Long-term outcome of spinal cord electrical stimulation in patients with refractory chest pain

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.

The appropriate use of neurostimulation of the spinal cord and peripheral nervous system for the treatment of chronic pain and ischemic diseases: the Neuromodulation Appropriateness Consensus Committee

INTRODUCTION

The Neuromodulation Appropriateness Consensus Committee (NACC) of the International Neuromodulation Society (INS) evaluated evidence regarding the safety and efficacy of neurostimulation to treat chronic pain, chronic critical limb ischemia, and refractory angina and recommended appropriate clinical applications.

METHODS

The NACC used literature reviews, expert opinion, clinical experience, and individual research. Authors consulted the Practice Parameters for the Use of Spinal Cord Stimulation in the Treatment of Neuropathic Pain (2006), systematic reviews (1984 to 2013), and prospective and randomized controlled trials (2005 to 2013) identified through PubMed, EMBASE, and Google Scholar.

RESULTS

Neurostimulation is relatively safe because of its minimally invasive and reversible characteristics. Comparison with medical management is difficult, as patients considered for neurostimulation have failed conservative management. Unlike alternative therapies, neurostimulation is not associated with medication-related side effects and has enduring effect. Device-related complications are not uncommon; however, the incidence is becoming less frequent as technology progresses and surgical skills improve. Randomized controlled studies support the efficacy of spinal cord stimulation in treating failed back surgery syndrome and complex regional pain syndrome. Similar studies of neurostimulation for peripheral neuropathic pain, postamputation pain, postherpetic neuralgia, and other causes of nerve injury are needed. International guidelines recommend spinal cord stimulation to treat refractory angina; other indications, such as congestive heart failure, are being investigated.

CONCLUSIONS

Appropriate neurostimulation is safe and effective in some chronic pain conditions. Technological refinements and clinical evidence will continue to expand its use. The NACC seeks to facilitate the efficacy and safety of neurostimulation.

Spinal cord stimulation: Current applications for treatment of chronic pain

Spinal cord stimulation (SCS) is thought to relieve chronic intractable pain by stimulating nerve fibers in the spinal cord. The resulting impulses in the fibers may inhibit the conduction of pain signals to the brain, according to the pain gate theory proposed by Melzack and Wall in 1965 and the sensation of pain is thus blocked. Although SCS may reduce pain, it will not eliminate it. After a period of concern about safety and efficacy, SCS is now regaining popularity among pain specialists for the treatment of chronic pain. The sympatholytic effect of SCS is one of its most interesting therapeutic properties. This effect is considered responsible for the effectiveness of SCS in peripheral ischemia, and at least some cases of complex regional pain syndrome. The sympatholytic effect has also been considered part of the management of other chronic pain states such as failed back surgery syndrome, phantom pain, diabetic neuropathy, and postherpetic neuralgia. In general, SCS is part of an overall treatment strategy and is used only after the more conservative treatments have failed. The concept of SCS has evolved rapidly following the technological advances that have produced leads with multiple contact electrodes and battery systems. The current prevalence of patients with chronic pain requiring treatment other than conventional medical management has significantly increased and so has been the need for SCS. With the cost benefit analysis showing significant support for SCS, it may be appropriate to offer this as an effective alternative treatment for these patients.

Spinal cord stimulation: an update

Spinal cord stimulation has been used in the treatment of many chronic pain disorders since 1967. In this update, the indications for spinal cord stimulation are reviewed with attention to recent publications. A focused review of the literature on abdominal and visceral pain syndromes is also provided. Furthermore, the technology has evolved from the use of monopolar electrodes to complex electrode arrays. Similarly, the power source has changed from a radio frequency-driven system to a rechargeable impulse generator. These topics are covered, along with a short discussion of implant technique. Finally, we include a review of complications of such therapy. SCS as a technology and therapy continues to evolve.

