Effect of spinal cord stimulation on regional myocardial perfusion assessed by positron emission tomography

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.

Newer Therapies for Management of Stable Ischemic Heart Disease With Focus on Refractory Angina

Ischemic heart disease remains a major public health problem nationally and internationally. Stable ischemic heart disease (SIHD) is one of the clinical manifestations of ischemic heart disease and is generally characterized by episodes of reversible myocardial demand/supply mismatch, related to ischemia or hypoxia, which are usually inducible by exercise, emotion, or other stress and reproducible-but which may also be occurring spontaneously. Improvements in the treatment of acute coronary syndromes along with increasing prevalence of cardiovascular risk factors, including diabetes and obesity, have led to increasing population of patients with SIHD. A significant number of these continue to have severe angina despite medical management and revascularization procedures performed and may progress to refractory angina. This article reviews the newer therapies in the treatment of SIHD with special focus in treating patients with refractory angina.

Positron range in PET imaging: non-conventional isotopes

In addition to conventional short-lived radionuclides, longer-lived isotopes are becoming increasingly important to positron emission tomography (PET). The longer half-life both allows for circumvention of the in-house production of radionuclides, and expands the spectrum of physiological processes amenable to PET imaging, including processes with prohibitively slow kinetics for investigation with short-lived radiotracers. However, many of these radionuclides emit 'high-energy' positrons and gamma rays which affect the spatial resolution and quantitative accuracy of PET images. The objective of the present work is to investigate the positron range distribution for some of these long-lived isotopes. Based on existing Monte Carlo simulations of positron interactions in water, the probability distribution of the line of response displacement have been empirically described by means of analytic displacement functions. Relevant distributions have been derived for the isotopes (22)Na, (52)Mn, (89)Zr, (45)Ti, (51)Mn, (94 m)Tc, (52 m)Mn, (38)K, (64)Cu, (86)Y, (124)I, and (120)I. It was found that the distribution functions previously found for a series of conventional isotopes (Jødal et al 2012 Phys. Med. Bio. 57 3931-43), were also applicable to these non-conventional isotopes, except that for (120)I, (124)I, (89)Zr, (52)Mn, and (64)Cu, parameters in the formulae were less well predicted by mean positron energy alone. Both conventional and non-conventional range distributions can be described by relatively simple analytic expressions. The results will be applicable to image-reconstruction software to improve the resolution.

Spinal cord stimulation is safe and feasible in patients with advanced heart failure: early clinical experience

AIMS

Pre-clinical work suggests that upper thoracic spinal cord stimulation (SCS) may have therapeutic effects in the treatment of heart failure (HF). We therefore aim to assess the safety and feasibility of SCS in HF patients.

METHODS AND RESULTS

A prospective, randomized, double-blind, crossover pilot study was conducted in symptomatic HF patients receiving optimal medical therapy. Patients were implanted with an SCS system and randomized to an SCS-ACTIVE, delivered at 90% paraesthesia threshold, or an SCS-INACTIVE phase for 3 months, followed by a 1-month washout period and crossover to the alternative phase. The safety of SCS therapy was assessed by death and cardiac events. Implantable cardioverter defibrillator (ICD) function in the presence of SCS was tested by defibrillation testing during SCS system implant and review of real-time and stored electrograms during follow-up. The efficacy of SCS therapy was assessed by changes in patient symptoms, LV function, and BNP level. Nine patients were investigated. In all cases, ICD sensing, detection, and therapy delivery were unaffected by SCS. During follow-up, one patient died and one was hospitalized for HF while in the SCS-INACTIVE phase, and two patients had HF hospitalizations during the SCS-ACTIVE phase. Symptoms were improved in the majority of patients with SCS, while markers of cardiac structure and function were, in aggregate, unchanged.

CONCLUSION

This study shows that an SCS system can be safely implanted in patients with advanced HF and that the SCS system does not interfere with ICD function.

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.

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.

