EGG recording faces several technical challenges, many of them related to measuring cutaneous signals, rather than directly measuring electrical activity along the stomach mucosa or serosa. One of the parameters of the EGG analyses is the power of the signal, commonly thought to increase after the digestion of a meal. However, the power of the signal can also be influenced by the proximity of the electrode to the stomach wall, which can change as the stomach distends after a meal. Changes in frequency, such as tachyarrhythmias and bradyarrhythmias, are commonly reported. However, EGG artifacts, such as movement artifacts and signal drift, may limit interpretation. Simultaneous recordings of cutaneous and internal EGGs suggest that cutaneous EGG records more episodes of tachyarrhythmias, probably due to the accumulation of artifacts. The use of computer-assisted analysis, which may not be able to identify and eliminate movement artifacts, must be interpreted very cautiously. Day to day variability of the EGG is another important issue, as measured by repeated EGG in the same patient over a short period of time.
Several studies have compared EGG with gastric emptying tests and have reported a poor correlation between the two. Chen and colleagues performed both EGG and scintigraphic gastric emptying in 97 patients with symptoms suggestive of gastroparesis. Considering gastric emptying tests as the gold standard, the authors concluded that patients with delayed gastric emptying had either a lower percentage of normal slow waves, or a higher prevalence of gastric dysrhythmias, or both. However, the sensitivities of these three parameters were 24%, 42%, or 14%, respectively, while the corresponding specificities were 92%, 87%, and 100%. The authors concluded that an abnormal EGG may predict delayed gastric emptying, although a normal EGG will not rule out delayed gastric emptying. One hypothesis is that normal gastric myoelectrical activity is one of many prerequisites for normal gastric emptying.
Parkman and colleagues (1997) correlated abnormalities in EGG with gastric emptying and symptom severity in 72 patients with functional dyspepsia. Patients were recruited from those who were referred for a gastric emptying scintigraphy. A total of 22 patients (31%) had an abnormal EGG, and 22 (31%) had an abnormal gastric emptying test. The EGG was abnormal in 11 of the 22 patients (50%) with an abnormal gastric emptying test. If the gastric emptying scintigraphy is considered the gold standard, the EGG had a sensitivity of 50% and a specificity of 78%. While these data suggest that EGG cannot be substituted for gastric emptying scintigraphy, it must be noted that the two tests are measuring different aspects of gastric activity. Therefore, another question is the clinical significance of those with abnormal EGGs but negative emptying tests and whether the two tests are complementary. Patients with abnormalities in both tests tended to report increased symptom severity, but the authors did not comment on the diagnostic significance of this observation.
One study did focus on how EGG could be used as an adjunct to gastric emptying studies, by focusing on the subset of patients with known delayed gastric emptying and no dysrhythmias observed on the EGG. The authors concluded that while the patients with idiopathic gastroparesis were likely to have gastric dysrhythmias, patients with mechanical obstruction were more likely to have persistent and prominent three cycles per minute EGG patterns, which are seen in normal EGGs. This observation suggests that patients with known gastroparesis based on gastric emptying studies may be further evaluated with an EGG. If no dysrhythmias are found, the patients may be referred for further tests to identify subtle mechanical obstructions. If EGG dysrhythmias are found, the patients might benefit from a trial of a prokinetic agent. However, this study was retrospective in nature, and the results must be confirmed in larger prospective studies.
Other studies have focused on the use of EGG in diabetic patients as a research tool to study the pathogenesis of diabetic gastroparesis. Kawagishi and colleagues studied the relationship between glucose control, autonomic neuropathy, and EGG findings. They concluded that improved glycemic control and improved autonomic nerve function were associated with normalization of gastric myoelectrical activity. Mantides and colleagues reported that abnormalities in the EGG are frequently detected in diabetes even without symptoms of gastroparesis.
No study focused on the final patient outcomes in patients undergoing EGGs. Outcomes of interest could include the avoidance of unnecessary tests or unnecessary treatment, or the institution of potentially more effective treatment. Based on the studies reviewed here, due to the low sensitivity of EGG for diagnosis of gastric motility disorders compared to scintigraphic gastric emptying studies, it is unlikely that EGG can supplant tests of gastric emptying. As an adjunct to gastric emptying tests, one study suggested that EGG could be used to distinguish patients with mechanical obstruction from idiopathic gastroparesis. However, this one study did not include patient outcomes.
The current literature (2002 through 2006) suggests that EGG is primarily used as a research tool in patients with a variety of disorders. Other studies continue to focus on the technical performance of the test. No study was identified that elucidated the diagnostic performance of EGG in different populations of patients or how this information could be used to benefit patient management. In 2001, the American Gastroenterological Association published a medical position statement which offers the following conclusions:
"Although well-documented disorders of enteric nerve and muscle such as the pseudo-obstruction syndrome may result in nausea and vomiting, the role of gastrointestinal dysmotility and gastroparesis, in particular, in the patient with isolated chronic nausea and vomiting remains unclear. Although gastroparesis is common among patients in this category, its primacy remains in dispute, and the interrelationships between such entities as functional and psychogenic vomiting, idiopathic gastroparesis, and functional dyspepsia remain unclear. For these same reasons, the place of such tests of motor function as gastric emptying studies, electrogastrography, and manometry have not been defined, and the yield of such diagnostic studies has not been adequately compared with a therapeutic trial of an antiemetic and/or prokinetic agents."
