stomach: Electrical Control Activity (ECA)and Electrical Response Activity (ERA). Ithas been demonstrated4,5 that intracellularelectrical depolarization due to spontaneousionic exchange through the membrane pre-cedes contraction of the gastric smooth mus-cle fibers. However, not all depolarizationsare followed by contractile activity and this isthe main difference between gastric and car-diac muscles. Weber and Kohatsu6, Kelly andCode7 showed as possible origin of gastricelectrical activity an area of the corpus alongthe greater curvature where begin the longi-tudinal muscle fibers that continue into theduodenum. The mechanism of propagation ofgastric electrical activity is still unknown butthere are well definite temporal and spatialrules that regulate the propagation.

ECA is considered to be the initial rapiddepolarization of the cell and is a necessarycondition, even if not sufficient, so that thecontraction could happen. It is periodic in na-ture, with a period of about 20 seconds (fre-quency of 3 cycles per minute). Only the ap-pearance of the plateau of the ERA, andeventually the second component of theERA, the spikes that are superimposed overthe plateau, indicate that the contraction willfollow.

During the fasting state the GEA canshow the patterns of the so called MigratingMyoelectrical Complex (MMC)8 and it canbe separated into four phases: (1) quiescentphase 1, when only ECA is present; (2) tran-sitional phase 2 when cycle of ECA aremixed with cycles in which both ECA andERA are present; (3) phase 3 during whichECA is always followed by ERA with its twocomponents; (4) transitional phase 4, verysimilar to phase 2. The total duration of the 4phases is 1.5-2.0 hours.

Mirizzi and Scafoglieri9, Mirizzi et al10,11

have modelled the electrical field produced

29

Abstract. – Electrogastrography (EGG) isthe recording and the interpretation of gastricelectrical activity. Recordings can be made fromthe gastrointestinal mucosa, serosa, or skin sur-face. Because of its ease of use, cutaneous EGGhas gained wide acceptance. Many technicalproblems have been solved to obtain a goodgraph. The EGG is usually evaluated in terms ofchanges in the EGG waves amplitude and fre-quency. Deviations from the normal frequency of3 cycles per minute may be referred to asbrachy- or tachyarrhythmia. The clinical use ofEGG has been most widely evaluated in patientswith gastroparesis and functional dyspepsia.Scintigraphic gastric emptying is considered thegold standard test for evaluating gastroparesisand 13C-octanoate breath test an ideal alternativebecause does not use ionizing radiation. Whilegastric emptying evaluates the efficiency of gas-tric emptying, EGG focuses on the underlyingmyoelectrical activity. Using both EGG and 13C-octanoate breath test will be possible to detectmany subset of dyspeptic patients and to under-stand the underlying problem.

Key Words:

Electrogastrography, Gastroparesis, Functional dys-pepsia.

Introduction

The electrogastrography is a method torecord the electric activity of the stomach po-sitioning some electrodes on the skin surfaceof the abdominal wall. A general agreementthat the electric activity of the stomach is cor-related to its contractile activity exists1-3. Thetarget is to find a relationship between differ-ent pattern of electric activity and clinicalpresentation of dyspeptic disturbances.

Gastric Electric Activity (GEA)In vitro two major types of GEA have

been recognized in the distal two/thirds of the

European Review for Medical and Pharmacological Sciences 2005; 9(Suppl 1): 29-35

Electrogastrography

Z. ROSSI, G. FORLINI, P. FENDERICO, R. CIPOLLA, S. NASONI

Struttura Complessa di Gastroenterologia ed Epatologia, Ospedale Regina Apostolorum – Albano Laziale, Roma (Italy)

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by the human stomach and demonstratedthat the optimal position for the EGG elec-trodes is along the projection of the stom-ach axis on the abdomen wall, as shown inFigure 1.

Many authors12-20 have tried to use electro-gastrography for clinical assessment of gastricmotility disorders. Unfortunately, only quali-tative methods (and therefore subjective) ofevaluation of the EGG were suggested.Myntchev et al21 have tried to produce an ob-jective quantitative method of evaluation ofgastric electrical activity, including EGG.They demonstrated that the most reliableEGG parameter is gastric electrical frequen-cy. It shows a good level of stability in all con-ditions when registered maintaining standardmodalities. A further parameter that seemsto be of interest is the variation of signal am-plitude after meal.

The ECA (slow waves) is responsible forcontrolling the maximum frequency and theaboral propagation of distal gastric contrac-tions. As reported above, the normal gastricslow waves frequency is approximately 3cpm. Meal ingestion increases the amplitudeof the EGG signal which is believed to resulteither from increased antral contractility orfrom mechanical distension of the stomach.

The more common procedure of evalua-tion of the electrogastrographic recording isthe spectral analysis that uses the “FastFourier Transform” (FFT) to convert thetemporal signal in its components of frequen-cy (Figure 2). According to the theory ofFourier every periodic signal can be consid-ered as constituted by a series of sinusoidalwaves. The application of the FFT to the sig-

nal over time determines the decompositionof the signal in its components of frequencyproducing a spectrum of frequencies.” Theamplitude of every component of frequencypoints out the contribution of that compo-nent in the original signal. The energy of acomponent of frequency is calculated as thesquare of the amplitude.

