***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 Cardiac resynchronization therapy ( CRT ) improves functional outcomes in patients with severe systolic heart failure . Whether the effects of CRT on left ventricular ( LV ) diastolic function and clinical outcomes are influenced by the cause as either ischemic or nonischemic cardiomyopathy ( CM ) has not been well established . METHODS A total of 57 patients ( age 60 + /- 11 years ; 25 % women ; LV ejection fraction 25 + /- 5 % ) were studied before and 4 + /- 2 months after  CRT  by echocardiography . Heart failure cause was ischemic CM in 19 and nonischemic CM in 38 . Measurements of LV systolic and diastolic function were determined by 2-dimensional and Doppler echocardiography with Doppler tissue imaging of regional myocardial velocities . Clinical outcome events were assessed at long-term follow-up and included hospitalization for heart failure exacerbation , heart transplantation , or cardiac-related death . RESULTS There were significant increases in LV ejection fraction , reductions in end-systolic volumes , and improved LV systolic dyssynchrony in both groups . However , significant improvements in LV diastolic function were observed only in the patients with nonischemic CM . Clinical events occurred in 53 % of the ischemic group versus 26 % of the nonischemic group ( P < .05 ) after 20 + /- 11 months of CRT . Univariate and multivariate analysis revealed that Doppler-estimated LV filling pressures were predictors of clinical outcome events . CONCLUSIONS After CRT patients with ischemic CM exhibit lack of improvement in LV diastolic function despite favorable effects on LV systolic performance . The Doppler-derived LV filling indices may be an important predictor of long-term clinical outcomes after CRT OBJECTIVES We assessed the clinical efficacy of single-site left ventricular ( LV ) pacing and determined the impact of baseline conduction delay severity on the magnitude of benefit . BACKGROUND Multisite biventricular pacing can improve heart failure ( HF ) symptoms in patients with an intraventricular conduction delay by resynchronizing abnormal ventricular contractions and improving LV systolic function . METHODS Eighty-six patients with at least New York Heart Association functional class II HF , chronic LV systolic dysfunction , normal sinus rhythm , and a QRS interval over 120 ms were implanted for atrial-synchronized LV pacing . The single-blinded , r and omized , controlled , crossover study stratified patients 1:1 by the baseline QRS interval into long ( QRS > 150 ms ) and short ( QRS 120 to 150 ms ) groups , which were compared during a three-month period of active ( univentricular ) pacing and a three-month period of inactive ( ventricular inhibited ) pacing . The primary end point was peak oxygen consumption ( VO(2 ) ) followed by anaerobic threshold , distance walked in 6 min , and quality -of-life question naire score . PATIENTS Twelve patients were withdrawn before r and omization and 17 could not complete both study periods . The short QRS group did not improve in any end point with active pacing . For the long QRS group , peak VO(2 ) increased 2.46 ml/min/kg ( p < 0.001 ) , the anaerobic threshold increased 1.55 ml/min/kg ( p < 0.001 ) , the distance walked in 6 min increased 47 m ( p = 0.024 ) , and the quality -of-life score improved 8.1 points ( p = 0.004 ) . CONCLUSIONS Left ventricular pacing significantly improves exercise tolerance and quality of life in patients with chronic HF , LV systolic dysfunction , and a QRS interval over 150 ms Background —Cardiac resynchronization therapy ( CRT ) has recently emerged as an effective treatment for patients with moderate to severe systolic heart failure and ventricular dyssynchrony . The purpose of the present study was to determine whether improvements in left ventricular ( LV ) size and function were associated with CRT . Methods and Results —Doppler echocardiograms were obtained at baseline and at 3 and 6 months after therapy in 323 patients enrolled in the Multicenter InSync R and omized Clinical Evaluation ( MIRACLE ) trial . Of these , 172 patients were r and omized to CRT on and 151 patients to CRT off . Measurements were made of LV end-diastolic and end-systolic volumes , ejection fraction , LV mass , severity of mitral regurgitation ( MR ) , peak transmitral velocities during early ( E-wave ) and late ( A-wave ) diastolic filling , and the myocardial performance index . At 6 months , CRT was associated with reduced end-diastolic and end-systolic volumes ( both P < 0.001 ) , reduced LV mass ( P < 0.01 ) , increased ejection fraction ( P < 0.001 ) , reduced MR ( P < 0.001 ) , and improved myocardial performance index ( P < 0.001 ) compared with control . & bgr;-Blocker treatment status did not influence the effect of CRT . Improvements with CRT were greater in patients with a nonischemic versus ischemic cause of heart failure . Conclusions —CRT in patients with moderate-to-severe heart failure who were treated with optimal medical therapy is associated with reverse LV remodeling , improved systolic and diastolic function , and decreased MR . LV remodeling likely contributes to the symptomatic benefits of CRT and may herald improved longer-term survival BACKGROUND Cardiac resynchronization reduces symptoms and improves left ventricular function in many patients with heart failure due to left ventricular systolic dysfunction and cardiac dyssynchrony . We evaluated its effects on morbidity and mortality . METHODS Patients