Rocking will tell it.

During the past years, cardiac resynchronization therapy (CRT) has become a recognized treatment option for patients with heart failure and conduction delays. In the meantime, the principle of re-synchronizing a dyssynchronous ventricle can be regarded as established. The challenge of correctly identifying the patient candidates who will benefit from this costly and not completely noninvasive therapy, however, remains. With its wide availability, feasibility, and its potential to analyse regional myocardial function with excellent temporal and good spatial resolution, echocardiography may be regarded as the ideal imaging modality for CRT patient selection. Many attempts have been made in the past years to utilize tissue Doppler for this task. A plethora of parameters came upon us, mostly based on differences in timing of systolic velocity peaks in up to 12 different myocardial regions. Only a few attempts have been made, however, to analyse the underlying mechanics of these measurements and to optimize measurement methods for them. There are several reasons, why velocity peak-based parameters are suboptimal for analysing left ventricular dyssynchrony. First, there is no direct relationship between regional velocity and regional myocardial contraction. This is true in particular in a dyssynchronous ventricle, where one region of the ventricular myocardium pulls the other and passive motion is a common finding. Secondly, peak velocities are subject to afterload and their timing does not reflect the timing of mechanical activation. Thirdly, parameters calculated from timing of peak velocities in several segments relinquish precious regional information on the contraction sequence. In addition, measurement reproducibility worsens with the number of measurements needed. As a consequence, the excellent results of smaller, single-centre studies using velocity peak-based parameters could not be reproduced in larger trials, which put false colours upon the—in principle—convincing concept of measuring what you want to treat, i.e. the mechanical dyssynchrony of the left ventricle (LV). Besides that, dyssynchrony is probably the most important, but not the only factor influencing the success of CRT in an individual patient. Suboptimal lead placement and device settings, limited myocardial viability, and features of the underlying disease may have a confounding impact. The two recent studies of Parsai et al. have shed refreshingly new light on the scene. In ‘Toward understanding response to cardiac resynchronization therapy: left ventricular dyssynchrony is only one of multiple mechanisms’, the authors try first to separate different pathomechanisms that contribute to the deterioration of LV function in heart failure patients. Not only intraventricular dyssynchrony, but also disturbed atrioventricular coupling and interactions between the right and left ventricle are identified as aetiological factors. The successful treatment of these factors was mostly associated with reverse remodelling or clinical improvement. It may be the subject of discussion as to whether, given its rather low specificity, the suggested clinical path for identifying responders is sufficiently supported by data, but it is certainly to the merit of this study that the authors have refrained from a mono-causal approach to this complex disease. By far the largest group of the study population presented with intraventricular dyssynchrony. Parsai et al. suggest using a phenomenon for its detection which represents the early septal contraction in an LV with left branch bundle block (LBBB). It is the same early septal contraction that causes the ‘apical rocking’ which can be typically visualized in an echocardiographic fourchamber view of a dyssynchronous heart. As a study from our group has shown, this parameter is a surrogate, reflecting both temporal and functional inhomogeneities in the LV with LBBB. Parsai et al. call the phenomenon ‘septal flash’ and suggest objectifying it by demonstrating an early septal excursion in a parasternal grey-scale or colour tissue Doppler M-mode. With the ‘septal flash’, Parsai et al. introduce a novel and elegant approach to assess dyssynchrony. It overcomes several of the above-mentioned limitations of peak velocity-based parameters, but avoids the challenges of myocardial deformation measurements. The parameter is