***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: INTRODUCTION cardiac resynchronization therapy ( CRT ) may improve prognosis in patients with chronic right ventricular ( RV ) pacing , and optimal lead position can decrease nonresponders . We evaluated the clinical and echocardiographic response to CRT in patients with previous chronic RV pacing , using pressure-volume loop analyses to determine the optimal left ventricular ( LV ) lead position during implantation . METHODS AND RESULTS In this single-blinded , r and omized , controlled crossover study , 40 patients with chronic RV apical pacing and symptoms of heart failure , decreased LV ejection fraction ( LVEF ) or dyssynchrony were included . During implantation , stroke work ( SW ) , LVEF , cardiac output , and LV dP/dt(max ) were assessed by a conductance catheter . Clinical and echocardiographic response was studied during a 3-month period of RV pacing ( RV period , LV lead inactive ) and a 3-month period of biventricular pacing ( CRT period ) . At the optimal LV lead position , SW ( 37 ± 41 % ) , LVEF ( 16 ± 13 % ) , cardiac output ( 29 ± 16 % ) , and LV dP/dt(max ) increased ( 11 ± 11 % ) significantly during biventricular pacing compared to baseline . Additional benefit could be achieved by pressure-volume loop guided selection of the best left-sided pacing location . RV outflow tract pacing did not improve hemodynamics . During follow-up , symptoms improved during CRT , VO(2,max ) increased 10 % and significant improvements in LVEF , LV volumes , and mitral regurgitation were observed as compared to the RV period . CONCLUSIONS CRT in patients with chronic RV pacing causes significant improvement of both LV function as measured by pressure-volume loops during implantation and clinical and echocardiographic improvement during follow-up . Pressure-volume loops during implantation may facilitate selection of the most optimal pacing site AIMS To investigate whether cardiac resynchronization therapy ( CRT ) by means of biventricular ( BiV ) pacing can improve left ventricular ( LV ) function , remodelling and clinical status in chronically right ventricular ( RV ) paced patients with mild cardiomyopathy . METHODS AND RESULTS Thirty-six chronically ( 10 + /- 7 years ) RV paced patients with left ventricular ejection fraction ( LVEF ) < 40 % or LVEDD > 55 mm , without an established indication for CRT  , were subjected to 6 months RV and BiV pacing in a patient-blinded , r and omized crossover design . Treatment-effects of BiV pacing were evaluated for LV function , LV remodelling and clinical status . As compared with RV pacing , BiV pacing significantly improved LV function ( LVEF 46 + /- 12 vs. 39 + /- 12 % and LVFS 24 + /- 7 vs. 21 + /- 7 % ) and reduced LV end-diastolic and end-systolic diameters and volumes ( LVEDD 56 + /- 8 vs. 59 + /- 8 mm , LVESD 43 + /- 8 vs. 47 + /- 9 mm , LVEDV 132 + /- 65 vs.144 + /- 62 mL and LVESV 77 + /- 56 vs. 92 + /- 55 mL , respectively ) . In 19 patients ( 53 % ) response to BiV pacing was clinical ly relevant , defined as LVESV reduction > 15 % . BiV pacing also significantly improved NYHA classification . CONCLUSION BiV pacing following chronic RV pacing may improve LV function and reverse LV remodelling in patients with relatively mild LV dysfunction or remodelling . Hence , up grade to BiV pacing might be considered in chronically RV paced patients with mild cardiomyopathy Background — Benefits of cardiac resynchronization therapy ( CRT ) on morbidity and mortality in selected patients are well known . Although the number of up grade procedures from single- or dual-chamber devices to CRT is increasing , there are only sparse data on the outcomes of up grade procedures compared with de novo CRT . This study aim ed to evaluate clinical response and survival in patients receiving de novo versus up grade CRT defibrillator therapy .  