***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 
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    Input: Background — The objective of the present study was to investigate the effect of cardiac resynchronization therapy ( CRT ) on cardiac autonomic function . Methods and Results — This prospect i ve study included 45 consecutive patients with heart failure who received CRT devices with defibrillator and 20 age-matched , healthy control subjects . At baseline and 3 months and 6 months after CRT , we assessed New York Heart Association ( NYHA ) class , 6-minute walk distance , plasma sympathetic biomarker nerve growth factor , echocardiography , heart rate variability and cardiac presynaptic sympathetic function determined by  iodine 123 metaiodobenzylguanidine scintigraphy . After CRT , NYHA class improved by 1 class ( P<0.001 ) , and left ventricular ejection fraction increased by 8 % ( P<0.001 ) . Along with improvement in the st and ard deviation of all normal-to-normal R-R intervals ( 85.63±31.66 ms versus 114.79±38.99 ms ; P=0.004 ) and the st and ard deviation of the averaged normal-to-normal R-R intervals ( 82.62±23.03 ms versus 100.50±34.87 ms ; P=0.004 ) , the delayed heart/mediastinum ( H/M ) ratio increased ( 1.82 [ 0.58 ] versus 1.97 [ 0.59 ] ; P=0.03 ) , whereas the mean ( SD ) H/M washout rate was reduced ( 48 % [ 19 % ] versus 37 % [ 22 % ] ; P=0.01 ) . Twenty-two of 45 study patients responded to CRT , with a reduction of left ventricular end-systolic volume index > 15 % . Compared with nonresponders , responders had a higher delayed H/M ratio ( 2.11 versus 1.48 ; P=0.003 ) and lower H/M washout rate ( 37 % versus 62 % ; P=0.003 ) at baseline . Conclusions — CRT  improved sympathetic function . Cardiac sympathetic reserve may be a marker for the reversibility of failing myocardial function AIMS The European cardiac resynchronization therapy ( CRT ) survey is a joint initiative taken by the Heart Failure Association and the European Heart Rhythm Association of the European Society of Cardiology . The primary aim of this survey is to describe current European practice associated with CRT implantations . METHODS AND RESULTS A total of 140 centres from 13 European countries contributed data from consecutive patients successfully implanted with a CRT device with or without an ICD between November 2008 and June 2009 . The total number of patients enrolled was 2438 . The median age of the patients was 70 years ( IQR 62 - 76 ) and 31 % were > or = 75 years . It was found that 78 % were in NYHA functional class III or IV and 22 % in I or II . The mean ejection fraction was 27 % + /- 8 and the mean QRS duration 157 ms + /- 32 . The QRS duration was < 120 ms in 9 % . Atrial fibrillation was reported in 23 % . It was found that 26 % of patients had a previously implanted permanent pacemaker or ICD ; 76 % of procedures were performed by an electrophysiologist ; 82 % had an elective admission for implantation and the median duration of hospitalization was 3 days ( IQR 2 - 7 ) ; and 73 % received a CRT-D device which was more often implanted in men , younger patients , and with ischaemic aetiology . The mean QRS duration was reduced to 133 ms + /- 27 ( P < 0.0001 ) at discharge . Peri-procedural complication rates were comparable to the rates reported in r and omized trials . CONCLUSION This CRT survey provides important information describing current European practice with regard to patient demographics , selection criteria , procedural routines , and status at discharge . These data should be useful for benchmarking individual patient management and national practice against wider experience INTRODUCTION Cardiac resynchronization therapy ( CRT ) and implantable cardioverter-defibrillators ( ICD ) are effective therapies for heart failure ( HF ) patients with cardiac dyssynchrony . Patients receiving primary prevention CRT-defibrillator  that positively remodel might no longer qualify for ICD indication due to CRT-induced left ventricular ejection fraction ( LVEF ) improvement . We aim ed to evaluate the outcome of  CRT-D patients at the time of device