Spinal cord stimulation for ischemic heart disease and peripheral vascular disease

Ischemic disease (ID) is now an important indication for electrical neuromodulation (NM), particularly in chronic pain conditions. NM is defined as a therapeutic modality that aims to restore functions of the nervous system or modulate neural structures involved in the dysfunction of organ systems. One of the NM methods used is chronic electrical stimulation of the spinal cord (spinal cord stimulation: SCS). SCS in ID, as applied to ischemic heart disease (IHD) and peripheral vascular disease (PVD), started in Europe in the 1970s and 1980s, respectively. Patients with ID are eligible for SCS when they experience disabling pain, resulting from ischaemia. This pain should be considered therapeutically refractory to standard treatment intended to decrease metabolic demand or following revascularization procedures. Several studies have demonstrated the beneficial effect of SCS on IHD and PVD by improving the quality of life of this group of severely disabled patients, without adversely influencing mortality and morbidity. SCS used as additional treatment for IHD reduces angina pectoris (AP) in its frequency and intensity, increases exercise capacity, and does not seem to mask the warning signs of a myocardial infarction. Besides the analgesic effect, different studies have demonstrated an anti-ischemic effect, as expressed by different cardiac indices such as exercise duration, ambulatory ECG recording, coronary flow measurements, and PET scans. SCS can be considered as an alternative to open heart bypass grafting (CABG) for patients at high risk from surgical procedures. Moreover, SCS appears to be more efficacious than transcutaneous electrical nerve stimulation (TENS). The SCS implantation technique is relatively simple: implanting an epidural electrode under local anesthesia (supervised by the anesthesist) with the tip at T1, covering the painful area with paraesthesia by external stimulation (pulse width 210, rate 85 Hz), and connecting this electrode to a subcutaneously implanted pulse generator. In PVD the pain may manifest itself at rest or during walking (claudication), disabling the patient severely. Most of the patients suffer from atherosclerotic critical limb ischemia. All patients should be therapeutically refractory (medication and revascularization) to become eligible for SCS. Ulcers on the extremities should be minimal. In PVD the same implantation technique is used as in IHD except that the tip of the electrode is positioned at T10-11. In PVD the majority of the patients show significant reduction in pain and more than half of the patients show improvement of circulatory indices, as shown by Doppler, thermography, and oximetry studies. Limb salvage studies show variable results depending on the stage of the trophic changes. The underlying mechanisms of action of SCS in PVD require further elucidation.

Failure modes of spinal cord stimulation hardware

Object

Epidural spinal cord stimulation (SCS) is effective at treating refractory pain. The failure modes of the implanted hardware, however, have not been well studied. A better understanding of this could aid in improving the current procedure or designing future devices.

Methods

The authors reviewed electronic charts and operative reports of 289 patients who had undergone SCS implantation between 1998 and 2002 at the Cleveland Clinic Foundation. Data were collected on demographics, type of hardware, date of implantation procedure, indication for treatment, time to failure, and failure mode. Data were then analyzed to identify significant differences.

A total of 577 procedures were performed, 43.5% of which involved revision or removal of SCS hardware. The most common indication was complex regional pain syndrome 1, and this was followed by failed–back surgery syndrome. The median number of procedures per patient was two. Approximately 80% of all leads were the percutaneous type. The majority (62%) of leads were placed in the thoracic region, and 33.5% of all leads required revision. Poor pain relief coverage was the most common indication for revision. Surgically implanted leads broke twice as often as percutaneous leads. In 46% of the patients, hardware revision was required, and multiple revisions were necessary in 22.5%. Three-way ANOVA revealed significant differences in failure mode rates according to location (cervical compared with thoracic, p = 0.037) and failure modes (p = 0.019). Laminotomy leads tended to break and migrate sooner than percutaneous leads. Thoracic leads became infected sooner than cervical leads.

Conclusions

The results of this analysis of SCS hardware failures may be used as a basis for refining surgical technique and designing the next generation of SCS hardware.

