Fig. 4

The leading pacemaker site did not necessarily occur in the region of maximum action potential duration and maximum phase-4 slope. The pseudocolor images represent the activation map and the spatial distributions of the onset of activation, the phase-0 slope, the phase-4 slope, and APD50, respectively. The leading pacemaker site (open circles), and the region of maximum phase-4 slope (open triangles) if it does not coincide with the leading pacemaker site, are indicated. Isochrones were calculated at 2-ms intervals from the leading pacemaker site. a A case in which there exists a single region of globally maximum phase-4 slope and the leading pacemaker site coincided with it. b A case in which there exist multiple regions of locally maximum phase-4 slope and the leading pacemaker site occurred in one of these regions. c The leading pacemaker did not emerge at the site of maximum phase-4 slope. Note that optical imaging was performed at a relatively high magnification in this case, and thus ΔF/F was higher than that of other cases. d Optical membrane potential trajectories of the region of leading pacemaker site (open circles) and the region of maximum phase-4 slope (open triangles) in a–c. IVC Inferior vena cava, SVC superior vena cava, SEP internal septum, RA right atrium