Optical Mapping of Pacing-Elicited Slow Waves in the Swine Stomach: Role of Virtual Electrodes

Stomach contractions are coordinated in part by bioelectric slow waves (SW). Dysfunctional SWs are associated with motility disorders. Electrical pacing is a potential strategy for managing motility disorders but remains poorly understood with inconsistent efficacy.

We used a newly-developed optical mapping method to image gastric pacing in 4 pigs (35.0 ± 1.3 kg). The method imaged transmembrane potential, primarily from the circular smooth muscle layer, with high spatiotemporal resolution. We delivered unipolar pacing pulses to the serosal surface or to the luminal side of the circular muscle layer. Pulses were 100 ms in duration with 4 or 8 mA amplitude.

Pacing elicited transmembrane potential polarization patterns consistent with bidomain theory: For cathodal pacing, there was an elongated depolarized region (virtual cathode) oriented orthogonally to the smooth muscle fibers and centered on the electrode. It was flanked on either side by hyperpolarized virtual anodes. For anodal pacing, virtual electrode polarity was reversed. Of 175 pulses, 18% induced SWs that activated the entire mapping region. The remaining pulses failed completely (38%) or induced SWs that only partially activated the mapping region (43%). All SWs initiated from virtual cathode sites approximately 1 cm from the pacing electrode and not from the electrode site itself.

These results suggest that close to the electrode, pacing pulses inhibited the network of interstitial cells of Cajal (ICC) that propagates SW. SWs may have initiated when the ICC network was activated by depolarized smooth muscle in the virtual cathodes remote from the electrode.