Effects of spinal cord stimulation in angina pectoris induced by pacing and possible mechanisms of action

Cardiovascular Effects of Spinal Cord Stimulation: The Highs, the Lows, and the Don't Knows

BACKGROUND AND OBJECTIVES

There are many potential etiologies of impaired cardiovascular control, from chronic stress to neurodegenerative conditions or central nervous system lesions. Since 1959, spinal cord stimulation (SCS) has been reported to modulate blood pressure (BP), heart rate (HR), and HR variability (HRV), yet the specific stimulation sites and parameters to induce a targeted cardiovascular (CV) change for mitigating abnormal hemodynamics remain unclear. To investigate the ability and parameters of SCS to modulate the CV, we reviewed clinical studies using SCS with reported HR, BP, or HRV findings.

MATERIALS AND METHODS

A keyword-based electronic search was conducted through MEDLINE, Embase, and PubMed data bases, last searched on February 3, 2023. Inclusion criteria were studies with human participants receiving SCS with comparison with SCS turned off, with reporting of either HR, HRV, or BP findings. Non-English studies, conference abstracts, and studies not reporting standalone effects of SCS when comparing SCS with non-SCS interventions were excluded. Results were plotted for visual analysis. When available, participant-specific stimulation parameters and effects were extracted and quantitatively analyzed using ordinary least squares regression.

RESULTS

A total of 59 studies were included in this review; 51 studies delivered SCS invasively through implanted/percutaneous leads. Eight studies used noninvasive, transcutaneous electrodes. We found numerous reports of cervical, high thoracic, and mid-to-low thoracolumbar SCS increasing resting BP, and cervical/mid-to-low thoracolumbar SCS decreasing BP. The effect of SCS location on HR and HRV was equivocal. We were unable to analyze stimulation parameters owing to inadequate parameter reporting in many publications.

CONCLUSIONS

Our findings suggest CV neuromodulation, particularly BP modulation, with SCS to be a promising frontier. Further research with larger randomized controlled trials and detailed reporting of SCS parameters will be necessary for appropriate evaluation of SCS as a CV therapy.

Spinal Cord Stimulation Attenuates Neural Remodeling, Inflammation, and Fibrosis After Myocardial Infarction

OBJECTIVES

Spinal cord stimulation (SCS) is an established neuromodulation method that regulates the cardiac autonomic system. However, the biological mechanisms of the therapeutic effects of SCS after myocardial infarction (MI) remain unclear.

MATERIALS AND METHODS

Twenty-five rabbits were divided into five groups: SCS-MI (voltage: 0.5 v; pulse width: 0.2 ms; 50 Hz; ten minutes on and 30 minutes off; two weeks; n = 5), MI (n = 5), sham SCS-MI (voltage: 0 v; two weeks; n = 5), sham MI (n = 5), and blank control (n = 5) groups. MI was induced by permanent left anterior descending artery ligation. SCS-MI and sham SCS-MI rabbits received the corresponding interventions 24 hours after MI. Autonomic remodeling was evaluated using enzyme-linked immunosorbent assay and immunohistochemistry. Inflammation and myocardial fibrosis were assessed using immunohistochemistry, quantitative polymerase chain reaction, hematoxylin and eosin staining, Masson staining, and Western blot.

RESULTS

SCS improved the abnormal systemic autonomic activity. Cardiac norepinephrine decreased after MI (p < 0.01) and did not improve with SCS. Cardiac acetylcholine increased with SCS compared with the MI group (p < 0.05). However, no difference was observed between the MI and blank control groups. Growth-associated protein 43 (p < 0.001) and tyrosine hydroxylase (p < 0.001) increased whereas choline acetyltransferase (p < 0.05) decreased in the MI group compared with the blank control group. These changes were attenuated with SCS. SCS inhibited inflammation, decreased the ratio of phosphorylated-Erk to Erk (p < 0.001), and increased the ratio of phosphorylated-STAT3 to STAT3 (p < 0.001) compared with the MI group. Myocardial fibrosis was also attenuated by SCS.

CONCLUSIONS

SCS improved abnormal autonomic activity after MI, leading to reduced inflammation, reactivation of STAT3, and inhibition of Erk. Additionally, SCS attenuated myocardial fibrosis. Our results warrant future studies of biological mechanisms of the therapeutic effects of SCS after MI.

