***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: PURPOSE To investigate whether magnetic resonance imaging ( MRI ) cine-derived dyssynchrony indices provide additional information compared to conventional tagged MRI ( tMRI ) acquisitions in heart failure patients undergoing cardiac resynchronization therapy ( CRT ) . MATERIAL S AND METHODS Patients scheduled for CRT ( n = 52 ) underwent preprocedure MRI including cine and tMRI acquisitions .  Segmental strain curves were calculated for both cine and tMRI to produce a range of st and ard indices for direct comparison between modalities . We also proposed and evaluated a novel index of " dyscontractility , " which detects the presence of focal areas with paradoxically positive circumferential strain . RESULTS Across conventional strain indices , there was only moderate-to-poor ( R = 0.3 - 0.6 ) correlation between modalities ; eight cine-derived indices showed statistically significant ( P < 0.05 ) relations to CRT outcome compared to just two tMRI-based counterparts . The novel dyscontractility index calculated on basal slice cine images ( cine dyscontractility index , " CDI " ) was the single best predictor of clinical response to CRT ( area under the curve AUC = 0.81 , P < 0.001 ) . While poorly correlated to its tMRI counterpart ( R = 0.33 ) , CDI performed significantly better in predicting response to CRT ( P < 0.005 ) , and was also numerically better than all other tMRI indices ( AUC 0.53 - 0.76 , all P for AUC comparisons < 0.17 ) . CONCLUSION Cine-derived strain indices offer potentially new information compared to tMRI . Specifically , the novel CDI is most strongly linked to response to cardiac resynchronization therapy in a contemporary patient cohort . It utilizes readily available MRI data , is relatively straightforward to process , and compares favorably with any conventional tagging index . J. Magn . Reson . Imaging 2016;44:1483 - 1492 AIMS The aim of the study was to assess the predictive value for outcomes of various response criteria currently used in patients undergoing cardiac resynchronization therapy ( CRT ) .  METHODS AND RESULTS Data from TRUST CRT r and omized trial in patients with New York Heart Association ( NYHA ) III-IV class , QRS ≥ 120 ms , ejection fraction ≤ 35 % , and mechanical dyssynchrony was analysed . Ninety-seven subjects who survived 6 months after implantation of CRT-defibrillator  were classified as responders or non-responders depending on 15 criteria used in most of the previous trials . Blindly adjudicated data on major adverse cardiac events ( MACEs ) within 1 year after classification were used to calculate the predictive value of response criteria . After adjustment for baseline confounding variables only eight criteria were significantly predictive for future MACEs . Sensitivity and specificity ranged substantially for clinical ( 32 - 94 % and 26 - 63 % ) and echocardiographic criteria ( 40 - 93 % and 22 - 70 % , respectively ) . The most powerful clinical predictor was > a NYHA class reduction ≥ 1 [ adjusted relative risk ( RR ) 4.41 for non-responders ; 95 % confidence interval ( CI ) 1.75 - 11.04 , P = 0.002 ] , while the strongest echocardiographic predictor was a reduction in the left ventricular end-systolic index by > 15 % ( RR 3.49 ; 95 % CI 1.59 - 7.64 , P = 0.002 ) . A combination of these two criteria did not improve the predictive value of a single parameter . Both criteria showed multiple significant interactions with baseline patients ' characteristics . CONCLUSION Only some of the commonly used response criteria predict outcome in patients  undergoing CRT .  The predictive value varies substantially across different criteria , with a higher sensitivity observed for the clinical parameters and a higher specificity observed for echocardiographic parameters . Combining various criteria adds little to their prognostic value . The predictive accuracy of various criteria can be different in various subgroups due to multiple interactions with baseline characteristics . CLINICAL TRIALS . GOV IDENTIFIER : NCT00814840 Background — Cardiac resynchronization therapy ( CRT ) decreases mortality , improves functional status , and induces reverse left ventricular remodeling in selected population s with heart failure . We aim ed to assess the impact of baseline QRS duration and morphology and the change in QRS duration with pacing on CRT