replacement ( DR ) . METHODS AND RESULTS Patients undergoing primary prevention CRT-D DR were prospect ively included from November 2007 to March 2011 in 2 centers . CRT response was as defined as ≥1 NYHA class improvement and an increase in LVEF ≥10 % . Before DR , all patients underwent echocardiography and device interrogation . Patients without theoretical ongoing ICD indication ( TOII ) at DR were defined as those with LVEF ≥40 % without appropriate ICD therapy ( appropriate therapy ) during the first ICD service-life . A total of 107 consecutive patients were enrolled . Sixty-one patients ( 57 % ) were considered CRT responders after the index procedure . At the time of DR ( 56.4 ± 14.4 months from initial implant ) , 87 % of CRT responders were free of appropriate therapy , compared with 70 % of CRT nonresponders ( P = 0.02 ) . Thirty-nine patients ( 37 % ) did not meet the criteria for TOII . During follow-up ( mean 26.4 ± 14.4 months after DR ) , 37 patients ( 95 % ) without TOII were free of appropriate therapy versus 49 of 68 patients ( 72 % ) with ongoing TOII ( P = 0.007 ) . By multivariable analysis , the only independent predictor of appropriate therapy after DR was TOII ( hazard ratio = 6.43 ; P = 0.01 ) . CONCLUSION Absence of theoretical ICD indication occurs in more than one-third of CRT-D patients undergoing DR . In addition , appropriate therapy rate is relatively low ( 2.2 % per year ) in this subgroup of patients OBJECTIVE To estimate the baseline risk of arrhythmic death required for prophylactic implantable cardiac defibrillators ( ICDs ) to result in clinical ly meaningful survival benefits in the population . BACKGROUND While proven efficacious , the absolute survival impact of ICDs for the primary prevention of sudden cardiac death among patients with left ventricular ( LV ) dysfunction is highly dependent upon patient 's baseline risk of arrhythmic death . METHODS Using echocardiographic data from a r and om sample of patients identified from community echocardiographic laboratories , patients with moderate or severe LV dysfunction ( ejection fraction < 35 % ) were linked to administrative data bases to characterize baseline mortality risk ( median follow-up duration of 4.85 years ) . Relative efficacy was ascertained from meta- analysis and clinical trial data . The baseline annual risk of arrhythmic death required for prophylactic ICDs to result in clinical ly meaningful survival benefits in the population was estimated at different ranges of relative efficacy and numbers needed to treat ( NNTs ) thresholds . RESULTS LV dysfunction was a significant independent predictor of adverse outcomes . In total , 35.4 % of the patients with moderate to severe LV dysfunction died during the follow-up period . Assuming a base-case relative efficacy of 66 % , we estimated that the baseline risk for arrhythmic death required to exert a clinical ly meaningful NNT threshold of 50 in order to prevent one death ( from any cause ) was 3 % per year or higher . CONCLUSIONS The survival impact and cost-effectiveness of prophylactic ICDs in the population will depend upon the ability to risk-stratify and identify patients whose baseline risk for sudden cardiac death exceed 3 % per year Objectives The beneficial effects of cardiac resynchronization therapy ( CRT ) are thought to result from favorable left ventricular ( LV ) reverse remodeling , however CRT is only successful in about 70 % of patients . Whether response to CRT is associated with a decrease in ventricular arrhythmias ( VA ) is still discussed controversially . Therefore , we investigated the incidence of VA in CRT responders in comparison with non-responders . Methods In this nonr and omized , two-center , observational study patients with moderate-to-severe heart failure , LV ejection fraction ( LVEF ) ≤35 % , and QRS duration > 120 ms undergoing CRT were included . After 6 months patients were classified as CRT responders or non-responders . Incidence of VA was compared between both groups by Kaplan-Meier analysis and Cox regression analysis . ROC analysis was performed to determine the aptitude of LVEF