Neuromodulation in patients with refractory angina pectoris: a review

The number of patients with coronary artery disease (CAD) who have persisting angina pectoris despite optimal medical treatment known as refractory angina pectoris (RAP) is growing. Current estimates indicate that 5-10% of patients with stable CAD have RAP. In absolute numbers, there are 50 000-100 000 new cases of RAP each year in the USA and 30 000-50 000 new cases each year in Europe. The term RAP was formulated in 2002. RAP is defined as a chronic disease (more than 3 months) characterized by diffuse CAD in the presence of proven ischaemia which is not amendable to a combination of medical therapy, angioplasty, or coronary bypass surgery. There are currently few treatment options for patients with RAP. One such last-resort treatment option is spinal cord stimulation (SCS) with a Class of recommendation IIB, level of evidence B in the 2019 European Society of Cardiology guidelines for the diagnosis and management of chronic coronary syndromes. The aim of this review is to give an overview of neuromodulation as treatment modality for patients with RAP. A comprehensive overview is given on the history, proposed mechanism of action, safety, efficacy, and current use of SCS.

Pseudoanginal chest pain associated with vagal nerve stimulation: a case report

Background

Vagal nerve stimulation (VNS) can be an effective therapy for patients with epilepsy refractory to anti-epileptic drugs or intracranial surgery. While generally well tolerated, it has been associated with laryngospasm, hoarseness, coughing, dyspnea, throat and atypical chest pain, cardiac symptoms such as bradycardia and occasionally asystole. We report on a patient receiving vagal nerve stimulation who experienced severe typical anginal chest pain during VNS firing without any evidence of cardiac ischemia or dysfunction. Thus, the pain appeared to be neuropathic from the stimulation itself rather than nociceptive secondary to an effect on heart function.

Case presentation

A 29-year-old man, with a history of intractable frontal lobe epilepsy refractory to seven anti-epileptic medications and subsequent intracranial surgery, underwent VNS implantation without complications. On beginning stimulation, he began to have intermittent chest pain that corresponded temporally to his intermittent VNS firing. The description of his pain was pathognomonic of ischemic cardiac chest pain. On initial evaluation, he displayed Levine’s sign and reported crushing substernal chest pain radiating to the left arm, as well as shortness of breath walking upstairs that improved with rest. He underwent an extensive cardiac workup, including 12-lead ECG, cardiac stress test, echocardiogram, 12-day ambulatory cardiac monitoring, and continuous ECG monitoring each with and without stimulation of his device. The workup was consistently negative. Inability to resolve the pain necessitated the disabling and eventual removal of the device.

Conclusion

To our knowledge, this is the first report of pseudoanginal chest pain associated with VNS. This occurrence prompted our review of the mechanisms of cardiac chest pain and suggests that vagal afferents may convey anginal pain separately or in parallel with known spinal cord pain mechanisms. These insights into the physiology of chest pain may be of general interest and important to surgeons implanting VNS devices who may potentially encounter such symptoms.

The Effects of Spinal Cord Stimulators on End Organ Perfusion: A Literature Review

Spinal cord stimulators (SCS) have been gaining momentum in the last decade as their role in the management of chronic pain has become more apparent. Our intention was to search, analyze and highlight the effects of spinal cord stimulators on end-organ perfusion. We also looked at vascular diseases of atherosclerotic and nonatherosclerotic nature by examining objective evidence of improved circulation, pain control, limb salvage, and quality of life. We paid specific attention to disease processes such as cerebral hypoperfusion, Chronic-Critical Limb Ischemia, Intractable Angina Pectoris (IAP), Raynaud's syndrome and Thromboangiitis Obliterans. We performed a Medline database search for medical literature relevant to Spinal cord stimulators encompassing the years 1950 to 2019. Search terms included "Spinal cord stimulator," plus one of the following search terms: vasculopathy, stroke, cerebral blood flow, angina pectoris, diabetic ulcers, chronic critical leg ischemia, thromboangiitis obliterans and peripheral vascular disease. We included both clinical and experimental human studies that investigated the effect of SCS's on end-organ perfusion. We also investigated the pathophysiological mechanism of action of SCS's on the vasculature. We found 497 articles of which 43 more relevant and impactful articles investigating the hemodynamic effects of SCS and its possible mechanism were selected. Animal studies were excluded from the literature review as they provided heterogeneity. In addition to reporting literature supporting the use of stimulators for currently FDA approved uses, we also actively looked for potential future uses. Spinal Cord stimulators showed improvement in cerebral blood flow, increased capillary recruitment, and better quality of life in many studies. Patients also had increased exercise capacity and a significant reduction in the use of narcotic drug use and daily anginal attacks in patients suffering from IAP.

