Signal processing of the cardiac ANS occurs at several levels: i) central; ii) intrathoracic extracardiac; and iii) intrinsic cardiac level ⁸. Neural trafficking is influenced by the brain, spinal cord, extrinsic and intrinsic cardiac ganglia Figure 1. Autonomic neural signals from other organ systems (e.g. kidneys) can affect the cardiac ANS through complex interactions in the ANS ^9-12.
心脏ANS的信号处理发生在几个层面:i)中央;Ii)胸内心外;iii)心脏内禀水平 ⁸ 。神经运输受脑、脊髓、外源性和内在心神经节的影响(图1)。来自其他器官系统(如肾脏)的自主神经信号可以通过ANS中的复杂相互作用影响心脏ANS ^{9 12} 。

Figure 1. Neurohumoral control and functional organization of cardiac autonomic innervation.
图1所示。心脏自主神经支配的神经体液控制与功能组织。

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The autonomic nervous system related to arrhythmias consists of neurons and nerves in the brain, spinal cord, heart and kidneys and is similar to a closed-loop circuit that modulates the function of target organs. Activation of both the afferent and efferent vagal nerve fibers can increase the vagal tone in the cardiac closed-loop circuit and protect the heart. Blue lines represent sympathetic nerve fibers and green lines represent vagus nerve fibers. Inset: At the cellular level, sympathetic nervous system primarily releases norepinephrine, which stimulates the cardiac β-receptors. Parasympathetic nervous system primarily releases acetylcholine, stimulating cholinergic muscarinergic receptors on the myocytes and activating the α7nAChR pathway to reduce inflammation and fibrosis in the heart. SG, stellate ganglion; DRG, dorsal root ganglia; PVN, paraventricular nucleus; NTS, nucleus tractus solitaries; β1, β-adrenergic receptor; M2, muscarinic receptor; Gi, inhibitory G-protein; Gs, stimulatory G-protein; AC, adenylate cyclase; α7nAChR, α7 nicotinic acetyl-choline receptor.
与心律失常有关的自主神经系统由大脑、脊髓、心脏和肾脏中的神经元和神经组成，类似于调节靶器官功能的闭环回路。同时激活传入和传出迷走神经纤维可以增加心脏闭环的迷走神经张力，保护心脏。蓝线代表交感神经纤维，绿线代表迷走神经纤维。插图:在细胞水平上，交感神经系统主要释放去甲肾上腺素，刺激心脏β受体。副交感神经系统主要释放乙酰胆碱，刺激肌细胞上的胆碱能肌碱能受体，激活α7nAChR通路，减轻心脏炎症和纤维化。SG，星状神经节;DRG，背根神经节;PVN，室旁核;NTS，孤束核;β-肾上腺素能受体;M2，毒蕈碱受体;Gi，抑制性g蛋白;g:刺激g蛋白;AC，腺苷酸环化酶;α7烟碱乙酰胆碱受体

The cardiac sympathetic preganglionic fibers originate in the central nervous system primarily in the brainstem and are modulated by higher centers such as the subthalamic and periaqueductal grey as well as the rostral ventrolateral medulla ^9-12. Then, the sympathetic preganglionic fibers reach postganglionic neurons in the superior cervical, middle cervical, cervicothoracic (stellate) ganglia and mediastinal ganglia along the cervical and thoracic spinal cord (e.g. from C2 to T4 or T5) ^9-12. These postganglionic neurons project axons via multiple cardiopulmonary nerves to the atrial and ventricular myocardium as well as limited populations of intrinsic cardiac adrenergic neurons. The major post-ganglionic neurotransmitter of the sympathetic nervous system is norepinephrine. The most important mechanism underlying sympathetic-mediated arrhythmogenesis is the activation of the β-adrenergic receptors and stimulatory Gs proteins, which leads to stimulation of adenylyl cyclase followed by protein kinase A–mediated phosphorylation of the L-type calcium channels (increasing calcium influx) and ryanodine receptors ¹³. Phosphorylation of the latter enhances the opening probability of the ryanodine receptors and increases calcium release from the sarcoplasmic reticulum (SR). Excessive calcium influx and SR calcium release are known to be arrhythmogenic because calcium homeostasis is crucial in maintaining normal cardiomyocyte functions such as excitability and mitochondrial stability. Elevated intracellular calcium concentration can activate the sodium-calcium exchanger (NCX) to extrude intracellular calcium to the extracellular space. However, extruding one calcium ion occurs at the expense of importing 3 sodium ions, which is electrogenic and can lead to early or delayed after-depolarization ¹⁴. Therefore, disturbed calcium homeostasis has been implicated as a leading mechanism underling high sympathetic outflow induced ventricular tachyarrhythmias (VAs) such as catecholaminergic polymorphic VT, long QT syndrome and heart failure.
心脏交感神经节前纤维起源于主要位于脑干的中枢神经系统，并受诸如丘脑下和导水管周围灰质以及延髓吻侧腹外侧等高级中枢调节 ^{9 12} 。然后，交感神经节前纤维沿颈、胸脊髓(如从C2到T4或T5)到达颈上、颈中、颈胸(星状)神经节和纵隔神经节的神经节后神经元 ^{9 12} 。这些神经节后神经元通过多条心肺神经将轴突投射到心房和心室心肌以及有限数量的内在心脏肾上腺素能神经元。交感神经系统的主要神经节后神经递质是去甲肾上腺素。交感神经介导的心律失常最重要的机制是β-肾上腺素能受体和刺激性Gs蛋白的激活，这导致腺苷酸环化酶的刺激，随后是蛋白激酶a介导的l型钙通道磷酸化(增加钙内流)和ryanodine受体 ¹³ 。后者的磷酸化提高了ryanodine受体的打开概率，并增加了钙从肌浆网(SR)的释放。由于钙稳态对维持正常心肌细胞功能(如兴奋性和线粒体稳定性)至关重要，因此过量的钙流入和SR钙释放可引起心律失常。细胞内钙浓度升高可激活钠钙交换器(NCX)将细胞内钙挤压到细胞外空间。 然而，挤出1个钙离子是以输入3个钠离子为代价的，这是电致的，可导致去极化后提前或延迟 ¹⁴ 。因此，受干扰的钙稳态被认为是高交感神经流出引起的室性心动过速(VAs)的主要机制，如儿茶酚胺能多形性室性心动过速、长QT综合征和心力衰竭。

