Do increased electrogastrographic frequencies always correspond to internal tachygastria?

This study was undertaken to investigate the possible origin of some cutaneously recorded higher frequency electrogastrographic signals. Computer modeling of gastric electrical uncoupling was performed using previously described conoidal dipole model. Cutaneous electrogastrograms were simulated after uncoupling was introduced. In separate, real-life experiments, 6 pairs of bipolar electrodes were inserted into the gastric wall (3 anterior, 3 posterior) of 15 anesthetized dogs at laparotomy to record 6 channels of internal gastric electrical activity (GEA). Eight-channel bipolar cutaneous electrogastrography (EGG) was simultaneously recorded. Three separate 1/2-hr recordings were made from each dog in the basal state and after each of two circumferential cuts of all gastric muscle. Distal stomach was surgically divided into three equal-sized areas, each with an electrode pair in its anterior and posterior walls. Gastric electrical activity and EGG were digitized, bandpass-filtered and analyzed in frequency domain using the fast Hartley transform. The phenomena of tachygastria and tachyarrhythmia were quantitatively compared in internal and cutaneous recordings. Computer modeling indicated that it is possible to record cutaneous "tachygastric" or "tachyarrhythmic" signals without them being present internally. Real experiments on dogs showed higher percentage of tachyarrhythmia in EGG than in the internal signal in the basal state. After the first circumferential cut, the periods of tachygastria and tachyarrhythmia increased, with EGG signals showing again a higher percentage. This tendency persisted after the second circumferential cut. A similar pattern was observed when monitoring the percentage of uncorresponding tachygastrias/tachyarrhythmias. Our findings indicate that gastric electrical uncoupling can be another possible reason for abnormal frequency characteristics of EGG. Not all cutaneously recognized tachygastrias and/or tachyarrhythmias could be related to objectively existing internal tachygastric events.