Spinal Cord Stimulation

Spinal cord stimulation (SCS) has been well established as a safe and effective treatment of pain derived from a wide variety of etiologies. Careful patient selection including a rigorous trial period and psychological evaluation are essential. When patients proceed to permanent implantation, various considerations should be made, such as the type of lead, type of anesthesia, and waveform patterns for SCS. This article discusses the common indications for SCS, patient selection criteria, and pertinent outcomes from randomized clinical trials related to common indications treated with SCS. Technical considerations, such as type of implant, anesthesia, and programming, are also discussed.

Treatment of Inoperable Coronary Disease and Refractory Angina: Spinal Stimulators, Epidurals, Gene Therapy, Transmyocardial Laser, and Counterpulsation

Intractable angina from refractory coronary disease is a severe form of myocardial ischemia for which revascularization provides no prognostic benefit. Inoperable coronary disease is also accompanied by a “vicious cycle” of myocardial dystrophy from a chronic alteration of the cardiac sympathetic tone and sensitization of damaged cardiac tissues. Several adjunctive treatments have demonstrated efficacy when revascularization is either unsuccessful or contraindicated. Spinal cord stimulation modifies the neurologic input and output of the heart by delivering a very low dose of electrical current to the dorsal columns of the high thoracic spinal cord. Neural fibers then release CGRP and other endogenous peptides to the coronary circulation reducing myocardial oxygen demand and enhancing vasodilation of collaterals to improve the myocardial blood flow of the most diseased regions of the heart. Randomized study has shown the survival data at five years is comparable to bypass for high-risk patients. Transmyocardial laser revascularization creates small channels into ischemic myocardium in an effort to enhance flow though studies have shown no improvement in prognosis over medical therapy alone. Enhanced external counterpulsation uses noninvasive pneumatic compression of the legs to improve diastolic filling of the coronary vessels and promote development of collateral flow. The compressor regimen requires thirty-five hours of therapy over a seven-week treatment period. Therapeutic angiogenesis requires injection of cytokines to promote neovascularization and improve myocardial perfusion into the regions affected by chronic ischemia. Phase 3 trials are pending. High thoracic epidural blockade produces a rapid and potent sympatholysis, coronary vasodilation and reduced myocardial oxygen demand in refractory coronary disease. This technique can be used as an adjunct to bypass surgery or medical therapy in chronic or acute unstable angina. Epidurals are easy to perform and often available for outpatient or inpatient use. The rapid anti-ischemic effect may complement therapeutic angiogenesis or other interventions with delayed onset to clinical benefit. A new era for interventional and implant cardiology is beginning to emerge as more clinicians, including cardiologists, gradually learn new procedures to safely provide more therapeutic options for patients suffering refractory angina.

The nervous heart

Many cardiac electrophysiological abnormalities are accompanied by autonomic nervous system dysfunction. Here, we review mechanisms by which the cardiac nervous system controls normal and abnormal excitability and may contribute to atrial and ventricular tachyarrhythmias. Moreover, we explore the potential antiarrhythmic and/or arrhythmogenic effects of modulating the autonomic nervous system by several strategies, including ganglionated plexi ablation, vagal and spinal cord stimulations, and renal sympathetic denervation as therapies for atrial and ventricular arrhythmias.

Neural mechanisms of spinal cord stimulation

Neuromodulation, specifically spinal cord stimulation (SCS), relieves pain and improves organ function. This chapter discusses the limited information presently available about the underlying mechanisms that explain the beneficial effects of treating patients with SCS. Where applicable, information is presented about translational research that illustrates the importance of collaboration between clinicians, basic scientists, and engineers. This chapter presents the infant stage of studies that attempt to explain the mechanisms which come into play for treating neuropathic pain, ischemic pain in peripheral vascular disease, and diseases of the visceral organs, specifically the gastrointestinal tract and the heart. The basic science studies will demonstrate how SCS acts on various pain syndromes and diseases via multiple pathways in the central nervous system as well as in somatic structures and visceral organs.

Dorsal column stimulator applications

Background:

Spinal cord stimulation (SCS) has been used to treat neuropathic pain since 1967. Following that, technological progress, among other advances, helped SCS become an effective tool to reduce pain.

Methods:

This article is a non-systematic review of the mechanism of action, indications, results, programming parameters, complications, and cost-effectiveness of SCS.

Results:

In spite of the existence of several studies that try to prove the mechanism of action of SCS, it still remains unknown. The mechanism of action of SCS would be based on the antidromic activation of the dorsal column fibers, which activate the inhibitory interneurons within the dorsal horn. At present, the indications of SCS are being revised constantly, while new applications are being proposed and researched worldwide. Failed back surgery syndrome (FBSS) is the most common indication for SCS, whereas, the complex regional pain syndrome (CRPS) is the second one. Also, this technique is useful in patients with refractory angina and critical limb ischemia, in whom surgical or endovascular treatment cannot be performed. Further indications may be phantom limb pain, chronic intractable pain located in the head, face, neck, or upper extremities, spinal lumbar stenosis in patients who are not surgical candidates, and others.

