Rick Schreurs

96 Chapter 5 Thirdly, an increase in SonR1 when pacing at short AV-delays has been attributed to atrial contraction against a closed or quickly closing mitral valve. Shah et al . have shown that S1 amplitudes were larger at high speed closure of the mitral valve in patients with complete heart block and various intervals between atrial and ventricular systole [21]. Stept et al . reported that the amplitude of S1 significantly incremented at short PR-intervals while LV dP/dt max did not change compared to those at longer PR-intervals in a healthy dog model [22]. However, in our study such SonR1 increase only occurs in resynchronized, responding animals. This may be explained by the considerable drop in LV contractility and systolic pressure when pacing at short AV-delay in the NResp animals. Apparently, a large SonR1 at short AV-delays is only obtained when, due to resynchronization, ventricular pump function is fairly well maintained when the atrium contracts against a closed mitral valve. Whatever the exact mechanism of the large SonR1 signals is, these data indicate that SonR1 amplitude is sensitive to the interval between atrial and ventricular systole (in the present study modified by changing paced AV-delay). The use of SonR1 for ambulatory AV optimization Programming an optimal AV-delay has been an issue of continuous debate. Several studies using ‘static’ (i.e. a single, in rest) AV optimization were not able to show a long-term benefit of CRT as compared to using a default setting [23-25]. However, acute hemodynamic studies have shown benefit of CRT optimization and that the optimal AV-delay varies from one patient to another and may change between rest and exercise [26-29]. Dynamic, automated algorithms for AV optimization have been developed, but except for the SonR system, all are based on electrograms, so using an electrical signal. The Adaptive CRT algorithm provides LV-only pacing timed with native RV activation when the AV-interval is normal, optimizing AV and VV-delay on the basis of periodic automatic evaluation of intrinsic conduction intervals [24, 30]. A recent study in HF patient with normal AV-conduction, without atrial fibrillation (AF) and with an indication for CRT showed that LV-only pacing timed with native RV activation may result in greater improvements in LV ejection fraction and myocardial strain compared with BiV pacing due to better apical and septal function [31]. The SyncAV algorithm provides a concept of BiV pacing by periodically measuring intrinsic conduction and dynamically adjusting AV-delays 50ms shorter than the intrinsic AV-interval, allowing for paced BiV wavefronts to fuse with intrinsic conduction (triple wavefront fusion) [32, 33]. Compared to QuickOpt optimization, SyncAV CRT led to narrower QRS complexes and higher aortic VTI in HF patients with a class I indication for CRT [34]. It is the strength of the SonR system that it uses a mechanical sensor, so far the only clinically applied one for this purpose. Ritter et al . were the first to use the SonR signal to obtain a tailored AV-delay that correlated closely to AV-delays as determined by echocardiography in patients with high degree AV-block paced in DDD mode [35]. Also in total AV-block patients receiving CRT RV SonR1 amplitude correlated significantly with