***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: BACKGROUND The use of left ventricular assist devices is an accepted therapy for patients with refractory heart failure , but current pulsatile volume-displacement devices have limitations ( including large pump size and limited long-term mechanical durability ) that have reduced widespread adoption of this technology . Continuous-flow pumps are newer types of left ventricular assist devices developed to overcome some of these limitations . METHODS In a prospect i ve , multicenter study without a concurrent control group , 133 patients with end-stage heart failure who were on a waiting list for heart transplantation underwent implantation of a continuous-flow pump . The principal outcomes were the proportions of patients who , at 180 days , had undergone transplantation , had cardiac recovery , or had ongoing mechanical support while remaining eligible for transplantation . We also assessed functional status and quality of life . RESULTS The principal outcomes occurred in 100 patients ( 75 % ) . The median duration of support was 126 days ( range , 1 to 600 ) . The survival rate during support was 75 % at 6 months and 68 % at 12 months . At 3 months , therapy was associated with significant improvement in functional status ( according to the New York Heart Association class and results of a 6-minute walk test ) and in quality of life ( according to the Minnesota Living with Heart Failure and Kansas City Cardiomyopathy question naires ) . Major adverse events included postoperative bleeding , stroke , right heart failure , and percutaneous lead infection . Pump thrombosis occurred in two patients . CONCLUSIONS A continuous-flow left ventricular assist device can provide effective hemodynamic support for a period of at least 6 months in patients awaiting heart transplantation , with improved functional status and quality of life . ( Clinical Trials.gov number , NCT00121472 [ Clinical Trials.gov ] . ) The authors previously published data that describe acute alterations in ventricular dimensions and in the severity of mitral and tricuspid regurgitation ( MR/TR ) after initiation of left ventricular assist device ( LVAD ) pumping . In the current study , measurements of ventricular size and regurgitant jet area acquired after LVAD implantation are presented . Eight patients had LVAD implanted pending cardiac transplantation ( duration of assist 70 - 279 days ; mean , 162 + /- 29 days ) .  Echocardiograms  were obtained at the time of LVAD implant and later during LVAD support ( mean time for late echo , 95 + /- 32 days post-implant ) . Comparisons of pre-implant with late post-implant data showed : increased TR jet area ( 4.8 + /- 1.0 cm2 vs. 8.0 + /- 1.7 cm2 P < 0.05 ) ; increased right ventricular ( RV ) end-systolic dimension ( 31 + /- 4 vs 40 + /- 5 mm , P < 0.05 ) ; and increased RV end-diastolic dimension ( 35 + /- 4 vs. 45 + /- 5 mm , P < 0.065 ) . Decreased MR jet area and decreased LV dimensions ( P < 0.05 ) also were noted on comparison of pre-implant and late post-implant data . There were no significant differences between any immediate post-implant and late post-implant echocardiographic measurements . No patient had clinical evidence of RV failure . LV mechanical assist causes an acute increase in TR , presumably by volume loading the RV . TR and RV enlargement persisted but did not discernibly worsen on subsequent post-implant echocardiograms . LV dimensions and MR remained less than the pre-implant values on later post-implant determinations Background The effects of mechanical left ventricular assist on the nonassisted right ventricle have not been fully eluci date d. Current information indicates that the right ventricle benefits from a lower left atrial pressure ; however , ventricular septal shifting and increased venous return caused by left ventricular assist impair right ventricular function . Acute intraoperative alterations in mitral and tricuspid valve regurgitation ( MR and TR , respectively ) may occur as a result of mechanical left ventricular assist but have not yet been documented . Methods and Results Eight patients undergoing implantation of a left ventricular assist device ( LVAD ) as a bridge to transplantation were studied during surgery by transesophageal echocardiography . MR was present in seven of eight patients , and TR was present in eight of eight patients before LVAD implant ( mean MR jet area , 10.6±2.4 cm2 , mean TR jet area , 4.8± 1.0 cm2 ) . Immediately after LVAD placement , MR was still present in seven of eight patients , and TR was present in eight of eight patients ( mean MR jet area , 4.2±0.9 cm2 ; mean TR jet area , 8.4±1.9 cm2 ) ( P<.05 preimplant versus postimplant jet area ) . These changes in MR and TR were associated with a decrease in left ventricular end-systolic dimension ( 62±4 versus 48±3 mm ) and an increase in right ventricular end-systolic dimension ( 31±4 versus 40±5 mm ) ( P<.05 preimplant versus postimplant end-systolic dimension ) . No patients developed progressive right ventricular failure during 70 to 279 days of LVAD support . Conclusions Mechanical left ventricular assist causes an acute decrease in preexisting MR . However , left ventricular assist may acutely worsen TR , presumably by shifting the ventricular septum leftward and increasing venous return to the right ventricle 
    Output:
    
The results of our systematic review and meta- analysis of 8 studies consisting of 445 patients demonstrates that the addition of mitral valve intervention to CF-LVAD implantation appears to be safe with comparable survival to those undergoing CF-LVAD implantation alone .