Preganglionic neurons of the parasympathetic nervous system are located in the nucleus ambiguous and dorsal motor nucleus of the medulla oblongata as well as scattered regions between these two structures ^15,16. Their axons project to the postganglionic parasympathetic neurons in the numerous intrinsic cardiac ganglia via bilateral vagosympathetic trunks and multiple intrathoracic cardiopulmonary nerves ¹⁷. Postganglionic neurons, concentrated in epicardial fat pads, then provide direct innervation to the sinus node, atrioventricular node as well as both atria and ventricles ^9,18,19. Acetylcholine is the major parasympathetic neurotransmitter of the heart; stimulation of the cholinergic muscarinic receptors (mainly the M2 receptors) inhibits adenylyl cyclase and reduces cyclic adenosine monophosphate via pertussis toxin-sensitive inhibitory G-proteins (Gi), which inhibits the L-type calcium current and hyperpolarization-activated current If as well as activates the Achgated potassium current (IKACh) ²⁰. Important co-transmitters released with vagus nerve stimulation include nitric oxide and vasoactive intestinal peptide ²¹.
副交感神经系统的节前神经元位于延髓的模糊核和背运动核以及这两个结构之间的分散区域 ^{15 16} 。它们的轴突通过双侧迷走交感干和多个胸内心肺神经投射到众多心内神经节的神经节后副交感神经元 ¹⁷ 。神经节后神经元，集中在心外膜脂肪垫，然后直接神经支配窦结、房室结以及心房和心室 ^{9 18 19} 。乙酰胆碱是心脏主要的副交感神经递质;刺激胆碱能毒蕈碱受体(主要是M2受体)通过百日咳毒素敏感抑制g蛋白(Gi)抑制腺苷酸环化酶，减少环磷酸腺苷，从而抑制l型钙电流和超极化激活电流If，激活乙酰化钾电流(IKACh) ²⁰ 。迷走神经刺激释放的重要共递质包括一氧化氮和血管活性肠肽 ²¹ 。

Sympathetic and parasympathetic nerves and neurons as well as interconnecting nerves and neurons form a complex cardiac neural network. These neural elements converge at several ganglionated plexi (GP) embedded within epicardial fat pads ^22,23. In the atria, the great majority of GP are concentrated at the pulmonary veinatrial junctions. In contrast, the ventricular GP are primarily located at the origins of major coronary arteries or aortic root ²⁴. These GP act as integration centers that modulate the interactions between the extrinsic cardiac ANS and the heart ²⁵ and contain both afferent and efferent sympathetic as well as parasympathetic nerves and neurons. For example, the bradycardic response elicited by cervical VNS was mediated by the anterior right GP adjacent to the sinus node; ablation of that GP greatly attenuated the bradycardic response ²⁵.
交感和副交感神经和神经元以及相互连接的神经和神经元形成了一个复杂的心脏神经网络。这些神经元件会聚在心外膜脂肪垫内的几个神经节丛(GP) ^{22 23} 。在心房，绝大多数GP集中在肺静脉心房连接处。相反，心室GP主要位于冠状动脉或主动脉根部 ²⁴ 。这些GP作为整合中心，调节外源性心脏ANS和心脏之间的相互作用 ²⁵ ，并包含传入和传出交感神经以及副交感神经和神经元。例如，颈VNS引起的心动过缓反应是由靠近窦房结的右前GP介导的;消融该GP极大地减弱了心动过缓反应 ²⁵ 。

