Guidelines aim at translating inclusion criteria of high-quality clinical landmark trials into indications for treatment recommendations in order to guarantee a solid evidence base for the clinical practice. In the field of cardiac resynchronization therapy (CRT), the inclusion criteria of landmark trials that impacted the current recommendations for patient selection were left ventricular ejection fraction <-35%3,4, <-40%5), New York Heart Association (NYHA) Class (I-II,1,5 II,4 II-III,2 III,3 II-IV,6 III-IV7,8), and QRS width (>-120ms,2,5 >-130ms,4,7,9 >-150ms3,10). Recommendations have been further influenced by study results showing a better response of patients with left bundle branch block (LBBB) than non-LBBBmorphology. 11 The suggested possible harm of CRT implantation in patients with QRS duration less than 130 ms by some studies12 has led to increasing the threshold for CRT implantation from 120ms in 2013 guidelines13 to 130ms in the 2016 edition of the European guidelines.14 While this approach ensures a strong evidence base for a certain treatment, it does not necessarily guarantee the optimal strategy for patient selection, as relevant or potentially favourable selection criteria might not have been tested. In the case of CRT, which has become an established treatment option for patients with heart failure, left ventricular (LV) dysfunction and conduction delays, still approximately one-third of the patients remain non-responders to this costlyand invasive therapy.15 One such potential selection criterion, which is not considered in current guidelines is mechanical dyssynchrony. This is in particular due to the disappointing results of studies that tested the additional predictive value of parameters derived from the timing of longitudinal myocardial velocity peaks as surrogate of mechanical dyssynchrony, which failed to show any additional value over conventional guideline criteria despite promising results from single-centre studies.16 In the meantime, however, there is growing evidence that advanced concepts such as the detection of specific motion patterns could be a potential guide for CRT candidate selection.17,18 The PREDICT-CRT trial investigated the association between CRT outcome and a novel parameter of mechanical dyssynchrony, characterized by a short septal contraction pulling the apex septally ['septal flash' (SF)] followed by a delayed lateral wall contraction which causes a lateral motion of the apex ['apical rocking' (ApRock)]. This specific pattern of contraction in addition to similar parameters which rely on the same phenomena, have been shown to be strongly associated with better survival and CRT response.17,19-26 In this study, we relate current CRT guideline recommendations for patient selection with patient outcome and investigate the potential additive prognostic value of echocardiographic markers of mechanical dyssynchrony.