Transcutaneous electrical nerve stimulation induces vasodilation in healthy controls but not in refractory angina patients

CONTEXT

Transcutaneous electrical nerve stimulation (TENS) is an effective treatment option to relieve ischemic pain in refractory angina pectoris (RAP). In healthy persons, TENS enhances local blood flow, but the mechanism responsible for the anti-ischemic effect in RAP seems to be different.

OBJECTIVE

The aim of the present investigation was to compare the difference in blood flow and vasodilatory response to TENS between angina patients and healthy controls and evaluate how vascular response in these groups is affected by amperage dosage above and below motor threshold levels.

METHODS

Our study evaluated upper limb vascular responses to low- and high-dose TENS (below and above motor threshold) in RAP patients compared with healthy controls. TENS was applied on the nondominating forearm. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. Forearm vascular resistance (FVR) was determined (mean arterial pressure [MAP]/FBF). Measurements were done during baseline, low-dose TENS, high-dose TENS, and during recovery.

RESULTS

A significant dose-dependent increase in FBF in response to TENS stimulation was seen in controls (n=18) but not in RAP (n=23) (P=0.008). There was no significant difference in FVR ratio (FVR(stim)/FVR(ctrl)) between control (n=7) and RAP (n=23) groups at low dose (controls, 5.7+/-21%; RAP, 9.7+/-20%) or recovery (controls, -4.6+19%; RAP, 5.9+25%). High-dose TENS resulted in a significantly reduced FVR ratio (-16.8+/-11%) in controls (n=7) compared with RAP (1.6+/-32%, n=23) (P=0.02).

CONCLUSION

High-dose TENS induces forearm vasodilation in healthy subjects but not in patients with RAP. These findings suggest that TENS has different vascular effects in patients with severe coronary artery disease compared with healthy controls.

A study to assess changes in myocardial perfusion after treatment with spinal cord stimulation and percutaneous myocardial laser revascularisation; data from a randomised trial

Background

Spinal cord stimulation (SCS) and percutaneous myocardial laser revascularisation (PMR) are treatment modalities used to treat refractory angina pectoris, with the major aim of such treatment being the relief of disabling symptoms. This study compared the change in myocardial perfusion following SCS and PMR treatment.

Methods

Subjects with Canadian Cardiovascular Society class 3/4 angina and reversible perfusion defects as assessed by single-photon emission computed tomographic myocardial perfusion scintigraphy were randomised to SCS (34) or PMR (34). 28 subjects in each group underwent repeat myocardial perfusion imaging 12 months post intervention. Visual scoring of perfusion images was performed using a 20-segment model and a scale of 0 to 4.

Results

The mean (standard deviation) baseline summed rest score (SRS) and stress scores (SSS) were 4.6 (5.7) and 13.6 (9.0) in the PMR group and 6.1 (7.4) and 16.8 (11.6) in the SCS group. At 12 months, SRS was 5.5 (6.0) and SSS 15.3 (11.3) in the PMR group and 6.9 (8.2) and 15.1 (10.9) in the SCS group. There was no significant difference between the two treatment groups adjusted for baseline (p = 1.0 for SRS, p = 0.29 for SSS).

Conclusion

There was no significant difference in myocardial perfusion one year post treatment with SCS or PMR.

Neurostimulation for refractory angina pectoris

Spinal cord stimulation (SCS) has been shown to be particularly useful, safe and effective treatment in the management of patients with refractory angina pectoris and those unsuitable for percutaneous or surgical revascularisation. Clinical and experimental research has shown that it decreases myocardial ischemia without masking the clinical symptoms of its imminent development. In addition to providing pain relief, neurostimulation has also been shown to improve microcirculatory blood flow and increase the myocardial threshold for ischaemia. The anti-ischaemic effects of SCS have been evaluated by: (a) exercise testing, (b) ambulatory electrocardiogram (ECG), and (c) invasive measurements of lactate from coronary sinus blood samples. Patients have reported not only significantly fewer angina attacks but also decreased consumption of glyceryl trinitrate and improved quality of life. A number of mechanisms have been proposed including placebo effects, primary anti-nociceptive effects, involvement of endogenous opiates, anti sympathetic nervous system effects, increases in coronary blood flow, and redistribution of myocardial blood flow.

