Electrogastrography is a non-invasive technique for recording gastric myoelectrical activity using cutaneous electrodes placed on the abdominal skin over the stomach. The surface recording obtained using electrography is called the electrogastrogram. In this review, both electrogastrography and electrogastrogram are abbreviated to EGG: "EGG" refers to the electrogastrography (the technique of recording the electrogastrogram) and "the EGG" refers to the electrogastrogram (the recording).
The EGG was first introduced in 1922 by Alvarez,1
rediscovered by Davis et al2
in 1957 and popularized in 1990s.3
Due to its non-invasive nature, EGG has received substantial attention among researchers and clinicians and also the controversies and concerns arosed. Some researchers use the EGG as a non-invasive measure of gastric slow waves and even consider it as a surrogate of gastric motility, whereas, others claim the EGG is flawed or even merely an artifact of gastric motions. In this article we will review available information in the literature and try to give readers an objective assessment of this non-invasive technique in detecting gastric slow waves.
To judge whether EGG is useful as a research and/or clinical tool, one needs to first understand completely what can be measured by EGG and how the EGG should be recorded and interpreted. Although it was unclear before 1960s whether the EGG was a recording of gastric myoelectrical activity or contractile activity, it is now clear that the EGG is a measurement of gastric slow waves. We will first review electrophysiology of the stomach, that is, gastric myoelectrical activity that can be measured using internal electrodes implanted on gastric serosa.
Secondly, we will provide technical details on how to measure the EGG. Since the EGG is a non-invasive measure using abdominal skin electrodes, it is sensitive to motion artifacts and electrical interferences from other internal organs. Therefore, it is critically important to measure the EGG appropriately and accurately. Detailed information will be provided on how to prepare the abdominal skin, where to place electrodes, how to choose filtering range (extremely important) and how to avoid and minimize motion artifacts.
Recently, some researchers have suggested that the EGG or any extracellular recordings of the stomach might be a mere measure of stomach movement artifact or contractile artifact.4
To answer this question, we will review numerous findings published in the literature as well as from our own labs regarding the validity of EGG. Data will be reviewed in 3 categories: (1) the relationship between the internal extracellular myoelectrical recording and gastric contractions: this will tell whether the internal extracellular myoelectrical recording is a measurement of true gastric myoelectrical activity or just an artifact of gastric contractions, (2) the relationship between the EGG and the internal serosal recording of the gastric slow wave: this will determine whether the EGG is an accurate measurement of gastric slow waves, and (3) the relationship between the EGG and gastric contractions. We believe that by reviewing these materials, the reader will be capable of determining whether the EGG is a measurement of gastric slow waves or just gastric contractile artifacts.
Last but not least, we will review applications of EGG, including the application of EGG for the study of gastric electrophysiology, the use of EGG in assessing the effect of an intervention and the clinical relevance of EGG in patients with symptoms suggestive of functional gastric dysmotility.