 37% +/- 4% vs 43% +/- 5% at a heart rate of 250 beats/min, and 39% +/- 4% vs 88% +/- 7% at a heart rate of 350 beats/min) after a 30-minute period of global ischemia, activated cell-survival Akt cascade, prevented downregulation of the antiapoptotic protein Bcl-2, and suppressed cytochrome-c release and caspase-3 activation. Furthermore, vagal stimulation-treated hearts exhibited a significant improvement in left ventricular developed pressure (78 +/- 5 vs 45 +/- 8 mm Hg) and a significant attenuation in an incremental change in left ventricular end-diastolic pressure during reperfusion. These beneficial effects of vagal stimulation were abolished by a permeability transition pore opener, atractyloside. In the in vitro study with primary-cultured cardiomyocytes, acetylcholine prevented a reoxygenation-induced collapse in mitochondrial transmembrane potential through inhibition of permeability transition pore opening.

CONCLUSION

Vagal stimulation would be a potential adjuvant therapy for the rescue of ischemic myocardium from reperfusion injury, and the protective effects are independent of its bradycardiac effects.

Post-operative atrial fibrillation management by selective epicardial vagal fat pad stimulation

PURPOSE

Post-operative atrial fibrillation (POAF) is a common complication after cardiac surgery and often leads to poorly tolerated fast ventricular rates. Negative dromotropic drugs are not always effective and may not be well tolerated in heart failure patients. Aim of this study is to verify if high-frequency stimulation of the right inferior fat pad (RIFPS) allows an effective decrease in ventricular rate (VR) during POAF.

METHODS

We enrolled 32 consecutive patients submitted to bypass; during surgery, a temporary heart wire was implanted in a site where RIFPS evoked a functional AV block. During POAF, RIFPS was delivered from the heart wire to decrease VR.

RESULTS

Intra-operative RIFPS evoked complete AV block in 29 patients (91%). Fourteen patients (44%) developed POAF (mean VR 127 +/- 12 bpm). In these patients, RIFPS achieved a 25% reduction of VR and complete AV block with 6.0 +/- 1.9 and 7.5 +/- 1.8 V (duration 0.2 ms, frequency 50 Hz), respectively.

CONCLUSION

Epicardial RIFPS represents an effective and feasible technique to decrease VR during POAF.

Autonomic nervous system activity and decline as prognostic indicators of cardiovascular and cerebrovascular events: the 'PROOF' Study. Study design and population sample. Associations with sleep-related breathing disorders: the 'SYNAPSE' Study

BACKGROUND

Transversal studies have underlined the association between the decline in autonomic nervous system (ANS) activity and all-cause mortality. However, the predictive value of ANS has never been prospectively assessed in a general population-based cohort.

METHOD

The PROOF (PROgnostic indicator OF cardiovascular and cerebrovascular events) cohort study was designed to prospectively assess the predictive value of ANS activity level in the general population, with regard to cardiovascular and cerebrovascular events, and death. This predictive power will be compared with the usual and newly discovered risk factors for the purposes of developing a risk model.

RESULTS

A prospective cohort of elderly subjects aged 65 years upon study entry were recruited from the electoral list of the city of Saint-Etienne, France. Three initial 2-year examination programs were scheduled for 7 years (2001-2007), followed by late events monitoring. At each examination, ANS activity was assessed along with clinical and biological cardiovascular risk factors, brain MRI, neuropsychological evaluation, physical activity profile, and sleep-related breathing disorders. The main study outcomes are stroke, myocardial infarction and death from any cause. A cohort consisting of 1,011 subjects aged 65.6 (0.8) years was constituted.

CONCLUSION

Despite other selective characteristics, the associations between ANS activity and events will be applicable to other populations.