Safety and efficacy of spinal cord stimulation for the treatment of chronic pain: a 20-year literature review

OBJECT

The purpose of this report was to examine the available literature to determine the safety and efficacy of spinal cord stimulation (SCS) for the treatment of chronic pain of the trunk and limbs.

METHODS

The author identified 68 studies that fulfilled the efficacy inclusion/exclusion criteria, grouped on the basis of pain indication, with an overall population of 3679 patients. Fifty-one studies fulfilled all safety inclusion/exclusion criteria. Based on the literature review, the author found that SCS had a positive, symptomatic, long-term effect in cases of refractory angina pain, severe ischemic limb pain secondary to peripheral vascular disease, peripheral neuropathic pain, and chronic low-back pain, and that, in general, SCS was a safe and effective treatment for a variety of chronic neuropathic conditions.

CONCLUSIONS

Despite the positive findings, there is an urgent need for randomized, controlled, long-term studies on the efficacy of SCS involving larger patient sample sizes.

Spinal cord stimulation for the treatment of angina pectoris

Spinal cord stimulation (SCS) has been demonstrated to cause clinical improvement in patients with refractory angina pectoris in the number of anginal episodes, in nitroglycerin consumption, in maximal exercise time, in exercise time until angina, in the number of episodes of myocardial ischemia, in the duration of episodes of myocardial ischemia, and in ischemic ST-segment depression at a comparable workload. Double-blind, randomized, placebo-controlled studies have not been performed with SCS. The clinical improvement from SCS occurred despite no improvement in measured regional myocardial blood flow during exercise or in myocardial oxygen consumption as assessed by the heart rate times systolic pressure product at maximal exercise. The mechanisms of clinical improvement by SCS are unclear. SCS must be considered experimental at this time, and it remains a potential therapeutic option for the treatment of refractory angina pectoris in patients unable to have coronary revascularization or at very high risk for coronary revascularization.

Immediate and long-term clinical outcome after spinal cord stimulation for refractory stable angina pectoris

The treatment of patients with angina pectoris refractory to medical therapy and unsuitable for revascularization procedures has yet not been well standardized. Previous retrospective studies and small prospective studies have suggested beneficial effects of spinal cord stimulation (SCS) in these patients. We created a Prospective Italian Registry of SCS to evaluate the short- and long-term clinical outcome of patients who underwent SCS device implantation because of severe refractory angina pectoris. Overall, 104 patients were enrolled in the registry (70 men, aged 68 +/- 17 years), most of whom (83%) had severe coronary artery disease. Average follow-up was 13.2 +/- 8 months. Overall, 17 patients (16%) died, 8 (8%) due to cardiac death. Among clinical variables, only age was found to be significantly associated both with total mortality (p = 0.04) and cardiac mortality (p = 0.02) on Cox regression analysis. A significant improvement of anginal symptoms (> or =50% reduction of weekly anginal episodes, compared with baseline) occurred in 73% of patients, and Canadian Cardiovascular Society angina class improved by > or =1 class in 80% and by > or =2 classes in 42% of patients, with a relevant reduction in the rate of hospital admission and days spent in the hospital because of angina (p <0.0001 for both). No life-threatening or clinically serious complications were observed. The most frequent side effect consisted of superficial infections, either at the site of puncture of electrode insertion or of the abdominal pocket, which occurred in 6 patients. In conclusion, our prospective data point out that SCS can be performed safely and is associated with a sustained improvement of anginal symptoms in a relevant number of patients with refractory stable angina pectoris.

