***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 Biventricular ( BiV ) stimulation is the preferred means of delivering cardiac resynchronization therapy ( CRT ) , although left ventricular (LV)-only stimulation might be as safe and effective . B-LEFT HF is a prospect i ve , multicenter , r and omized , double-blind study aim ed to examine whether LV-only is noninferior to BiV pacing regarding clinical and echocardiographic responses . METHODS B-LEFT HF r and omly assigned 176 CRT-D recipients , in New York Heart Association class III or IV , with an LV ejection fraction < or = 35 % and QRS > or = 130 milliseconds , to a BiV ( n = 90 ) versus LV ( n = 86 ) stimulation group . Clinical status and echocardiograms were analyzed at baseline and 6 months after CRT-D implant to test the noninferiority of LV-only compared with BiV stimulation . RESULTS The proportion of responders was in line with current literature on CRT , with improvement in heart failure composite score in 76.2 % and 74.7 % of patients in BiV and LV groups , respectively . Comparing LV versus BiV pacing , the small differences in response rates and corresponding 95 % CI indicated that LV pacing was noninferior to BiV pacing for a series of response criteria ( combination of improvement in New York Heart Association and reverse remodeling , improvement in heart failure composite score , reduction in LV end-systolic volume of at least 10 % ) , both at intention-to-treat and at per- protocol analysis . CONCLUSIONS Left ventricular-only pacing is noninferior to BiV pacing in a 6-month follow-up with regard to clinical and echocardiographic responses . Left ventricular pacing may be considered as a clinical alternative option to BiV pacing Aims The choice of resynchronization therapy between  with ( CRT-D ) and without ( CRT-P ) a defibrillator  remains a contentious issue . Cause-of-death analysis among CRT-P , compared with CRT-D , patients could help evaluate the extent to which  CRT-P patients would have additionally benefited from a defibrillator in a daily clinical practice . Methods and results A total of 1705 consecutive patients implanted with a CRT ( CRT-P : 535 and CRT-D : 1170 ) between 2008 and 2010 were enrolled in CeRtiTuDe , a multicentric prospect i ve follow-up cohort study , with specific adjudication for causes of death at 2 years . Patients with  CRT-P  compared with CRT-D were older ( P < 0.0001 ) , less often male ( P < 0.0001 ) , more symptomatic ( P = 0.0005 ) , with less coronary artery disease ( P = 0.003 ) , wider QRS ( P = 0.002 ) , more atrial fibrillation ( P < 0.0001 ) , and more co-morbidities ( P = 0.04 ) . At 2-year follow-up , the annual overall mortality rate was 83.80 [ 95 % confidence interval ( CI ) 73.41–94.19 ] per 1000 person-years . The crude mortality rate among CRT-P patients was double compared with CRT-D ( relative risk 2.01 , 95 % CI 1.56–2.58 ) . In a Cox proportional hazards regression analysis , CRT-P remained associated with increased mortality ( hazard ratio 1.54 , 95 % CI 1.07–2.21 , P = 0.0209 ) , although other potential confounders may persist . By cause-of-death analysis , 95 % of the excess mortality among CRT-P subjects was related to an increase in non-sudden death . Conclusion When compared with CRT-D patients , excess mortality in CRT-P recipients was mainly due to non-sudden death . Our findings suggest that CRT-P patients , as currently selected in routine clinical practice , would not potentially benefit with the addition of a defibrillator Background — The Sudden Cardiac Death in Heart Failure Trial ( SCD-HeFT ) demonstrated that implantable cardioverter-defibrillator ( ICD ) therapy reduces all-cause mortality in patients with New York Heart Association class II/III heart failure and a left ventricular ejection fraction ≤35 % on optimal medical therapy . Whether ICD therapy reduced sudden death caused by ventricular tachyarrhythmias without affecting heart failure deaths in this population is unknown . Methods and Results — SCD-HeFT r and omized 2521 subjects to placebo , amiodarone , or shock-only , single-lead ICD therapy .  