Effects of spinal cord stimulation on heart rate variability in patients with Failed Back Surgery Syndrome

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.

Low- and high-frequency spinal cord stimulation and arterial blood pressure in patients with chronic pain and hypertension: a retrospective study

PURPOSE

Evidence suggests that traditional low-frequency spinal cord stimulation (LF-SCS) reduces arterial blood pressure (BP) in patients with chronic pain and hypertension independent of improved pain symptoms. However, it remains unclear whether high-frequency spinal cord stimulation (HF-SCS) also lowers BP in chronic pain patients with hypertension. Therefore, in a retrospective study design, we tested the hypothesis that clinic BP would be significantly reduced following implantation of HF-SCS in patients with chronic pain and hypertension.

METHODS

Clinic BP within 3 months before and after surgical implantation of either a LF-SCS or HF-SCS device between 2010 and 2020 were collected from electronic medical records at The University of Kansas Health System (TUKHS).

RESULTS

A total of 132 patients had available records of clinic BP (64 ± 13 years of age). Patients with hypertension (n = 32) demonstrated a significantly greater reduction in systolic BP (-8 ± 12 versus 2 ± 9 mmHg, P < 0.001) following implantation compared with normotensive patients (n = 100). Importantly, the change in BP was inversely related to baseline BP independent of age and sex following implantation of HF-SCS (n = 70, R =  -0.50, P < 0.001) or LF-SCS (n = 62, R =  -0.42, P = 0.001). Higher pain scores before implantation were not associated with reduction in systolic BP (R = 0.10, P = 0.43) or diastolic BP (R =  -0.08, P = 0.53) (n = 69) after implantation.

CONCLUSION

These findings confirm previous studies showing reduced BP following implantation of LF-SCS in patients with chronic pain and hypertension and provide novel data regarding reduced BP following implantation of newer generation HF-SCS devices.

Evaluation of External Trigeminal Nerve Stimulation to Prevent Cerebral Vasospasm after Subarachnoid Hemorrhage Due to Aneurysmal Rupture: A Randomized, Double-Blind Proof-of-Concept Pilot Trial (TRIVASOSTIM Study)

Cerebral vasospasm remains the most frequent and devastating complication after subarachnoid aneurysmal hemorrhage because of secondary cerebral ischemia and its sequelae. The underlying pathophysiology involves vasodilator peptide release (such as CGRP) and nitric oxide depletion at the level of the precapillary sphincters of the cerebral (internal carotid artery network) and dural (external carotid artery network) arteries, which are both innervated by craniofacial autonomic afferents and tightly connected to the trigeminal nerve and trigemino-cervical nucleus complex. We hypothesized that trigeminal nerve modulation could influence the cerebral flow of this vascular network through a sympatholytic effect and decrease the occurrence of vasospasm and its consequences. We conducted a prospective double-blind, randomized controlled pilot trial to compare the effect of 10 days of transcutaneous electrical trigeminal nerve stimulation vs. sham stimulation on cerebral infarction occurrence at 3 months. Sixty patients treated for aneurysmal SAH (World Federation of Neurosurgical Societies scale between 1 and 4) were included. We compared the radiological incidence of delayed cerebral ischemia (DCI) on magnetic resonance imaging (MRI) at 3 months in moderate and severe vasospasm patients receiving trigeminal nerve stimulation (TNS group) vs. sham stimulation (sham group). Our primary endpoint (the infarction rate at the 3-month follow-up) did not significantly differ between the two groups (p = 0.99). Vasospasm-related infarctions were present in seven patients (23%) in the TNS group and eight patients (27%) in the sham group. Ultimately, we were not able to show that TNS can decrease the rate of cerebral infarction secondary to vasospasm occurrence. As a result, it would be premature to promote trigeminal system neurostimulation in this context. This concept should be the subject of further research.

Heart rate variability is not suitable as surrogate marker for pain intensity in patients with chronic pain