2012 Year Update
A search of peer reviewed literature through April 2012 identified the following:
Ingestible pH and pressure capsule
Diagnostic Accuracy of Wireless Pressure and pH Capsule
Gastric emptying. Although gastric emptying scintigraphy is considered the reference standard for evaluating gastric emptying, several issues complicate its use as a reference test. Until recently, there has been a lack of standardization of the test (Abell, 2008). Differences in the test meal used, patient positioning, frequency, duration, and interpretation of imaging all limit the clinical utility of the test. Significant day-to-day variability in the rate of gastric emptying has been noted (Parkman, 2004, Gastroenterology, 1592-622).
There is limited knowledge regarding the capability of the gastric emptying test to discriminate between healthy individuals and those with known gastroparesis due to lack of standardization of the test and small patient samples in published studies. The study, which proposed a threshold of normality at 10% meal retention at four hours, included only 123 healthy subjects (Tougas, 2000). The cutoff point was set to include 95% of normal persons. However, it appears to be unknown if this same threshold adequately identifies persons who would otherwise be classified as having gastroparesis and who are candidates or responders to treatment.
There are few published studies that evaluate the ingestible capsule in relation to another measure of gastric emptying. Cassilly et al. (2008) evaluated the SmartPill and simultaneous gastric emptying scintigraphy in 15 healthy subjects. The capsule was ingested immediately after ingesting the radiolabeled test meal. In this study, the mean time for 50% gastric emptying by scintigraphy was 95 minutes, 90% gastric emptying by scintigraphy was 194 minutes, and gastric residence time by SmartPill was 261 minutes. The correlation of SmartPill to 50% gastric emptying time was 0.606 and to 90% gastric emptying time was 0.565. The average amount of meal remaining in the stomach at the time the SmartPill exited the stomach was 5.4%. This study only shows modest correlation of the SmartPill and gastric emptying scintigraphy. The study is too small to establish reference values for the SmartPill.
In the other study by Kuo et al. (2008), 87 healthy subjects and 61 subjects with symptoms and prior positive test results for gastroparesis were evaluated with both the SmartPill and gastric emptying scintigraphy. In this study, subjects ingested the capsule just before ingesting the standard meal. This resulted in five subjects who passed the SmartPill in less than 30 minutes, who were then subsequently considered to have invalid tests. Sixteen other subjects had equipment malfunctions, and two others dropped out.
Among the remaining 125 subjects, the correlation of SmartPill emptying time and scintigraphy at two hours was 0.63, and between SmartPill emptying time and scintigraphy at four hours was 0.73. In terms of the capability to discriminate between gastroparetic patients and healthy subjects, the area under the curve (AUC) was 0.83 for SmartPill, 0.82 for scintigraphy at four hours, and 0.79 for scintigraphy at two hours (all p>0.05 for statistical significance), indicating similar capability for discriminating between the two patient groups. At a cutoff point of 300 minutes for the SmartPill, which was established by calculating the ideal cutoff point from the data, the sensitivity was 65% and specificity was 87%. The sensitivity and specificity for scintigraphy using an established cutoff point from the literature of 10% at four hours was 44% and 93%, respectively.
In terms of adverse events reported in the study by Kuo et al. (2008), five subjects of 67 who did not retrieve the capsule required a second additional plain radiograph (x-ray) beyond five days to demonstrate that the capsule had been passed. Another patient had ingested a laxative that caused the capsule to be entrapped in a viscous mass. An unsuccessful endoscopy and treatment with intravenous erythromycin was required to pass the capsule from the stomach.
These data have several shortcomings regarding the use of the SmartPill. Because of the change in the protocol for use of the SmartPill from ingesting the capsule before the standard meal to after the standard meal to avoid fast exit of the SmartPill from the stomach, the results of Kuo et al (2008) may no longer represent the performance of the device as it is now intended to be used. The cutoff point for sensitivity and specificity was not prespecified; using visual inspection to identify a cutoff point overestimates the diagnostic characteristics of the test. Although overall, the AUCs between the SmartPill and scintigraphy are similar, the modest correlation between the two tests means that there are often discordant results. What such discordant results mean in terms of diagnosis and treatment are uncertain. Overall, the data are scant regarding the diagnostic performance of the SmartPill.
Whole gut transit time. Two studies assessed the use of the device for the purpose of measuring whole gut transit times. In one study by Maqbool et al. (2009), healthy asymptomatic individuals underwent simultaneous whole-gut scintigraphy and SmartPill assessment of whole gut transit times. The two techniques correlated with each other reasonably well. In another study by Rao et al. (2009), normal subjects and subjects with constipation had whole gut transit times assessed with radio-opaque markers and the SmartPill. The diagnostic accuracy of the two techniques in differentiating the two groups of patients was similar.