Topography of the porcine epicardiac nerve plexus as revealed by histochemistry for acetylcholinesterase

The aim of the present study was to map the topography of the porcine epicardiac nerve plexus (ENP) and to re-examine the total number and distribution of the porcine intracardiac ganglia and neurons. Eleven juvenile pigs (Sus scrofa domestica, 3-4 weeks of age) were examined employing histochemistry for acetylcholinesterase to reveal the ENP on total hearts. The nerves entered porcine epicardium at five sites: (1) ventro-medially to the origin of the superior vena cava, (2) dorsally to the origin of the superior vena cava, (3) among the pulmonary veins, (4) dorso-medially to the origin of the left azygos vein, and (5) ventrally to the left pulmonary vein. Within the porcine epicardium, the nerves connected to the groups of the intrinsic ganglia and proceeded into the discrete atrial and ventricular regions via five topographical pathways (subplexuses). In general, the porcine left atrium received nerves by four subplexuses, left ventricle by three subplexuses, right atrium and right ventricle each by two subplexuses. The estimated total number of the intrinsic ganglia per porcine heart was 362+/-52. About 55% of ganglia per porcine heart were accumulated on the left atrium while 36% on the right atrium. The percentage of ganglia within porcine ventricular and para-aortic regions was 7.6% and 1.6%, respectively. On average, porcine heart contained about 12,000 intrinsic neurons. In summary, the results of the present study imply that (1) the porcine epicardiac nerves are grouped into distinct topographical pathways, and (2) the porcine atria contain significantly more intrinsic ganglia and neurons compared to the ventricles.

Autonomic control and innervation of the atrioventricular junctional pacemaker

BACKGROUND

The main physiologic function of the AV junction is control of timing between atrial and ventricular excitation. However, under pathologic conditions, the AV junction may become the pacemaker of the heart. Unlike the well-characterized sinoatrial node (SAN), autonomic control of the AV junctional pacemaker has not been studied.

OBJECTIVE

The purpose of this study was to characterize the autonomic control and innervation of the AV junctional pacemaker.

METHODS

The response of rabbit AV junctional pacemaker to autonomic stimulation was investigated using optical mapping, autonomic modulation via subthreshold stimulation (n = 12), and quantitative immunohistochemistry (n = 5), and the density of parasympathetic and sympathetic innervation in optically mapped preparations was quantified.

RESULTS

Subthreshold stimulation applied adjacent to the conduction system in the triangle of Koch autonomically modulates the junctional rate, and parasympathetic and sympathetic components can be separated with atropine and the beta-blocker nadolol. Subthreshold stimulation increased the rate maximally to 2.1 +/- 0.4 times when applied with atropine. Unlike the SAN pacemaker, which shifts significantly in response to autonomic stimulation, the AV junctional pacemaker remains stationary (most often in the inferior nodal extension), moving in only 5% of subthreshold stimulation trials. Staining with tyrosine hydroxylase and choline acetyltransferase revealed heterogeneous innervation within the AV junction.

CONCLUSION

AV junctional rhythm can be autonomically modulated with subthreshold stimulation to produce junctional rates of 145 +/- 16 bpm (cycle length 412 +/- 29 ms), similar to sinus rates in rabbit. Unlike the SAN, the anatomic location of the AV junctional pacemaker is stable during autonomic modulation.

Lead Design and Initial Applications of a New Lead for Long-Term Endovascular Vagal Stimulation

BACKGROUND

Vagal nerve stimulation (VNS) has negative chronotropic and dromotropic effects. We developed and tested an endovascular spiral vagal stimulation lead (ESVL) designed to follow the projection of the cardiac branches of the vagus nerve around the superior vena cava (SVC) to optimize VNS.

METHODS

ESVL contained six 5-mm coil electrodes, spaced 5-mm apart with a spiral guidewire to provide shape. The tightness and diameter of the guidewire were changed before each placement to simulate different lead designs. Various 2-, 3-, and 4-electrode combinations were used and several lead positions were tested each time. Each VNS protocol included 2-12 V, 15-second pulse trains at 20 Hz, with 2 ms pulse duration. A basket catheter (BC) was used as control and to approximate the initial VNS location. The VNS protocol was performed at the optimal location, using first the BC and then several ESVL configurations.

