***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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    ***EXAMPLES*** 
    Input: Antiplatelet agents are used for prevention of thromboembolism in surgical patients and in patients with chronic atrial fibrillation . However , up-to- date results of r and omized studies comparing antiplatelet agents and oral anticoagulation have not been reported . The aim of this study is to compare the efficacy and safety profile of triflusal versus acenocoumarol for primary prevention of thromboembolism in the early postoperative period after implantation of a bioprosthesis . This is a prospect i ve , multicentric , r and omized , open , pilot trial in which four acute-care teaching hospitals participate . Patients will be r and omly assigned to treatment with triflusal or acenocoumarol the day before valve replacement with a bioprosthesis . Primary outcome will be the combined endpoint of the rate of either thromboembolism or hemorrhage and valve-related mortality in each treatment group . Secondary outcomes will include the analysis of each of these rates separately together with permanent valve-related impairment according to the guidelines for reporting morbidity and mortality after cardiac valvular operations . A total of 200 patients will be recruited in a competitive manner ( 100 patients per arm ) over an 18-month period . The study will be completed in 2 years . Treatment assigned will be open to investigators and patients because of the need of blood monitoring and dosage adjustment in oral anticoagulant therapy . In order to minimize the bias , r and omization is central ly performed . The study medication will be given for 3 months being discontinued afterwards . Follow-up visits are scheduled at the time of patient 's inclusion in the study and at 1 , 3 , and 6 months thereafter . Homogeneity of groups will be analyzed using the Student 's t test , the Mann-Whitney U test , and the chi-square test , when appropriate . Rates of thromboembolism and hemorrhage will be calculated with the hazard function . In conclusion , antiplatelet treatment for patients undergoing valve replacement with a bioprosthesis is clinical ly relevant because of avoidance of inconveniences of oral anticoagulation ( monthly blood testing , dosage adjustment ) and decreased risk of bleeding . In case the results favor the use of antiplatelet drugs in these patients , this study will contribute to future development of strategies in the prevention of thromboembolism 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 AND AIM OF THE STUDY Patients with bioprosthetic heart valves have a higher risk of developing peripheral arterial embolic phenomena than the normal population . Antithrombotic therapy during the early postoperative period after bioprosthetic aortic valve replacement ( BAVR ) is controversial . This prospect i ve pilot study sought to investigate the feasibility of a larger trial and the efficacy of postoperative warfarin compared to acetyl salicylic acid ( aspirin ; ASA ) in patients after AVR with the St. Jude Epic porcine bioprosthesis ( SJEP ) , and the feasibility of conducting a larger trial . METHODS Patients undergoing isolated BAVR were allocated at r and om to two groups , each of which received different antithrombotic therapies : ( i ) warfarin ( INR ; range 2 - 3 ) for the first three months , followed by ASA ( 100 mg/day ) ; or ( ii ) ASA alone ( 100 mg/day ) . RESULTS During 2003 and 2004 , a total of 75 patients underwent isolated BAVR with the SJEP . Six patients who developed postoperative de-novo atrial fibrillation that did not revert to sinus rhythm were excluded from the analysis , but included in the follow up . One postoperative cerebral ischemic event occurred in each group between 24 h and three months ( 2.8 % versus 2.9 % , p = NS ) . The rates of major bleeding , stroke-free survival and overall survival were similar in both groups . CONCLUSION The early results of this WoA Epic pilot trial did not support the suggestion that patients receiving the SJEP , and tissue valves in general , should be administered warfarin to prevent valve thrombosis and peripheral arterial embolic phenomena Background — No human physiological data exists on whether aspirin only is as effective as warfarin plus aspirin in preventing cerebral microembolization in the early postoperative period after bioprosthetic aortic valve replacement ( bAVR ) . Methods and Results — We prospect ively enrolled 56 patients who had no other indication for oral anticoagulation , who underwent bAVR and received , in an open-label fashion , either daily warfarin ( for INR 2.0–3.0 ) plus 81 mg of aspirin ( n=28 ) or 325 mg of aspirin only ( n=28 ) . Cerebral microembolization was quantified at 4 hours ( baseline ) and at 1 month postoperatively , by recording 1-hour bilateral middle cerebral artery ( MCA ) microembolic signals ( MES ) . Platelet-function analysis ( PFA ) of closure times ( CT ) on collagen was also used as a marker of platelet-dependent activation . Follow-up to 1 year was complete . Preoperative demographics and baseline platelet function were equivalent in both groups . There was no mortality , stroke , or transient ischemic attack at 1 year in either group . No significant differences were found in the