2.6 Evaluation methods

The simulation results are analyzed in terms of the spatial repolarization time gradients (RTG) map. This map is created for the last S1 stimulus in the simulation, where repolarization time is defined as the moment at which the membrane voltage repolarized to −70 mV. From these RTG maps, RTG _vol and RTG _mean metrics are extracted where RTG_vol [ml] represents the tissue volume with gradients ≥10 ms/mm, which are critical for conduction block (Restivo et al., 1990). RTG_mean [ms/mm] indicates the mean RTG value within this volume with RTGs above 10 ms/mm. These metrics are computed for all performed experiments, such that the effects of mechanical feedback and parameter variability on RTG can be explored. The RTG metrics during baseline rhythm are an indication for VT risk (Cluitmans et al., 2021), and only require S1 stimuli. For the sensitivity test, these metrics are computed for one pacing site only (site A in Figure 2E) to save computational costs.

For the virtual stress test simulations, all six pacing sites are used and S2 stimuli are applied as well. The results are captured in vulnerable windows. These windows define for each pacing site and S1-S2 interval whether VT was induced or not. Here, VT is defined as electrical activity sustained for at least 800 ms after S2. In case of occurrence of VT, exit points are defined as the location with earliest second activation time, counted from the start of S2 sustained for at least 800 ms after S2. In case of occurrence of VT, exit points are defined as the location with earliest second activation time, counted from the start of S2.