Disturbances in the propagation of the slow wave during acute local ischaemia in the feline small intestine.

OBJECTIVE AND DESIGN: The normal aborad propagation of the slow wave in the small intestine is easily distorted by pacing, hypoxia or transection. We studied whether acute local ischaemia would also induce serious conduction disturbances and ectopic pacemaking. METHODS: After general anaesthesia and a mid-abdominal incision, a multi-electrode array of 240 extracellular electrodes was positioned on the serosal surface of an exteriorized intestinal loop. Simultaneous recordings of all 240 surface electrodes was performed during a control period and for 5-10 min following local acute arterial occlusion. After the experiments activation maps were constructed describing the pattern of propagation of the slow waves. RESULTS: During control periods, the activation maps showed homogeneous aborad conduction of the slow wave. During acute ischaemia, local areas of inexcitability developed rapidly, merging together to form lines of conduction block. This in turn often provoked the appearance of subsidiary ectopic pacemakers. The location of the conduction blocks as well as that of ectopic pacemakers was highly variable and could disappear and reappear at other sites. CONCLUSION: Within minutes, acute ischaemia disturbed the organized homogeneous aborad propagation of the slow wave leading to pronounced inhomogeneous depression of conduction, local inexcitability, conduction block and the appearance of subsidiary pacemakers.

Wave mapping: detection of co-existing multiple wavefronts in high-resolution electrical mapping.

High-resolution mapping makes it possible to reconstruct and display the conduction pattern of the action potential as it propagates through cardiac or smooth muscles. During slow and regular activity, time mapping of the spread of activation muscles. During slow and regular activity, time mapping of the spread of activation is relatively simple and straightforward. However, when frequencies are high or conduction is slow, such as seen during atrial fibrillation or found in the pregnant uterus, the tracking of individual waves may become more difficult and uncertain. In order to reconstruct the pathway of a single wave, a search and sorting routine was developed which makes it possible to distinguish, track and display individual wavelets. The algorithm is able to detect variations in conduction block, spontaneous shifts in the location of the pacemaker and changes in the direction of conduction. It is less sensitive when two or more wavefronts intermingle in space and time, such as during collision or fusion. Wave mapping is especially useful, in addition to current time mapping, in sorting quickly through the large amount of data produced by high-resolution mapping of electrical activities in cardiac and smooth muscle.

Spatial and temporal variations in local spike propagation in the myometrium of the 17-day pregnant rat.

Detailed spatial analysis of propagation of individual action potential was performed during spontaneous bursts of activity in the isolated 17-day pregnant rat myometrium. Use was made of high-resolution mapping with simultaneous recordings from 240 extracellular electrodes. Positioning of the electrode assembly by itself did not have any adverse effects, and no differences were found in the period or duration of spontaneous bursts recorded with and without the electrode assembly touching the tissue. The spread of propagation of individual action potentials was reconstructed at several moments during myometrial spike bursts. Both the direction and the sequence of activation of the myometrium were found to be highly variable and depended on 1) the level and spatial dispersion of excitability and 2) whether conduction occurred predominantly in the longitudinal or the circumferential direction. Furthermore, conduction was frequently complicated by the spontaneous occurrence of 1) lines of conduction block, 2) focal sites of pacemaking, or 3) merging of two or more wavelets into a single wave. In contrast, when the myometrium was divided into small segments, activity became much more regular, and both the location of the pacemaker and the direction of propagation were much more stable than in the whole myometrium. In conclusion, spontaneous spatial variations in local spike propagation at the preterm stage could provide for the necessary asynchrony in activation and play a role in the prevention of forceful contractions and premature labor.