Conclusion:

Spinal cord stimulation is a useful tool for neuromodulation, if an accurate patient selection is carried out prior, which should include a trial period. Undoubtedly, this proper selection and a better knowledge of its underlying mechanisms of action, will allow this cutting edge technique to be more acceptable among pain physicians.

Physiology of spinal cord stimulation: review and update

Spinal cord stimulation (SCS) was an outgrowth of the well-known gate control theory presented by Melzack and Wall in 1965. Although the method has been used to treat chronic severe pain for more than three decades, very little was known about the physiological and biochemical mechanisms behind the beneficial effects until recently. We now know that SCS activates several different mechanisms to treat different types of pain such as neuropathic and ischemic. In general, these mechanisms seem most dependent on activation of only a few segments of the spinal cord. However, both animal studies and human observations have indicated that supraspinal circuits may contribute as well. In the treatment of neuropathic pain, intermittent SCS may give several hours of pain relief after cessation of the stimulation. This protracted effect indicates long-lasting modulation of neural activity involving changes in the local transmitter systems in the dorsal horns. In ischemic pain, animal experiments demonstrate that inhibition of afferent activity in the spinothalamic tracts, long-term suppression of sympathetic activity, and antidromic effects on peripheral reflex circuits may take part in the pain alleviation. Moderate SCS intensities seem to evoke sympathetic inhibition, but higher stimulation intensities may induce antidromically mediated release of vasoactive substances, eg, the calcitonin gene-related peptide (CGRP), resulting in peripheral vasodilation. The anti-ischemic effect of SCS in angina pectoris due to intermittent coronary ischemia probably occurs because application of SCS appears to result in a redistribution of cardiac blood supply, as well as a decrease in tissue oxygen demand. Recent studies indicate that SCS modulates the activity of cardiac intrinsic neurons thereby restricting the arrythmogenic consequences of intermittent local coronary ischemia. The present state of knowledge is briefly reviewed and recent research directions outlined.

Spinal Cord Stimulation and the Induction of c-fos and Heat Shock Protein 72 in the Central Nervous System of Rats

For more than a decade, spinal cord stimulation (SCS) has been used as an adjuvant treatment for patients who are unresponsive to conventional therapies for angina pectoris. Many studies showed that SCS has both electro-analgesic and anti-ischemic effects. Nonetheless, the biological substrates by which SCS acts have not yet been unraveled, although recently areas in the brain have been described that show changes in blood flow, following SCS, and during provocation of angina. In search of a putative mechanism of action of SCS, we hypothesized that SCS affects processing of nociceptive information within the central nervous system (CNS). Moreover, it may alter the limbic system activity that maintains the balance between sympathetic and parasympathetic activity in the heart. Hence, we have developed a rat model to investigate its suitability for studying the induction of neural activity during SCS. To characterize neural activity, we used the expression of both the immediate early gene c-fos and the heat shock protein 72 (HSP72). c-Fos was used to identify structures in the CNS affected by SCS, and HSP72 was applied in order to ascertain whether SCS might operate as a stressor. In 20 halothane-anesthetized male Wistar rats, two electrodes were placed epidurally, one at the C7 level and the other at the T2 level. Two days after surgery, the rats were either stimulated "treated" animals, n = 10) or used as controls ("unstimulated" = "sham," n = 10) in random order. Furthermore, we studied the effect of SCS on behavior in five treated and five control rats. Three hours after stimulation, the rats were euthanized and the brain and spinal cord were removed. The treated group showed regional increased c-fos expression in regions of the limbic system (periaqueductal gray, paraventricular hypothalamic nucleus, paraventricular thalamic nucleus, central amygdala, agranular and dysgranular insular cortex, (peri)ambiguus, nucleus tractus solitarius, and spinal cord) that are involved in the processing of pain and cardiovascular regulation, among other things. Moreover, in both treated rats and controls, HSP72-expression was found in the endothelium of the enthorhinal cortex, the amygdala, and the ventral hypothalamus, but not in the neurons. Finally, treated animals were significantly more alert and active than controls. In conclusion, the rat model we developed appears to be suitable for studying potential mechanisms through which SCS may act. In addition, SCS affects c-fos expression in specific parts of the brain known to be involved in regulation of pain and emotions. HSP72-expression is limited to the endothelium of certain parts of the CNS and thereby excludes physical stress effects as a potential mechanism of SCS.

