## 3 Results
### Training Data
#### 3.1.1 Left Bundle Branch Block Simulations  
Table 1 summarizes the accuracy obtained with the meshless SPH-based in the training dataset, as quantified by the metrics detailed above. Equivalent results were obtained for both LBBB and CRT conditions. Figure 5 shows the local activation time maps for a non-infarcted and an infarcted case of the training database at LBBB and CRT conditions, provided by the EAM, and from FEM- and SPH-based simulations. The initial impulses set for the non-ischemic case shown in Figure 5 (Fig 1) were established with a difference of 12 ms between them. The first, located in the RV endocardium, was set at 2 ms, and the second, the septal one, at 14 ms. Table A1 and Figure 5 revealed similar activation patterns in the biventricular epicardium with an average regional LAT RMSE of 5.7 ms compared to the EAM data. However, larger differences were observed in the LV endocardial layer, increasing the regional error to 9.1 ms (Table A1). The remaining metrics (e.g., TAT, IVD and LV-TD) were similar between meshless simulations and measurements, with a difference <3 ms, while the overall error was 6.8 ms, as reported in Table 1.  
For the infarcted case shown in Figure 5 (Fig 3), the initial stimulus was placed as in Pig 1, but at 2.5 ms in the RV endocardial layer, and in the septal area at 12 ms to better match the EAM data. Figure A3 in the Appendix shows simulation results obtained with only one stimulus. The scar in Pig 3, which had a transmurality of 86%, was located in the septo-apical and antero-septal LV regions. In the scar region, a 75% conduction velocity reduction with respect to the Purkinje system was established from the best simulation result. Although the electrical activation pattern provided by the SPH simulations was very close to the EAM measurements (5.1 ms average LAT error), differences in conductivity were appreciated between both ventricles. The posterior basal region of the RV epicardial layer had a slower activation than the ground-truth data, whereas LV layers (endo- and epicardium) had a higher conductivity. The metrics in Table 1 show differences greater than 6 ms for LV-TD, 9 ms for TAT, and less than 1 ms for IVD. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Pig 1**} & \multicolumn{4}{c}{**Pig 2**} & \multicolumn{4}{c}{**Pig 3 (*)**} \\  & \multicolumn{2}{c}{**EAM**} & \multicolumn{2}{c}{**SPH-Sim**} & \multicolumn{2}{c}{**EAM**} & \multicolumn{2}{c}{**SPH-Sim**} & \multicolumn{2}{c}{**EAM**} & \multicolumn{2}{c}{**SPH-Sim**} \\ \hline  & LBBB & CRT & LBBB & CRT & LBBB & CRT & LBBB & CRT & LBBB & CRT & LBBB & CRT \\ \cline{2-13} TAT (ms) & 72.0 & 70.0 & 70.0 & 66.0 & 66.0 & 45.0 & 78.0 & 39.0 & 59.0 & 35.0 & 49.7 & 46.0 \\ \hline LAT RMSE (ms) & & & 6.8 & 7.9 & & & 9.4 & 7.7 & & & 5.1 & 6.6 \\ \hline
17 IVD (ms) & 18.0 & 7.3 & 18.6 & 11.4 & 19.8 & \(-\)3.3 & 14.3 & 0.0 & 17.7 & \(-\)12.5 & 16.9 & \(-\)4.8 \\ \hline LV-TD (ms) & 7.2 & 0.0 & 9.0 & 2.0 & 9.9 & \(-\)6.6 & 13.0 & 0.4 & 11.8 & \(-\)5.2 & 18.4 & 0.6 \\ \hline Recovery (\%) & \(-\)2.6 & & \(-\)8.0 & & 47.7 & & 69.6 & & 342.9 & & 185.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Metrics characterizing the electrical activation maps in training cases from measurements and meshless simulations. EAM: electroanatomical maps. SPH-Sim: Simulation with smoothed particle hydrodynamics meshless method. LBBB: left bundle branch block. CRT: cardiac resynchronization therapy. TAT: total activation time. LAT-RMSE: local activation time root mean square error. IVD: inter-ventricular delay. LV-TD: left ventricle transmural delay. (*) indicates an infarcted pig. Table 2 shows the conduction velocity values estimated by the SPH-based model in the five selected regions for an ischemic and a non-ischemic cases of the LBBB training dataset. Additionally, the corresponding parameters obtained with the FEM-based approach of [PERSON] and [PERSON] [29] on the same cases are also included for comparison purposes.