https://orcid.org/0000-0002-9083-1582
This editorial refers to ‘The value of septal rebound stretch analysis for the prediction of volumetric response to cardiac resynchronization therapy’ by Salden et al., pp. 37–45.
Besides the simple assessment of QRS duration and left ventricular ejection fraction (LVEF), which still have a pivotal role in current guidelines,1 several different parameters have been proposed in the last decades to improve patient selection for cardiac resynchronization therapy (CRT) and to predict left ventricular (LV) reverse remodelling (CRT volumetric response).2
In recent years, the simple measure of opposite wall delay has been abandoned in favour of a more pathophysiological approach, which takes into account the electro-mechanical substrate associated with LV dyssynchrony. A particular importance has been given to the identification and localization of LV scar,3,4 as well as to the dynamic assessment of myocardial deformation.5–7
The role of septal rebound stretch (SRS) in predicting CRT volumetric response has already been demonstrated through cardiac modelization,7 and in retrospective studies.8 In their article, Salden et al. have the merit to underscore the relationship between SRSseptal and CRT response in a prospective observational multicentre trial including 200 CRT candidates.9 CRT was implanted according to guidelines and not according to imaging results. Interestingly, authors looked at the best specificity of SRSseptal in predicting volumetric response. They reached a specificity of 0.728. SRSseptal cannot be used to exclude any patient but in case of alternative treatment for heart failure, it might be considered.
Compared to the visual assessment of LV-mechanical dyssynchrony by septal flash (SF) and/or apical rocking (ApR), which can be largely influenced by the experience of the echo-reader,10 SRSseptal can be estimated directly from strain traces in apical four-chamber view (focused on the septum ideally). It provides a complementary information for selecting patients who will respond to CRT.11 A fair reproducibility is reported but automatization of SRSseptal quantification is required for a large clinical use.9
From a pathophysiological point of view, stretched in systole segments do not actively contribute to LV ejection, and correspond to the waste of cardiac energy. CRT has to restore a maximum of shortening of the septum in systole. After implantation, quantification of the remaining mechanical dyssynchrony could be proposed for best predicting LV-remodelling that will secondarily occur12 (Figure 1).
Septal stretch rebound, regional myocardial work…different approaches providing a quantitative and robust measurement of the wasted myocardial energy that has to be corrected by CRT: promising but in addition to other factors including electrical and/or other imaging tools before, during and perhaps after the device implantation.
SRSseptal above 2.4% is, according to the present study, an independent predictor of LV remodelling after CRT.9 SRSseptal is able to increase the predictive value of the ApR. It is important to keep in mind that with the simple ApR, the prediction of LV reverse remodelling after CRT implantation is predicted with an area under the curve >0.80.13 In Figure 3 of the Salden et al.’s manuscript, it is well illustrated the value of ApR and the complementary value of SRSseptal.9 This result is particularly interesting because LV-dyssynchrony could be attributable to different sort of substrates (scar, local increase in wall stress…), that should be detected for best estimating the non-response to CRT and that requires additional imaging tools to visual simple ones (ApR or septal flash).14
Despite these interesting results, several concerns remain about the application of SRSseptal. to the selection of CRT candidates. First, despite the amount of SRS is largely influenced by myocardial scarring and stiffening, no specific assessment of LV scar or viability has been performed in the study, so that the association between SRSseptal, and regional LV intrinsic contractility is only inferred. Second, the results of the current study are applicable to patients with strict LBBB or wide QRS (QRS >150 ms), which excludes a substantial proportion of patients who receive CRT in clinical practice. Third, the association between SRSseptal and LV reverse remodelling after CRT is only fair, with a β = 0.22 on multivariable analysis and a C-statistic of 0.65. These values are far from being optimal, and are very similar to those observed for other predictors of CRT-response described in literature, such as the presence of ‘typical’ LBBB,6 and myocardial constructive work.15 Fourth, the cut-off of SRSseptal provided in the current study is quite different from the cut-off provided before by De Boeck et al.8 Larger studies with randomization for treatment based on imaging tools remain fundamental for achieving a high level of evidence that could affect the guidelines for CRT.
In addition, CRT candidates represent a heterogeneous group of patients with several differences in the electrical and mechanical activity of the LV, clinical history, comorbidities, and disease duration. The characterization of this complex population cannot be identified neither by the simple assessment of QRS-width, nor by the description of specific and isolated imaging parameters. The combination of clinical, biological, imaging parameters in a more individualized approach for deciding for a treatment such as CRT is probably important. Thus imaging characteristics such as SRSseptal will be integrated in models of prediction.16
Conflict of interest: none declared.
The opinions expressed in this article are not necessarily those of the Editors of EHJCI, the European Heart Rhythm Association or the European Society of Cardiology.
