21 Relationship between standard EGG electrode configurations and the stomach location

Abstract

Aim: To determine the appropriateness of EGG electrode configurations and where the EGG electrodes are located relative to the stomach musculature.Background: It has become common practice to place EGG electrodes at specific locations relative to external landmarks (e.g. xiphoid and umbilicus) instead of locating the stomach via ultrasound or other imaging modalities. Electric fields decay rapidly with distance from the source so placing EGG electrodes close to the stomach is critical for obtaining reliable signals. If regional variability is of interest it is also important to place electrodes along the axis of the stomach.Methods: Informed consent was obtained from four normal male subjects (average age 34 yrs). Subjects ingested 16 oz of oral contrast (containing 10 g hypaque sodium powder, Amersham Health) over 90 min prior to an abdominal spiral CT scan (3 mm slices). Stomach and skin surfaces were manually segmented and these data used to create virtual computer models. EGG electrodes were positioned according [1–3]. The distance between each electrode and the closest point to the stomach surface was calculated. A fourth configuration was defined where four electrodes were placed along the known stomach axis.Results: The average distances between the electrodes and the stomach was (42.4 ± 15.0; 60.7 ± 24.2; and 33.4 ± 12.2) mm for [1–3] respectively. When electrodes were placed manually given prior knowledge of the stomach location this distance was reduced to 29.5 ± 5.4 mm.Conclusion: The umbilicus was used as an external landmark by [1] and [3]. Although [2] did not use the umbilicus, it gave the largest distance and standard error between electrodes and the stomach, primarily due to the positioning of two electrodes on the right side of the abdomen. We propose that either structural imaging be used to locate the stomach, or that an improved set of external landmarks be developed that better reflect the stomach location to provide improved EGG signal quality.Acknowledgements: This study was supported by an NIH grant (R01 DK64775) and the Royal Society of New Zealand Marsden Fund.