Tissue block 1

The isochrone maps generated for the first tissue block are shown in the top row of Fig- ure 6.3. The second recording shows a burst which has been deemed separate from the main excitation wave, which may indicate a second initiation point. A comparison of elec- trograms from the main excitation wave and this secondary wave is shown in Figure 6.4. The difference in burst length and start time between these two electrograms suggests

Figure 6.5: An example of fibres situated across the mesometrial border in tissue block 1. Here the fibres appear to connect; however the precise level of connectivity cannot be determined from two-dimensional images alone. The three-dimensional structure is required to determine the full connectivity, which is discussed in Chapter 7. Left panel scale bar represents 200µm, right panel scale bar represents 5 mm.

that these are indeed two separate excitation waves. The presence of two excitation waves indicates that activity is being initiated from multiple sources simultaneously.

The second row of Figure 6.3 shows the isochrones in comparison to the top surface of the in silico tissue block. The direction of the fibres on the surface in the area covered by the excitation waves in each recording is generally vertical in the image plane, indi- cated by green. The main excitation wave in all three isochrone maps is restricted to the same approximate area. This might indicate a mechanism preventing current flowing past the given bounds for the duration of the recordings. The bounds perpendicular to the fibre direction are narrower than along the fibre direction, which suggests of a low level of communication between adjacent fibres. In particular, there is no communication across the mesometrial border. Figure 6.5 shows fibres connected across the mesometrial border;

Figure 6.6: Fibres crossing into the placental bed in tissue block 1 in close proximity to a termination point of excitation along the fibre direction. The arrow indicates the direction of propagation in the myometrium. The conduction is blocked at some point within the volume containing this cross-sectional area. This slide shows the fibres are embedded in the placenta, suggesting that the placenta could play a role in preventing further propagation. M indicates myometrium,Pindicates placenta. Left panel scale bar represents 500 µm, right panel scale bar represents 5 mm.

however the level of connectivity for the whole of the mesometrial border cannot be deter- mined from two-dimensional histological slides alone. In Chapter 7 the three-dimensional in silico reconstruction will be used to determine the connectivity across the mesometrial border to assess whether this could be a factor in preventing propagation. The bounds along the fibre direction suggests a mechanism restricting propagation along the fibres. Figure 6.6 shows the tissue at the approximate location of a conduction block along the fibre direction. This shows that a possible path of conduction passes through fibres which penetrate the placental bed. The precise path that the excitation wave takes to reach this point is unknown due to the two-dimensional nature of the recording, but if the wave was restricted to these fibres then modification of the conductivity through these fibres by the

Figure 6.7: Fibres extending from the placental bed into the myometrium in tissue block 1. The middle histological image on the left shows this fibre, as indicated by the arrow. The images above and below this image are from sections above and below the middle section in the stack. These three images approximately occupy the space in the reconstructed tissue indicated by the pink square, which is in close proximity to the initiation point of the second and third recordings in tissue block 2. M indicates myometrium, P indicates placental bed. Left panel scale bars represents 200µm, right panel scale bar represents 5 mm.

Cumulative frequency

Speed (cm/s)

Figure 6.8: Empirical CDF of propagation speeds for each recording in tissue block 1. Blue

represents recording 1, yellow represents recording 2, and green represents recording 3. The general shift to the right with time indicates that the speed is increasing between recordings; however, these recordings were made∼10 minutes apart, which suggests that this increase is coincidental.

placental tissue could cause the wave to terminate at this point.

The initiation points for all recordings appear to lie in the vicinity of the mesometrial border, with the second and third recording showing initiation close to a specific implanta- tion site. Moreover, the range of potential initiation points for the first recording includes locations adjacent to implantation sites. The secondary excitation in the second recording is also located at an implantation site. This suggests that the implantation sites determine the location at which excitation is initiated in these recordings. Figure 6.7 shows a fibre which extends into the placental bed from the myometrium. This fibre is located in close proximity to the initiation points of the second and third recordings, which suggests that it could be the location at which the excitation waves are initiated.

The mean propagation speeds for the recordings are summarised in Table 6.1. The distribution of the propagation speeds along the fibre direction for each recording is rep- resented in Figure 6.8, showing variable distributions of speeds between recordings, which

20 cm/s

5 cm/s

0 cm/s 10 cm/s 15 cm/s

Figure 6.9: Representation of the propagation speeds as a function of space in tissue block 1.

Scale bars represents 5 mm.

suggests that the propagation speeds vary with time. The images in Figure 6.9 represent the average propagation speed along the fibre direction through each point where a speed was recorded. The general increase in brightness between recordings suggests that this increase in speed is generally representative of the active tissue as a whole. There does not appear to be a general pattern for the spatial variation in speed within the recordings. This would suggest that the spatial variation does not strongly correlate with discernible anatomical features.

Figure 6.10: Isochrones for tissue block 2, in order of time of recording. Top row: isochrones taken at 200 ms intervals, with colour indicating time at which the excitation wave reached the electrode. White points indicate electrodes where bursts were recorded. Bottom row: comparison of isochrone initiation points and bounds with the top surface of virtual tissue. The tissue is pseudocoloured based on fibre direction, with green indicating vertical direction in the image plane, red indicating horizontal direction in the image plane, and blue indicating the direction perpendicular to the image plane. The ovarian end of the tissue is located at the top of each image. Scale bars represent 5 mm.

Figure 6.11: Comparison of electrograms taken from events detected as being separate in record- ing 2 from tissue block 2. The bursts appear similar toward the start of the recording, but the burst in the lower electrogram extends beyond the end of the burst in the upper electrogram. This would suggest that the two recordings are indeed from separate events. Scale bar represents 5 mm.