Rick Schreurs

112 Chapter 6 RV pre-excitation led to the largest LV TAT while LV pre-excitation resulted in an increase of RV TAT. During simultaneous pacing, two wave fronts originating from the RV and LV pacing electrodes fused and resynchronized the heart as indicated by a decrease in LV TAT. LV pre-excitation RV pre-excitation Simultaneous pacing 100ms 50ms 0ms Activation time LV TAT = 82ms RV TAT = 36ms VEU = -51ms LV TAT = 61ms RV TAT = 28ms VEU = 8ms LV TAT = 92ms RV TAT = 28ms VEU = 26ms Figure 2. Epicardial electric activation maps in a paced dog heart with complete AV block during LV pre-excitation (left), simultaneous pacing (middle) and RV pre-excitation (right). Black arrows indicate capture, whereas grey arrows indicate loss of capture. TAT: total activation time, VEU: ventricular electrical uncoupling. Figure 3 shows the changes in electrical dyssynchrony indexes in dogs with variation of pacing delay settings. There was no change in LV and RV TAT and VEU when changing the AV-delay during simultaneous activation of the LV and RV (left column). Both LV and RV TAT (first 2 rows of figure 3 ) were lowest during simultaneous RV+LV pacing. The RV showed the largest TAT during LV pre-excitation or LV-only pacing (upper left corners in the heat maps). LV TAT showed a relatively large increase with large RV pre-excitation (right side of middle panels and lower right corners in heat maps), while RV TAT did not increase much. As indicated by the VEU (bottom row figure 3 ), during LV-only pacing the LVFW was activated more than 40ms before the RVFW. During RV-only pacing the LVFW was, on average, activated more than 20ms later than the RVFW. The LVFW and RVFW were activated simultaneously with very slight LV pre-excitation ( Figure 3 bottom right, VEU=0). Hemodynamic effects of altering pacing delay settings The changes in LV and RV dP/dt max in response to changes in pacing delay settings are presented in figure 4 (top and bottom, respectively). Increasing AV-delay during simultaneous RV and LV pacing (left column and identity line in the heat maps) hardly affected LV and RV dP/dt max in both measurements and simulations. The relative effect of changing VV-delay (green, second column from left) was largest in RV dP/dt max . Changing pacing settings from RV to LV pre-excitation decreased RV dP/dt max with more than 30% in the experiment. The decrease in RV dP/dt max­ was less pronounced in the simulations but followed the same pattern. LV dP/dt max was highest with LV pre-excitation and simultaneous pacing in both the experiment and simulations. The heat maps of both the animal experiments and computer simulations (right side of figure 4 ) show a qualitatively similar pattern where the largest changes in both LV and RV dP/dt max are observed when changing the VV-delay. The largest increase in LV