An electrogastrogram (EGG) is a graphic produced by an electrogastrograph, which records the electrical signals that travel through the stomach muscles and control the muscles' contractions. An electrogastroenterogram (or gastroenterogram) is a similar procedure, which writes down electric signals not only from the stomach, but also from intestines.
These names are made of different parts: electro, because it is related to electrical activity, gastro, Greek for stomach, entero, Greek for intestines, gram, a Greek root meaning "to write".
An electrogastrogram and a gastroenterogram are similar in principle to an electrocardiogram (ECG) in that sensors on the skin detect electrical signals indicative of muscular activity within. Where the electrocardiogram detects muscular activity in various regions of the heart, the electrogastrogram detects the wave-like contractions of the stomach (peristalsis).
Walter C. Alvarez pioneered early studies of electrogastrography in 1921-22.[1]
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Motility of GI tract is results from coordinated contractions of smooth muscle, which in turn derive from two basic patterns of electrical activity across the membranes of smooth muscle cells — slow waves and action potentials.[2] Slow waves are initiated by pacemakers — the interstitial cells of Cajal (ICC). Slow wave frequency varies in the different organs of the GI tract and is characteristic for that organ. They set the maximum frequency at which the muscle can contract:
The electrical activity of the GI tract can be subdivided into two categories: electrical control activity (ECA) and electrical response activity (ERA). ECA is characterized by regularly recurring electrical potentials, originating in the gastric pacemaker located in the body of stomach. The slow waves are not a direct reason of peristalsis of a GI tract, but a correlation between deviations of slow waves from norm and motility abnormalities however is proved.[5]
Electrogastrogram can be made from the gastrointestinal mucosa, serosa, or skin surface. The cutaneous electrogastrography and provides an indirect representation of the electrical activity but it is much easier and therefore cutaneous electrogastrography has been used most frequently.
Several EGG signals are recorded from various standardized positions on the abdominal wall and to select the one with the highest amplitude for further analysis. For this purpose usually use three or more Ag-AgCl electrodes.[6] Recordings are made both fasting (usually 30 minutes) and after a meal (usually 60 minutes) with the patient lying quietly. Deviations from the normal frequency may be referred to as bradygastria or tachygastria.
In normal individuals the power of the electrical signals increases after the meal. In patients with abnormalities of stomach motility, the rhythm often is irregular or there is no postprandial increase in electrical power.
Terms bradygastria and tachygastria are used at the description of deviations of frequency of an electric signal from slow waves are initiated by pacemaker in the stomach from normal frequency of 3 cycles per minute.
A bradygastria is defined, how decreased rate of electrical activity in the stomach, as less than 2 cycles per minute for at least 1 minute.
A tachygastria is defined, how increased rate of electrical activity in the stomach, as more than 4 cycles per minute for at least 1 minute.
A bradygastria and tachygastria may be associated with nausea, gastroparesis, irritable bowel syndrome, and functional dyspepsia.[7]
There are following Current Procedural Terminology (CPT) and Healthcare Common Procedure Coding System (HCPCS) codes (maintained by the American Medical Association) for cutaneous electrogastrography:[8]
CPT/HCPCS-code | Procedure |
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91132 | Electrogastrography, diagnostic, transcutaneous |
91133 | Electrogastrography, diagnostic, transcutaneous; with provocative testing |
An electrogastroenterography (EGEG) is based that different organs of a GI tract give different frequency slow wave.
Organ of gastrointestinal tract | Investigated range (Hz) | Frequency number (i) |
---|---|---|
Large intestine | 0.01 – 0.03 | 5 |
Stomach | 0.03 – 0.07 | 1 |
Ileum | 0.07 – 0.13 | 4 |
Jejunum | 0.13 – 0.18 | 3 |
Duodenum | 0.18 – 0.25 | 2 |
EGEG electrodes are as much as possible removed from a stomach and an intestines — usaually three electrodes are placed on the extremities. It allows to receive stabler and comparable results.
An electrogastroenterography analysis program calculate[9]
where S(n) — spectral components in the rank from sti to fini (defined by received investigated range of this organ of GI tract) by Discrete Fourier transform of the electric signal from GI tract.
EGEG parametres for normal patients:[9]
Organ of gastrointestinal tract | Electric activity P(i)/PS | Rhythm factor Kritm(i) | P(i)/P(i+1) |
---|---|---|---|
Stomach | 22.4±11.2 | 4.85±2.1 | 10.4±5.7 |
Duodenum | 2.1±1.2 | 0.9±0.5 | 0.6±0.3 |
Jejunum | 3.35±1.65 | 3.43±1.5 | 0.4±0.2 |
Ileum | 8.08±4.01 | 4.99±2.5 | 0.13±0.08 |
Large intestine | 64.04±32.01 | 22.85±9.8 | — |
There are some lacks limiting an electrogastroenterography use in practice:
Electrogastrography or gastroenterography used when a patient is suspected of having a motility disorder, which can be shown, as recurrent nausea and vomiting, signs that the stomach is not emptying food normally. The clinical use of electrogastrography has been most widely evaluated in patients with gastroparesis and functional dyspepsia.
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