Rick Schreurs

116 Chapter 6 Figure 7 shows the response of stroke volume of the LV and RV after simulated programming of nine different pacing settings. In the first beat RV stroke volume remained either unchanged or decreased as compared to baseline, indicating little direct mechanical benefit of the change in pacing delay for the RV. However, similar to the example in figure 6 , copied into the left upper panel of figure 7 , RV stroke volume changed considerably in subsequent beats. While changes in LV stroke volume initially differed from RV stroke volume, a steady state was reached after several simulated beats. Note that the largest benefit in stroke volume, and therefore cardiac output, was primarily dependent on AV- delay. For example, in the bottom row (A-RV 70ms) the optimized RV filling improved stroke volume to such a degree that, through the serial coupling, LV preload increased, leading to a further increase in LV stroke volume after the second cycle. On the other hand, at longer AV-delays this atrial-ventricular coupling decreases, resulting in a lower steady- state cardiac output. Δ Stroke volume (%) Δ Stroke volume (%) 10 5 0 -5 -10 10 5 0 -5 -10 10 5 0 -5 -10 1 2 3 4 5 6 7 8 SS 1 2 3 4 5 6 7 8 SS 1 2 3 4 5 6 7 8 SS Delay change Delay change Delay change Δ Stroke volume (%) Right ventricle Left ventricle Baseline Baseline Baseline A-LV 70ms, A-RV 190ms A-LV 190ms, A-RV 70ms A-LV 190ms, A-RV 130ms A-LV 130ms, A-RV 130ms A-LV 190ms, A-RV 190ms A-LV 70ms, A-RV 70ms A-LV 70ms, A-RV 130ms A-LV 130ms, A-RV 70ms A-LV 130ms, A-RV 190ms Δ Stroke e (%) Δ Str ( ) 5 -5 1 Δ Strok ( ) i i l i le Baseline Baseline Baseline - , , , Figure 7. Relative change in stroke volume of the left (black circles) and right (red squares) ventricle over a number of simulated cycles until steady-state (SS) after changing pacing delay (the 9 settings shown in the black bars). Black dashed line indicates the moment of changing the pacing delays while the yellow line marks the first beat.