Implantable devices for pain control: spinal cord stimulation and intrathecal therapies

Untreated chronic pain is costly to society and to the individual suffering from it. The treatment of chronic pain, a multidimensional disease, should rely on the expertise of varying health care providers and should focus not only on the neurobiological mechanisms of the process but also on the psychosocial aspects of the disease. Implantable devices are costly and invasive, and such efficacious therapies should be used only when more conservative and less costly therapies have failed to provide relief of pain and suffering. Spinal cord stimulation provides neuromodulation of neuropathic, but not nociceptive, pain signals and when used for appropriate indications in the right individuals provides approximately 60-80% long-term pain relief in 60-80% of patients trialled for efficacy. Intrathecal therapies with opioids such as morphine, fentanyl, sufentanil or meperidine--or non-opioids such as clonidine or bupivacaine--provide analgesia in patients with nociceptive or neuropathic pain syndromes. Baclofen, intrathecally, provides profound relief of muscle spasticity due to multiple sclerosis, spinal cord injuries, brain injuries or cerebral palsy.

Spinal Cord Stimulation: A Comparison of Efficacy versus Other Novel Treatments for Refractory Angina Pectoris

Recently much attention has been directed toward novel treatment alternatives for refractory angina pectoris. Refractory angina is persistent stable class III or IV angina despite maximally tolerated medical treatment in patients with end-stage coronary artery disease. Transmyocardial laser revascularization (TMLR), gene therapy, intermittent urokinase therapy, enhanced external balloon counterpulsation, and spinal cord stimulation have all been employed to treat refractory angina pectoris. TMLR and gene therapy are invasive open-chest procedures that have yielded controversial results. Intermittent urokinase and enhanced external balloon counterpulsation studies have limited follow-up times and require multiple clinic visits for treatment. Spinal cord stimulation has a proven short- and long-term efficacy and cost-effectiveness in the treatment of refractory angina. When compared to coronary artery bypass grafting (CABG), it has been shown to decrease the frequency of anginal attacks and consumption of short-acting nitrates to the same extent in refractory angina. Spinal cord stimulation's safety profile has also been well established and it can be used concurrently with cardiac pacemakers or MRI systems, provided the proper precautions are taken. Since spinal cord stimulation is a minimally invasive procedure with a favorable efficacy and safety profile, it should be considered as a valid treatment alternative after medical management has failed in refractory angina prior to implementing invasive modalities such as TMLR or gene therapy.

Syndrome X

Syndrome X, defined as typical angina with positive exercise test results and normal coronary angiographic findings, represents a multifactorial pathophysiologic state that may range from abnormalities in pain perception to abnormalities in endothelial- and nonendothelial-dependent coronary flow reserve associated with myocardial ischemia. Treatment begins with accurate diagnosis by means of a comprehensive coronary vascular reactivity evaluation. This may lay the groundwork for appropriate treatment. The management of patients with syndrome X is challenging, and it may be necessary to attempt various medications depending on the patient's response. We feel that the first step in the treatment is accurate diagnosis. This is done by performing a functional angiogram (assessment of endothelial-dependent and endothelial-independent coronary flow reserve). In those without evidence of coronary flow reserve abnormalities, reassurance might be curative; however, in those who continue to have symptoms, a trial of imipramine therapy at a dose of 50 mg/d may be attempted, provided other organic disorders (in particular gastrointestinal disorders) are excluded. Those who demonstrate evidence of abnormal coronary vascular reactivity are approached as outlined in Figure 1. Patients are advised to avoid medications that may cause coronary "spasm." We routinely refer our patients to the cardiovascular health clinic for risk factor management and an exercise program. Our first choice of medications usually consists of slow-release calcium channel blockers. We tend to start with a once-a-day regimen, and based on the response, we occasionally change the regimen to twice a day. If the functional angiogram reveals concomitant epicardial disease, then nitrates are added to the medical regimen. Angiotensin-converting enzyme inhibitors are part of the treatment if the patient has hypertension or diabetes or if calcium channel blocker therapy fails. l-Arginine at an initial dosage of 1 g three times daily is added and may be increased to 3 g three times daily if no contraindications are present. Because there are no data regarding the effect of l-arginine, which may affect insulin secretion, in patients with diabetes, we use caution in this patient population. There is no "gold standard" therapy for syndrome X, so each patient may respond differently to the initial medical therapy. Thus, we follow these patients closely to monitor their response to treatment.