CVs were calculated for each pacing frequency (5 15 Hz).
Figure 3 and Table 3 present the mean data for each pacing programme.
Results for each pacing mode are presented as an average of the three pacing cycles for that mode.
For each pacing mode, the global efficient strain was calculated as the area under the curve (AUC) of the global positive strain.
For each pacing site, at least six consecutive pacing stimuli were analysed in order to average the influence of random factors such as patient breathing or ECG signal noise.
For each pacing configuration, a 10-s programming period was required and a 30-s recording period was preceded by a stabilization period of 30 s (i.e. a total of 70 s for each configuration).
These functional parameters were then grouped by pacing frequencies, and for each pacing frequency the average functional parameter value was identified (for example, 15 steady-state APs were recorded at 2-Hz pacing, and the representative APD value was the average of the 15 APDs).
Functional parameter maps (like the APD80 maps shown in Fig. 1 I and the AP skewness map shown in Fig. 1 K ) were plotted for each pacing frequency, with each point on the map representing the averaged functional parameter value per slice.
The nearest point on the NEEES mesh model (ref PS) was determined for each CARTO pacing site (CARTO PS) previously marked on the CARTO mesh model (see Supplementary material online, Figure S1 ).
Electrocardiogram recordings were taken at each pacing mode for later analysis.