RESULTS

VNS caused a voltage-dependent decrease in heart rate (HR). Using the optimal ESVL configuration at 7 V, HR decreased by 30.4% (37.2 bpm) in dog no. 1 and 12.4% (16.6 bpm) in dog no. 2, versus 15.5% (16.6 bpm) and 16.7% (19.5 bpm) with the BC.

CONCLUSIONS

A new endovascular spiral lead that takes advantage of the anatomy of the cardiac branches of the vagus nerve in the SVC was developed. VNS using ESVL produced significant HR slowing at voltages slightly below the highest pulse generator output of 7.5 V, which may be suitable for long-term implantation.

Determinants and Effects of Electrical Stimulation of the Inferior Interatrial Parasympathetic Plexus During Atrial Fibrillation

INTRODUCTION

Catheter stimulation of the inferior interatrial ganglionated parasympathetic plexus decreases the ventricular rate during atrial fibrillation (AF) in humans. However, the relatively high stimulation voltages might prevent implementation of neurostimulation in chronic implantable devices. From myocardial electrostimulation it is known that the required impulse energy and charge is lowest at the chronaxie time. In order to lower energy requirements for cardiac neurostimulation, the present study evaluates the impulse-strength versus impulse-duration relationship for a neurostimulation lead that was implanted into the inferior interatrial ganglionated plexus.

METHODS AND RESULTS

In nine dogs, permanent epicardial bipolar screw-in electrodes were fixed in the inferior interatrial ganglionated plexus. AF was maintained via rapid atrial pacing. During AF, neural stimulation was performed at various frequencies (1-100 Hz), impulse durations (0.05-2 msec), and voltages (0.02-11.5 V). There was a linear correlation between R-R interval lengthening and stimulus voltage (R = 0.99; P < 0.001) and a bell-shaped relationship between stimulation frequency and negative dromotropic effect with maximum rate slowing at 30-50 Hz. The rheobase for a 50% R-R interval prolongation during AF was 1.81 V and 2.72 V for high-grade AVB yielding a chronaxie time of 0.14 msec and 0.18 msec, respectively. The impulse energy (charge) at the chronaxie time was 4-6 microJ (6-8 microC).

CONCLUSIONS

Cardiac neurostimulation follows a chronaxie/rheobase behavior. Energy, charge, and voltage values needed to achieve significant negative dromotropic effects are within the limits of conventional cardiac pacemaker outputs, which may allow implementation of neurostimulation capabilities in current pacemaker technology.

Selective Increase of Cardiac Neuronal Sympathetic Tone

OBJECTIVES

This study was designed to develop a technique to selectively increase the sympathetic tone to the heart by cardiac sympathetic nerve stimulation (SNS).

BACKGROUND

Access to the cardiac sympathetic neurons may allow modulating the adrenergic tone of the heart while avoiding systemic side effects.

METHODS

Cardiac sympathetic nerves course within neural sleeves along the subclavian artery. Because of this proximity, transvascular SNS was attempted with electrode catheters inside the subclavian artery in 16 pigs.

RESULTS

Right/left (R-/L-) SNS (20 Hz) during ventricular pacing at 200/min evoked a >100% increase of left ventricular systolic pressure (baseline: 51 +/- 1 mm Hg; L-SNS: 118 +/- 26 mm Hg; R-SNS: 116 +/- 33 mm Hg; p < 0.001) while systemic vascular resistance remained unchanged. There was a sigmoid dose-response curve with rapid on- and offset of the effect during SNS initiation/cessation. Positive inotropic effects persisted for 12 h of continued SNS (n = 4). Besides positive dromotropic effects, L-SNS/R-SNS yielded a 41% and 77% sinus rate increase, respectively.

CONCLUSIONS

The neural adrenergic tone to the heart can be selectively increased by catheter stimulation of cardiac efferent sympathetic nerves.

