The primary functions of the stomach are to mix secreted enzymes and peptides and store, grind, digest, and empty food into the duodenum. Multiple levels of neuronal mechanisms of the central, spinal, and enteric nervous systems are in place to coordinate the stomach's ordered movement.1 The stomach muscle itself also exhibits myoelectrical activity that mediates stomach motility. Both slow waves (electrical control activity) and spikes (electrical response activity) are well-known components of stomach myoelectricity.2 In 1922, Alvarez3 recorded a three-cycles per minute (cpm) sinusoidal wave using electrodes placed on the abdominal skin. Noninvasiveness is the greatest advantage of electrogastrographies (EGGs), which use surface-placed electrodes to record stomach myoelectricity.2,4,5,6 Since Alvarez's report, a number of studies concerning EGG have determined that gastric electrical potentials break out from a pacemaker located on the upper gastric body along the greater curvature.7,8 These potentials are related to an electrical pacing function and the power of gastric contraction.9,10,11 The EGG result is a combination of gastric signals and noise. The gastric signal consists of normal slow waves (regular frequency, 2~4 cpm), tachygastria (regular frequency, 4~9 cpm), bradygastria (regular frequency, 0.5~2 cpm), and arrhythmia (irregular rhythmic activities). The noise is composed of respiratory and motion artifacts, electrocardiography, and electrical interference of the small intestine.9 Gastric emptying (GE) is a function of the net inhibitory and excitatory results of antropyloroduodenal coordination among all portions of the stomach, pylorus, and duodenum.1 Partial or total removal of the upper gastrointestinal organs impairs GE. In the present study, we investigated postoperative changes on the EGGs of patients with stomach cancer and analyzed the relationship between the EGG system and the quality of life (QOL) of patients with stomach cancer who were treated with distal gastrectomy.

Table 1 illustrates the characteristics of the patients with gastric cancer. According to the tumor location, there were 10 cases (50%) in the body and 10 cases (50%) in the antrum. According to the Union for International Cancer Control 7th TNM classification (2010), there were seven cases (35%) of stage Ia, five cases (25%) of stage Ib, two cases (10%) of stage IIa, two cases (10%) of stage IIb, and four cases (20%) of stage IIIa. Open distal gastrectomy was performed in 11 cases (55%) and laparoscopic-assisted distal gastrectomy was performed in nine cases (45%). Twelve cases (60%) received adjuvant chemotherapy.

Table 2 illustrates the effect of the meal on EGG parameters during the postoperative period (~24 weeks). According to the effect of the meal on EGG parameters during the early postoperative period, between the fasting and postprandial recordings, there were no significance differences in dominant frequency (DF), dominant power (DP), and percentage of normal frequency, but there were significant decreases in the percentage of bradygastria and increases in the percentage of tachygastria (P<0.05). The percentage of bradygastria decreased significantly on the postprandial recordings between 1 week and 3 months, between 1 week and 6 months, but not between 3 months and 6 months. The percentage of tachygastria increased between 1 week and 6 months but not between 3 months and 6 months. The percentage of normal frequency was slightly increased in the postprandial recordings, but there were no significant differences except in postoperative week 1.

Global health status and physical, emotional, and social functioning scales were improved, but role and cognitive functioning were not changed. Most symptom scales were slightly improved, whereas pain, insomnia, diarrhea, and financial difficulties were significantly improved according to the postoperative periods regarding the European Organisation for Research and Treatment of Cancer (EORTC) quality of life questionnaire QOL-C30 version 3.0 (P<0.05) (Table 3). Comparison of QOL with the EORTC QLQ-STO22 questionnaire during the postoperative periods (~12 weeks) revealed no statistically significant differences (P>0.05) (Fig. 2), and the correlation between QOL and EGG parameters was not statistically significant (P>0.05) (Table 4).

Stomach surgery may influence gastric motor function. Even gastric restrictive surgery without resection in obese subjects leads to altered DF and DP but not power ratio.12 Truncal vagotomy with gastric resection for peptic ulcer disease impairs esophageal sphincter tone, food accommodation, and the grinding and emptying ability.13 Distal gastrectomy is severely destructive to the stomach anatomy and its neighboring organs and may lead to poor motility.14,15,16

