Rick Schreurs

132 Chapter 7 Measurements of in particular LA pressure are cumbersome, the wedge pressure is a surrogate, but does not show the dynamic behavior of this pressure. Another issue where the porcine experiments enriched the patient study is that stroke volume could be measured using a flow probe mounted around the ascending aorta, thus selectively determining the real forward flow over the aortic valve. In patients, stroke volume calculated from the change in LV volume using the conductance catheter may also include systolic MR, which possibly leads to an overestimation of the stroke volume and thereby underestimate the diastolic MR fraction compared to animals. Clinical implementation of cardiac pacing for prolonged PR-interval Before pacemaker therapy for first degree AV-block can be implemented in the clinic several steps have to be undertaken. First of all, the results presented in chapter 3 were all acute hemodynamic improvements. The benefit for cardiac output in this study was comparable to the improvement in cardiac output as seen in conventional CRT, whereas the increase in stroke work was lower [13, 14]. However, from these studies we also know that acute increases in stroke volume and stroke work in CRT are associated with long term benefits [15]. Secondly, we managed to replicate the abovementioned results in healthy porcine hearts in chapter 3 and chapter 4 . This suggests that optimizing the AV-delay is not only effective for severely symptomatic patients (NYHA class II-III) but also for patients with preserved pump function and mild complaints. Furthermore, as we hypothesized above, synchronous activation of the ventricles is mandatory and can not only be achieved by BiV pacing, but also by His-bundle pacing [16], left bundle area pacing [17] or LV septal pacing [18]. All these pacing modalities are becoming increasingly popular and make the use of a third LV lead unnecessary and thereby easier and cheaper. Of course, the feasibility, safety and efficacy of pacing-based AV-optimization in patients with first degree AV-block without LBBB and with narrow QRS complex requires additional investigation in prospective trials. These studies should also identify which patient categories benefit most from restoring AV-coupling, and whether the indication should be made based on the ECG derived PR-interval, or the presence of E-A fusion or diastolic MR on echocardiography. Additional studies should also evaluate which pacing modalities are most suitable. The influence of interatrial delay and interventricular dyssynchrony on the optimal AV-delay Chapter 4 further focuses on the mechanisms of AV-delay optimization, with emphasis on atrioventricular timing for both the right and left heart. This evaluation of the whole heart was applied, because total cardiac output depends on the pump function of both ventricles, due to their serial coupling (see also chapter 6 ). The use of pressure measurements in all four cardiac chambers showed that delays in activation between RA and LA as well as between RV and LV have an impact on optimal pump function of the whole heart. It should