Fig. 3

Propagation of the excitation in the electrically paced AZV. The photographs (a, b) of the mapped area in two sites in the AZV (proximal and distal, also indicated as 1 and 2 in Fig. 1a) with superimposed optical signals (optical AP, red peaks) registered by individual photodiodes. Representative examples (c, d) of the isochronic maps from the proximal and distal regions of the AZV which demonstrate anterograde conduction of the excitation under electrical pacing. Blue color corresponds with earlier excitation; red color with later excitation. Horizontal arrows indicate general direction of the excitation propagation. Optical traces (e, f) of a three consecutive excitation cycles (cycle length 300 ms) from the points in AZV which are indicated in the isochronic maps (in c, d). No substantial beat-to-beat AP variability was observed under pacing with 300-ms cycle length. Note that isocronic maps were received from same tissue preparation but consecutively from the proximal and distal portions of the vein. AZV _prox and AZV _dist the proximal and distal regions of the AZV. CV left superior vena cava. Asterisks denote position of the pacing electrodes. Sloped arrows in (e) and (f) indicate motion artifacts (color figure online)