***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 Transcatheter aortic valve replacement ( TAVR ) is an option in certain high-risk surgical patients with severe aortic valve stenosis . It is unknown whether TAVR can be safely introduced to lower-risk patients . OBJECTIVES The NOTION ( Nordic Aortic Valve Intervention Trial ) r and omized clinical trial compared TAVR with surgical aortic valve replacement ( SAVR ) in an all-comers patient cohort . METHODS Patients ≥ 70 years old with severe aortic valve stenosis and no significant coronary artery disease were r and omized 1:1 to TAVR using a self-exp and ing bioprosthesis versus SAVR . The primary outcome was the composite rate of death from any cause , stroke , or myocardial infa rct ion ( MI ) at 1 year . RESULTS A total of 280 patients were r and omized at 3 Nordic centers . Mean age was 79.1 years , and 81.8 % were considered low-risk patients . In the intention-to-treat population , no significant difference in the primary endpoint was found ( 13.1 % vs. 16.3 % ; p = 0.43 for superiority ) . The result did not change in the as-treated population . No difference in the rate of cardiovascular death or prosthesis reintervention was found . Compared with SAVR-treated patients , TAVR-treated patients had more conduction abnormalities requiring pacemaker implantation , larger improvement in effective orifice area , more total aortic valve regurgitation , and higher New York Heart Association functional class at 1 year . SAVR-treated patients had more major or life-threatening bleeding , cardiogenic shock , acute kidney injury ( stage II or III ) , and new-onset or worsening atrial fibrillation at 30 days than did TAVR-treated patients . CONCLUSIONS In the NOTION trial , no significant difference between TAVR and SAVR was found for the composite rate of death from any cause , stroke , or MI after 1 year . ( Nordic Aortic Valve Intervention Trial [ NOTION ] ; NCT01057173 ) OBJECTIVES The aim of this study was to determine long-term results between bioprosthetic ( BP ) and mechanical ( MP ) aortic valves in middle-aged patients . BACKGROUND It has not been established which is the best aortic valve substitute in patients ages 55 to 70 years . We conducted a r and omized study to compare long-term outcomes between BP and MP aortic valves . METHODS Between January 1995 and June 2003 , 310 patients were r and omized to receive a BP or an MP aortic valve .  Primary end points of the study were survival , valve failure , and reoperation . RESULTS One hundred fifty-five patients received a BP valve , and 155 patients received an MP valve . Four patients died , perioperatively , in the MP group ( 2.6 % ) , and 6 patients died in the BP group ( 3.9 % , p = 0.4 ) . At late follow-up ( mean 106 + /- 28 months ) 41 patients died in the MP group and 45 patients died in the BP group ( p = 0.6 ) . There was no difference in the survival rate at 13 years between the MP and BP groups . Valve failures and reoperations were more frequent in the BP group compared with the MP group ( p = 0.0001 and p = 0.0003 , respectively ) . There were no differences in the linearized rate of thromboembolism , bleeding , endocarditis , and major adverse prosthesis-related events ( MAPE ) between the MP and BP valve groups . CONCLUSIONS At 13 years , patients undergoing aortic valve replacement either with MP  or  BP valves had a similar survival rate as well the same rate of occurrence of thromboembolism , bleeding , endocarditis , and MAPE , but patients who had undergone aortic valve replacement with BP valves faced a significantly higher risk of valve failure and reoperation OBJECTIVES We sought to determine whether changes in quality of life at 18 months following aortic valve replacement differ depending on the use of tissue valves or mechanical valves . METHODS We prospect ively studied 73 patients with tissue valve replacements and 53 patients with mechanical valve replacements performed from April 1998 through March 1999 at Yale-New Haven Hospital .  Quality of life was measured at baseline and at 18 months using the Medical Outcomes Trust Short Form 36-Item Health Survey . RESULTS Baseline unadjusted mean quality -of-life scores were lower in tissue valve recipients than in mechanical valve recipients and , for both groups , were generally lower than US population norms . At 18 months postoperatively , quality -of-life scores were greatly improved in both groups and were comparable to population norms ( ie , within one-half a st and ard deviation ) . After adjusting for baseline quality of life , age , and other prognostic factors in an analysis of covariance , improvements in quality -of-life scores for tissue valve recipients versus mechanical valve recipients were similar . Of 10 ( 8 domains and 2 summary ) scales examined , the only significant difference between the 2 groups was for the improvement in role limitations due to physical problems ( Role Physical ) , which was more favorable in patients with mechanical valve implants ( P = .04 ) . CONCLUSIONS The use of tissue valve implants versus mechanical valve implants has little influence on improvement in quality of life at 18 months following aortic valve replacement . Thus , decisions about whether to choose a tissue valve or mechanical valve implant should depend upon other factors such as rates of complications and differences in the life span of the implants Objective : To compare survival and outcome in patients receiving a mechanical or bioprosthetic heart valve prosthesis .  