Over a median follow-up of 45.5 months , a total of 666 deaths occurred , which were review ed by an Events Committee and initially categorized as cardiac or noncardiac . Cardiac deaths were further adjudicated as result ing from sudden death presumed to be ventricular tachyarrhythmic , bradyarrhythmia , heart failure , or other cardiac causes . ICD therapy significantly reduced cardiac mortality compared with placebo ( adjusted hazard ratio , 0.76 ; 95 % confidence interval , 0.60 to 0.95 ) and tachyarrhythmia mortality ( adjusted hazard ratio , 0.40 ; 95 % confidence interval , 0.27 to 0.59 ) and had no impact on mortality result ing from heart failure or noncardiac causes . The cardiac and tachyarrhythmia mortality reductions were evident in subjects with New York Heart Association class II but not in subjects with class III heart failure . The reduction in tachyarrhythmia mortality with ICD therapy was similar in subjects with ischemic and nonischemic disease . Compared with placebo , amiodarone had no significant effect on any mode of death . Conclusions — ICD therapy reduced cardiac mortality and sudden death presumed to be ventricular tachyarrhythmic in SCD-HeFT and had no effect on heart failure mortality . Amiodarone had no effect on all-cause mortality or its cause-specific components , except an increase in non-cardiac mortality in class III patients . Clinical Trial Registration Information— URL : http://www . clinical trials.gov . Unique identifier : NCT00000609 The number needed to treat ( NNT ) is a simple measure of a treatment 's impact , increasingly reported in r and omized trials and observational studies . Its calculation in studies involving varying follow-up times or recurrent outcomes has been criticized . We discuss the NNT in these context s , illustrating using several published studies . The computation of the NNT is founded on the cumulative incidence of the outcome . Instead , several published studies use simple proportions that do not account for varying follow-up times , or use incidence rates per person-time . We show that these approaches can lead to erroneous values of the NNT and misleading interpretations . For example , after converting the incidence rate to a cumulative incidence , we show that a trial reporting a NNT of 4 " to prevent one exacerbation in 1 year " should have reported a NNT of 9 . A survey of all papers reporting NNT , published in four major medical journals in 2009 , found that 6 out of all 10 papers involving varying follow-up times did not correctly estimate the NNT . As the " number needed to treat " becomes increasingly used in complex studies and in the comparative effectiveness of therapies , its accurate estimation and interpretation become crucial to avoid erroneous clinical and public health decisions Objective : To compare the effects of cardiac resynchronisation therapy ( CRT ) in patients with heart failure ( HF ) in either atrial fibrillation ( AF ) or sinus rhythm ( SR ) . Design : Prospect i ve observational study . Patients : 295 consecutive patients with HF ( permanent AF in 66 , paroxysmal AF in 20 , SR in 209 ; New York Heart Association ( NYHA ) class III or IV ; left ventricular ejection fraction ( LVEF ) ⩽35 % , QRS ⩾120 ms ) . Interventions : All patients underwent CRT without atrioventricular junction ablation . Main outcome measures : The primary end point was the composite of cardiovascular death or unplanned hospitalisation for major cardiovascular events . Secondary end points included the composite of cardiovascular death or hospitalisation for worsening HF . Cardiovascular mortality , total mortality and changes in NYHA class , 6-minute walking distance , quality of life ( Minnesota Living with Heart Failure question naire ) and echocardiographic variables were also considered . Results : Over a follow-up period of up to 6.8 years , no differences emerged between patients in AF or SR in any of the mortality or morbidity end points . The AF and SR groups derived similar improvements in mean NYHA class ( −1.3 vs –1.2 ) , 6-minute walking distance ( 92.3 vs 78.4 m ) and quality of life scores ( −25.2 vs –18.7 ) ( all