Substance P release in response to cardiac ischemia from rat thoracic spinal dorsal horn is mediated by TRPV1

Spinal cord stimulation (SCS) inhibits substance P (SP) release and decreases the expression of the transient receptor potential vanilloid 1 (TRPV1) in the spinal cord at thoracic 4 (T4) during cardiac ischemia in rat models (Ding et al., 2007). We hypothesized that activation of TRPV1 in the T4 spinal cord segment by intermittent occlusion of the left anterior descending coronary artery (CoAO) mediates spinal cord SP release. Experiments were conducted in urethane-anesthetized Sprague-Dawley male rats using SP antibody-coated microprobes to measure SP release at the central terminal endings of cardiac ischemic-sensitive afferent neurons (CISAN) in the spinal T4 dorsal horns. Vehicle, capsaicin (CAP; TRPV1 agonist) and capsazepine (CZP; TRPV1 antagonist) were injected into the left T4 prior to stimulation of CISAN by intermittent CoAO (with or without upper cervical SCS). CAP induced endogenous SP release from laminae I and II in the T4 spinal cord above baseline. Conversely, CZP injections significantly inhibited SP release from laminae I-VII in the T4 spinal cord segment below baseline. CZP also attenuated CoAO-induced SP release, while T4 injections of CZP with SCS completely restored SP release to basal levels during CoAO activation. CAP increased the number of c-Fos (a marker for CISAN activation) positive T4 dorsal horn neurons compared to sham-operated animals, while CZP (alone or during CoAO and SCS+CoAO) significantly reduced the number of c-Fos positive neurons. These results suggest that spinal release of the putative nociceptive transmitter SP occurs, at least in part, via a TRPV1 mechanism.

Spinal cord stimulation for refractory angina pectoris -a case report-

Refractory angina pectoris is defined as angina refractory to optimal medical treatment and standard coronary revascularization procedures. Despite recent therapeutic advances, patients with refractory angina pectoris are not adequately treated. Spinal cord stimulation is a minimally invasive and reversible technique which utilizes electrical neuromodulation by means of an electrode implanted in the epidural space. It has been reported to be an effective and safe treatment for refractory angina pectoris. We report a case of spinal cord stimulation which has effectively relieved chest pain due to coronary artery disease in a 40-year-old man. This is the first report of spinal cord stimulation for treatment of refractory angina pectoris in South Korea.

Spinal cord stimulation for long-term treatment of severe angina pectoris: what does the evidence say?

Patients who continue to suffer from severe and disabling angina pectoris, despite optimum treatment in terms of conventional pharmacological therapy and/or revascularization procedures, have been termed as having refractory angina pectoris. The future group of patients with refractory angina pectoris will be different from today’s patients and represent a ‘moving target’ as risk factors, efficacy of treatment and indications continue to change. Spinal cord stimulation (SCS) is today considered as first-line treatment of refractory angina pectoris, by the European Society of Cardiology, with an anti-ischemic effect. There is strong evidence for SCS giving symptomatic benefits (decrease in anginal attacks), improved quality of life and improvement of functional status. In addition, SCS seems to be cost effective with a ‘break-even’ after approximately 15–16 months.

24. Chronic refractory angina pectoris

Angina pectoris, cardiac pain associated with ischemia, is considered refractory when optimal anti-anginal therapy fails to resolve symptoms. It is associated with a decreased life expectancy and diminishes the quality of life. Spinal cord stimulation (SCS) may be considered for patients who have also undergone comprehensive interventions, such as coronary artery bypass graft (CABG) and percutaneous transluminal coronary angioplasty (PTCA) procedures. The mechanism of action of SCS is not entirely clear. Pain reduction is related to the increased release of inhibitory neuropeptides as well as normalization of the intrinsic nerve system of the heart muscle, and may have a protective myocardial effect. SCS in patients with refractory angina pectoris results in reduced anginal attacks as well as improved rate pressure product prior to the occurrence of ischemic events. This may be the result of reduced Myocardial Volume Oxygen (MVO(2) ) and possibly the redistribution of the coronary blood flow to ischemic areas. There are a number of studies that demonstrate that SCS does not mask acute myocardial infarction. The efficacy of the treatment has been investigated in two prospective, randomized studies. The long-term results showed an improvement of the symptoms and of the quality of life. SCS can be an alternative to surgical intervention in a selected patient population. In addition, SCS is a viable option in patients in whom surgery is not possible. SCS is recommended in patients with chronic refractory angina pectoris that does not respond to conventional treatment and in whom revascularization procedures have been attempted or not possible, and who are optimized from a medical perspective.

