Rick Schreurs

73 Effective mechanical atrioventricular delay 85 90 95 100 0 20 40 60 Cardiac output (% of max) 85 90 95 100 0 100 200 300 400 85 90 95 100 0 100 200 300 400 Cardiac output (% of max) 85 90 95 100 0 100 200 300 400 Cardiac output (% of max) 85 90 95 100 0 100 200 300 400 Effective AV-delay Cardiac output (% of max) Programmed AV-delay (ms) Right effective AV-delay (ms) Left effective AV-delay (ms) Mean effective AV-delay (ms) Mean effective AV-delay corrected for HR (%) Cardiac output (% of max) Atrial pacing - BiV Atrial pacing - LV Atrial pacing - RV Atrial sensing - BiV Atrial sensing - LV Atrial sensing - RV Figure 6. Average AV-optimization curves for cardiac output presented as percentage of maximal value for all six pacing modes. The x-axis changes for every panel. The paced AV-delay (upper left), right effective AV-delay (upper middle), left effective AV-delay (upper right), mean effective AV-delay (lower left) and mean effective AV-delay as percentage of RR-interval (lower right) are being presented. Right-eAVD and left-eAVD is the time difference between RA dP/dt max and RV dP/dt max­ and LA dP/ dtmax and LV dP/dt max respectively. The mean-eAVD is the average between right and left-eAVD. Table 4. Values for optimal programmed and effective AV-delays and their coefficient of variation. Programmed AV-delay (ms) Right-eAVD (ms) Left-eAVD (ms) Mean-eAVD (ms) Mean-eAVD corrected for HR (%) CO Mean±SEM 149±47 190±54* 166±58* 178±55* 27±7 CV 0.31 0.28 0.35 0.31 0.27 SW Mean±SEM 138±56 178±53* 157±56* 168±53* 25±7 CV 0.40 0.30 0.35 0.32 0.27 MAP Mean±SEM 154±60 194±53* 172±57* 183±54* 28±8 CV 0.39 0.27 0.33 0.30 0.28 Values were calculated from all individual data. eAVD: effective atrioventricular delay, HR: heart rate, CO: cardiac output, SW: stroke work, MAP: mean arterial pressure, CV: coefficient of variation. * indicates P<0.05 compared to programmed AV-delay. DISCUSSION The main finding of this animal study is that the AV-delay that creates the maximal increase in cardiac output (“optimal AV-delay”), is influenced by altered diastolic filling patterns due to changes in interatrial delay (atrial pacing vs. atrial sensing) and interventricular 4