Table 1.

Glossary of terms used to describe intestinal slow wave propagation and re-entry. Several cardiac electrophysiology terms (25),(28) have been adapted to describe similar phenomena in the intestine.

Terminology	Description
Leading Edge	Depolarized / excited tissue at the front of a propagating slow wave wavefront.
Refractory Tail	Depolarized tissue behind the leading edge of a slow wave that is unable to be excited.
Wavefront Spacing	The distance between two successive wavefronts.
Anisotropic Conduction	A propagation profile that is directionally non-uniform. In the case of gastric and intestinal slow waves, anisotropic conduction manifests as circumferential propagation being faster than longitudinal propagation (36).
Conduction Block	Abnormal termination of a propagating wavefront, for example when refractory tissue or a structural defect is encountered.
Functional Block	A specific type of conduction block resulting from dynamic interactions between the leading edge and refractory tissue rather than by anatomical means.
Focal Pacemaker	Slow wave/s arising from a point-source and propagating in all directions, colliding in the opposite aspect of the intestine circumferentially, and forming rings of activation propagating longitudinally.
Re-entry	A slow wave propagation pattern where slow wave activity propagates in a circuit around a defined obstacle, forming a loop pattern of activation and re-activating that circuit over successive cycles.
Excitable Gap	A section of excitable tissue between the refractory tail of one cycle of re-entry and the leading edge of the following cycle. The presence of an excitable gap is necessary to maintain re- entry, as re-entry will terminate if there is a collision between the leading edge and refractory tail. The size of the excitable gap is governed by the size of the re-entrant circuit, the slow wave velocity, and the refractory period.
Anatomical Re-entry	A type of re-entry where a structural feature forms the obstacle around which slow wave activity establishes a re- entrant loop (27).
Circumferential Re-entry	A specific type of anatomical re-entry where the intestinal lumen forms the anatomical obstacle around which slow wave activation establishes a re-entrant loop.
Functional Re-entry	A type of re-entry where a functional conduction block forms the obstacle around which slow wave activation establishes a re-entrant loop of propagation (24)(25).
Figure-of-Eight Re-entry	A variant of functional re-entry where a common wavefront divides into clockwise and anticlockwise wavelets that propagate around separate functional blocks before rejoining, forming a re-entrant circuit in a figure-of-eight pattern (26).