p<0.001 ) . In both the AF and the SR groups , reductions were seen in left ventricular end-systolic ( −25.9 vs –34.5 ml , both p<0.001 ) and end-diastolic ( −20.2 ml , p = 0.001 vs 26.2 ml , p<0.001 ) volumes and improvements in LVEF ( 4.69 % vs 7.86 % , both p<0.001 ) . Conclusions : Cardiac resynchronisation therapy leads to similar prognostic and symptomatic benefits in patients in AF and SR , even without atrioventricular junction ablation . Echocardiographic improvements are also comparable 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 , r and omized trial of CRT among patients with mild heart failure . Long-term annual follow-up for 5 years was preplanned . The present analysis was confined to the 419 patients who were r and omized to active CRT group .  CRT-pacemakers or CRT-D devices were implanted based on national guidelines at the time of enrollment , with 74 patients receiving CRT pacemaker devices and the remaining 345 patients receiving CRT-D devices .  After 12 months of CRT , changes in the clinical composite score , left ventricular end systolic volume index , 6-minute walk time , and quality of life indices were similar between CRT pacemaker and CRT-D patients . However , long-term follow-up showed lower morality in the CRT-D group . Specifically , multivariable analysis showed that CRT-D ( hazard ratio , 0.35 ; P=0.003 ) was a strong independent predictor of survival . Female sex , longer unpaced QRS duration , and smaller baseline left ventricular end systolic volume index also were also associated with better survival . Conclusions —REVERSE demonstrated that the addition of implantable cardioverter-defibrillator therapy to CRT is associated with improved long-term survival compared with CRT pacing alone in mild heart failure . Clinical Trial Registration —URL : http:// clinical trials.gov . Unique Identifier : NCT00271154 AIMS The CArdiac REsynchronization-Heart Failure study r and omized patients with left ventricular ejection fraction < or = 35 % , markers of cardiac dyssynchrony , and persistent moderate or severe symptoms of heart failure despite pharmacological therapy , to implantation of a cardiac resynchronization therapy ( CRT ) device or not . The main study observed substantial benefits on morbidity and mortality during a mean follow-up of 29.4 months [ median 29.6 , interquartile range ( IQR ) 23.6 - 34.6 ] . Prior to study closure , an extension phase lasting a further 8 months ( allowing time for data analysis and presentation ) was declared during which cross-over was discouraged . METHODS AND RESULTS This was an extension of the already reported open-label r and omized trial described above . The primary outcome of the extension phase was all-cause mortality from the time of r and omization to completion of the extension phase . The secondary outcome was mode of death . The mean follow-up was 37.4 months ( median 37.6 , IQR 31.5 - 42.5 , range 26.1 - 52.6 months ) . There were 154 deaths ( 38.1 % ) in 404 patients assigned to medical therapy and 101 deaths ( 24.7 % ) in 409 patients assigned to CRT ( hazard ratio 0.60 , 95 % CI 0.47 - 0.77 , P<0.0001 ) without evidence of heterogeneity in pre-specified subgroups . A reduction in the risk of death due to heart failure ( 64 vs. 38 deaths ; hazard ratio 0.55 , 95 % CI 0.37 - 0.82 , P=0.003 ) and sudden death was observed ( 55 vs. 32 ; hazard ratio 0.54 , 95 % CI 0.35 - 0.84 , P=0.005 ) . CONCLUSION The benefits of CRT observed in the main trial persist or increase with longer follow-up . Reduction in mortality was due to fewer deaths both from worsening heart failure and from sudden death 
    Output:
    
The extent of SCD in CRT-P patients significantly increased in studies with higher percentage of males , ischaemic cardiomyopathy and NYHA class 3 .
Conclusion Overall , compared with CRT-D patients , unadjusted mortality rate was almost two-fold higher in CRT-P recipients , with SCD representing one third of the excess mortality .
Rate of SCD was significantly higher in certain subgroups ( males , ischaemic cardiomyopathy , NYHA class 3 ) , where a CRT-D may be of more pronounced benefit .