Debate persists regarding when to record postoperative EGG parameters. Abnormal GE and associated dyspeptic symptoms are common in the early days after an operation, while GE may require 12 months after stomach surgery to return to normal.1,15 Some changes in EGG parameters occur in the early days after subtotal gastrectomy.17 Lee et al.18 enrolled subjects for distal robotic sleeve gastrectomy (RSG) who had undergone stomach surgery at least 1 year previously. Homma et al.19 reported that a series of regular peaks of 3 cpm activity were not clearly visible in the EGGs running spectra recorded from patients who had undergone a distal gastrectomy with a short postoperative period (13~71 days in 13 subjects). Imai and Sakita20 recorded postoperative EGGs in gastrectomy patients 3 to 5 weeks after surgery. Hayashi et al.21 recorded EGGs at least 1 year after surgery. In our study, we recorded and analyzed EGGs in patients who had undergone distal gastrectomy over postoperative periods from 1 to 24 weeks to investigate postoperative changes according to the various time intervals.

Bradygastria (regular frequency, 0.5~2.0 cpm) is currently defined as values below the normal range (regular frequency, 2~4 cpm), whereas tachygastria (regular frequency, 4~9 cpm) is defined as values above the normal range.9,22,23 Unfortunately, the normal range is very difficult to define due to variations in the recording system and a lack of standard analysis methods.24 Moreover, the occurrence of tachygastria is influenced by electrode position and configuration.25 However, the association between tachygastria and gastric motor disorders has been substantiated in other studies. For example, You et al.26 observed tachygastria in a 26-year-old woman with persistent nausea, vomiting, and abdominal pain and severely impaired antral motor function. The correlation between bradygastria and gastric motility is not yet as clear. van der Schee and Grashuis27 observed bradygastria in dogs and found that it was correlated with strong antral contractions.

In the present study, comparison of temporal changes in EGG parameters revealed no significant temporal differences for DF, DP, percentage of normal frequency, or percentage of tachygastria. However, it did reveal significant temporal differences in the percentage of bradygastria for postprandial recordings between 1 week and 3 months and between 1 week and 6 months but not between 3 months and 6 months. Unlike other studies that obtained a DF of ~3 cpm in the gastric remnant, Lee et al.18 found that distal RSG patients had a lower DF value with an increased percentage of bradygastria (<2 cpm) irrespective of meal ingestion. Bracci et al.28 observed the less common 3 cpm with an increased chance of bradygastria in children who underwent partial gastrectomy to augment bladder function. Although they lacked a clear definition of bradygastria, they suggested that this is the effect of the removal of stomach pacemaker cells.

Roux-en-Y reconstruction in previous gastrectomy patients also led to bradygastria, which was closely related to the time after surgery.29 Hayashi et al.21 pointed out that proximal subtotal gastrectomy subjects with more than half of the stomach resected had lower percentages of normal rhythm, DF, and even DP compared with those with greater stomach preservation. Lee et al.18 suggested that removal of part of the main pacemaker in distal RSG patients leads to an increased percentage of bradygastria and that the ectopic pacemaker of the rest of the stomach in lower frequency values would replace the originally removed main pacemaker cells to dominate the gastric SW rhythm. Murakami et al.30 reported that longer periods of normal gastric function (normogastria, 2.0~4.0 cycles min^-1) were detected in channel 1 in the vagus nerve-preserving distal gastrectomy group (VP-DG) than in the standard distal gastrectomy without vagus nerve preservation group (DG) in either the fasted or fed state (P<0.05). The VP-DG group showed better preserved gastric myoelectric activity than the DG group.

Homma et al.19 recognized serial 3 cpm peaks in the running spectra of EGGs recorded in patients who had undergone distal gastrectomy 15 to 20 years previously and suggested that the reorganization of gastric pacemaker activity represents reorganization of the interstitial cells of Cajal in the remnant stomach of distally gastrectomized patients. According to the effect of the meal on EGG parameters during the early postoperative period, comparison of fasting to postprandial recordings revealed significant decreases in the percentage of bradygastria and increases in the percentage of tachygastria. According to time intervals, there was a significant decrease in the percentage of bradygastria in fasting and postprandial recordings between 1 and 12 weeks and between 1 and 24 weeks. The percentage of normal frequency was increased in the postprandial recording between 1 and 24 weeks. These results suggest that the decreased percentage of bradygastria and the increased percentage of tachygastria indicate a change in EGG parameters that represents reorganization of the interstitial cells of Cajal in the remnant stomach of distally gastrectomized patients.

In conclusion, these findings suggest that EGG may be a noninvasive method for evaluating the motility and autonomic functions of the remnant stomach after distal gastrectomy. However, the present study has shortcomings including its lack of a control group and preoperative baseline EGGs and its small number of patients.