Rick Schreurs

136 Chapter 7 The amplitude of the SonR signal as used in chapter 5 is larger in the RV than RA location, comparable to previous studies [44-48]. We hypothesize that the position of the sensor defines which part of the heart dominates the signal. When the SonR sensor is placed in the RA lead it is able to give information on both ventricles because of its remote position, while a sensor placed in the RV might focus more on RV function than LV function. Because of this hypothesis it is expected that positioning the sensor in the RA lead will be more reliable in defining the optimal AV-delay because it gives information of both ventricles. Since the SonR1 signal is compromised out of a tricuspid and mitral valve component it could well be that the signal becomes wider during a greater amount of IVD. Future research should focus on how the different components of the SonR signal can be used to obtain better timing of atrial and ventricular contraction. Also, the second heart sound (or SonR2), which is a consequence of aortic and pulmonary valve closure might aid in better synchronization of the heart by analyzing splitting of the aortic and pulmonary component [49]. The SonR system is currently clinically used for AV- and VV-delay optimization in CRT patients. Of course, when first degree AV-block ( chapter 3 ) will be seen as a new indication for pacing therapy, additional research has to be performed to see whether this algorithm is successful in this new patient category. Much will depend on ongoing research involving the location of the ventricular leads. In case of His bundle, LV septal or LBB area pacing only one ventricular pacemaker lead will be present, meaning optimization algorithms can focus on optimizing AV-delay. THE IMPORTANCE OF THE RIGHT VENTRICLE Optimization of CRT or other pacing therapies mainly focusses on the LV, while the RV is often overlooked. In chapter 6 we studied the changes in LV and RV dP/dt max during variations of AV- and VV-delays in a canine total AV-block model. LV dP/dt max showed the largest increase compared to the reference setting during LV pre-excitation, while RV dP/ dt max was highest with RV pre-excitation. Interestingly, the setting with the highest cardiac output differed from the settings with the best LV or RV dP/ ­ dt­ max in computer simulations, indicating that improving LV contractility through LV pre-excitation does not necessarily lead to the best overall cardiac pump function. Since the RV and LV are coupled in series, decreasing RV function due to LV pre-excitation leads to reduced pre-load of the LV and thereby a decrease in cardiac output. We found that the settings with the highest cardiac output were during simultaneous pacing of both ventricles, suggesting that overall cardiac function is a compromise of left and right function. In chapter 4 we proposed the mean effective AV-delay as better predictor for AV- optimization. This parameter is a combination of left and right AV-delay, indicating once again that also RA-RV coupling is important to obtain optimal whole heart cardiac function. Also chapter 5 gives clues that the RV is important as the SonR lead placed in the RA that ‘oversees’ both ventricles is better that the RV SonR1 signal in predicting the optimal AV-