Title:
Gastric electrical stimulation: an evidence-based analysis.

Abstract:
The objective of this analysis was to assess the effectiveness, safety and cost-effectiveness of gastric electrical stimulation (GES) for the treatment of chronic, symptomatic refractory gastroparesis and morbid obesity.
GASTROPARESIS - EPIDEMIOLOGY: Gastroparesis (GP) broadly refers to impaired gastric emptying in the absence of obstruction. Clinically, this can range from the incidental detection of delayed gastric emptying in an asymptomatic person to patients with severe nausea, vomiting and malnutrition. Symptoms of GP are nonspecific and may mimic structural disorders such as ulcer disease, partial gastric or small bowel obstruction, gastric cancer, and pancreaticobiliary disorders. Gastroparesis may occur in association with diabetes, gastric surgery (consequence of peptic ulcer surgery and vagotomy) or for unknown reasons (idiopathic gastroparesis). Symptoms include early satiety, nausea, vomiting, abdominal pain and weight loss. The majority of patients with GP are women. The relationship between upper gastrointestinal symptoms and the rate of gastric emptying is considered to be weak. Some patients with markedly delayed gastric emptying are asymptomatic and sometimes, severe symptoms may remit spontaneously. Idiopathic GP may represent the most common form of GP. In one tertiary referral retrospective series, the etiologies in 146 GP patients were 36% idiopathic, 29% diabetic, 13% postgastric surgery, 7.5% Parkinson's disease, 4.8% collagen vascular disorders, 4.1% intestinal pseudoobstruction and 6% miscellaneous causes. The true prevalence of digestive symptoms in patients with diabetes and the relationship of these symptoms to delayed gastric emptying are unknown. Delayed gastric emptying is present in 27% to 58% of patients with type 1 diabetes and 30% with type 2 diabetes. However, highly variable rates of gastric emptying have been reported in type 1 and 2 diabetes, suggesting that development of GP in patients with diabetes is neither universal nor inevitable. In a review of studies examining gastric emptying in patients with diabetes compared to control patients, investigators noted that in many cases the magnitude of the delay in gastric emptying is modest. GP may occur as a complication of a number of different surgical procedures. For example, vagal nerve injury may occur in 4% to 40% of patients who undergo laparoscopic fundoplication for gastroesophageal reflux disease. The prevalence of severe, refractory GP is scantily reported in the literature. Using data from a past study, it has been estimated that the prevalence of severe, symptomatic and refractory GP in the United States population is 0.017%. Assuming an Ontario population of 13 million, this would correspond to approximately 2,000 people in Ontario having severe, symptomatic, refractory GP. The incidence of severe refractory GP estimated by the United States Food and Drug Administration (FDA) is approximately 4,000 per year in the United States. This corresponds to about 150 patients in Ontario. Using expert opinion and FDA data, the incidence of severe refractory GP in Ontario is estimated to be about 20 to 150 per year.
To date, there have been no long-term studies confirming the beneficial effects of maintaining euglycemia on GP symptoms. However, it has been suggested that consistent findings of physiologic studies in healthy volunteers and diabetes patients provides an argument to strive for near-normal blood glucose levels in affected diabetes patients. Dietary measures (e.g., low fibre, low fat food), prokinetic drugs (e.g., domperidone, metoclopramide and erythromycin) and antiemetic or antinausea drugs (e.g, phenothiazines, diphenhydramine) are generally effective for symptomatic relief in the majority of patients with GP. For patients with chronic, symptomatic GP who are refractory to drug treatment, surgical options may include jejunostomy tube for feeding, gastrotomy tube for stomach decompression and pyloroplasty for gastric emptying. Few small studies examined the use of botulinum toxin injections into the pyloric sphincter. However, the contribution of excessive pyloric contraction to GP has been insufficiently defined and there have been no controlled studies of this therapy. Treatment with GES is reversible and may be a less invasive option compared to stomach surgery for the treatment of patients with chronic, drug-refractory nausea and vomiting secondary to GP. In theory, GES represents an intermediate step between treatment directed at the underlying pathophysiology, and the treatment of symptoms. It is based on studies of gastric electrical patterns in GP that have identified the presence of a variety of gastric arrhythmias. Similar to a cardiac pacemaker, it was hypothesized that GES could override the abnormal rhythms, stimulate gastric emptying and eliminate symptoms.