Methods and Results — Prospect ively collected outcome data were compared in patients undergoing de novo or up grade CRT defibrillator implantation at 3 implant centers in Germany and Hungary . Clinical response was defined as an improvement by at least one New York Heart Association ( NYHA ) functional class . CRT implantation was performed in 552 consecutive patients of whom 375 underwent a de novo and 177 an up grade procedure . Up grade patients were more often implanted for secondary prevention , suffered more often from atrial fibrillation , chronic kidney disease , diabetes mellitus , and dyslipidemia , and had more often a non-LBBB ( left bundle branch block ) wide QRS complex , and lower left ventricular ejection fraction . Up grade procedures were associated with a lower response rate compared to the de novo group ( 57 % versus 69 % , P univariate=0.008 , P multivariate=0.021 ) . During the follow-up of 37±28 months , survival was worse after up grade compared with de novo CRT defibrillator implantations ( hazard ratio , 1.65 ; 95 % confidence interval , 1.22–2.24 ; P=0.001 ) even after careful adjustment for important baseline variables ( adjusted hazard ratio , 1.68 ; 95 % confidence interval , 1.20–2.34 ; P=0.002 ) and after propensity-score matching ( propensity-adjusted hazard ratio , 1.79 ; 95 % confidence interval , 1.08–2.95 ; P=0.023 ) . Conclusions — Both clinical response and long-term survival were less favorable in patients undergoing CRT up grade compared to de novo implantations BACKGROUND Observational studies suggest that conventional right ventricular apical pacing may have a deleterious effect on left ventricular function . In this study , we examined whether biventricular pacing is superior to right ventricular apical pacing in preventing deterioration of left ventricular systolic function and cardiac remodeling in patients with bradycardia and a normal ejection fraction . METHODS In this prospect i ve , double-blind , multicenter study , we r and omly assigned 177 patients in whom a biventricular pacemaker had been successfully implanted to receive biventricular pacing ( 89 patients ) or right ventricular apical pacing ( 88 patients ) . The primary end points were the left ventricular ejection fraction and left ventricular end-systolic volume at 12 months . RESULTS At 12 months , the mean left ventricular ejection fraction was significantly lower in the right-ventricular-pacing group than in the biventricular-pacing group ( 54.8+/-9.1 % vs. 62.2+/-7.0 % , P<0.001 ) , with an absolute difference of 7.4 percentage points , whereas the left ventricular end-systolic volume was significantly higher in the right-ventricular-pacing group than in the biventricular-pacing group ( 35.7+/-16.3 ml vs. 27.6+/-10.4 ml , P<0.001 ) , with a relative difference between the groups in the change from baseline of 25 % ( P<0.001 ) . The deleterious effect of right ventricular apical pacing occurred in prespecified subgroups , including patients with and patients without preexisting left ventricular diastolic dysfunction . Eight patients in the right-ventricular-pacing group ( 9 % ) and one in the biventricular-pacing group ( 1 % ) had ejection fractions of less than 45 % ( P=0.02 ) . There was one death in the right-ventricular-pacing group , and six patients in the right-ventricular-pacing group and five in the biventricular-pacing group were hospitalized for heart failure ( P=0.74 ) . CONCLUSIONS In patients with normal systolic function , conventional right ventricular apical pacing result ed in adverse left ventricular remodeling and in a reduction in the left ventricular ejection fraction ; these effects were prevented by biventricular pacing . ( Centre for Clinical Trials number , CUHK_CCT00037 . Abstract Aims There is lack of conclusive evidence from r and omized clinical trials on the efficacy and safety of up grade to cardiac resynchronization therapy ( CRT ) in patients with implanted pacemakers ( PM ) or defibrillators ( ICD ) with reduced left ventricular ejection fraction ( LVEF ) and chronic heart failure ( HF ) . The BUDAPEST-CRT Up grade Study was design ed to compare the efficacy and safety of CRT up grade from conventional PM or ICD therapy in patients with intermittent or permanent right ventricular ( RV ) septal/apical pacing , reduced LVEF , and symptomatic HF . Methods and results The BUDAPEST-CRT study is a prospect i ve , r and omized , multicentre , investigator-sponsored clinical trial . A total