Afferent nerve fibers from the mechanosensory and chemosensory receptors provide critical feedback from the cardiovascular system ²⁶. Trafficking from these nerve fibers are processed in the intrinsic cardiac ganglia, intrathoracic ganglia, dorsal root ganglia of the spinal cord, nodose ganglia (the inferior ganglia of the vagosympathetic trunk) and brainstem ²⁷. Afferent cardiac sympathetic neural trafficking is transmitted to the nucleus tractus solitaries (NTS) and the paraventricular nucleus (PVN) ^28-31. In addition to projections from the PVN to the neurohypophysis, anatomic and electrophysiological studies revealed that axons from the PVN also project directly to the autonomic centers in the medulla and spinal cord, indicating that the PVN is a key integrative center for the sympathetic neural trafficking in the brain and is involved in cardiovascular regulation ^32,33. Parasympathetic afferent fibers carry peripheral information to the NTS first; axons from the NTS project to the autonomic and cardiovascular centers in the brainstem as well to the hypothalamus and cerebrum. It is important to note that the afferent parasympathetic neural trafficking from peripheral organs back to the brain allows the brain to modulate the ANS and maintain autonomic homeostasis.
来自机械感觉和化学感觉受体的传入神经纤维提供来自心血管系统的关键反馈 ²⁶ 。这些神经纤维的运输在心脏固有神经节、胸内神经节、脊髓背根神经节、结节神经节(迷走交感干的下神经节)和脑干 ²⁷ 进行处理。传入心脏交感神经传递到孤束核(NTS)和室旁核(PVN) ^{28 31} 。除了从PVN投射到神经垂体外，解剖学和电生理学研究表明PVN的轴突也直接投射到髓质和脊髓的自主神经中枢，这表明PVN是大脑交感神经运输的关键整合中心，并参与心血管调节 ^{32 33} 。副交感神经传入纤维首先将外周信息传递到NTS;从NTS项目的轴突到脑干的自主神经和心血管中心，以及下丘脑和大脑。重要的是要注意，从外周器官传入的副交感神经运输回到大脑允许大脑调节ANS和维持自主神经稳态。

Simultaneous recordings of the canine left stellate ganglion (LSG) and left vagus nerve over several weeks revealed that coactivation of the sympathetic and parasympathetic nervous systems may precede paroxysmal AF Figure 2^34,35. That is, sympathetic and parasympathetic activity act synergistically to facilitate AF initiation^38,39. In isolated atrial myocytes, parasympathetic stimulation shortened the atrial effective refractory period (ERP), whereas sympathetic stimulation increases calcium influx and SR calcium release which activates NCX, depolarizes the myocytes and elicit and early after-depolarization ^36,37. Parasympathetic stimulation activates acetylcholine dependent potassium currents (IKACh), leading to shortening the atrial ERP and action potential duration (APD) ^20,40,41 as well as a reduction in the atrial reentrant wavelength (the product of ERP and conduction velocity) to increase the probability that multiple reentrant circuits coexist in the atrial myocardium and facilitate AF maintenance ⁴².
犬左星状神经节(LSG)和左迷走神经在数周内的同时记录显示，交感和副交感神经系统的共同激活可能先于阵发性心房颤动(图2 ^{34 35} )。也就是说，交感神经和副交感神经活动协同作用，促进心房颤动的发生 ^{38 39} 。在离体心房肌细胞中，副交感刺激可缩短心房有效不应期(ERP)，而交感刺激可增加钙内流和SR钙释放，从而激活NCX，使肌细胞去极化并引发去极化及去极化后早期 ^{36 37} 。副交感神经刺激激活乙酰胆碱依赖性钾电流(IKACh)，缩短心房ERP和动作电位持续时间(APD) ^{20 40 41} ，减少心房重入波(ERP和传导速度的产物)，增加心房心肌多个重入回路共存的可能性，促进房颤维持 ⁴² 。

Figure 2. Simultaneous recording of ECG, stellate ganglion nerve activity (SGNA), vagus nerve activity (VNA) and superior left GP nerve activity (SLGPNA) in ambulatory dogs.
图2。同时记录行走犬的心电图、星状神经节神经活动(SGNA)、迷走神经活动(VNA)和左上GP神经活动(SLGPNA)。

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A. Paroxysmal AF was preceded by nearly simultaneous activation of the SGNA, VNA and LSLGPNA.
A.阵发性房颤发生前，SGNA、VNA和LSLGPNA几乎同时激活。
B. LL-VNS immediately suppressed SGNA, demonstrating its anti-adrenergic effect. Reproduced with permission from reference ⁵⁰.
B. LL-VNS立即抑制SGNA，显示其抗肾上腺素能作用。转载请注明出处 ⁵⁰ 。

Direct VNS produces atrial ERP heterogeneity due to the heterogeneous distribution of vagal innervation and varying density of the M2 receptors in the atria ⁴³. In past decades, VNS, at the strength to slow the sinus rate or atrioventricular (AV) conduction, was used as an experimental tool to induce and maintain AF ^44,45. In contrast, mild activation of vagal tone through the baroreflex has been shown to suppress firing of pulmonary veins ⁴⁶. This paradox illustrates the complexity of the cardiac ANS and arrhythmogenicity. That is, VNS can either enhance or suppress AF, depending on the strength of stimulation ⁴⁷.
由于迷走神经支配的不均匀分布和心房M2受体的不同密度，直接VNS产生心房ERP的异质性 ⁴³ 。在过去的几十年里，VNS以减慢窦率或房室(AV)传导的强度被用作诱导和维持AF的实验工具 ^{44 45} 。相反，通过压力反射轻度激活迷走神经张力已被证明可以抑制肺静脉放电 ⁴⁶ 。这一悖论说明了心脏ANS和心律失常的复杂性。也就是说，视神经刺激可以增强或抑制房颤，这取决于刺激的强度 ⁴⁷ 。