ABSTRACT

The search towards more objective outcome measurements and consequently surrogate markers for pain started decades ago; however, no generally accepted biomarker for pain has qualified yet. The goal is to explore the value of heart rate variability (HRV) as surrogate marker for pain intensity chronic pain setting. Pain intensity scores and HRV were collected in 366 patients with chronic pain, through a cross-sectional multicenter study. Pain intensity was measured with both the Visual Analogue Scale and Numeric Rating Scale, while 16 statistical HRV parameters were derived. Canonical correlation analysis was performed to evaluate the correlation between the dependent pain variables and the HRV parameters. Surrogacy was determined for each HRV parameter with point estimates between 0 and 1 whereby values close to 1 indicate a strong association between the surrogate and the true endpoint at the patient level. Weak correlations were revealed between HRV parameters and pain intensity scores. The highest surrogacy point estimate was found for mean heart rate as marker for average pain intensity on the Numeric Rating Scale with point estimates of 0.0961 (95% CI from 0.0384 to 0.1537) and 0.0209 (95% CI from 0 to 0.05) for patients without medication use, and medication use respectively. This study indicated that HRV parameters as separate entities are no suitable surrogacy candidates for pain intensity, in a population of chronic pain patients. Further potential surrogate candidates and clinical robust true endpoints should be explored, in order to find a surrogate measure for the highly individual pain experience.

A Feasibility Study Exploring Measures of Autonomic Function in Patients With Failed Back Surgery Syndrome Undergoing Spinal Cord Stimulation

OBJECTIVES

Failed back surgery syndrome (FBSS) is associated with impaired autonomic tone, characterized by sympathetic prevalence and vagal withdrawal. Although spinal cord stimulation (SCS) alleviates pain in FBSS, there is limited research investigating how SCS affects measures of autonomic function. This was a prospective, open-label, feasibility study exploring measures of autonomic function in patients with FBSS receiving SCS therapy.

MATERIALS AND METHODS

A total of 14 patients with FBSS were recruited for baseline measurements and underwent a trial of 10-kHz SCS. There were three failed trials, resulting in the remaining 11 participants receiving a fully implanted 10-kHz SCS system. One participant requested an explant, resulting in ten participants completing both baseline and follow-up (three to six months after SCS implant) measurements. Autonomic function was assessed using time- and frequency-domain heart rate variability (HRV), baroreceptor reflex sensitivity (BRS), and muscle sympathetic nerve activity (MSNA) using microneurography. Because this was a feasibility study, most of the analysis was descriptive. However, paired t-tests and Wilcoxon signed-rank tests tested for differences between baseline and follow-up.

RESULTS

In the whole (N = 14) and final (N = 10) samples, there was between-participant variation in baseline and follow-up measures. This, combined with a small sample, likely contributed to finding no statistically significant differences in any of the measures between baseline and follow-up. However, plotting baseline and follow-up scores for individual participants revealed that those who showed increases in MSNA frequency, square root of the mean of the squared differences between adjacent RR intervals (RMSSD), percentage of the number of RR intervals >50 ms (pRR50), total power, and up BRS between baseline and follow-up had distinct clustering of baseline values compared with those who showed decreases in these measures.

CONCLUSIONS

Findings from this feasibility study will aid with informing hypotheses for future research. A key aspect that should be considered in future research concerns exploring the role of baseline measures of autonomic function in influencing change in autonomic function with SCS therapy.

Detection of Changes on Parameters Related to Heart Rate Variability after Applying Current Interferential Therapy in Subjects with Non-Specific Low Back Pain

Interferential current therapy (ICT) is an electrotherapeutic intervention that combines the advantages of high permeability from middle frequency currents and efficient tissue stimulation from low frequency currents, delivering the maximum current with high tissue permeability. The aim was to evaluate the effects of ICT on heart rate variability (HRV) and on pain perception in patients with non-specific chronic low back pain (NSCLBP). In the study, 49 patients with NSCLBP were randomly divided into an experimental (EG) and a sham group (SG). All participants received a single intervention, ICT, or simulated intervention. Outcome measures including baseline (sit-down position) and postintervention (prone position) pain, heart rate (HR), time domain parameter (rMSSD), diameters of the Poincaré plot (SD1, SD2), stress score (SS), and sympathetic/parasympathetic (S/PS) ratio were investigated. In both groups, significant statistical differences were found in perceived pain and in all HRV parameters except in HRmax. Between-group comparisons showed statistically significant differences in all variables except for HRmin and HRmean in favor of the experimental group. These changes reported an increase in parasympathetic activity (rMSSD) (p < 0.05) and a decrease in sympathetic activity (increase in SD2 and decrease in SS) (p < 0.001) and perceived pain (p < 0.001), with a greater size effect (η2 = 0.44) in favor of the experimental group. In conclusion, a single session of ICT can shift the autonomic balance towards increase parasympathetic dominance and decrease the sympathetic dominance and intensity of pain perceived by patients with NSCLBP.

