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Purpose: The aim of the present study was to assess long-term effects of CRT and to value the role of pre-CRT left ventricular (LV) dyssynchrony by tissue Doppler imaging (TDI) in predicting response.Methods: We enrolled 51 patients undergoing CRT between December 2009 and April 2011. All patients were investigated with Minnesota Living with Heart Failure Questionnaire (MLHFQ), ECG, echocardiography including TDI and implant control. We collected pre-implantation instrumental and clinical data for all patients, 34 of which were subsequently recalled for a follow-up 3 months later and 16 patients for a follow-up 1 year later. Interventricular dyssynchrony was considered as an aorto-pulmonary pre-ejection delay >40 ms. Intraventricular dyssynchrony was measured by TDI velocity curves and defined as septal-lateral wall delay >60ms. An increase of LVEF >10% defined an echo response whereas the improvement of at least 1 NYHA class defined clinical response.Results: In the whole population, the short-term significant effects at 3 months follow-up were:• An improvement in mean EF (from 25.5 ± 5.3 % to 34.3 ± 7.3 %; p<0.001)• A reduced width of spontaneous QRS (p=0.007)• An improvement in clinical performance, as assessed by a reduction of mean NYHA class (p<0.001) and a decreased MHLFQ score (p=0.009)• An inverse left ventricular remodeling, as shown by reduced diastolic (from 72 ± 8 mm to 67 ± 10.mm; p=0.019) and systolic diameters (from 62 ± 10 mm to 55 ± 11; p=0.041)• An improvement in Holter monitoring parameters, as denoted by a slower mean 24 hours cardiac frequency (p= 0.003) and better SDANN (p=0.020) and footprint (from 27 ± 9% to 36 ±8%, p=0.034).At 1 year follow-up, main benefits remained significant:• EF improvement (+7.8% from baseline; p<0.001)• Spontaneous QRS width shortening (-18.2 ms from baseline; p=0.048)• NYHA class reduction (p=0.001)and MLHFQ improvement (-22.5 from baseline; p=0.006).Among the whole population, 17% were full non-responder, 29% were only clinical responders and 54% were both echo and clinical responders. Both clinical and echocardiographical responses were not significantly associated with interventricular dyssynchrony and intraventricular dyssynchrony (all p= ns).Conclusions: After only 3 months, CRT was associated with an improvement in quality of life and left ventricular function and was able to significantly modify the sympathetic-parasympathetic interaction to the heart. After 1 year, most of these benefits persisted; however, pre-implantation dyssynchrony assessment did not predict long-term clinical or echo response.