outcomes in mild heart failure . Methods and Results — Resynchronization Reverses Remodeling in Systolic Left Ventricular Dysfunction ( REVERSE ) was a multicenter r and omized trial of CRT  among 610 patients with mild heart failure . Baseline and CRT-paced QRS duration s and baseline QRS morphology were evaluated by blinded core laboratories . The mean baseline QRS duration was 151±23 milliseconds , and 60.5 % of subjects had left bundle-branch block ( LBBB ) . Patients with LBBB experienced a 25.3-mL/m2 mean reduction in left ventricular end-systolic volume index ( P<0.0001 ) , whereas non-LBBB patients had smaller decreases ( 6.7 mL/m2 ; P=0.18 ) . Baseline QRS duration was also a strong predictor of change in left ventricular end-systolic volume index with monotonic increases as QRS duration prolonged . Similarly , the clinical composite score improved with CRT for LBBB subjects ( odds ratio , 0.530 ; P=0.0034 ) but not for non-LBBB subjects ( odds ratio , 0.724 ; P=0.21 ) . The association between clinical composite score and QRS duration was highly significant ( odds ratio , 0.831 for each 10-millisecond increase in QRS duration ; P<0.0001 ) , with improved response at longer QRS duration s. The change in QRS duration  with CRT pacing was not an independent predictor of any outcomes after correction for baseline variables . Conclusion — REVERSE demonstrated that LBBB and QRS prolongation are markers of reverse remodeling and clinical benefit with CRT in mild heart failure . Clinical Trial Registration — URL : http://www . clinical trials.gov . Unique identifier : NCT00271154 The aim of this study was to assess the effectiveness of cardiac resynchronization therapy ( CRT ) by intracardiac delay optimization using echocardiography . Sixty-five patients were implanted with a CRT device r and omly assigned to receive simultaneous biventricular pacing or echo-optimized sequential CRT .  Forty-two patients were defined as responders and 23 patients were classified as non-responders . During a 12-month follow-up period , the positive response rate , QRS duration , New York Heart Association class , mitral insufficiency grade , left ventricular end-systolic volume and LV end-diastolic volume were similar in the optimized and non-optimized groups ( P>0.05 ) , whereas 6-minute walking distance , quality -of-life score , left ventricular ( LV ) ejection fraction and aortic velocity time integral were significantly improved in the optimized group ( P<0.05 ) . The baseline QRS duration s of the responders and non-responders were similar ( P>0.05 ) , whereas heart failure aetiology , clinical and echocardiographic measurements showed significant differences ( P<0.05 ) . The mean decrease in QRS duration after 12 months of CRT used for separating responders and non-responders was significantly different ( P<0.05 ) , and significant differences were observed in the mean decrease of QRS duration between responders and non-responders ( P<0.05 ) . Echocardiographic optimization may further improve the effectiveness of CRT . Moreover , severe mitral regurgitation and greater LV volume are likely to indicate a poor response to CRT In the GRADE approach , r and omized trials start as high- quality evidence and observational studies as low- quality evidence , but both can be rated down if most of the relevant evidence comes from studies that suffer from a high risk of bias . Well-established limitations of r and omized trials include failure to conceal allocation , failure to blind , loss to follow-up , and failure to appropriately consider the intention-to-treat principle . More recently recognized limitations include stopping early for apparent benefit and selective reporting of outcomes according to the results . Key limitations of observational studies include use of inappropriate controls and failure to adequately adjust for prognostic imbalance . Risk of bias may vary across outcomes ( e.g. , loss to follow-up may be far less for all-cause mortality than for quality of life ) , a consideration that many systematic review s ignore . In deciding whether to rate down for risk of bias -- whether for r and omized trials or observational studies -- authors should not take an approach that averages across studies . Rather , for any individual outcome , when there are some studies with a high risk , and some with a low risk of bias , they should consider including only