Spinal Cord Stimulation for Refractory Angina in a Patient Implanted with a Cardioverter Defibrillator

Spinal cord stimulation is currently used to treat refractory angina. Some concerns may arise about the possible interaction concerning the spinal cord stimulator in patients already implanted with a pacemaker or a cardioverter defibrillator. We are going to describe the successful implantation of a spinal cord stimulator in a patient previously implanted with a cardioverter defibrillator.

Spinal Cord Stimulation Significantly Improves Refractory Angina Pectoris-A Local Experience

BACKGROUND

Severe refractory angina pectoris can occur in end-stage coronary artery disease despite maximal medical and revascularization therapy. Spinal cord stimulation is an under-utilized but well-established modality for the treatment of intractable angina pain.

AIM

To illustrate the practical, beneficial and effective use of spinal cord stimulation as a treatment option for refractory angina in a local context.

METHOD

A case series clinical audit of 11 patients with refractory angina treated with spinal cord stimulation over a one-year period was carried out. Baseline, three-month, six-month and two-year functional assessment data and subjective patient reports on their symptoms were evaluated.

RESULTS

Spinal cord stimulation improves six-minute walk distance, exercise duration, New York Heart Association functional class, Likert score, and number of angina free days per week for at least one year over two years of follow-up.

CONCLUSION

Spinal cord stimulation is an effective medium-term treatment option for refractory angina pectoris with significant benefits to functional parameters and patient symptoms. Spinal cord stimulation is an under-utilized but well-established modality for the treatment of intractable angina pain. We report a small case series clinical audit of patients who gained significant functional and symptomatic benefits from this treatment.

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.

History of neuroaugmentative procedures

Neuroaugmentation, the use of chronic stimulation of the brain and spinal cord for pain management, developed during the past 30 years. It evolved, however, from concepts of pain treatment that were based on observations and clinical experience dating back an additional two decades or more. The appreciation of the role of the extralemniscal system and descending influences from the brain in modulation of pain perception led to the Melzack-Wall gate theory. The concept proposed in that theory, that pain perception could be lessened by increasing activity in neural structures not associated with pain, led to chronic stimulation of deep brain and spinal cord as a modality for the management of chronic pain. Both brain and spinal structures emerged as targets for neuroaugmentation.

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.

Neuromodulation therapy does not influence blood flow distribution or left-ventricular dynamics during acute myocardial ischemia

OBJECTIVES

Electrical stimulation of the dorsal aspect of the upper thoracic spinal cord is used increasingly to treat patients with angina pectoris refractory to conventional therapeutic strategies. The purpose of this study was to determine whether spinal cord stimulation (SCS) in dogs affects regional myocardial blood flow and left-ventricular (LV) function before and during transient obstruction of the left anterior descending coronary artery (LAD).

METHODS

In anesthetized dogs, regional myocardial blood flow distribution was determined using radiolabeled microspheres and left-ventricular function was measured by impedance-derived pressure-volume loops. SCS was accomplished by stimulating the dorsal T1-T2 segments of the spinal cord using epidural bipolar electrodes at 90% of motor threshold (MT) (50 Hz, 0.2-ms duration). Effects of 5-min SCS were assessed under basal conditions and during 4-min occlusion of the LAD.

RESULTS

SCS alone evoked no change in regional myocardial blood flow or cardiovascular indices. Transient LAD occlusion significantly diminished blood flow within ischemic, but not in non-ischemic myocardial tissue. Left ventricular pressure-volume loops were shifted rightward during LAD occlusion. Cardiac indices were altered similarly during LAD occlusion and concurrent SCS.

