Origin, propagation and regional characteristics of porcine gastric slow wave activity determined by high-resolution mapping

Abstract

Background: The pig is a popular model for gastric electrophysiology studies. However, its normal baseline gastric activity has not been well characterized. High-resolution (HR) mapping has recently enabled an accurate description of human and canine gastric slow wave activity, and was employed here to define porcine gastric slow wave activity.

Methods: Fasted pigs underwent HR mapping following anesthesia and laparotomy. Flexible printed-circuit-board arrays were used (160-192 electrodes; spacing 7.62 mm). Anterior and posterior surfaces were mapped simultaneously. Activation times, velocities, amplitudes and frequencies were calculated, and regional differences evaluated.

Key results: Mean slow wave frequency was 3.22 ± 0.23 cpm. Slow waves propagated isotropically from the pacemaker site (greater curvature, mid-fundus). Pacemaker activity was of higher velocity (13.3 ± 1.0 mm s(-1)) and greater amplitude (1.3 ± 0.2 mV) than distal fundal activity (9.0 ± 0.6 mm s(-1), 0.9 ± 0.1 mV; P < 0.05). Velocities and amplitudes were similar in the distal fundus, proximal corpus (8.4 ± 0.8 mm s(-1), 1.0 ± 0.1 mV), distal corpus (8.3 ± 0.8 mm s(-1), 0.9 ± 0.2 mV) and antrum (6.8 ± 0.6 mm s(-1), 1.1 ± 0.2 mV). Activity was continuous across the anterior and posterior gastric surfaces.

Conclusions & inferences: This study has quantified normal porcine gastric slow wave activity at HR during anesthesia and laparotomy. The pacemaker region was associated with high-amplitude, high-velocity slow wave activity compared to the activity in the rest of the stomach. The increase in distal antral slow wave velocity and amplitude previously described in canines and humans is not observed in the pig. Investigators should be aware of these inter-species differences.

Figure 1

(A) The flexible Printed Circuit Board (PCB) recording head used in this study (4 × 8 array, interelectrode distance 7.62 mm). (B) Porcine gastric anatomy. FD, fundal diverticulum; Eso, esophagus; TP, torus pyloricus. Two anatomical lines were used to divide the stomach into fundus, corpus, and antrum: (i) FL, fundal line: a horizontal line drawn from the angle of His to the greater curvature; (ii) C/A, corpus–antrum line: a line drawn at a 45° angle from the incisura (a notch on the lesser curvature) to the greater curvature. (C) A dot-matrix representation of the PCB array. (D) An example of slow wave recordings from a PCB electrode (4–6 PCB electrodes were used during this study), placed over the lower corpus (position shown in B), using the configuration shown in C. The inset demonstrates amplitude (a) calculation: the difference between the maximum and the minimum voltage during a slow wave event. (E) The temporal profile of propagating slow wave fronts is graphically represented by activation time mapping. In this example, the isochronal lines demarcate 1 s time intervals. (F) Velocity values at the individual electrode points are represented graphically by velocity arrow plots. The arrow heads are aligned in the direction of the propagating slow wave form, and the arrow lengths are proportional to the slow wave velocity at each electrode point.

Figure 2

Examples of slow wave propagation within the pacemaker and fundal regions of two experimental animals. (A, E) Printed Circuit Board (PCB) position diagrams showing the site of the PCB arrays during the recordings; the red rectangles highlight the region represented in the subsequent maps. (B, F) Representative electrograms recorded from the pacemaker region. Activation times from the first cycle are shown in red, and amplitudes from the next cycle are shown in purple. Amplitudes are higher in the vicinity of the gastric pacemaker. (C, G) Activation time maps of the pacemaker region, corresponding to the cycles marked with the arrow in B, F. The isochronal color bands indicate the area of slow wave propagation per 0.5 s intervals. Activity propagates isotropically from the pacemaker site. (D, H) Velocity plots from the same data, demonstrating fast activity in the vicinity of the gastric pacemaker.

Figure 3

Slow wave propagation in the corpus and antrum. (A) Printed Circuit Board (PCB) positions for the demonstrated mapped sequence (five PCBs; 160 electrodes total; 77 cm²). The red outline shows the area of interest in the subsequent maps. (B) Representative electrograms from nine channels, showing consistent slow wave activity through the corpus and antrum. The corpus wavefronts propagate aborally as a circumferential band of activation. (C) Activation time map of the cycle marked by the arrow in (B). The isochronal color bands demonstrate the area of slow wave propagation per 2 s intervals. (D) Velocity plot of the same cycle. There was no difference in wave amplitude or velocity between the proximal corpus, distal corpus, and antrum.

Figure 4

Simultaneous mapping of the anterior and posterior stomach. (A) Six Printed Circuit Boards (192 electrodes; ~96 cm²) were wrapped around the greater curvature of the corpus. The red rectangle highlights the region represented in the subsequent maps. (B, C) Representative simultaneous electrogram sequences from the anterior (B) and posterior (C) serosa, showing similar propagation patterns in both regions. (D) Activation time mapping of the sequences designated by arrows in B and C, revealing a circumferential band of activity that propagates down both gastric surfaces in synchrony. (E) The corresponding velocity plot, displaying consistent slow wave velocities across the majority of the mapped field (mean velocity in mapped field = 8.8 mm s⁻¹). GC, greater curvature.

Figure 5

Examples of electrical quiescence near the lesser curvature, from two experiments. (A, E) Printed Circuit Board (PCB) position diagrams showing the site of the PCB arrays during recording; the red rectangles reflect the regions represented in the subsequent activation maps. (B, F) Activation time (AT) maps of gastric slow waves captured by the PCB arrays. The isochronal color bands indicate the area of slow wave propagation per 1 s intervals. (C, D, G) Representative electrograms recorded from the corpus and antrum from the electrodes indicated on the AT maps. An electrically quiescent region is seen along the left (medial) side of the maps, close to the lesser curvature.

Figure 6

Summary of porcine gastric slow wave activity. Slow waves originate from a pacemaker site along the greater curvature of the mid fundus. The activity initially propagates radially, but only activates a limited region of the fundus. The shaded areas are electrically quiescent. Propagation is isotropic, rapid and of high-amplitude in the vicinity of the pacemaker region, before dropping by ~30% in velocity and ~30% in amplitude in the adjacent stomach. Propagation continues aborally at a similar amplitude and velocity throughout the corpus and antrum, toward the torus pyloricus, which is electrically quiescent. Slow wave propagation is consistent and continuous across both the anterior and posterior gastric serosal surfaces as shown in Figure 4. Eso, esophagus, TP, torus pyloricus.