of 360 subjects will be enrolled with LVEF ≤ 35 % , NYHA functional classes II – IVa , paced QRS ≥ 150 ms , and a RV pacing ≥ 20 % . Patients will be followed for 12 months . R and omization is performed in a 3:2 ratio ( CRT-D vs. ICD ) . The primary composite endpoint is all-cause mortality , a first HF event , or less than 15 % reduction in left ventricular ( LV ) end-systolic volume at 12 months . Secondary endpoints are all-cause mortality , all-cause mortality or HF event , and LV volume reduction at 12 months . Tertiary endpoints include changes in quality of life , NYHA functional class , 6 min walk test , natriuretic peptides , and safety outcomes . Conclusion The results of our prospect i ve , r and omized , multicentre clinical trial will provide important information on the role of cardiac resynchronization therapy with defibrillator ( CRT-D ) up grade in patients with symptomatic HF , reduced LVEF , and wide-paced QRS with intermittent or permanent RV pacing . Clinical trials.gov identifier NCT02270840 BACKGROUND The current guidelines do not clearly state when we should up grade a patient with right ventricular pacing ( RVP ) to cardiac resynchronization therapy ( CRT )  , although the deleterious effect of chronic RVP has been established with recent trials . OBJECTIVES The aims of this study were to compare the long-term survival after CRT in patients up grade d from RVP with that in patients with left bundle branch block ( LBBB ) with QRS duration ≥ 150 ms and to compare the mechanical properties associated with CRT response in these groups . METHODS Overall , 135 patients with implanted CRT from a single center ( 85 ( 63 % ) with native wide LBBB and 50 ( 37 % ) with RVP ) were studied prospect ively . Baseline left ventricular typical contraction pattern was determined using speckle tracking echocardiography in the apical 4-chamber view . The predefined end point was death , heart transplantation , or left ventricular assist device implantation over a period of 4 years . RESULTS Patients with RVP had a significantly favorable long-term outcomes with adjusted hazard ratio of 0.36 ( 95 % confidence interval 0.14 - 0.96 ; P = .04 ) . Both groups had ~70 % of patients with typical contraction pattern . The absence of typical contraction pattern was associated with a higher risk of an end point with adjusted hazard ratio of 5.43 ( 95 % confidence interval 2.31 - 12.72 ; P < .001 ) . In patients with typical contraction pattern , activation of the apical septal segment occurred more frequently in the RVP group and of the base or mid septal segments in the LBBB group . CONCLUSION Patients with HF up grade d from RVP have more favorable long-term outcomes  after CRT than do native LBBB patients with QRS duration ≥ 150 ms . Contraction pattern assessment can be used to identify potential responders in the RVP group Background Dual‐chamber ( DDDR ) pacing preserves AV synchrony and may reduce heart failure ( HF ) and atrial fibrillation ( AF ) compared with ventricular ( VVIR ) pacing in sinus node dysfunction ( SND ) . However , DDDR pacing often results in prolonged QRS duration s ( QRSd ) as the result of right ventricular stimulation , and ventricular desynchronization may result . The effect of pacing‐induced ventricular desynchronization in patients with normal baseline QRSd is unknown . Methods and Results Baseline QRSd was obtained from 12‐lead ECGs before pacemaker implantation in MOST , a 2010‐patient , 6‐year , r and omized trial of DDDR versus VVIR pacing in SND .  Cumulative percent ventricular paced ( Cum%VP ) was determined from stored pacemaker data . Baseline QRSd < 120 ms was observed in 1339 patients ( 707 DDDR , 632 VVIR ) . Cum%VP was greater in DDDR versus VVIR ( 90 % versus  
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Our systematic review and meta- analysis of currently available studies reports that CRT up grade is associated with similar risk for all-cause mortality compared to de novo resynchronization therapy .
Benefits on reverse remodelling and functional capacity improved similarly in both groups suggesting that CRT up grade may be safely and effectively offered in routine practice .