CONCLUSIONS

SCS does not influence the distribution of blood flow within the non-ischemic or ischemic myocardium. Nor does it modify LV pressure-volume dynamics in the anesthetized experimental preparation.

Clinical outcome of patients treated with spinal cord stimulation for therapeutically refractory angina pectoris. The Working Group on Neurocardiology

OBJECTIVE

To determine morbidity and mortality characteristics in patients treated with electrical neuromodulation for refractory angina pectoris.

DESIGN

A retrospective multicentre study of patients treated with spinal cord stimulation between 1987 and 1997; 21 centres were contacted and 14 responded.

SETTING

Specialist centres worldwide.

PATIENTS

Questionnaires were returned on 517 patients, of whom 71% were male. One was lost to follow up. Mean (SD) age was 63.9 (10.1) years. Duration of angina pectoris was 8.1 (6.3) years.

RESULTS

Before spinal cord stimulation, 66% of the patients had experienced myocardial infarction, 68% had three vessel disease, and in 24% the left ventricular ejection fraction (LVEF) was </= 40%. Percutaneous transluminal coronary angioplasty and bypass surgery were performed in 17% and 58% of the subjects, respectively. During a median follow up of 23 months (range 0 to 128), 103 patients died (52 from a cardiac cause, 25 from a non-cardiac cause, and 26 from an unknown cause). Annual all cause mortality was 7-8%; annual cardiovascular fatality was 3.5-5%. Mortality was univariately related to sex, number of diseased vessels, number of revascularisation procedures, previous myocardial infarction, LVEF, insulin dependent diabetes, beta blocking agents, and angiotensin converting enzyme inhibitors. Multiple variate analysis showed that LVEF, sex, beta blockers, and age >/= 71 years were independent predictors of mortality. During spinal cord stimulation, New York Heart Association functional class improved from 3.5 to 2.1 (p < 0.01); 25 of the deceased patients (24%) and 32 survivors (8%) experienced myocardial infarction; hospital admissions were significantly (p < 0.001) more common in the deceased group (66% v 37%).

CONCLUSIONS

The clinical outcome of patients with intractable angina is not adversely affected by the chronic use of neurostimulation.

Visceral chest pain in unstable angina pectoris and effects of transcutaneous electrical nerve stimulation. (TENS). A review

A substantial proportion of patients with chest pain referred to hospital, show signs of coronary artery disease. Anginal pain could be conceptualized as a warning signal for coronary artery disease and impending death. But, for many reasons this theory is partly disputed. Firstly, not all ischemic episodes are accompanied by anginal pain (silent ischemia). Secondly, chest pain indistinguishable from true angina pectoris may be the result of other abnormalities of thoracic viscera. Nevertheless acute severe cardiac ischemia often gives rise to anginal chest pain. Unstable angina pectoris is carrying a higher risk for future events in spite of intensive medical treatment. A special problem are patients awaiting coronary intervention because of severe ischemia and maximum medical treatment, who experience ischemic pain. New treatment regimens are needed for these patients. This review discusses the symptom of visceral pain from the heart, angina pectoris, its relation to ischemia and unstable angina pectoris. It also addresses the role of afferent nerve stimulation (transcutaneous electrical nerve stimulation, TENS) in the treatment of severe angina pectoris as well as recent findings of TENS applicability in unstable angina.

Spinal cord stimulation for the treatment of refractory angina pectoris: a two-year follow-up

Twenty-three patients affected by severe, refractory angina were submitted to permanent spinal cord stimulation (SCS) and then followed in our outpatient clinic for 24 months. During the follow-up period, the number of weekly angina episodes drastically dropped from 9.2 (preimplant) to 1.8 in the 3rd, 2.5 in the 6th, 4.5 in the 12th, and 4.2 in the 24th month, with a statistically significant difference (P < 0.01) between the first and last values. A significant increase in the average exercise time from 320 +/- 120 seconds (in baseline condition) to 410 +/- 115 seconds (during SCS) was observed at the treadmill stress test (P < 0.01). SCS was well tolerated by all the patients. However, 7 patients died during follow-up (3 myocardial infarctions, 2 noncardiac deaths, and 2 sudden deaths). Three generators were replaced because of battery depletion after 15, 17, and 21 months. No serious complication was observed. In conclusion, in patients with otherwise intractable angina or already submitted to myocardial revascularization, SCS is very effective in reducing the number of angina episodes. The time of the work during exercise stress test is also significantly prolonged.