with New York Heart Association class III or IV heart failure due to left ventricular systolic dysfunction and cardiac dyssynchrony who were receiving st and ard pharmacologic therapy  were r and omly assigned to receive medical therapy alone or with cardiac resynchronization . The primary end point was the time to death from any cause or an unplanned hospitalization for a major cardiovascular event . The principal secondary end point was death from any cause . RESULTS A total of 813 patients were enrolled and followed for a mean of 29.4 months . The primary end point was reached by 159 patients in the cardiac-resynchronization group , as compared with 224 patients in the medical-therapy group ( 39 percent vs. 55 percent ; hazard ratio , 0.63 ; 95 percent confidence interval , 0.51 to 0.77 ; P<0.001 ) . There were 82 deaths in the cardiac-resynchronization group , as compared with 120 in the medical-therapy group ( 20 percent vs. 30 percent ; hazard ratio 0.64 ; 95 percent confidence interval , 0.48 to 0.85 ; P<0.002 ) . As compared with medical therapy , cardiac resynchronization reduced the interventricular mechanical delay , the end-systolic volume index , and the area of the mitral regurgitant jet ; increased the left ventricular ejection fraction ; and improved symptoms and the quality of life ( P<0.01 for all comparisons ) . CONCLUSIONS In patients with heart failure and cardiac dyssynchrony , cardiac resynchronization improves symptoms and the quality of life and reduces complications and the risk of death . These benefits are in addition to those afforded by st and ard pharmacologic therapy . The implantation of a cardiac-resynchronization device should routinely be considered in such patients BACKGROUND Previous studies of pacing therapy for dilated congestive heart failure ( CHF ) have not established the relative importance of pacing site , AV delay , and patient heterogeneity on outcome . These variables were compared by a novel technique that evaluated immediate changes in hemodynamic function during brief periods of atrial-synchronous ventricular pacing . METHODS AND RESULTS Twenty-seven CHF patients with severe left ventricular ( LV ) systolic dysfunction and LV conduction disorder were implanted with endocardial pacing leads in the right atrium and right ventricle ( RV ) and an epicardial lead on the LV and instrumented with micromanometer catheters in the LV , aorta , and RV . Patients in normal sinus rhythm were stimulated in the RV , LV , or both ventricles simultaneously ( BV ) at preselected AV delays in a repeating 5-paced/15-nonpaced beat sequence .  Maximum LV pressure derivative ( LV+dP/dt ) and aortic pulse pressure ( PP ) changed immediately at pacing onset , increasing at a patient-specific optimal AV delay in 20 patients with wide surface QRS ( 180+/-22 ms ) and decreasing at short AV delays in 5 patients with narrower QRS ( 128+/-12 ms ) ( P<0.0001 ) . Overall , BV and LV pacing increased LV+dP/dt and PP more than RV pacing ( P<0.01 ) , whereas LV pacing increased LV+dP/dt more than BV pacing ( P<0.01 ) . CONCLUSIONS In this population , CHF patients with sufficiently wide surface QRS benefit from atrial-synchronous ventricular pacing , LV stimulation is required for maximum acute benefit , and the maximum benefit at any site occurs with a patient-specific AV delay OBJECTIVES We sought to compare the short- and long-term clinical effects of atrial synchronous pre-excitation of one ( univentricular ) or both ventricles ( biventricular ) , that provide cardiac resynchronization therapy ( CRT ) . BACKGROUND In patients with heart failure ( HF ) who have a ventricular conduction delay , CRT improves systolic hemodynamic function . The clinical benefit of CRT is still being investigated . METHODS Forty-one patients were r and omized to four weeks of first treatment with biventricular or univentricular stimulation  , followed by four weeks without treatment , and then four weeks of a second treatment with the opposite stimulation . The best CRT stimulation was continued for nine months . Cardiac resynchronization therapy was optimized by hemodynamic testing at implantation . The primary end points were exercise capacity measures . Data were analyzed by two-way repeated- measures analysis of variance . RESULTS The left ventricle was selected for univentricular pacing in 36 patients . The clinical effects of univentricular and biventricular CRT were not significantly different . The results of each method were pooled to assess sequential treatment effects . Oxygen uptake during bicycle exercise increased from 9.48 to 10.4 ml/kg/min at the anaerobic threshold ( p = 0.03 ) and from 12.5 to 14.3 ml/kg/min at peak exercise ( p < 0.001 ) with the first treatment , and from 10.0 to 10.7 ml/kg/min at the anaerobic threshold ( p = 0.2 ) and from 13.4 to 15.2 ml/kg/min at peak exercise ( p = 0.002 ) with the second treatment . The 6-min walk distance increased from 342 m at baseline to 386 m after the first treatment ( p < 0.001 ) and to 416 m after the second treatment ( p = 0.03 ) . All improvements persisted after 12 months of therapy . CONCLUSIONS Cardiac resynchronization therapy produces a long-term improvement in the clinical symptoms of patients with HF who have a ventricular conduction delay . The differences between optimized biventricular and univentricular therapy appear to be small for short-term treatment 
    Output:
    
In conclusion , CRT is associated with a modest increase in SBP and PP in patients with heart failure