The graph obtained by the spectrumanalysis shows the mean contribution of adate frequency on the whole signal expressedas energy of that frequency. The dominantmean frequency is 3.0 cpm and the corre-sponding energy it is express in nV2. Suchrepresentation doesn’t allow following thevariations of frequency and energy over time.This problem has been overcome with the in-troduction of the analysis Running Spectra(Figure 3). The graphic representation mostlyused for the analysis Running Spectra ispseudo-three-dimensional that is able toshow the variations of frequency and ampli-tude in the time.

Clinical ApplicationThe cutaneous registration of the electri-

cal activity of the stomach allows to quantifythe dominant frequency, the regularity of my-oelectrical activity, the percentage of time inwhich abnormal slow or fast wave rhythms

Z. Rossi, G. Forlini, P. Fenderico, R. Cipolla, S. Nasoni

Figure 1. The best position of electrodes, along thegastro-duodenal axis.

Figure 2. Spectrum analysis by Fast Fourier Transformshowing the different frequency components in the gas-tric recorded signal. From Linkens DA, Datardina SP.Med Biol Eng Comput 1978; 16:262-68.

Frequency (Cpm)

Ener

gy

(µV

2 )

Art. 1.1404 13-03-2006 11:57 Pagina 30

are present during fasting and postprandially,and to assess the increase in amplitude aftermeal22 (Figures 4 and 5).

Using the same terminology of the elec-trocardiography it is possible to describethe gastric dysrhythmias as tachygastria andbradigastria. Normally the 3 cpm frequencyrepresents the 70% of the recorded cycles.When this percentage is reduced the electri-cal activity of the stomach is altered. Thetachygastria and the bradigastria and theabnormal low amplitude of the signal aftermeal ingestion have been defined in pa-tients with idiopathic or diabetic gastro-paresis23 (Figure 6). Camilleri et al22 de-scribed also abnormalities in patients with

unexplained nausea and vomiting, motionsickness, and nausea and vomiting of preg-nancy. Parkman et al24 showed EGG abnor-malities in 75% of patients with gastropare-sis versus 25% of symptomatic patients withnormal gastric emptying. EGG abnormali-ties and delayed gastric emptying may de-fine different patient populations with dys-peptic symptoms25 (Figures 7 and 8). Kochet al26 showed that the symptomatic re-sponse to antiemetic or prokinetic drugtreatments correlated better with resolutionof gastric dysrhythmias than acceleration ofdelayed emptying in some groups of pa-tients. Even hyperglycaemia may provokedysrhythmias in diabetic patients27.

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Electrogastrography

Figure 3. Running Spectra analysis allowsto visualize the components of gastric sig-nal over time. From Van der Schee ET,Grashuis JT. Med Biol Eng Comput 1987;25:57-62.

Figure 4. Healthy subject. Thedominant frequency in the fast-ing state and after the meal in-gestion is 3 cpm.

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In clinical practice EGG has been used todemonstrate gastric myoelectrical abnormali-ties in patients with unexplained nausea andvomiting or functional dyspepsia. It seemscorrect to consider the EGG, joined toscintigraphy, as a tool of a general evaluation

of patients with symptoms suggestive of anupper gastrointestinal motility disorder22,23.To date there have been little investigation todemonstrate the utility of EGG in the man-agement of patients with suspected gastricmotility abnormalities.

Z. Rossi, G. Forlini, P. Fenderico, R. Cipolla, S. Nasoni

Figure 5. Healthy subject. Normal increase of the gastric signal after meal ingestion with dominant 3 cpm frequency.

Figure 6. Diabetic not compen-sated patient with dominant br-adigastria before meal. Aftermeal ingestion irregular in-crease of frequency of the gas-tric electric activity.

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PerspectiveGastric emptying scintigraphy of a solid-

phase meal is considered the gold standardfor the study of gastroparesis. Breath test us-ing the non radioactive isotope 13C bound todigestible substance have been validated formeasuring gastric emptying. Most commonly,

13C-labeled octanoate, a medium chaintriglyceride, is bound into a solid meal (eggswith ham, butter, bread). After ingestion andstomach emptying, 13C-octanoate is absorbedin the small intestine and metabolized to13CO2, which is then expelled from the lungs.The limiting step is the rate of gastric empty-

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Electrogastrography

Figure 7. Patient with unex-plained nausea. Dysrhythmia isevident before meal. The nor-mal 3 cpm appears after the in-gestion of foods.

Figure 8. Patient with unexplained nausea. Amplitude increment of the signal with dominant 3 cpm frequency aftermeal ingestion.

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ing. Octanoate breath testing provide a mea-sure of solid phase emptying and its resultsare reproducible and correlate with findingson gastric emptying scintigraphy21,29,30. 13Cbreath test do not use ionizing radiation andcan be used to test patients in the communityor even at the bedside where the gammacamera facilities are not available. Breathsamples can be preserved and shipped to alaboratory for analysis by means a mass spec-trometer. This possibility can make easy toperform a double test: EGG registrationwhile the person is eating a 13C-octanoatemeal allowing to elaborate a correlation be-tween electric gastric activity and gastric me-chanical activity in different subsets of dys-peptic patients for search use or, may be, forclinical use. EGG could make its first stepstowards reliable clinical applications.

Electrogastrography has the potential tobecome a routine clinical procedure in thenear future.

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