Time Course and Predictors of Autonomic Dysfunction After Ablation of the Slow Atrioventricular Nodal Pathway

Withdrawal of parasympathetic tone has been reported after ablation in the posteroseptal right atrium and has been attributed to injury of vagal efferent fibers. The purpose of this study was to assess the time course and predictors of autonomic dysfunction after slow pathway ablation. In 30 patients with AV nodal reentrant tachycardia, time- and frequency-domain measures of heart rate variability (HRV) were measured before, 30 minutes after, and 1 day after slow pathway ablation. There were significant reductions in mean RR interval (724 +/- 163 vs 836 +/- 164 ms, P < 0.05), SD of RR intervals (29 +/- 17 vs 40 +/- 18 ms, P < 0.05), root mean squared difference (15 +/- 8 vs 29 +/- 17 ms, P < 0.05), and high frequency power (4.1 +/- 0.4 vs 4.5 +/- 0.6 log10ms2, P < 0.05) 30 minutes after ablation. However, these parameters returned to baseline 1 day after ablation. Multivariate regression identified isoproterenol dose during the diagnostic study (P = 0.02) and radiofrequency duration (P = 0.02) as statistically significant predictors of heart rate change (R2= 0.45). These findings suggest that changes in autonomic tone after ablation in the posteroseptal right atrium are transitory and resolve within 1 day of the procedure. These short-term changes may be related to procedural variables rather than direct injury to vagal efferent fibers.

Achieving regular slow rhythm during atrial fibrillation without atrioventricular nodal ablation: Selective vagal stimulation plus ventricular pacing

OBJECTIVES

The aim of this study was to achieve regular slow ventricular rhythm during atrial fibrillation (AF) without destroying the AV node (AVN).

BACKGROUND

Recent experimental and clinical studies have demonstrated that selective AVN vagal stimulation (AVN-VS) can be used to slow ventricular rate during AF; however, an irregular rhythm remains. Alternatively, ventricular on-demand (VVI) pacing achieves rate regularization but at rates faster than the already fast intrinsic rate during AF. We hypothesized that AVN-VS combined with VVI pacing would achieve slow, regular rhythm during AF without requiring AVN ablation.

METHODS

AF was induced in eight dogs. AVN-VS was applied to the epicardial fat pad that projects vagal nerve fibers to the AVN. A computer-controlled algorithm adjusted AVN-VS intensity to achieve three levels of mean ventricular RR interval: 75%, 100%, or 125% of the spontaneous sinus cycle length. At each of the three levels, concomitant VVI pacing was delivered at a constant cycle length equal to the corresponding target. Hemodynamic measurements were performed during the study to elucidate the advantages of the proposed method.

RESULTS

AF resulted in rapid, irregular ventricular rates (RR = 287 +/- 36 ms, or 56% of sinus cycle length). AVN-VS achieved average ventricular rate slowing to the three target levels in all dogs (RR increased to 381 +/- 41, 508 +/- 54, and 632 +/- 68 ms, respectively). At each of the three target rate levels, AVN-VS combined with VVI pacing fully eliminated rate irregularities. The regular slow ventricular rhythms during AF were associated with significant hemodynamic improvement.

CONCLUSIONS

A novel approach combining AVN-VS with VVI pacing results in a regular, slow ventricular rhythm during AF that does not necessitate AVN ablation. Rate regularization achieved by this approach was associated with pronounced hemodynamic benefits during AF.

Ventricular rate control during atrial fibrillation and AV node modifications: past, present, and future

Atrial fibrillation (AF) is the most common arrhythmia. Currently there are two broad strategic treatment options for AF: rhythm control and rate control. For rhythm control, the treatment is directed toward restoring and maintaining the sinus rhythm. For rate control, the intention is to slow ventricular rate while allowing AF to continue. In both cases anticoagulation therapy is recommended. The results of currently available clinical trials demonstrated clearly that rate control is not inferior to rhythm control. Thus, rate control is an acceptable primary therapy for many AF patients. The rate control can be achieved essentially by depressing or modifying the filtering properties of the atrioventricular (AV) node. This can be attained by medications that depress the impulse transmission within the AV node, by anatomic modification of the AV communications, as well as by autonomic manipulations that produce AV node negative dromotropic effect. We are reviewing current clinical and newer experimental modalities aimed at enhancing the lifesaving function of this remarkable nodal structure.