Spinal Cord Stimulation Improves Ventricular Function and Reduces Ventricular Arrhythmias in a Canine Postinfarction Heart Failure Model

Background— Spinal cord stimulation (SCS) reduces the incidence of ventricular tachyarrhythmias in experimental models. This study investigated the effects of long-term SCS on ventricular function in a postinfarction canine heart failure model.

Methods and Results— In stage 1, dogs underwent implantable cardioverter-defibrillator implantation and embolization of the left anterior descending artery followed by right ventricular pacing (240 ppm) for 3 weeks to produce heart failure. In stage 2, 28 surviving animals were assigned to the SCS (delivered at the T4/T5 spinal region for 2 hours 3 times a day), medicine (MED; carvedilol therapy at 12.5 mg PO BID), or control (CTRL; no therapy) group for the initial phase 1 study. In a subsequent phase 2 study, 32 stage 1 survivors were equally randomized to the SCS, MEDS (carvedilol plus ramipril 2.5 mg PO QD), SCS plus MEDS (concurrent therapy), or CTRL group. Animals were monitored for 5 weeks (phase 1) or 10 weeks (phase 2). In stage 3, all phase 1 animals underwent circumflex artery balloon occlusion for 1 hour. In the SCS group, left ventricular ejection fraction was 65±5% at baseline, 17±3% at the end of stage 1, and 47±7% at the end of stage 2. In the MED group, left ventricular ejection fraction was 61±4% at baseline, 18±3% at the end of stage 1, and 34±4% at the end of stage 2. In the CTRL group, left ventricular ejection fraction was 64±5% at baseline, 19±5% at the end of stage 1, and 28±3% at the end of stage 2. Left ventricular ejection fraction was significantly improved in the SCS compared with the MED and CTRL groups ( P <0.001 for both). The mean number of spontaneous nonsustained ventricular tachyarrhythmias during stage 2 and the occurrence of ischemic ventricular tachyarrhythmias during stage 3 also were significantly decreased in the SCS (27±17 and 27%, respectively; P <0.03) and MED (58±42 and 33%; P <0.05) versus CTRL (88±52 and 76%) group. After 10 weeks in the phase 2 studies, the greatest recovery in ejection fraction was noted in the SCS (52±5%) and SCS+MEDS (46±4%) groups compared with the MEDS (38±2%) and CTRL (31±4%) groups.

Conclusion— SCS significantly improved cardiac contractile function and decreased ventricular arrhythmias in canine heart failure.

Dorsal spinal cord stimulation obtunds the capacity of intrathoracic extracardiac neurons to transduce myocardial ischemia

Populations of intrathoracic extracardiac neurons transduce myocardial ischemia, thereby contributing to sympathetic control of regional cardiac indices during such pathology. Our objective was to determine whether electrical neuromodulation using spinal cord stimulation (SCS) modulates such local reflex control. In 10 anesthetized canines, middle cervical ganglion neurons were identified that transduce the ventricular milieu. Their capacity to transduce a global (rapid ventricular pacing) vs. regional (transient regional ischemia) ventricular stress was tested before and during SCS (50 Hz, 0.2 ms duration at 90% MT) applied to the dorsal aspect of the T1 to T4 spinal cord. Rapid ventricular pacing and transient myocardial ischemia both activated cardiac-related middle cervical ganglion neurons. SCS obtunded their capacity to reflexly respond to the regional ventricular ischemia, but not rapid ventricular pacing. In conclusion, spinal cord inputs to the intrathoracic extracardiac nervous system obtund the latter's capacity to transduce regional ventricular ischemia, but not global cardiac stress. Given the substantial body of literature indicating the adverse consequences of excessive adrenergic neuronal excitation on cardiac function, these data delineate the intrathoracic extracardiac nervous system as a potential target for neuromodulation therapy in minimizing such effects.

Spinal cord stimulation for chronic intractable angina pectoris: a unified theory on its mechanism

The use of spinal cord stimulation (SCS) for chronic intractable anginal pain was first described in 1987. Numerous studies have demonstrated its efficacy in improving exercise tolerance, decreasing frequency of anginal episodes, and prolonging time to electrocardiographic signs of ischemia. This review will examine the potential mechanisms of this antianginal effect and propose a unified hypothesis explaining it. The effect of SCS involves a mutual interaction of decreased pain, decreased sympathetic tone, and a likely redistribution of myocardial blood flow to ischemic regions. Spinal cord stimulation reduces the transmission of nociceptive impulse via the spinothalamic tract due to an enhanced release of gamma aminobutyric acid (GABA) from dorsal horn interneurons. Improvement of myocardial blood flow at the microvascular level has been demonstrated by positron emission tomography (PET). A decreased sympathetic tone has been shown by norepinephrine kinetics, tests of sympathetic reflexes, and the use of ganglionic blockers. We hypothesize that SCS exerts its beneficial effects by decreasing pain and decreasing sympathetic tone, the result of which is decreased myocardial oxygen consumption along with an improved myocardial microcirculatory blood flow.