Electrical stimulation versus coronary artery bypass surgery in severe angina pectoris: the ESBY study

BACKGROUND

Spinal cord stimulation (SCS) has been shown to have antianginal and anti-ischemic effects in severe angina pectoris. The present study was performed to investigate whether SCS can be used as an alternative to coronary artery bypass grafting (CABG) in selected patient groups, ie, patients with no proven prognostic benefit from CABG and with an increased surgical risk.

METHODS AND RESULTS

One hundred four patients were randomized (SCS, 53; CABG, 51). The patients were assessed with respect to symptoms, exercise capacity, ischemic ECG changes during exercise, rate-pressure product, mortality, and cardiovascular morbidity before and 6 months after the operation. Both groups had adequate symptom relief (P<.0001), and there was no difference between SCS and CABG. The CABG group had an increase in exercise capacity (P=.02), less ST-segment depression on maximum (P=.005) and comparable (P=.0009) workloads, and an increase in the rate-pressure product both at maximum (P=.0003) and comparable (P=.03) workloads compared with the SCS group. Eight deaths occurred during the follow-up period, 7 in the CABG group and 1 in the SCS group. On an intention-to-treat basis, the mortality rate was lower in the SCS group (P=.02). Cerebrovascular morbidity was also lower in the SCS group (P=.03).

CONCLUSIONS

CABG and SCS appear to be equivalent methods in terms of symptom relief in this group of patients. Effects on ischemia, morbidity, and mortality should be considered in the choice of treatment method. Taking all factors into account, it seems reasonable to conclude that SCS may be a therapeutic alternative for patients with an increased risk of surgical complications.

Refractory angina pectoris in end-stage coronary artery disease: evolving therapeutic concepts

Refractory angina pectoris in coronary artery disease is defined as the persistence of severe anginal symptoms despite maximal conventional antianginal combination therapy. Further, the option to use an invasive revascularization procedure such as percutaneous coronary balloon angioplasty or aortocoronary bypass grafting must be excluded on the basis of a recent coronary angiogram. This coronary syndrome, which represents end-stage coronary artery disease, is characterized by severe coronary insufficiency but only moderately impaired left ventricular function. Almost all patients demonstrated severe coronary triple-vessel disease with diffuse coronary atherosclerosis, had had one or more myocardial infarctions, and had undergone aortocoronary bypass grafting (70% of cases). We present three new approaches with antiischemic properties: long-term intermittent urokinase therapy, transcutaneous and spinal cord electrical nerve stimulation, and transmyocardial laser revascularization.