The Oklahoma group first reported the antiarrhythmic effect of applying low-level VNS (LL-VNS) to canine cervical vagus nerve ⁴⁸. LL-VNS, without slowing the sinus rate or AV conduction, increased the ERP in the atrium and pulmonary veins, suppressed AF inducibility, and shortened the duration of acetylcholine-induced AF ^48,49. Since the atrial autonomic neural network is dominated by parasympathetic neural elements, inhibiting the GP by LLVNS leads to anti-cholinergic effects on GP and prolonged the ERP. Other mechanisms that LL-VNS suppresses AF have been proposed, including suppression of the LSG activity ⁵⁰, release of the neurotransmitter vasostatin-1 ⁵¹ and nitric oxide ⁵². Direct neural recordings of the canine atrial GPs showed that LL-VNS could inhibit the neural activity of GPs, thereby suppressing AF ⁴⁹. Studies on ambulatory dogs demonstrated that paroxysmal AF was often initiated by simultaneous or sequential firing of the stellate ganglion, vagus nerve and GP Figure 2. LL-VNS inhibited the LSG activity and sympathetic nerve density in the LSG, thereby suppressing paroxysmal atrial tachyarrhythmias ⁵³. These findings indicated that LL-VNS was both anticholinergic and antiadrenergic, which may account for its antiarrhythmic effects.
俄克拉何马研究小组首次报道了将低水平VNS (LL-VNS)应用于犬颈迷走神经 ⁴⁸ 的抗心律失常效果。l - vns在不减慢窦率和房室传导的情况下，增加心房和肺静脉ERP，抑制AF诱导，缩短乙酰胆碱诱导AF持续时间 ^{48 49} 。由于心房自主神经网络以副交感神经成分为主，LLVNS抑制GP可导致GP的抗胆碱能作用，延长ERP。已经提出了LL-VNS抑制AF的其他机制，包括抑制LSG活性 ⁵⁰ ，释放神经递质血管抑素-1 ⁵¹ 和一氧化氮 ⁵² 。犬心房GPs的直接神经记录显示，LL-VNS可抑制心房GPs的神经活动，从而抑制AF ⁴⁹ 。对活动犬的研究表明，阵发性房颤通常由星状神经节、迷走神经和GP同时或连续放电引起(图2)。LL-VNS抑制LSG活动和LSG交感神经密度，从而抑制阵发性房性心动过速 ⁵³ 。这些发现表明，LL-VNS具有抗胆碱能和抗肾上腺素能的双重作用，这可能解释了其抗心律失常的作用。

High sympathetic outflow enhances inflammation; inflammation leads to fibrosis through activation of pro-inflammatory cells (e.g. T-lymphocytes, monocytes/macrophages) and the cytokines they release. Inflammation, therefore, plays an important role in the pathogenesis of AF as well as neural, electrical and structural remodeling ⁵⁴. Since the discovery of the α7 nicotinic acetylcholine receptor (α-7nAChR)-mediated cholinergic anti-inflammatory pathway, the anti-inflammatory effects of the parasympathetic nervous system on cardiovascular diseases have attracted substantial attention ⁵⁵. Some studies suggested that activation of α7nAChR significantly reduces inflammation and fibrosis in the heart, in which the expression levels of high-mobility group box 1 (HMGB1), chemokine receptors and pro-inflammatory factors such as interleukin-6 and TNF-∝ were decreased⁵⁶. In an ischemia/reperfusion model, VNS increased STAT3 phosphorylation and inhibited NF-kB activation. The cholinergic anti-inflammatory pathway was involved in these effects ⁵⁷.
高交感神经流出增强炎症;炎症通过激活促炎细胞(如t淋巴细胞、单核细胞/巨噬细胞)及其释放的细胞因子导致纤维化。因此，炎症在房颤的发病机制以及神经、电和结构重塑中起着重要作用 ⁵⁴ 。自α7烟碱乙酰胆碱受体(α-7nAChR)介导的胆碱能抗炎途径被发现以来，副交感神经系统在心血管疾病中的抗炎作用备受关注 ⁵⁵ 。有研究表明α7nAChR的激活可显著降低心脏炎症和纤维化，其中高迁移率组盒1 (HMGB1)、趋化因子受体及促炎因子如白细胞介素-6、TNF-∝的表达水平降低 ⁵⁶ 。在缺血/再灌注模型中，VNS增加STAT3磷酸化，抑制NF-kB活化。胆碱能抗炎途径参与了这些作用 ⁵⁷ 。

Pre-clinical evidence indicates that LL-VNS is anti-arrhythmic and anti-inflammatory. Because of the invasive nature of cervical LLVNS, it has only been tested acutely in post-operative AF in patients undergoing open heart surgery. The incidence of postoperative AF was reduced by 66% by LL-VNS (20 Hz) for 72 hours after cardiac surgery ⁵⁸.
临床前证据表明，LL-VNS具有抗心律失常和抗炎作用。由于颈部LLVNS的侵袭性，它只在接受心脏直视手术的患者的术后房颤中进行了急性试验。在心脏手术后72小时，使用20 Hz的低剂量vns治疗可使术后房颤发生率降低66% ⁵⁸ 。