Interference of transcutaneous electrical nerve stimulation with permanent ventricular stimulation: a new clinical problem?

AIMS

To assess the compatibility of thoracic TENS and permanent PM treatment and to identify any signs of interference of TENS with the PM function.

METHODS AND RESULTS

Twenty-seven patients treated with PM were tested. Transcutaneous electric nerve stimulation electrodes were placed above each mamilla, and the stimulation intensity was increased to the maximum level tolerated for 30 s or until electrocardiogram revealed signs of interference. Transcutaneous electric nerve stimulation of 2 and 80 Hz was tested with the PM ventricular sensing level set to the clinically chosen level as well as to maximal sensitivity. Interference was detected in 22 of 27 patients (81%). Low-frequency (2 Hz) stimulation was more associated with PM interference (52% at normal vs. 81% at maximal ventricular sensitivity) than high-frequency (80 Hz) stimulation (33% at normal vs. 63% at maximal ventricular sensitivity); although the differences were not statistically significant.

CONCLUSION

Transcutaneous electric nerve stimulation frequently induces inhibition of the PM function already at the clinically set ventricular sensitivity. Therefore, individual testing is warranted before TENS treatment is considered in patients with a PM. A test protocol for TENS and PM interaction is proposed.

Spinal cord stimulation in severe angina pectoris--a systematic review based on the Swedish Council on Technology assessment in health care report on long-standing pain

Patients who continue to suffer from lasting and severely disabling angina pectoris despite optimum drug treatment and who are not suitable candidates for invasive procedures, suffer from a condition referred to as "chronic refractory angina pectoris". Based on the available data, spinal cord stimulation, SCS, is considered as the first-line additional treatment for these patients by the European Society of Cardiology. However, no systematic review of randomised controlled studies has yet been published. A systematic literature research, 1966-2003, as part of the Swedish Board of Health and Welfare (SBU) report on long-standing pain, and an additional research covering the years 2003-2007, were carried out. Acute studies, case reports and mechanistic reviews were excluded, and the remaining 43 studies were graded for study quality according to a modified Jadad score. The eight medium- to high-score studies formed the basis for conclusions regarding the scientific evidence (strong, moderately strong or limited) for the efficacy of SCS. There is strong evidence that SCS gives rise to symptomatic benefits (decrease in anginal attacks) and improved quality of life in patients with severe angina pectoris. There is also a strong evidence that SCS can improve the functional status of these patients, as illustrated by the improved exercise time on treadmill or longer walking distance without angina. In addition, SCS does not seem to have any negative effects on mortality in these patients (limited scientific evidence). The complication rate was found to be acceptable.

C2 spinal cord stimulation induces dynorphin release from rat T4 spinal cord: potential modulation of myocardial ischemia-sensitive neurons

During myocardial ischemia, the cranial cervical spinal cord (C1-C2) modulates the central processing of the cardiac nociceptive signal. This study was done to determine 1) whether C2 SCS-induced release of an analgesic neuropeptide in the dorsal horn of the thoracic (T4) spinal cord; 2) if one of the sources of this analgesic peptide was cervical propriospinal neurons, and 3) if chemical inactivation of C2 neurons altered local T4 substance P (SP) release during concurrent C2 SCS and cardiac ischemia. Ischemia was induced by intermittent occlusion of the left anterior descending coronary artery (CoAO) in urethane-anesthetized Sprague-Dawley rats. Release of dynorphin A (1-13), (DYN) and SP was determined using antibody-coated microprobes inserted into T4. SCS alone induced DYN release from laminae I-V in T4, and this release was maintained during CoAO. C2 injection of the excitotoxin, ibotenic acid, prior to SCS, inhibited T4 DYN release during SCS and ischemia; it also reversed the inhibition of SP release from T4 dorsal laminae during C2 SCS and CoAO. Injection of the kappa-opioid antagonist, nor-binaltorphimine, into T4 also allowed an increased SP release during SCS and CoAO. CoAO increased the number of Fos-positive neurons in T4 dorsal horns but not in the intermediolateral columns (IML), while SCS (either alone or during CoAO) minimized this dorsal horn response to CoAO alone, while inducing T4 IML neuronal recruitment. These results suggest that activation of cervical propriospinal pathways induces DYN release in the thoracic spinal cord, thereby modulating nociceptive signals from the ischemic heart.