Stimulation of the central and peripheral nervous system for the control of pain

After suffering some setbacks since its introduction in 1967, stimulation of the spinal and peripheral nervous systems has undergone rapid development in the last ten years. Based on principles enunciated in the Gate Control Hypothesis that was published in 1968, stimulation-produced analgesia [SPA] has been subjected to intensive laboratory and clinical investigation. Historically, most new clinical ideas in medicine have tended to follow a three-tiered course. Initial enthusiasm gives way to a reappraisal of the treatment or modality as side-effects or unanticipated problems arise. The last and third phase proceeds at a more measured pace as the treatment is refined by experience. This review is divided into three parts as it traces the progress of spinal cord stimulation [SCS] and peripheral nerve stimulation [PNS]. The review commences with a discussion of the theory of SCS and PNS, and is followed by early reports during which it became apparent that the modality is essentially only effective in the treatment of neuropathic pain. The last section describes the modern experience including efficacy in specific types of pain and concludes with recent accomplishments that dramatize the relief of pain which can be achieved in nonoperable peripheral vascular disease or myocardial ischemia. Over the years, a search for those transmitters that might be influenced by spinal cord stimulation focused on somatostatin, cholecystokinin (CCK), vasoactive intestinal polypeptide (VIP), neurotensin and other amines, although only substance "P" was implicated. More recently, in animal studies, evidence that GABA-ergic systems are affected may explain the frequent successful suppression of allodynia that follows spinal cord stimulation. During the past eight years, much attention has been directed to studies that use a chronic neuropathic pain model. While PNS held significant promise as a pain relieving modality, early electrode systems and their surgical implantation yielded variable results due to evolving technical and surgical skills. These results dramatically reduced the continued development of PNS, which then gave way to a preoccupation with SCS. Modern development of SCS with outcome studies, particularly in relation to failed back surgery syndrome [FBSS] and the outcome of peripheral nerve surgery for chronic regional pain syndromes, has earned both modalities a place in the ongoing management of patients with intractable neuropathic pain. The last section, dealing with pain of peripheral vascular and myocardial ischemia, is perhaps one of the more exciting developments in stimulation produced analgesia and as the papers discussed demonstrate, can provide a level of analgesia and efficacy that is unattainable by other treatment modalities. SCS and PNS has an important role to play in the management of conditions that are otherwise refractory to conservative or other conventional management.

Current views on neurostimulation in the treatment of cardiac ischemic syndromes

Most clinicians are still unacquainted with the beneficial effects of neurostimulation as an additional therapeutic strategy for severe angina pectoris. Patients with therapeutically refractory angina pectoris suffer from chest discomfort during minimal exercise, despite maximal tolerated antianginal drug therapy (at least 2 out of a beta-blocker, calcium-antagonist or long-acting nitrate). In these patients, revascularization procedures, such as a percutaneous transluminal coronary angioplasty or coronary artery bypass surgery, are often technically impossible because of diffuse coronary artery disease or should be withheld as a consequence of absolute contraindications such as severe left ventricular dysfunction. All patients have inoperable multivessel disease, experienced one or more myocardial infarctions, and were treated by earlier invasive interventions. This group of patients are severely physically and psychologically disabled by their intractable angina pectoris. Available published data and the neurostimulation experience of the authors are reviewed in relation to the treatment of cardiac ischemic syndromes. We conclude that neurostimulation is an effective therapeutic adjuvant for patients with severe angina pectoris unresponsive to standard treatment. This treatment modality appears to be safe, and a promising tool for other ischemic cardiac syndromes.

Effect of spinal cord stimulation on myocardial blood flow assessed by positron emission tomography in patients with refractory angina pectoris

Spinal cord stimulation in angina pectoris increases exercise capacity and reduces both anginal attacks and ischemic electrocardiographic signs. This suggests an anti-ischemic action, perhaps through changes in myocardial blood flow. In 9 patients, regional myocardial blood flow was studied with positron emission tomography before and after 6 weeks of spinal cord stimulation, both at rest and during a dipyridamole stress test. Frequency of anginal attacks and consumption of short-acting nitrates were assessed by patient diaries. Exercise duration and time to angina were measured with treadmill exercise tests. After 6 weeks of stimulation, both frequency of daily anginal attacks and nitrogen consumption decreased (3.7 +/- 1.7 vs 1.4 +/- 1.0 [p <0.01] and 2.8 +/- 2.2 vs 1.1 +/- 1.2 tablets [p = 0.01], respectively); exercise duration and time to angina increased (358 +/- 165 vs 493 +/- 225 seconds [p <0.01] and 215 +/- 115 vs 349 +/- 213 seconds [p = 0.02], respectively); and ST-segment depression during dipyridamole stress testing was reduced (0.17 [0 to 0.5] mV vs 0.09 [0 to 0.2] mV, p = 0.04) (all data mean +/- SD). Total resting blood flow remained unchanged (115 +/- 29 vs 127 +/- 31 ml/min/100 g, p = 0.31), but flow reserve decreased (146 +/- 43% vs 122 +/- 39%, p = 0.04). The coefficient of variation of flow, representing flow heterogeneity, decreased after treatment, both at rest (20.1 +/- 3.8% vs 17.4 +/- 2.6%, p = 0.04) and after dipyridamole stress (26.2 +/- 4.4% vs 22.9 +/- 5.5%, p = 0.02). Thus, spinal cord stimulation is clinically effective due to homogenization of myocardial blood flow. Since flow reserve decreases despite clinical improvement, the dipyridamole effect may be blunted by spinal cord stimulation.