A major drawback of cervical LL-VNS is its invasiveness, requiring surgical implantation of a neurostimulator and a cuff electrode around the cervical vagus nerve. Adverse effects include infection, Horner syndrome, discomfort and pain at implant site ^59-62. These adverse effects led to the investigation of transcutaneous LL-VNS. Tragus, a small pointed eminence of the external ear, is innervated by the auricular branch of the vagus nerve. The tragus is easily accessible to transcutaneous LL-VNS. Prior research using horseradish peroxidase to trace the cranial projection of the auricular branch of the vagus nerve found that the vagal afferent nerve fibers of the auricular branch terminate mainly in the NTS ⁶³. It is important to note that VNS through the tragus only activates the afferent vagal neural trafficking because there is no efferent vagus nerves in the tragus that innervates the heart.
颈椎LL-VNS的一个主要缺点是其侵入性，需要在颈迷走神经周围植入神经刺激器和袖带电极。不良反应包括感染、霍纳综合征、种植体部位不适和疼痛 ^{59 62} 。这些不良反应导致了经皮LL-VNS的研究。耳屏是外耳的一个小而尖的突起，受迷走神经耳支支配。耳屏易于经皮LL-VNS到达。前期研究利用辣根过氧化物酶追踪迷走神经耳支的颅投影，发现耳支的迷走传入神经纤维主要终止于NTS ⁶³ 。值得注意的是，通过耳屏的VNS只激活传入迷走神经运输，因为在耳屏中没有支配心脏的传出迷走神经。

Preclinical studies showed that low-level tragus stimulation (LLTS), at the strength not slowing the sinus rate or AV conduction, exerted similar electrophysiological effects to cervical LL-VNS in terms of lengthening the ERP, suppressing pulmonary vein firing and AF as well as inhibiting the neural activity of major atrial GPs Figure 3^64,65. Notably, the anti-arrhythmic effects of LL-TS were still profound at the stimulation strength 80% below the threshold that slowed the sinus rate or AV conduction, suggesting that this level of stimulation might be tolerable in ambulatory patients with arrhythmias.
临床前研究表明，在不减慢窦率或房室传导的强度下，低水平耳屏刺激(LLTS)在延长ERP，抑制肺静脉放电和房颤以及抑制主要心房gp的神经活动方面具有与颈椎低水平耳屏刺激相似的电生理效果(图3 ^{64 65} )。值得注意的是，当刺激强度低于减慢窦率或房室传导阈值的80%时，LL-TS的抗心律失常作用仍然很明显，这表明这种水平的刺激对动态心律失常患者可能是可耐受的。

Figure 3. Effects of transcutaneous low-level vagus nerve stimulation on effective refractory period of atria, pulmonary veins and on neural activity of ganglionated plexi.
图3。经皮低水平迷走神经刺激对心房、肺静脉有效不应期及神经节丛神经活动的影响。

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A. Parameters were measured during 6 hours of rapid atrial pacing (RAP) simulating paroxysmal AF. In the last 3 hours, LL-TS, 80% below threshold, was applied with RAP. At all sites, mean ERP decreased significantly after 3 hours of RAP (*:p<0.05; **:p<0.01; compared to baseline). After 3 hours of RAP+LL-TS, mean ERP at all sites showed a significant reversal toward baseline values (#:p<0.05 , ##:p<0.01; compared with the end of 3rd hour of RAP). Increased ERP dispersion by RAP was also reversed by LL-TS.
A.在模拟阵发性房颤的快速心房起搏(RAP) 6小时内测量参数。最后3小时，在低于阈值80%的情况下，应用RAP进行LL-TS。在所有地点，平均ERP在RAP 3小时后显著下降(*:p<0.05;* *: p < 0.01;与基线相比)。RAP+LL-TS治疗3小时后，所有部位的平均ERP与基线值有显著的逆转(#:p<0.05， ##:p<0.01;与RAP第3小时结束时比较)。RAP增加的ERP分散也被LL-TS逆转。
B. Top. A typical example of neural recordings from the anterior right ganglionated plexi (ARGP) taken each hour (during sinus rhythm) when RAP was temporarily stopped. The middle and bottom panels showed the average amplitude and frequency of neural recordings. During the first 3 hours of RAP, there was a progressive increase in both the amplitude as well as the frequency of neural firing in the ARGP. With the addition of LL-TS, at 80% below threshold, the amplitude and frequency returned toward initial levels. RSPV, LSPV, RIPV and LIPV: right superior, left superior, right inferior and left inferior pulmonary vein, respectively. Reproduced from reference 65 with permission.
b。当RAP暂时停止时，每小时(窦性心律期间)从右前神经节丛(ARGP)采集的典型神经记录。中间和底部显示神经记录的平均振幅和频率。在RAP的前3小时，ARGP区神经放电的幅度和频率均呈进行性增加。随着LL-TS的加入，在低于阈值80%时，振幅和频率恢复到初始水平。RSPV、LSPV、RIPV、LIPV分别为右上肺静脉、左上肺静脉、右下肺静脉、左下肺静脉。经许可转载自文献65。

