Ahmed Shafik, MD, PhD

Department of Surgery and Experimental Research, Faculty of Medicine, Cairo University, Cairo, Egypt.

Received 05/21/96; Accepted 06/12/96; On-line 07/01/96

RESULTS

No complications were encountered during the study and the recordings could be obtained from all the subjects. To determine the optimal location of the electrodes, many sites had to be tested. At some of these sites, no electrosigmoidographic signals were obtained over long periods of time. The electrodes were moved to new sites until continuous, marked and reproducible electrosigmoidographic signals were recorded. Finding the appropriate location for the electrodes was facilitated by studying the position of the sigmoid colon in the barium enema films.

The ESG showed pacesetter potentials (PPs). The PPs were slow waves, monophasic and consisted of negative deflections (Fig. 2).

Fig. 2: Transcutaneous ESG showing PPs. APs are not shown.

The frequency, amplitude and velocity of conduction of the PPs are shown in Table 1.

These parameters were constant when the examination was repeated in the same subject (p > 0.05) during the recording sessions which were performed for each of the 19 healthy volunteers and the 5 patients who had undergone sigmoidectomy. In none of the subjects the APs could be recorded.

It might be that these APs can be re-orded only when the electrodes are applied directly to the sigmoid wall. The intervening abdominal wall and the inconsistency and low amplitude of the APs seem to impede their recording transcutaneously.

The intra-sigmoid ESG recorded synchronously with the TC-ESG showed that the PPs of the TC-ESG had the same frequency, amplitude and velocity of conduction as those recorded by intra-sigmoid ESG without showing a significant difference (p > 0.05, Fig. 3). The only difference is that the intra-sigmoid ESG revealed APs which were not recorded by the TC-ESG. The APs were fast activityspikes; they occurred randomly and were inconsistent when the test was repeated in the same subject. They were displayed as negative deflections of a smaller amplitude than the PPs (Fig. 3).

Fig. 3: Intra-sigmoid ESG of the same subject as in Fig. 2 showing PPs as well as APs. The frequency, amplitude and velocity of conduction of the PPs are identical to those recorded by transcutaneous ESG.

Despite repeated attempts to obtain PPs by changing the position of the electrodes, no electric activity was recorded in the 5 patients whose sigmoid colons were removed (Fig. 4). The evidence that the PPs of TC-ESG are derived from the sigmoid colon is: a. the synchronicity and similarity of the transcutaneous to the intra-sigmoid waves, and b. that no waves could be recorded from the sigmoidectomy patients. This evidence also rules out the possibility

Fig. 4: Silent ESG in a patient who had undergone sigmoidectomy.

that these waves arise from the small bowel. It may be argued that these waves represent artifacts. However, the consistency and reproducibility of the waves are against this argument. The ESG could be easily differentiated from the electrocardiographic waves (EKG). The possibility of respiratory artifacts were excluded by recording respiratory electric activity via placement of a transducer attached to the chest wall. It may be presumed, that these waves arise from the colon, small bowel or rectum. However, the synchronicity and similarity of the TC-ESG to the intra-sigmoid one negates such a possibility. Furthermore, a recent study has demonstrated that the electric waves from the rectum could not be recorded from the abdomen; they were registered from the lower part of the back over the sacrum (14). The origin of the electric waves in the sigmoid colon is not known. It could be myogenic or neurogenic in nature. Some investigators provide evidence that the electric activity of the colon and stomach arises from the muscle of the organ (15, 16).

Various pathologies of sigmoid colon may disturb the electric activity of this part of bowel. Thus, TC-ESG may be a simple, non-invasive procedure that potentially can be used in the differential diagnosis of such conditions. The recording of the TC-ESG in colonic abnormalities such as cancer, diverticulitis, and ulcerative colitis should provide us with an insight whether TC-ESG may be useful in their diagnosis.