Electrogastrography (EGG) is a simple, non – invasive, painless and repeatable method of assessment of gastric myoelectrical activity. By means of cutaneous electrodes placed on surface of abdominal skin, the physicians are able to register myoelectrical activity of the stomach (some people are joking the EGG is some kind of ECG/EKG of the stomach).
First time the EGG was described in 1922 year by Walter Clement Alvarez (1884 - 1978). Unfortunately this method of examination has not been so popular for a long time. In late 1970s the development of computers and knowledge of electrophysiology of the stomach caused that scientist again paid attention to electrogastrography.
The EGG examination plays an important role in diagnosis of functional dyspepsia, and some of scientists, including me, suggest that it can be a screening examination in functional disorders of the gastrointestinal tract (http://www.termedia.pl/Czasopismo/Przeglad_Gastroenterologiczny-41/Streszczenie-10509).
Defilippi and her colleagues showed that incorrect EGG results were observed in patients suffering from diabetes mellitus (http://www.scielo.cl/scielo.php?pid=S0034-98872002001100002&script=sci_arttext).
EGG is the simplest way of monitoring the therapy of functional disorders especially of the stomach as well (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548127/).
The gastric myoelectrical activity is recorded when patients are lying on their backs. It should be performed in a calm and silent room. Patient should not use any electronic devices during that examination.
The basic gastric myoelectrical activity of the stomach is known as slow waves. Slow waves are spontaneous, characteristic for myocytes of the stomach (myocyte is a long muscle cell), slow, rhythmic and repeatable depolarizations of membrane of cells. Slow waves are responsible for frequency, celerity, and direction of peristaltic waves, but they do not cause the contraction of the myocytes of the stomach. Slow ways create action potentials and the action potenials bring on contractions of the myocytes of the stomach and determine the power of contractions of the stomach.
REGISTARTION OF EGG:
EGG registers slow waves of the gastric myoelectrical activity. We distinguish:
1) bradygastria, that means too slow gastric myoelectrical activity (below 2 cycles per minute),
2) normogastria, which is normal and correct gastric myoelectrical activity (between 2 - 4 cycles per minute),
3) tachygastria, too fast gastric myoelectrical activity, more than 4 cycles per minute, sometimes it occurs during pregnancy, nausea and also can dominate in patients suffering from functional dyspepsia (postprandial distress syndrome, PDS)
EGG is sometimes called cutaneous electrogastrography as well, because the electrodes are placed directly on surface of abdominal skin. Usually the EGG examination lasts from 2 hours even to 6 hours, it depends on the equipment that is used. For example using the recording device Digitrapper EEG manufactured by Synectics Medical AB (Sweden) OS Version 2.00 Hardware 3.00 (August 3, 1995) and the software ElectroGastroGram Software, Gastrosoft, Version 6.30, the examination lasts 6 hours. After an hour of recording of the gastric myoelectrical activity in patients on an empty stomach (under fasted conditions) a solid or liquid test meal is usually served. The patients have five minutes to drink the liquid meal, whereas the time for the solid meal is little longer. After the meal, for five consecutive hours of recording, the patients have no more meals or drinks. Test meals, both solid and liquid, should have approximately the same energy value for example about 300 kcal.
After examination the EGG device should be connected to the computer and then the following parameters should be analysed:
1) Percentage (%) of normogastria during recording time on an empty stomach, after a meal and in the total record;
2) Percentage (%) of bradygastria during recording time on an empty stomach, after a meal and in the total record;
3) Percentage (%) of tachygastria during recording time on an empty stomach, after a meal and in the total record;
4) Percentage (%) of of duo – resp. (impulses from other organs like duodenum and the respiratory system);
5) PDF – period dominant frequency on an empty stomach and after a meal;
6) DFIC – dominant frequency instability coefficient on an empty stomach and after a meal;
7) PDP - period dominant power on an empty stomach and after a meal;
8) DPIC – dominant power instability coefficient on an empty stomach and after a meal;
9) POWER RATIO – quotient of power after a meal and before a meal.
According to the opinion expressed by many authors the normal EGG records are the ones in which normogastria composed at least 70% of the total recording time both on an empty stomach and after a meal and when the POWER RATIO is ≥ 2.
1) EGG is an important diagnostic tool in gastroenterology, especially in the diagnosis of functional gastrointestinal disorders (http://www.ncbi.nlm.nih.gov/pubmed/10483996).
2) EGG can be useful during diagnosis of gastroparesis that is often caused by diabetes mellitus.
3) The EGG examination still needs to be improved and probably could be useful in many others gastrointestinal diseases as well, for example GERD (gastroesophageal reflux disease), irritable bowel syndrome (IBS),
4) Riezzo and others say that almost 50% patients with functional dyspepsia suffer from impaired gastric emptying as well, and if there are some disturbances in EGG examinations, the dyspeptic symptomes are much more expressed.
5) According to Leathy and his colleagues the results of EGG examinations are incorrect in 36% patients suffering from functional dyspepsia and in 25% patients with irritable bowel syndrome who complained of concurrent dyspepsia. It is necessarily to emphasize that the results of EGG examinations are correct in 93% healthy volunteers (http://www.ncbi.nlm.nih.gov/pubmed/10201477).
6) Xuemei Lin and Jiande Chen using the multichannel electrogastrography found that the patients with functional dyspepsia had impaired gastric slow wave propagation and coordination. It was observed both in the decreased percentages of slow wave propagation and coupling and in the inconsistencies in the percentage of the normal slow wave and its dominant frequency measured from different channels (http://ajpgi.physiology.org/content/280/6/G1370).
7) In 2003 the experts of American Motility Societu Clinical GI Motility Testing Task Force recommended the EGG examination to differentiate healthy people with patients suffering from disturbed gastric myoelectrical activity (http://www.ncbi.nlm.nih.gov/pubmed/12680908).
8) The EGG examination can be useful to clinical assessement of patients suffering from unexplained nausea and vomiting as well.