الفهرس 
Aim of the StudyOnly 14 pages are availabe for public view
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Abstract
The prevalence of heart failure (HF) is still high and is rising in developing countries. Despite optimal medical therapy, refractory HF is a common outcomes and remains a “global disease requiring global response (1).
According to the current guidelines, cardiac resynchronization therapy (CRT) is recommended in patients with advanced heart failure (HF), reduced left ventricular ejection fraction percent (LVEF%), and wide QRS complex. However, approximately 30% of CRT recipients do not respond to this treatment. A number of studies have investigated possible associations between baseline characteristics and response to CRT (2). Indeed, wider baseline QRS width which reflects a higher degree of mechanical dysynchrony represents a significant predictive tool for CRT response. Some studies indicated that QRS shortening after CRT also predicts a favorable response to CRT. However, the existing data about the association of QRS narrowing after biventricular pacing with CRT response rates are not clear. Although previous meta-analyses have shown a significant association between QRS narrowing and CRT response, the significant heterogeneity of the definitions of clinical and echocardiographic CRT response in the included studies limits the interpretation of the aforementioned association (3).
Unfortunately, to date, all the approaches have turned out to be suboptimal in this regard (4).
Therefore, its hypothesized that factors other than dyssynchrony may contribute to CRT response. Strain constitutes a sensitive method for quantifying global left ventricular function and can provide prognostic information beyond routine LVEF% (5). Echocardiographic strain by speckle-tracking precisely characterizes left ventricle performance, scar burden, and dyssynchrony. Left ventricle global longitudinal strain (LVGLS) is associated with the outcome in general population as well as in heart failure patients(6, 7).