the studies with a lower risk of bias Background —Despite benefits of cardiac resynchronization therapy ( CRT ) in patients with severe but less symptomatic heart failure , approximately 30 % of patients do not fully respond to treatment . We hypothesized that a combined assessment of left ventricular ( LV ) dyssynchrony and contractile function by strain-based imaging would identify patients who would most benefit from CRT . Methods and Results —We studied 1077 patients with New York Heart Association class I/II , LV ejection fraction ⩽30 % and QRS width ≥130 ms enrolled in the Multicenter Automatic Defibrillator Implantation Trial – Cardiac Resynchronization Therapy trial with sufficient echocardiographic image quality for cardiac deformation analysis ( implantable cardioverter-defibrillator [ ICD ] , n=416 ; CRT , n=661 ) . Patients were assigned to CRT plus an ICD or to ICD alone in 3:2 r and om assignment . We assessed the degree to which baseline echocardiographic assessment s of dyssynchrony , measured as the st and ard deviation of time-to-peak transverse strain over 12 segments , contractile function , measured as global longitudinal strain , or both predicted the effect of treatment on the primary outcome of death or heart failure . With 213 primary events occurring over a mean of 2.4 years , the benefit of CRT plus an ICD relative to ICD alone was greatest in patients with mild to moderate dyssynchrony ( time-to-peak transverse strain st and ard deviation , 142 to 230 ms ) and greater baseline contractile function ( global longitudinal strain ⩽−8.7 % ) . Overall , those patients with mild to moderate dyssynchrony and those with best contractile function at baseline demonstrated the greatest benefit from CRT ( adjusted hazards ratio , 0.20 ; 95 % confidence interval , 0.09 to 0.44 ) . Dyssynchrony and global longitudinal strain predicted response to CRT independent of each other , QRS width , LV ejection fraction , and presence versus absence of left bundle-branch block , although the observed benefit remained greatest in patients with left bundle-branch block . Conclusions —Both mechanical dyssynchrony and contractile function are important independent correlates of benefit from CRT . Clinical Trial Registration —URL : http://www . clinical trials.gov . Unique identifier : NCT00180271 Biventricular pacing results in left ventricular ( LV ) reverse remodeling in heart failure patients with wide QRS complexes . This study examines potential predictors of reverse remodeling . Echocardiography with tissue Doppler imaging was performed at baseline and 3 months after  biventricular pacing  in 30 patients ( 21 men and 9 women , mean age 62 + /- 14 years ) . There were 17 responders to reverse remodeling ( defined as a reduction in LV end-systolic volume by > 15 % ) and 13 nonresponders . Responders had significant improvement in 6-minute hall-walking distance ( p = 0.006 ) , metabolic equivalents ( p = 0.02 ) , peak oxygen uptake ( p = 0.02 ) , New York Heart Association functional class ( p < 0.001 ) , and quality of life ( p < 0.001 ) ; an increase in the sphericity index ( p = 0.007 ) , ejection fraction ( p < 0.001 ) , and diastolic filling time ( p = 0.03 ) ; a decrease in myocardial performance index ( p = 0.02 ) , isovolumic relaxation time ( p = 0.004 ) , and mitral regurgitation ( p = 0.007 ) ; and an improvement in systolic dyssynchrony ( SD of the time to peak myocardial systolic contraction of the 12 LV segments as dyssynchrony index ) ( 45.0 + /- 8.3 vs 32.5 + /- 14.5 ms , p = 0.003 ) . In contrast , nonresponders only had a small degree of clinical improvement in New York Heart Association class ( p = 0.03 ) and quality -of-life scores ( p = 0.03 ) , without any change in cardiac function , and worsening of systolic dyssynchrony ( 24.8 + /- 4.5 vs 34.1 + /- 13.5 ms , p = 0.02 ) . When all the above factors were put into univariate and multivariate analyses models , systolic dyssynchrony was the only independent predictor of reverse remodeling ( r = -0.76 , p < 0.001 ) ( beta = -1.54 , p = 0.007 ) . A preimplant dyssynchrony index of 3 
    Output:
    
The observed association was independent of the timing of QRS width measurement after CRT implantation .
Acute and late improvement of electrical dysynchrony as depicted by QRS narrowing following biventricular pacing is associated with clinical and echocardiographic response to CRT .