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Purpose: In patients with heart failure (HF), the effective diastolic filling time and an optimized auriculo-ventricular (A-V) coupling are critical determinants of stroke volume. Moreover, a shortened diastolic filling time is frequently observed in HF patients resulting in summation of transmitral E and A waves or interruption of A wave by early ventricular contraction. Optimization of ventricular filling is currently used as a tool in carriers of biventricular pacemakers. We hypothesized that a shortened diastolic filling time (measured by the ratio of diastolic filling time to cardiac cycle time - DFT/CT -) may predict outcomes in chronic heart failure patients without CRT.Methods: Single centre study of a Heart Failure Clinic population of non-valvular dilated cardiomyopathy patients. Pts undergoing CRT were excluded. The DFC/CT ratio was evaluated with echocardiography by spectral pulsed-wave Doppler of the mitral inflow tracing with optimized settings to clearly display the onset and cessation of LV inflow. The combined study endpoint was all-cause mortality, heart failure hospitalization or heart transplantation at follow-up. The cut-off for the DFC/CT ratio was assessed by ROC curve analysis; survival analysis with log rank test was used to determine the association between DFC/CT and the study endpoints.Results: We enrolled 66 patients (77% males, mean±SD age 54.1±14.1 years, mean±SD ejection fraction 40% ± 11%). Mean±SD heart rate was 66±12.7 bpm; the prevalence of atrial fibrillation was 14%. During a median follow-up of 20 months (12.8 to 30), 7.6% of patients met the study endpoint. Median values of DFC/CT were 0.53 (0.48 to 0.55). At ROC curve analysis (AUC 0.74, CI 95% 0.61-0.85), the summation of sensitivity and specificity was highest at a DFC/CT ratio of 0.49. Survival analysis showed a statistically significant difference (p=0.01) in the study endpoint when comparing the group of DFC/CT ratio <0.50 to a group of DFC/CT >0.50 (22% vs 2.9%). Cox regression confirmed the predictive power of the DFC/CT ratio <0.50 even when adjusted for the presence of atrial fibrillation, age or left ventricular ejection fraction (HR 14.9, 95% CI 1.3-176.2).Conclusions: In this study, a diastolic filling time <50% of the cardiac cycle time was an independent predictor of adverse outcome in heart failure patients without CRT, undergoing optimal medical therapy. Further studies are needed to evaluate if pharmacological treatment optimization should address this parameter.