Reply to the Editor—LA function is not the only key for best selection of candidates for cardiac resynchronization therapy, but LA strain provides valuable information!

International audience; To the Editor: We thank Margulescu et al for their letter. It provides us with a unique opportunity to emphasize a few points that are extremely important to keep in mind about estimation of left atrial (LA) performance in cardiac resynchronization therapy (CRT) candidates. First, the main result of our study is that “LA peak systolic strain rate might be useful in predicting response to CRT.” This is not surprising if we consider that (1) previous studies have shown that LA volumes and function can be influenced by CRT; (2) superresponders to CRT have greater improvement in LA function1, 2, 3 and 4; and (3) increasing relevance has been given to LA function in overall heart physiology.1, 2, 3 and 4 Second, Margulescu et al state that “concerns have been raised that LA deformation indices cannot discriminate intrinsic LA function from the influence of LV function.” We agree that, as for many other echocardiographic parameters, LA strain is influenced by preload and afterload, and is impacted by left ventricular (LV) function, particularly by LV descent during systole.5 However, we need to emphasize that it is impossible to perfectly assess the function of an isolated cardiac cavity using current in vivo imaging techniques. Many studies have shown that LA strain is a rapid and highly reproducible method for estimating LA function. 6 Moreover, impaired LA strain is associated with a greater degree of LA fibrosis and with poor prognosis in the general population and in patients with mitral disease, which supports a potentially wider use of LA strain in clinical practice. 7, 8 and 9 Third, Margulescu et al observe that the “predictive value of LA SR for CRT response was modest and similar to other echocardiographic indices that have not been found useful, and is not recommended in current guidelines for selecting CRT candidates.” However, the goal of the present study was to explore a hypothesis and not to change current guidelines.10 With respect to our results, authors and readers should acknowledge that it is always difficult to demonstrate that an imaging technique can impact patient prognosis, even when large perspective studies have been specifically designed to prove it.11 and 12 Further studies are needed to support the role of LA strain in predicting CRT response, but exploration of LA function in this field is full of promise!