Design : R and omised prospect i ve trial . Setting : Tertiary cardiac centre . Patients : Between 1975 and 1979 , patients were r and omised to receive either a Bjork-Shiley or a porcine prostheses . The mitral valve was replaced in 261 patients , the aortic in 211 , and both valves in 61 patients . Follow up now averages 20 years . Main outcome measures : Death , reoperation , bleeding , embolism , and endocarditis . Results : After 20 years there was no difference in survival  ( Bjork-Shiley v porcine prosthesis ( mean ( SEM ) ) : 25.0 (2.7)% v 22.6 (2.7)% , log rank test p = 0.39 ) . Reoperation for valve failure was undertaken in 91 patients with porcine prostheses and in 22 with Bjork-Shiley prostheses . An analysis combining death and reoperation as end points confirmed that Bjork-Shiley patients had improved survival with the original prosthesis intact ( 23.5 (2.6)% v 6.7 (1.6)% , log rank test p < 0.0001 ) ; this difference became apparent after 8–10 years in patients undergoing mitral valve replacement , and after 12–14 years in those undergoing aortic valve replacement . Major bleeding was more common in Bjork-Shiley patients ( 40.7 (5.4)% v 27.9 (8.4)% after 20 years , p = 0.008 ) , but there was no significant difference in major embolism or endocarditis . Conclusions : Survival with an intact valve is better among patients with the Bjork-Shiley spherical tilting disc prosthesis  than with a porcine prosthesis but there is an attendant increased risk of bleeding Background — Patients with prosthetic heart valves have a higher risk of developing valve thrombosis and arterial thromboembolism .  Antithrombotic therapy in the early postoperative period after biological aortic valve replacement ( BAVR ) is controversial . The American College of Cardiology/American Heart Association and European Society of Cardiology guidelines recommend the use of warfarin for the first 3 months after BAVR , although the American College Chest Physician guidelines suggest that the recommendations are very weak and that the risk/benefit is unclear . This prospect i ve study investigated the efficacy of postoperative warfarin compared with aspirin in patients after aortic valve replacement . Methods and Results — Patients undergoing BAVR between 2001 and 2002 received 2 antithrombotic therapies  : 141 patients received warfarin for the first 3 months , and 108 patients received only aspirin .  The major end points evaluated were the rate of cerebral ischemic events , bleeding , and survival . There were 3 and 5 postoperative cerebral ischemic events between 24 hours and 3 months for patients treated with aspirin and warfarin , respectively . After 3 months , the incidence of cerebral ischemic events did not differ between the 2 groups . The rate of major bleeding events , the stroke-free survival , and the overall survival rates were not statistically significant between the warfarin and aspirin groups . Conclusions —There seem to be no advantages in performing early anticoagulation therapy compared with a low-antiplatelet regimen with regard to early cerebral ischemic events , bleeding , and survival . Currently there is no evidence to support the fact that warfarin is more effective than aspirin Background —Leaflet escape is a mode of structural valve failure for mechanical prostheses . This complication previously has been reported for both monoleaflet and bileaflet valve models . We report 2 leaflet escape occurrences observed in 2 patients who underwent valve replacement with a TRI Technologies valve prosthesis .  Methods and Results —At the University of Padua , between November 2000 and February 2002 , 36 TRI Technologies valve prostheses ( 26 aortic and 10 mitral ) were implanted in 34 patients ( 12 women and 22 men ) with a mean age of 59.9±10.3 years ( range , 30 to 75 years ) . There were 5 deaths : 3 in hospital , 1 early after discharge , and 1 late . Two patients experienced a catastrophic prosthetic leaflet escape ; the first patient was a 52-year-old man who died 10 days after aortic valve and ascending aorta replacement , and the second was a 58-year-old man who underwent a successful emergency reoperation 20 months after mitral valve replacement . Examination of the explanted prostheses showed in both cases a leaflet escape caused by a leaflet ’s pivoting system fracture . Prophylactic replacement was then successfully accomplished so far in 12 patients , without evidence of structural valve failure in any of them . Among other significant postoperative complications , we observed 3 major thromboembolisms , 1 hemorrhage , and 1 paravalvular leak . Conclusion —These catastrophes prompted us to interrupt the implantation program , and they cast a shadow on the durability of the TRI Technologies valve prosthesis because of its high risk of structural failure AIM To study in patients performing international normalized ratio ( INR ) self-control the efficacy and safety of an INR target range of 1.6 - 2.1 for  aortic valve replacement ( AVR ) and 2.0 - 2.5 for mitral valve replacement ( MVR ) or double valve replacement ( DVR ) . METHODS AND RESULTS In total , 1304 patients undergoing AVR , 189 undergoing MVR and 78 undergoing DVR  were r and omly assigned to low-dose INR self-control ( LOW group ) ( INR target range , AVR : 1.8 - 2.8 ; MVR/DVR : 2.5 - 3.5 ) or very low-dose INR self-control once a week ( VLO group ) and twice a week ( VLT group ) ( INR target range , AVR : 1.6 - 2.1 ; MVR/DVR : 2.0 - 2.5 ) , with electronically guided transfer of INR values . We compared grade III complications ( major bleeding and thrombotic events ; primary end-points ) and overall mortality ( secondary end-point ) across the three treatment groups . FINDINGS Two-year freedom from bleedings in the LOW , VLO , and VLT groups was 96.3 , 98.6 , and 99.1 % , respectively ( P = 0.008 ) . The corresponding values for thrombotic events were 99.0 , 99.8 , and 98.9 % , respectively ( P = 0.258 ) . The risk-adjusted composite of grade III complications was in the per- protocol population ( reference : LOW-dose group ) as follows : hazard ratio = 0.307 ( 95 % CI : 0.102 - 0.926 ; P = 0.036 ) for the VLO group and = 0.241 ( 95 % CI : 0.070 - 0.836 ; P = 0.025 ) for the VLT group . The corresponding values of 2-year mortality were = 1.685 ( 95 % CI : 0.473 - 5.996 ; P = 0.421 ) for the VLO group and = 4.70 ( 95 % CI : 1.62 - 13.60 ; P = 0.004 ) for the VLT group . CONCLUSION Telemedicine-guided very low-dose INR self-control is comparable with low-dose INR in thrombotic risk , and is superior in bleeding risk . Weekly testing is sufficient . Given the small number of 
    Output:
    
However , there is currently no evidence to support lowering the age threshold for implanting a bioprosthesis .