Electrochemical Skin Conductance Alterations during Spinal Cord Stimulation: An Experimental Study

Despite the well-known clinical effects of spinal cord stimulation (SCS), the mechanisms of action have not yet been fully unraveled. The primary aim of this study was to measure whether electrochemical skin conductance, as a measure of peripheral sympathetic autonomic function, is altered by SCS. A second aim was to compare skin conductance levels of patients with failed back surgery syndrome (FBSS) with age- and sex-matched healthy controls. Twenty-three patients with FBSS treated with SCS participated in this study. Sudomotor function was measured with the Sudoscan^TM instrument on the hands and feet during SCS on and off states. Difference scores in skin conductance between patients and age- and sex-matched healthy controls were calculated. Normal sudomotor function at the painful lower limb was revealed for 61% of the patients when SCS was activated. Skin conductance levels were not altered between on and off states of SCS. Differences in scores between patients and healthy controls were significantly different from zero. This study showed that SCS does not influencing the sympathetic nervous system in patients with FBSS, as measured by skin conductance levels. Moreover, it suggested that there is no normalization of the functioning of the sympathetic nervous system, despite the effectiveness of SCS to reduce pain intensity.

Exhaled-Breath Testing Using an Electronic Nose during Spinal Cord Stimulation in Patients with Failed Back Surgery Syndrome: An Experimental Pilot Study

The increased awareness of discrepancies between self-reporting outcome measurements and objective outcome measurements within the field of neuromodulation has accelerated the search towards more objective measurements. The aim of this study was to evaluate whether an electronic nose can differentiate between chronic pain patients in whom Spinal Cord Stimulation (SCS) was activated versus deactivated. Twenty-seven patients with Failed Back Surgery Syndrome (FBSS) participated in this prospective pilot study. Volatile organic compounds in exhaled breath were measured with electronic nose technology (Aeonose™) during SCS on and off states. Random forest was used with a leave-10%-out cross-validation method to determine accuracy of discriminating between SCS on and off states. Our random forest showed an accuracy of 0.56, with an area under the curve of 0.62, a sensitivity of 62% (95% CI: 41–79%) and a specificity of 50% (95% CI: 30–70%). Pain intensity scores were significantly different between both SCS states. Our findings indicate that we cannot discriminate between SCS off and on states based on exhaled breath with the Aeonose™ in patients with FBSS. In clinical practice, these findings imply that with a noninvasive electronic nose, exhaled breath cannot be used as an additional marker of the effect of neuromodulation.

Treatment of Chronic Abdominal Pain With 10-kHz Spinal Cord Stimulation: Safety and Efficacy Results From a 12-Month Prospective, Multicenter, Feasibility Study

INTRODUCTION

Chronic abdominal pain (CAP) can arise from multiple conditions, including inflammatory disorders, trauma because of injury or surgery, or structural or functional causes. This prospective, single-arm study was designed to evaluate the safety and efficacy of 10-kHz spinal cord stimulation (SCS) in patients with intractable CAP over a 12-month follow-up period.

METHODS

Subjects with CAP who had been refractory to conventional medical treatment for at least 3 months resulting in self-reported pain scores of ≥5 cm on a 10-cm visual analog scale were enrolled at 4 centers in the United States. Study subjects underwent a trial stimulation lasting up to 14 days with epidural leads implanted from the vertebral levels T4 through T8. Subjects who had ≥40% pain relief during the trial stimulation period were implanted with a Senza system (Nevro Corp., Redwood City, CA) and followed up to 12 months after surgery.

RESULTS

Twenty-three of 24 subjects (95.8%) had a successful trial stimulation and proceeded to a permanent implant. After 12 months of treatment with 10-kHz SCS, 78.3% of subjects were responders (pain relief of ≥50%) and 14 of 22 subjects (63.6%) were remitters (sustained ≤3.0-cm visual analog scale scores). Secondary outcomes, including assessments of disability, mental and physical well-being, sleep quality, perception of improvement, and satisfaction, showed that 10-kHz SCS greatly improved the quality of life of patients with CAP. Observationally, most subjects also reported concurrent reduction or resolution of nausea and/or vomiting.

DISCUSSION

10-kHz SCS can provide durable pain relief and improve the quality of life in patients with CAP.

The Link Between Spinal Cord Stimulation and the Parasympathetic Nervous System in Patients With Failed Back Surgery Syndrome

OBJECTIVES

In patients with chronic pain, a relative lower parasympathetic activity is suggested based on heart rate variability measurements. It is hypothesized that spinal cord stimulation (SCS) is able to influence the autonomic nervous system. The aim of this study is to further explore the influence of SCS on the autonomic nervous system by evaluating whether SCS is able to influence skin conductance, blood volume pulse, heart rate, and respiration rate.