Modulation of cardiac ischemia-sensitive afferent neuron signaling by preemptive C2 spinal cord stimulation: effect on substance P release from rat spinal cord

The upper cervical spinal region functions as an intraspinal controller of thoracic spinal reflexes and contributes to neuronal regulation of the ischemic myocardium. Our objective was to determine whether stimulation of the C2 cervical spinal cord (SCS) of rats modified the input signal at the thoracic spinal cord when cardiac ischemia-sensitive (sympathetic) afferents were activated by transient occlusion of the left anterior descending coronary artery (CoAO). Changes in c-Fos expression were used as an index of neuronal activation within the spinal cord and brain stem. The pattern of substance P (SP) release, a putative nociceptive transmitter, was measured using antibody-coated microprobes. Two SCS protocols were used: reactive SCS, applied concurrently with intermittent CoAO and preemptive, sustained SCS starting 15 min before and continuing during the repeated intermittent CoAO. CoAO increased SP release from laminae I and II in the T4 spinal cord above resting levels. Intermittent SCS with CoAO resulted in greater levels of SP release from deeper laminae IV-VII in T4 than CoAO alone. In contrast, SP release from laminae I and II was inhibited when CoAO was applied during preemptive, sustained SCS. Preemptive SCS likewise reduced c-Fos expression in the T4 spinal cord (laminae I-V) and nucleus tractus solitarius but increased expression in the intermediolateral cell column of T4 compared with CoAO alone. These results suggest that preemptive SCS from the high cervical region modulates sensory afferent signaling from the ischemic myocardium.

The effect of high cervical spinal cord stimulation on the expression of SP, NK-1 and TRPV1 mRNAs during cardiac ischemia in rat

Spinal cord stimulation (SCS) is used to reduce angina that accompanies cardiac ischemia, but little is known about the molecular mechanisms mediating this effect. We studied the expression of SP, neurokinin-1 (NK-1) receptor, and transient receptor potential vanilloid type 1 (TRPV1) mRNA in the rat spinal cord at thoracic 4 (T4), cervical 2 (C2) and caudal brain stem by RT-PCR during intermittent occlusion of the left anterior descending coronary artery (CoAO), during sustained SCS by itself at the C2 spinal segment, and during sustained SCS plus intermittent CoAO. Only SP mRNA was increased significantly in T4 and brainstem during CoAO, while SCS decreased the mRNA levels of SP, NK-1 and TRPV1 significantly in T4 and the brainstem. SCS attenuated the increase of SP and TRPV1 mRNA levels at T4 level induced by intermittent CoAO when the stimulation was applied prior to the initiation of the cardiac ischemia. These results support the role for SP as a putative neurotransmitter for the myocardial ischemia-sensitive afferent neuron signal to the spinal level. They suggest that modification of the ischemic cardiac nociceptive afferent signal by SCS involves a change in SP and TRPV1 expression.

Spinal cord stimulation for refractory chronic angina pectoris: influence on quality of life

Percutaneous coronary revascularization, coronary artery bypass graft surgery and medical management are nowadays very effective in treating coronary artery disease. Nevertheless, the number of patients affected by refractory chronic angina pectoris is increasing. Epidemiological estimates for refractory angina pectoris predict the diagnosis of more than 100,000 patients each year in the USA and approximately 50,000 in Europe. Spinal cord stimulation is a valuable therapeutic option for patients who have failed multiple percutaneous and surgical revascularizations and who are not eligible for further revascularization procedures. The aim of this study is to assess the benefits, in terms of quality of life, of spinal cord stimulation in no-option patients affected by refractory angina pectoris.

The beneficial effect of spinal cord stimulation in a patient with severe cerebral ischemia and upper extremity ischemic pain

Spinal cord stimulation (SCS) is used in the treatment of chronic pain, ischemia because of obstructive arterial disease, and anginal pain. Recently, a number of studies have described the effects of the high cervical SCS, including increased cerebral blood flow, although the underlying mechanisms are unknown. This case report describes a patient with a severe complex ischemic condition affecting both cerebral and upper limb blood flow with an associated complex regional pain syndrome in upper limb. While all previous clinical treatments proved ineffective, cervical SCS afforded satisfactory results. Possible mechanisms underlying the cervical SCS effect are discussed.