DIAGNOSTIC AIDS IN GASTRIC DISORDERS: ELECTROGASTROGRAPHY
Electrogastrography (EGG) is the recording of gastric myoelectric activity. The technique usually uses superficial abdominal wall electrodes placed on the abdominal skin overlying the stomach. The recorded signal is called an electrogastrogram and usually consists of signals of 3 cycles per minute, reflecting gastric slow wave (pacemaker) activity, which set the frequency for subsequent gastric contractions. Meal ingestion increases the amplitude of the EGG signal by increasing gastric electrical activity and contractility or by distention of the stomach. EGG measures the frequency and regularity of gastric myoelectric activity, detects abnormal rhythms of gastric myoelectric activity, and assesses the amplitude or power increase after a meal.
Abnormalities
in the EGG signal have been demonstrated in patients with gastroparesis and
functional dyspepsia. A significant percentage of these patients may have slow
wave frequencies that are very rapid (tachygastria) or very slow (bradygastria).
The gastric electrical slow wave propagation velocity, electromechanical
uncoupling, or ectopic gastric pacemaker activity can be detected using more
advanced EGG recordings, such as a multichannel recording using electrodes
placed at different positions overlying the stomach. EGG can also be recorded
with serosal electrodes during surgery.
Gastric
dysrhythmias (tachygastria, bradygastria) and decreased postprandial amplitude
(or power) of the EGG recording have been described in idiopathic and diabetic
gastroparesis. Studies have suggested a good correlation between delayed
gastric emptying and an abnormal recording, particularly postprandial rhythm and amplitude
abnormalities. An abnormal recording is made in about 75% of patients with
gastroparesis, compared with only 25% of symptomatic patients with normal
gastric emptying. Gastric dysrhythmias have been suggested to be better
predictors of symptoms than delayed gastric emptying. In diabetic patients,
hyperglycemia may provoke dysrhythmias, primarily tachygastrias.
EGG is used
to demonstrate gastric myoelectric abnormalities in patients with unexplained
nausea and vomiting with abdominal discomfort or functional dyspepsia. The technique
is generally used as an adjunct to gastric emptying scintigraphy, as part of a
comprehensive evaluation of patients with refractory symptoms suggestive of an
upper gastrointestinal motility disorder.