cut-off values to predict VA . Results In total 126 consecutive patients ( 64±11years ; 67%male ) were included , 74 were classified as responders and 52 as non-responders . While the mean LVEF at baseline was comparable in both groups ( 25±7 % vs. 24±8 % ; P = 0.4583 ) only the responder group showed an improvement of LVEF ( 36±6 % vs. 24±7 ; p<0.0001 ) under CRT . In total in 56 patients VA were observed during a mean follow-up of 28±14 months , with CRT responders experiencing fewer VA than non-responders ( 35 % vs. 58 % , p<0.0061 ) . Secondary preventive CRT implantation was associated with a higher likelihood of VA . As determined by ROC analysis an increase of LVEF by > 7 % was found to be a predictor of a significantly lower incidence of VA ( AUC = 0.606 ) . Conclusions Improvement of left ventricular function under cardiac resynchronization therapy goes along with a reduced incidence of ventricular arrhythmia Background — The factors that determine the risk for sudden death or implantable cardioverter defibrillator therapy in patients receiving cardiac resynchronization therapy ( CRT ) therapies  are largely unknown . Methods and Results — We hypothesized that clinical measures of heart failure severity and the presence of comorbid conditions would predict the risk of malignant arrhythmias in the 1520 patients enrolled in the Comparison of Medical Therapy , Pacing , and Defibrillation in Heart Failure ( COMPANION ) Trial . Outcomes in the CRT group after implantable cardioverter defibrillator therapy were also evaluated . The CRT-defibrillator device reduced the risk of sudden death by 56 % compared with drug therapy ( 17 of 595 [ 2.9 % ] versus 18 of 308 [ 5.8 % ] , P<0.02 ) . CRT therapy was not associated with sudden death risk reduction ( 48 of 617 [ 7.8 % ] ) . Other factors associated with reduced sudden death risk were left ventricular ejection fraction > 20 % ( HR , 0.55 [ 95 % CI , 0.35 to 0.87 ] ; P=0.01 ) , QRS duration > 160 ms ( HR , 0.63 [ 95 % CI , 0.40 to 0.997 ] ; P=0.05 ) , and female gender ( HR , 0.56 [ 95 % CI , 0.34 to 0.94 ] ; P=0.003 ) . The risk for sudden death was increased by advanced New York Heart Association class IV heart failure ( HR , 2.62 [ 95 % CI , 1.61 to 4.26 ] ; P<0.011 ) and renal dysfunction ( HR , 1.69 [ 95 % CI , 1.06 to 2.69 ] ; P=0.03 ) . An appropriate shock was experienced in 88 ( 15 % ) of the 595 CTR-D patients . In the CRT-defibrillator patients , female gender ( HR , 0.54 [ 95 % CI , 0.31 to 0.94 ] ; P=0.03 ) and use of neurohormonal antagonists were associated with reduced risk . Class IV heart failure status increased risk . Appropriate implantable cardioverter defibrillator therapy was positively associated with risk of death or all-cause hospitalization ( HR , 1.57 ; P<0.002 ) , pump failure death or hospitalization ( HR , 2.35 ; P<0.001 ) , and sudden death ( HR , 2.99 ; P=0.03 ) , but not total mortality ( HR , 1.3 ; P=0.28 ) . Conclusions — In CRT c and i date s , sudden cardiac death risk is associated with higher New York Heart Association class and renal dysfunction . In CRT-defibrillator recipients , reduction in the risk of an appropriate shock is associated with medical therapy with neurohormonal antagonists , female gender , and New York Heart Association functional class III versus IV clinical status . Shock therapy was associated with worse outcome Background —Cardiac resynchronization therapy ( CRT ) decreases mortality , improves functional status , and induces reverse left ventricular remodeling in selected population s with heart failure . These benefits have been noted with both CRT-pacemakers as well as those devices with defibrillator backup ( CRT-D ) . However , there are little data comparing mortality between these 2 device types . Methods and Results —REsynchronization reVErses Remodeling in Systolic left vEntricular dysfunction ( REVERSE ) was a multicenter , 
    Output:
    
Recovery of LVEF post-CRT is associated with significantly reduced appropriate ICD therapy .
Patients with improvement of LVEF ≥45 % and those with primary prevention indication for ICD appear to be at lowest risk