Electrical stimulation of the tragus was tested in 48 healthy participants showing that tragus VNS significantly decreased the low-frequency/high-frequency ratio (LF/HF) measurement of heart rate variability, indicating a tendency toward parasympathetic tone ⁶⁶. In 2015, the Oklahoma group ⁶⁷ reported a randomized clinical study applying transcutaneous LL-TS to patients with refractory paroxysmal AF referred for catheter ablation. Only one hour of transcutaneous LL-TS was enough to suppress ERP shortening and AF inducibility, shorten the AF duration, and decrease proinflammatory markers such as tumor necrosis factor-∝ (TNF-∝) and C-reactive protein. A recent sham-controlled randomized clinical trial published by same group indicated that in ambulatory patients with paroxysmal AF, daily transcutaneous LL-TS (one hour, 20 Hz, 1 mA below the perception threshold) reduced the AF burden by 83% at 6 months Figure 4. Plasma level of the TNF-∝ was reduced by 23% as well. These results suggest that transcutaneous LL-TS may serve as a novel, non-invasive therapy for patients in early stage of AF ⁶⁸. However, as a major limitation of transcutaneous LL-TS, the response to transcutaneous LL-TS was variable among individual patients due to the lack of an acute biomarker of response to therapy that can predict the response to chronic transcutaneous LL-TS therapy Figure 4B. Although transcutaneous LL-TS has been shown to be able to affect heart rate variability and inflammatory markers within an hour ⁶⁷, if these biomarkers predict long-term success remains unknown. Future large scale randomized clinical trials will be needed to optimize patient selection for transcutaneous LL-TS based on biomarkers as well as to determine if patients with more advanced stage of AF (e.g. persistent AF) still respond to transcutaneous LL-TS.
在48名健康参与者中进行的耳屏电刺激测试显示，耳屏VNS显著降低心率变异性的低频/高频比(LF/HF)测量，表明副交感神经张力倾向 ⁶⁶ 。2015年，俄克拉何马州研究小组 ⁶⁷ 报道了一项随机临床研究，将经皮LL-TS应用于难治性阵发性房颤患者的导管消融。经皮LL-TS仅1小时就足以抑制ERP缩短和AF诱导，缩短AF持续时间，降低促炎标志物如肿瘤坏死因子-∝(TNF-∝)和c反应蛋白。同一组最近发表的一项假对照随机临床试验表明，在患有阵发性房颤的门诊患者中，每日经皮LL-TS(1小时，20 Hz，低于感知阈值1 mA)在6个月时减少了83%的房颤负担(图4)。血浆TNF-∝水平降低23%。这些结果表明，经皮LL-TS可能是早期AF患者的一种新颖的非侵入性治疗 ⁶⁸ 。然而，作为经皮LL-TS的主要限制，由于缺乏一种可以预测慢性经皮LL-TS治疗反应的急性生物标志物，个体患者对经皮LL-TS的反应是可变的(图4B)。虽然经皮LL-TS已被证明能够在一小时内影响心率变异性和炎症标志物 ⁶⁷ ，但这些生物标志物是否能预测长期成功仍不得而知。未来需要进行大规模随机临床试验，以优化基于生物标志物的经皮LL-TS患者选择，并确定晚期房颤患者(如: 持续性房颤)仍对经皮LL-TS有反应。

Figure 4. Effects of chronic transcutaneous low-level vagus nerve stimulation in atrial fibrillation burden.
图4。慢性经皮低水平迷走神经刺激对房颤负荷的影响。

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A. Comparison of AF burden between the 2 groups (median values and interquartile range). The p-value is based on a comparison of median AF burden levels at the 6-month time point after adjusting for baseline measures. In the control group, stimulation was delivered to the ear lobule where no vagal innervation exits. B. Patient-level data on AF burden change in the 2 groups. Patients whose AF burden decreased by >75% at follow up were categorized as responders. The proportion of responders was significantly larger in the active compared to the sham control group (47% vs. 5%, respectively, p=0.003). B = baseline; 3M = 3 months; 6M = 6 months. Reproduced from reference 68 with permission.
A.两组间房颤负担比较(中位数和四分位数范围)。p值基于基线测量调整后6个月时间点房颤中位负担水平的比较。在对照组中，刺激被传递到没有迷走神经支配的耳小叶。B.两组房颤负担变化的患者水平数据。随访时房颤负担减轻>75%的患者被归类为应答者。治疗组应答者的比例明显大于假对照组(47% vs. 5%， p=0.003)。B =基线;3M = 3个月;6个月。经许可转载自参考文献68。