MATERIALS AND METHODS

Twenty-eight patients with Failed Back Surgery Syndrome (FBSS), who are treated with SCS, took part in this multicenter study. Skin conductance and cardiorespiratory parameters (blood volume pulse, heart rate, and respiration rate) were measured during on and off states of SCS. Paired statistics were performed on a 5-min recording segment for all parameters.

RESULTS

SCS significantly decreased back and leg pain intensity scores in patients with FBSS. Skin conductance level and blood volume pulse were not altered between on and off states of SCS. Heart rate and respiration rate significantly decreased when SCS was activated.

CONCLUSIONS

Parameters that are regulated by the sympathetic nervous system were not significantly different between SCS on and off states, leading to the hypothesis that SCS is capable of restoring the dysregulation of the autonomic nervous system by primarily increasing the activity of the parasympathetic system, in patients with FBSS.

Mediation of Cardiac Macrophage Activity via Auricular Vagal Nerve Stimulation Ameliorates Cardiac Ischemia/Reperfusion Injury

Background

Myocardial infarction (MI) reperfusion therapy causes paradoxical cardiac complications. Following restoration of blood flow to infarcted regions, a multitude of inflammatory cells are recruited to the site of injury for tissue repair. Continual progression of cardiac inflammatory responses does, however, lead to adverse cardiac remodeling, inevitably causing heart failure.

Main Body

Increasing evidence of the cardioprotective effects of both invasive and non-invasive vagal nerve stimulation (VNS) suggests that these may be feasible methods to treat myocardial ischemia/reperfusion injury via anti-inflammatory regulation. The mechanisms through which auricular VNS controls inflammation are yet to be explored. In this review, we discuss the potential of autonomic nervous system modulation, particularly via the parasympathetic branch, in ameliorating MI. Novel insights are provided about the activation of the cholinergic anti-inflammatory pathway on cardiac macrophages. Acetylcholine binding to the α7 nicotinic acetylcholine receptor (α7nAChR) expressed on macrophages polarizes the pro-inflammatory into anti-inflammatory subtypes. Activation of the α7nAChR stimulates the signal transducer and activator of transcription 3 (STAT3) signaling pathway. This inhibits the secretion of pro-inflammatory cytokines, limiting ischemic injury in the myocardium and initiating efficient reparative mechanisms. We highlight recent developments in the controversial auricular vagal neuro-circuitry and how they may relate to activation of the cholinergic anti-inflammatory pathway.

Conclusion

Emerging published data suggest that auricular VNS is an inexpensive healthcare modality, mediating the dynamic balance between pro- and anti-inflammatory responses in cardiac macrophages and ameliorating cardiac ischemia/reperfusion injury.

Effects of Spinal Cord Stimulation on Heart Rate Variability in Patients With Failed Back Surgery Syndrome: Comparison Between a 2-lead ECG and a Wearable Device

OBJECTIVES

Heart rate variability recordings have the potential to examine the role of the autonomic nervous system. Several wearable devices are nowadays readily available. Up until now, no studies explored whether a wearable device is able to reliably measure a treatment response in chronic pain patients. Therefore, the aim of this study is to evaluate the reliability of a Polar V800 (Polar Electro Oy, Finland) wearable device to accurately measure RR intervals in patients with failed back surgery syndrome (FBSS) during spinal cord stimulation (SCS), as compared with an eMotion 2-lead ECG recording.

MATERIALS AND METHODS

Twenty-two patients diagnosed with FBSS and treated with SCS participated in this study. HRV was measured with a 2-lead ECG registration tool and a Polar V800 during on and off state of SCS. Intraclass correlation coefficients, correlations, limits of agreement, Cronbach's α, and effect sizes were calculated.

RESULTS

Analysis based on the recordings from the ECG and wearable device revealed the same HRV parameters (except for the time-frequency domain) to capture the treatment response of SCS. Parameters that are relevant for measuring the SCS treatment response have strong correlations (r ≥ .82), good ICC values (ICC ≥0.82), acceptable consistency (α ≥ .9), and limited bias.

CONCLUSIONS

Similar pre- to posttreatment changes were revealed between a wearable device and 2-lead ECG with reliable HRV estimates for parameters that are able to capture the treatment changes. This suggests that a wearable heart rate monitor might be a reliable wearable tool for the detection of pre- to post treatment changes of SCS, in patients with FBSS.