Simultaneous optical imaging of gastric slow waves and contractions in the in vivo porcine stomach

Abstract

Gastric peristalsis is governed by electrical "slow waves" generally assumed to travel from proximal to distal stomach (antegrade propagation) in symmetric rings. While alternative slow wave patterns have been correlated with gastric disorders, their mechanisms and how they alter contractions remain understudied. Optical electromechanical mapping, a developing field in cardiac electrophysiology, images electrical and mechanical physiology simultaneously. Here, we translate this technology to the in-vivo porcine stomach. Stomachs were surgically exposed and a fluorescent dye (di-4-ANEQ(F)PTEA) that transduces the membrane potential (Vm) was injected through the right gastroepiploic artery. Fluorescence was excited by LEDs and imaged with one or two 256x256 pixel cameras. Motion artifact was corrected using a marker-based motion tracking method and excitation ratiometry, which cancels common-mode artifact. Tracking marker displacement also enabled gastric deformation to be measured. We validated detection of electrical activation and Vm morphology against alternative non-optical technologies. Non-antegrade slow waves and propagation direction differences between the anterior and posterior stomach were commonly present in our data. However, sham experiments suggest they were a feature of the animal preparation and not an artifact of optical mapping. In experiments to demonstrate the method's capabilities, we found that repolarization did not always follow at a fixed time behind activation "wavefronts," which could be a factor in dysrhythmia. Contraction strength and the latency between electrical activation and contraction differed between antegrade and non-antegrade propagation. In conclusion, optical electromechanical mapping, which simultaneously images electrical and mechanical activity, enables novel questions regarding normal and abnormal gastric physiology to be explored.