Colon transit time. In 2010, Camilleri and colleagues compared the wireless motility capsule to radio-opaque markers in 158 patients with chronic functional constipation. In this multicenter validation study, the authors reported positive percent agreement between the wireless motility capsule and radio-opaque markers was approximately 80% for colon transit time (95% confidence interval [CI]: 0.67 – 0.98) and small and large bowel transit time (95% CI: 0.67 – 0.89). No serious adverse events occurred in the study.
The FDA has received one adverse event report according to their MAUDE (Manufacturer and User Facility Device Experience) database, in which the capsule was trapped in the stomach of a patient and required endoscopic removal.
Clinical Utility of Wireless Pressure Capsule
Demonstration of clinical utility requires that the technology be associated with change(s) in management that lead to improved health outcomes. The evidence on the clinical utility of wireless pressure capsule is very limited, consisting of two retrospective analyses.
In a retrospective study of 83 patients evaluated for gastroparesis, small intestinal dysmotility and constipation, Kuo and colleagues (2011) found wireless motility capsule testing resulted in a new diagnosis in 44 patients (53%). Clinical management changes were recommended in 65 patients. These included changes in medication regimens in 39 patients (60%) and in nutrition programs in nine patients (13.8%). Four patients (6.2%) were referred to surgery for colectomy. Abnormal gastric emptying or small intestinal transit times did not influence patient management at all (p=NS). Abnormal colon transit times did not influence nutritional program changes (p=0.72) but did influence medication changes (p=0.02) and resulted in a trend toward increased surgical referrals (p=0.12). The authors believe wireless motility capsule testing eliminated the need for nuclear gastric emptying testing in 9 of 52 patients (17.3%), barium radiography testing in 7 of 13 patients (53.8%), and radio-opaque marker testing in 41 of 60 patients (68.3%). The authors noted a need for prospective studies to further understand wireless motility capsule testing and its role in patient management.
In a retrospective study of 86 patients with persistent symptoms of gastrointestinal dysmotility, despite normal endoscopic and radiologic test results, Rao and colleagues found evaluations with wireless motility capsule testing resulted in new diagnostic information in 26 of 50 patients (53%) with lower gastrointestinal symptoms (LGI) and 17 of 36 patients (47%) with upper gastrointestinal symptoms (UGI) (Rao, 2011, J Clin Gastroenterol). Clinical management was influenced by wireless motility capsule testing in 30% of patients with LGI symptoms and in 50% of patients with UGI symptoms. The authors indicated the retrospective nature of this study limits interpretation of results.
Ongoing Clinical Trials
A search of online site www.ClinicalTrials.gov in December 2011 found three open studies using a wireless motility capsule (SmartPill): the Colonic Transit Time Validation (CTT) study (NCT00857363), a study to assess gastric emptying speed in patients with diarrhea (NCT01114113) and a study to assess gastric acid output (NCT00702533).
The American and European Neurogastroenterology and Motility Societies issued a position paper on gastrointestinal transit evaluation in 2011 (Rao, 2011, Neurogastroenterol Motil). In this position paper, the wireless motility capsule is recommended by consensus for assessing gastric emptying, small bowel, colonic, and whole gut transit times in patients with suspected gastroparesis or gastrointestinal dysmotility in multiple regions. However, the position paper notes the clinical utility of identifying delays in small bowel transit times is unknown.
The American Gastroenterological Association’s (AGA) medical position on gastroparesis diagnosis and treatment does not mention the wireless motility capsule (Parkman, 2004, Gastroenterology:1589-91). Gastric emptying scintigraphy is considered the best accepted method to test for delays in gastric emptying. This position statement was created in 2004 and has not been updated. The AGA’s medical position on gastroesophageal reflux disease (GERD) indicates wireless pH monitoring may be used to evaluate suspected GERD when endoscopy is normal and manometry does not show any major abnormalities (Grade B: indicates recommended with fair evidence that it improves important outcomes) (Kahrilas, 2008).
An ingestible pH and pressure-sensing capsule (e.g., SmartPill® GI Monitoring System) is proposed as a means of evaluating gastric emptying time and small bowel, colonic, and whole gut transit times. This technology is used to evaluate suspected gastrointestinal motility disorders such as gastroparesis, intestinal dysmotility, and constipation. Available studies provide some information regarding the comparison of SmartPill to other techniques for measuring gastric emptying and whole-gut transit times, but this evidence primarily consists of concordance with available tests. Since the available tests, such as nuclear scintigraphy, are imperfect gold standards, it is not possible to determine the true sensitivity and specificity of SmartPill. The results of the concordance studies reveal a moderate correlation with alternative tests but provide only limited further information on the true accuracy of the test in clinical care. Evaluation of cases with discordant results would be of particular value, and ideally, these studies should be linked to therapeutic decisions and to meaningful clinical outcomes. The evidence to date on clinical utility of testing is lacking, consisting of a small number of retrospective studies. This does not provide sufficient information to determine whether health outcomes are improved as a result of the information provided by the SmartPill. Since the impact of this technology on net health outcome is unknown, this technology is considered experimental, investigational and unproven.
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