VAs are often triggered by high sympathetic tone or reduced vagal tone ⁶⁹. Sympathetic activation can facilitate the initiation of VAs through the following mechanisms: 1) shortening of the ventricular ERP ⁷⁰ and increasing the steepness of the slope of the action potential duration restitution curve to facilitate ventricular fibrillation initiation ⁷¹; 2) increasing dispersion of refractoriness ⁷²; 3) enhancing of ventricular repolarization heterogeneity ⁷³; and 4) triggering of early and delayed after-depolarization Figure 5) ¹⁴, ⁷⁴, ⁷⁵,. Furthermore, underlying cardiomyopathy can enhance the sympathetic activity and further promote the occurrence of VAs, forming a vicious cycle between the sympathetic activity and VAs. For instance, in a canine model of myocardial infarction, LSG synapses and nerve density were increased due to ischemia, which in turn caused more instability in the electrophysiological properties and increase the propensity for VAs ⁷⁶.
VAs通常由高交感神经张力或迷走神经张力降低 ⁶⁹ 触发。交感神经激活可通过以下机制促进VAs的起始:1)缩短心室ERP ⁷⁰ ，增加动作电位时程恢复曲线斜率的陡度，促进心室颤动起始 ⁷¹ ;2)增加耐火度分散度 ⁷² ;3)心室复极异质性增强 ⁷³ ;图5) ¹⁴ ， ⁷⁴ ， ⁷⁵ ，。此外，潜在的心肌病可增强交感神经活动，进一步促进VAs的发生，形成交感神经活动与VAs的恶性循环。例如，在犬心肌梗死模型中，由于缺血，LSG突触和神经密度增加，从而导致电生理特性更加不稳定，并增加VAs倾向 ⁷⁶ 。

Figure 5. Arrhythmogenesis related to high sympathetic outflow.
图5。与高交感神经流出有关的心律失常。

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Both early afterdepolarization (EAD), A) and delayed afterdepolarization (DAD, B) can be elicited by the inward current generated by sodium-calcium exchanger (NCX). Reentry can be facilitated by shortened refractory period or action potential duration (C) as well as increased dispersion of the refractory period (D). Reproduced with permission from reference ¹⁴.
钠钙交换器(NCX)产生的向内电流可以诱发早期后去极化(EAD, A)和延迟后去极化(DAD, B)。通过缩短不应期或动作电位持续时间(C)以及增加不应期弥散(D)，可促进再入。转载经参考文献 ¹⁴ 许可。

The beneficial effects of VNS on VAs are mediated directly by reducing the sympathetic activity and indirectly by inhibiting myocardial remodeling and inflammation ^61-62,77. Activation of the IKACh current through the muscarinic receptors and augmentation of neuronal nitric oxide production also contributes to the beneficial effects of VNS ^78-81. In addition, inflammatory pathways have an important role in fibrosis ⁸², scar formation and hypertrophy ⁸³; inflammatory mediators such as interleukin-1 can be directly arrhythmogenic ⁸⁴. In a rat model of ischemia/reperfusion, VNS reduced the infarct size, inflammatory cell infiltration and the levels of circulating inflammatory cytokines ⁸⁵. Chronic VNS in a dog model of heart failure also normalized the levels of interleukin-6 and TNF-∝⁸⁶and reduced plasma levels of angiotensin-II ⁸⁷, a potent profibrotic mediator. Moreover, chronic VNS preserved the connexin 43 proteins and reduced the prevalence of spontaneous ventricular tachycardia after myocardial infarction ⁸⁸.
VNS对VAs的有益作用直接通过降低交感神经活动介导，间接通过抑制心肌重构和炎症 ^{61 62 77} 介导。通过毒蕈碱受体激活IKACh电流和增加神经元一氧化氮的产生也有助于VNS的有益作用 ^{78 81} 。此外，炎症通路在纤维化 ⁸² 、瘢痕形成和肥厚 ⁸³ 中起重要作用;炎症介质如白细胞介素-1可直接引起心律失常 ⁸⁴ 。在大鼠缺血/再灌注模型中，VNS降低了梗死面积、炎症细胞浸润和循环炎症细胞因子水平 ⁸⁵ 。在心力衰竭狗模型中，慢性VNS也使白细胞介素-6和TNF-∝ ⁸⁶ 水平正常化，并降低血浆血管紧张素- ii ⁸⁷ 水平，这是一种有效的促纤维化介质。此外，慢性VNS保留了连接蛋白43蛋白，降低了心肌梗死后自发性室性心动过速的发生率 ⁸⁸ 。

At present, clinical management of ventricular tachycardia/ ventricular fibrillation is often restricted to pharmacological therapy and catheter ablation. Lately, invasive procedures such as thoracic epidural anesthesia (TEA), stellate ganglion blockade and cardiac sympathetic denervation (CSD), aiming at decreasing sympathetic outflow to the heart, have been shown to reduce the incidence of VTs in various conditions ^89,91. The use of TEA is limited by antiplatelet or anticoagulation therapy due to concerns about bleeding. The effect of stellate ganglion blockade as well as left CSD or bilateral CSD often depends on the operator; collateral damage to sympathetic innervation to the head, neck, and eyes can cause significant adverse effects ^91-94.
目前，室性心动过速/室颤的临床治疗往往局限于药物治疗和导管消融。最近，侵入性手术，如胸椎硬膜外麻醉(TEA)、星状神经节阻滞和心脏交感神经去支配(CSD)，旨在减少交感神经向心脏的流出，已被证明可以减少各种情况下VTs的发生率 ^{89 91} 。由于担心出血，TEA的使用受到抗血小板或抗凝治疗的限制。星状神经节阻滞以及左侧或双侧CSD的效果往往取决于操作者;对头部、颈部和眼睛的交感神经的附带损害可引起严重的不良反应 ^{91 94} 。

