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Background: The aim of this study was to evaluate the ability of baseline clinical and echocardiographic parameters to predict a positive response to CRT. Methods: We analyzed 6-month data from the first 133 consecutive patients enrolled in a multicenter prospective study. These patients had symptomatic heart failure (HF) refractory to pharmacological therapy (NYHA class II-IV), left ventricular ejection fraction (LVEF) <=35%, and prespecified electrocardiographic, echocardiographic or tissue Doppler imaging markers of left ventricular (LV) dyssynchrony. Results: After a follow-up period of 6 months, 1 patient died and 13 were hospitalized for worsening HF. There were significant (P < 0.01) clinical, functional, and echocardiographic improvements that included: New York heart Association Class, Quality-of-Life Score, QRS duration, LVEF, LV end-diastolic and end-systolic diameter (LVESD), and severity of mitral regurgitation A positive response was documented in 90/133 (68%) patients who presented an improved clinical composite score associated to an increase in LVEF >= 5 units. A multivariate analysis identified that a smaller LVESD (OR = 0.957, 95% CI 0.920-0.996; P = 0.030) and longer interventricular mechanical delay (IVMD) (OR = 1.017, 95% CI 1.005-1.029, P = 0.007) as independent predictors of a positive response. Receiver-operating curve analysis showed that a positive response to CRT may be predicted in patients with IVMD > 44 ms (with a sensitivity of 66% and a specificity of 55%) or with LVESD < 60 mm (with a sensitivity of 66% and a specificity of 61%). Conclusions: Our results confirm the limited value of QRS duration in the selection of patients for CRT. A less-advanced stage of disease and echocardiographic evidence of interventricular dyssynchrony demonstrated to predict response to CRT, while intraventricular dyssynchrony did not predict response. [ABSTRACT FROM AUTHOR]