Obesity is defined as a body mass index (BMI) of at last 30 kg/m(2). Morbid obesity is defined as a BMI of at least 40 kg/m(2) or at least 35 kg/m(2) with comorbid conditions. Comorbid conditions associated with obesity include diabetes, hypertension, dyslipidemias, obstructive sleep apnea, weight-related arthropathies, and stress urinary incontinence. In the United States, the age-adjusted prevalence of extreme obesity (BMI ≥ 40 kg/m(2)) for adults aged 20 years and older has increased significantly in the population, from 2.9% (1988-1994) to 4.7% (1999-2000). An expert estimated that about 160,000 to 180,000 people are morbidly obese in Ontario.
Diet, exercise, and behavioural therapy are used to help people lose weight. Bariatric surgery for morbid obesity is considered an intervention of last resort for patients who have attempted first-line forms of medical management. Gastric stimulation has been investigated for the treatment of morbid obesity; the intention being to reduce appetite and induce early satiety possibly due to inhibitory effects on gastric motility and effects on the central nervous system (CNS) and hormones related to satiety and/or appetite. Possible advantages to GES for the treatment of morbid obesity include reversibility of the procedure, less invasiveness than some bariatric procedures, e.g., gastric bypass, and less side effects (e.g., dumping syndrome).
Electrical stimulation is delivered via an implanted system that consists of a neurostimulator and 2 leads. The surgical procedure can be performed via either an open or laparoscopic approach. An external programmer used by the physician can deliver instructions to the GES, i.e., adjust the rate and amplitude of stimulation (Figure 1). GES may be turned off by the physician at any time or may be removed. The battery life is approximately 4-5 years For treatment of GP, the GES leads are secured in the muscle of the lower stomach, 10 cm proximal to the pylorus (the opening from the stomach to the intestine), 1 cm apart and connected to an implantable battery-powered neurostimulator which is placed in a small pocket in the abdominal wall For treatment of morbid obesity, GES leads are implanted along the lesser curvature of the stomach where the vagal nerve branches spread, approximately 8 cm proximal to the pylorus. However, the implant positioning of the leads has been variably reported in the literature.
The Enterra Therapy System and the Transcend II Implantable Gastric Stimulation System (Medtronic Inc.) are both licensed as class 3 devices by Health Canada (license numbers 60264 and 66948 respectively). The Health Canada indications for use are:  ENTERRA THERAPY SYSTEM: "For use in the treatment of chronic intractable (drug-refractory) nausea and vomiting."
"For use in weight reduction for obese adults with a body mass index greater than 35."The GES device that is licensed by Health Canada for treatment of GP, produces high-frequency GES. Most clinical studies examining GES for GP have used high-frequency (4 times the intrinsic slow wave frequency, i.e., 12 cycles per minute), low energy, short duration pulses. This type of stimulation does not alter gastric muscular contraction and has no effect on slow wave dysrhythmias. The mechanism of action is unclear but it is hypothesized that high-frequency GES may act on sensory fibers directed to the CNS. The GES device licensed by Health Canada for treatment of morbid obesity produces low-frequency GES, which is close to or just above the normal/native gastric slow wave cycle (approximately 3 cycles/min.). This pacing uses low-frequency, high-energy, long-duration pulses to induce propagated slow waves that replace the spontaneous ones. Low-frequency pacing does not invoke muscular contractions. Most studies examining the use of GES for the treatment of morbid obesity use low-frequency GES. Under normal circumstances, the gastric slow wave propagates distally and determines the frequency and propagation direction of gastric peristalsis. Low-frequency GES aims to produce abnormal gastric slow waves that can induce gastric dysrhythmia, disrupt regular propagation of slow waves, cause hypomotility of the stomach, delay gastric emptying, reduce food intake, prolong satiety, and produce weight loss. In the United States, the Enterra Therapy System is a Humanitarian Use Device (HUD), meaning it is a medical device designated by the FDA for use in the treatment of medical conditions that affect fewer than 4,000 individuals per year. The Enterra Therapy System is indicated for "the treatment of chronic, drug- refractory nausea and vomiting secondary to GP of diabetes or idiopathic etiology" (not postsurgical etiologies). GES for morbid obesity has not been approved by the FDA and is for investigational use only in the United States. (ABSTRACT TRUNCATED)