Treatment of chronic unstable angina pectoris: use of a totally implantable programmable device for continuous intrathecal infusion of opiates: case report

We report the case of a 70-year-old man with a 17-year history of angina pectoris, who had previously suffered two documented myocardial infarctions and undergone multiple diagnostic cardiac catheterizations, two coronary artery bypass operations, and several percutaneous transluminal coronary angioplasty procedures. The patient had experienced unstable angina for the past 3 years refractory to maximal medical therapy and was unsuitable for further attempts at revascularization. After a successful trial of epidural infusion of morphine, a totally implantable programmable continuous-infusion device with an intrathecal catheter was implanted in the patient on August 18, 1993, resulting in maintained pain resolution. His gardening, carpentry, and other activities of daily living were limited only by shortness of breath. Six months later, the pump treatment did not mask the development of a myocardial infarction. To the best of our knowledge, this is the first report of the use of continuous intrathecal infusion of morphine or the use of a totally implantable programmable infusion device for angina pectoris. We propose that in carefully selected patients with chronic unstable angina, continuous intrathecal infusion of morphine may relieve effort-induced pain without resulting in myocardial infarction.

Effects of spinal cord stimulation on myocardial ischaemia during daily life in patients with severe coronary artery disease. A prospective ambulatory electrocardiographic study

BACKGROUND

Spinal cord stimulation (SCS) may be a useful additional therapy for pain in patients with therapeutically refractory angina pectoris. But doubts remain about whether it also relieves ischaemia.

METHODS

Indices of ischaemia were studied with and without SCS in 10 patients with otherwise intractable angina and evidence of myocardial ischaemia on 48 h ambulatory electrocardiographic (ECG) recording. Primary end points assessed by 48 h ECG recordings were total ischaemic burden, number of ischaemic episodes, and duration of ischaemic episodes. In addition, symptoms were assessed by a diary of glyceryl trinitrate intake and angina attacks.

RESULTS

During SCS the total ischaemic burden of the entire group was significantly reduced from a median of 27.9 (1.9-278.2) before SCS to 0 (0-70.2) mm x min with SCS (p < 0.03). In six out of the 10 patients there was no myocardial ischaemia during 48 h ambulatory ECG monitoring with SCS. The number of ischaemic episodes was reduced from a median of 3 (1-15) before SCS to 0 (0-9) with SCS (p < 0.04). The duration of ischaemic episodes decreased from a median of 20.6 (1.7-155.4) min before SCS to 0 (0-48.3) min with SCS (p < 0.03). This was accompanied by a significant improvement in symptoms with a reduction in daily glyceryl trinitrate intake from a median of 3.0 (0-10) before SCS to 0.3 (0-10) tablets per 48 h (p < 0.02) and a decrease in the frequency of anginal attacks from a median of 5.5 (2-14) before SCS to 1.0 (0-10) per 48 h with SCS (p < 0.03).

CONCLUSIONS

SCS not only reduced symptoms but also myocardial ischaemia. Therefore, SCS appears to be both a safe and an effective therapy for patients with refractory angina.