Rick Schreurs

89 SonR for AV-optimization RESULTS Of the 10 experiments performed, one was excluded from analysis because of premature death during the tachypacing period. LBBB creation was successful in six experiments, while in two experiments complete atrioventricular (AV) block developed (NResp1 and Resp1) and subsequently an RV lead was transvenously placed to mimic LBBB. In 1 animal LBBB creation was only temporary (Resp4). Heart failure was induced by tachypacing in 6 animals and isoflurane inhalation in 1 animal (Resp5). One animal was in heart failure without additional intervention (NResp4) and in 1 animal cardiac failure was induced using isoflurane only after the disappearance of the temporary LBBB (Resp4). The animals were divided into two groups (see table 1 ) based on the maximal relative increase of LV dP/dt max during LV or BiV pacing with a cut off value of >10%. Table 1 shows that in the 5 responding animals (Resp group) LV dP/dt max consistently increased (10.1- 35.1%), whereas the 4 non-responding animals (NResp group) had negligible hemodynamic benefits from LV and BiV pacing (-1.3-7.9%, P=0.023 vs Resp animals). Additionally, the Resp animals were more dyssynchronous than the NResp animals indicated by a greater MIVD (-32±3ms vs -13±4ms respectively, p=0.012). Animal NResp1 showed a synchronous contraction because the RV pacing lead was placed in an apical instead of lateral position. LBBB was incomplete in animal NResp3. Baseline hemodynamic parameters, like LVP max , LV end diastolic pressure and LV and RV dP/dt max , were not significantly different between the NResp and Resp groups. Importantly, RA SonR1 and RV SonR1 were higher in the NResp animals, however only significantly for RA SonR1 (306±47mG vs 166±25mG for NResp and Resp animals). 5