Increased sympathetic tone is typical in patients with myocardial infarction or heart failure and is an important contributing factor to VAs. Preclinical studies demonstrated that VNS can increase ventricular electrical stability and protect against VAs during acute ischemia and reperfusion in animal models ^95-99. Vanoli et al ¹⁰⁰ showed that VNS effectively prevents ventricular fibrillation in conscious animals with myocardial infarction. During the repeated exercise stress tests, VNS decreased the incidence of ventricular fibrillation from 92% to 10%. Furthermore, VNS may stabilize the infarct border zones and reduce the incidence of VAs ¹⁰¹. Chen et al ¹⁰² found that LL-VNS with a stimulation voltage below the 80% voltage threshold required to slow the heart rate significantly decreased the incidence of VAs and exerts protective effects on myocardial ischemia/reperfusion injury, presumably by preserving the acetylcholine levels and intact parasympathetic neuronal pathways. At present, several clinical trials of VNS for the treatment of advanced heart failure have yielded conflicting results, probably caused by the combination of heterogeneous study population and lack of the knowledge of the optimal stimulation parameters ^47,61,62.
交感神经张力增加是心肌梗死或心力衰竭患者的典型特征，是影响VAs的重要因素。临床前研究表明，VNS在动物模型急性缺血再灌注时可增加心室电稳定性，并对VAs有保护作用 ^{95 99} 。Vanoli等 ¹⁰⁰ 研究表明VNS可有效预防有意识的心梗动物心室颤动。在重复运动应激试验中，VNS将心室颤动的发生率从92%降低到10%。此外，VNS可以稳定梗死边界区，减少VAs的发生率 ¹⁰¹ 。Chen等 ¹⁰² 发现，刺激电压低于减慢心率所需的80%电压阈值的LL-VNS显著降低了VAs的发生率，并对心肌缺血/再灌注损伤具有保护作用，可能是通过保持乙酰胆碱水平和完整的副交感神经通路。目前，几项VNS治疗晚期心力衰竭的临床试验得出了相互矛盾的结果，这可能是由于研究人群异质性的结合以及缺乏对最佳刺激参数的了解 ^{47 61 62} 。

Due to the invasiveness of cervical LL-VNS, transcutaneous LLVNS has been investigated as a novel noninvasive method to treat VTs. Yu et al ¹⁰³ found that in a canine post-myocardial infarction model, chronic transcutaneous LL-VNS (2h/day) for 2 months reduced inducibility of VTs, LSG neuronal activity, left ventricular remodeling and ANS remodeling at the infarct border zone. Recently, this group provided the first clinical evidence that when transcutaneous LL-VNS, 50% below the threshold slowing the sinus rate or AV conduction, was delivered at the time of ST elevation myocardial infarction, transcutaneous LL-VNS reduced the infarct size, myocardial ischemia/reperfusion related ventricular premature contraction and ventricular tachycardia as well as pro-inflammatory markers such as interleukin-1β, interleukin-6 and TNF-∝ in patients presenting with ST-segment elevation myocardial infarction undergoing percutaneous coronary intervention 104. This first-inman trial suggests that transcutaneous LL-VNS may be applied to patients in early stage of myocardial infarction to reduce myocardial injury and VAs.
由于颈椎LL-VNS的侵袭性，经皮LL-VNS作为一种新的无创治疗方法被研究。Yu等 ¹⁰³ 研究发现，在犬心肌梗死后模型中，连续2个月慢性经皮LL-VNS(每天2小时)可降低梗死边界区VTs诱导、LSG神经元活性、左室重构和ANS重构。最近，该研究小组首次提供了临床证据，证明在ST段抬高型心肌梗死时，在低于阈值50%的情况下，经皮LL-VNS可降低梗死面积、心肌缺血/再灌注相关室性早搏和室性心动过速，以及促炎标志物如白细胞介素-1β、经皮冠状动脉介入治疗st段抬高型心肌梗死患者的白细胞介素-6和TNF-∝[j]。这项首次临床试验提示经皮LL-VNS可用于早期心肌梗死患者，以减少心肌损伤和VAs。

While preclinical cervical VNS showed promising results in suppressing VAs, long-term beneficial outcomes have not been verified in clinical trials ^61,62. For its noninvasiveness, transcutaneous LL-VNS is an attractive alternative to cervical VNS to treat VAs related to high sympathetic outflow such as ventricular tachycardia in patients with structural heart diseases and premature ventricular contraction. Future preclinical and clinical studies should focus on identifying the optimal stimulation parameters (e.g. frequency, pulse width, duty cycles) as well as acute biomarkers that can predict longterm efficacy.
虽然临床前颈椎VNS在抑制VAs方面显示出有希望的结果，但长期有益的结果尚未在临床试验中得到证实 ^{61 62} 。由于其无创性，经皮l -VNS是一种有吸引力的替代颈式VNS治疗与高交感血流相关的VAs，如结构性心脏病和室性早搏。未来的临床前和临床研究应侧重于确定最佳刺激参数(如频率、脉宽、占空比)以及可以预测长期疗效的急性生物标志物。