Parasympathetic cardiac nerve stimulation with implanted coronary sinus lead

A patient with drug-refractory paroxysmal atrial fibrillation associated with rapid ventricular rate underwent biatrial pacemaker implantation. During elective replacement of the pacemaker, a significant voltage- and frequency-dependent decrease in ventricular rate was achieved by high-frequency electrical stimulation (17 Hz) of parasympathetic cardiac nerves innervating the AV node with the implanted bipolar coronary sinus electrode. The negative dromotropic effect of parasympathetic stimulation was eliminated by intravenous administration of 1-mg atropine.

Effects of aging on cardiovascular responses to parasympathetic withdrawal

OBJECTIVES

The study was done to determine whether the effects of parasympathetic withdrawal on heart rate, blood pressure (BP), and systolic and diastolic function are altered with normal aging.

BACKGROUND

Cardiac responses to beta-adrenergic sympathetic stimulation decline with aging as does the heart rate response to parasympathetic withdrawal, but the extent to which other responses to parasympathetic withdrawal decrease is less clear.

METHODS

Heart rate, BP, systolic function, and diastolic filling responses to parasympathetic withdrawal induced by atropine (0.02 mg/kg) were compared in 50 healthy subjects, 28 older (ages 65 to 80 years, mean 70 years; 18 females all on estrogen) and 22 young (age 18 to 32 years, mean 26 years; 12 females) subjects, using radionuclide angiography.

RESULTS

Parasympathetic withdrawal in the older group caused less of an increase in heart rate (+33 vs. +48 beats/min), cardiac index (+0.6 vs. +1.5 l/m(2)), systolic blood pressure (-1 vs. +7 mm Hg), and early diastolic filling rate (+1.7 vs. +2.4 end-diastolic volumes/s) (all p < or = 0.01). At similar declines in the diastolic filling period, end-diastolic volume index (EDVI) fell substantially more in the older group (-11.6 vs. -2.4 ml/m(2), p < 0.001). The only gender difference was in diastolic filling rate, which was similar in the young males and females, but significantly less in older males than in older females.

CONCLUSIONS

The responses to parasympathetic withdrawal as well as sympathetic stimulation decline with aging, and both contribute to the reduced cardiovascular responses to stress with advancing age.

Endovascular stimulation of autonomic neural elements in the superior vena cava using a flexible loop catheter

It has been previously shown that parasympathetic nerve stimulation (PNS) can be achieved via basket electrode catheters (BEC) positioned in the superior vena cava (SVC). Since questions have been raised regarding formation of thrombi between and/or on the splines of the BECs, we investigated the use of a flexible loop "Lasso" catheter (LC) to achieve autonomic nerve stimulation in the SVC without clot formation. In 5 dogs, anesthetized with Na-pentobarbital, standard ECG leads II and aVR, blood pressure and right atrial electrograms were continuously monitored. The LC is a 7-French catheter at the end of which is a circular ring, 25 mm in diameter, equipped with ten 1-mm electrodes. The circular loop is made of a flexible, shape retaining, covered metal, which can be straightened in order to be inserted transvenously. The catheter was inserted through a sheath in the external jugular vein and positioned in the SVC. Stimulation was performed sequentially across each of the five bipolar pairs of electrodes, and consisted of square wave stimuli, each 0.1 msec duration, frequency 20 Hz at voltages from 1-40 V. The average voltage required to produce a 50% decrease in heart rate was 15 +/- 7 V, compared to 22 +/- 12 V with the standard BEC and 10 +/- 5 V with a modified BEC. We did not observe any thrombus formation at the end of a four-hour period during which the catheter was stabilized in the SVC. PNS can be achieved safely and effectively by the LC in the SVC in dogs.