proportion of patients with MES among those receiving warfarin plus aspirin versus aspirin only , at baseline ( 68 % versus 82 % , respectively ; P=0.4 ) and at 1 month ( 46 % versus 43 % ; P=1.0 ) after bAVR . The total MES and PFA were also equivalent between groups , at baseline and follow-up . Conclusions — Early after bAVR , the effects of these 2 antithrombotic regimens on cerebral microembolization and platelet function are equivalent . These data bring new mechanistic support to the premise that aspirin only may safely be used early after bAVR in patients who have no other indication for oral anticoagulation BACKGROUND The administration of antiplatelet agents versus anticoagulation after bioprosthetic aortic valve replacement ( AVR ) remains controversial . This study examined the safety and efficacy of anticoagulation with a vitamin-K antagonist ( VKA ) versus low-dose acetyl salicylic acid ( ASA ) , up to 6 months after bioprosthetic AVR . METHODS The ACTION Registry prospect ively collected data at 47 medical centers in Europe , Canada and India . The investigators were free to prescribe the postoperative antithrombotic regimen of their choice . Between January 2006 and June 2009 , 1118 patients underwent AVR alone or combined with coronary artery bypass graft ( CABG ) , of whom 500 received a VKA and 618 received ASA .  RESULTS Patients who received VKA had a higher prevalence of peripheral vascular disease , chronic renal insufficiency and coronary artery disease . At 180 days , 14 anticoagulated patients ( 2.8 % ) suffered a thromboembolism ( TE ) versus 9 patients ( 1.5 % ) treated with ASA ( P=0.12 ) and 18 anticoagulated patients ( 3.6 % ) suffered major bleeding ( MB ) versus 8 patients ( 1.3 % ) in the ASA group ( P=0.01 ) . MB or TE occurred in 31 patients ( 6 % ) treated with VKA versus 17 patients ( 2.8 % ) treated with ASA ( P=0.003 ) . By multiple variable analysis , preoperative cerebrovascular accident and peripheral vascular disease were strong predictors of postoperative TE , MB or both , in patients treated with VKA , though not in patients treated with ASA . CONCLUSIONS Compared with ASA , treatment with VKA was associated with higher morbidity within 6 months after bioprosthetic AVR , suggesting that , particularly after concomitant CABG surgery , recipients of bioprosthetic AVR should receive prophylactic ASA instead of VKA BACKGROUND Consensus reports over the past 10 years from the United States , Europe , United Kingdom , and Canada have not provided consistent guidelines for antithrombotic therapy of aortic valve bioprostheses for the three-month period after surgery . This study was conducted to determine if antithrombotic therapy was protective against TE with aortic bioprostheses 30 days or less after aortic valve replacement ( AVR ) . METHODS From 1994 to 2000 , 1,372 patients implanted with three currently marketed aortic bioprostheses , Medtronic Mosaic ( Medtronic , Inc , Minneapolis , MN ) ( 415 patients ) , Carpentier-Edwards SAV ( 462 ) , and Carpentier-Edwards PERIMOUNT ( 495 ) ( Edwards Lifesciences , Irvine , CA ) , with a mean age of greater than 70 years were evaluated . Patient population s were comparable , inclusive of concomitant coronary artery bypass grafting ( CABG ) for the overall population s and for patients greater than 70 years . RESULTS There were 37 thromboembolic ( TE ) events : major TE , 14 ; reversible ischemic neurologic deficit ( RIND ) , 12 ; and minor TE , 11 . There were 4 TE deaths . Multivariate ( stepwise logistic regression ) analysis revealed no predictive risk factors for overall TE . For the combination of major TE plus RIND there were two predictive risk factors with analysis of 12 risk variables : preoperative cerebrovascular accident ( odds ratio [ OR ] 4.45 , 95 % confidence interval [ CI ] 1.17 to 16.87 , p = 0.028 ) ; and concomitant CABG ( OR 3.19 , 95 % CI 1.16 to 8.76 , p = 0.025 ) . Neither anticoagulant nor antiplatelet therapies gave significant protection . CONCLUSIONS There does not appear to be an indication for routine antithrombotic management . The study supports the potential use of antithrombotic therapy for comorbidities of preoperative cerebrovascular accident and concomitant CABG but not atrial fibrillation , left ventricular dysfunction , or elderly age greater than 70 years . Vascular burden and advanced age are likely contributing factors to these independent predictors . There may still be a need for , or at least consideration of , a r and omized trial for AVR with bioprostheses BACKGROUND Opinion differs as to whether anticoagulation is beneficial in preventing ischemic stroke in the early postoperative period after biological aortic valve replacement ( AVR ) . The purpose of this study was to determine whether early anticoagulation with heparin and warfarin confers any significant advantage for patients undergoing such replacement . METHODS AND RESULTS Patients undergoing biological AVR between 1987 and 1996 were divided retrospectively into 2 groups based on their postoperative anticoagulation . Group A ( 109 patients ) received heparin followed by warfarin for 3 months ( prothrombin time , 20 to 25 seconds ) . Group B ( 76 patients ) received no postoperative anticoagulation . Patients were followed for cerebral ischemic events , bleeding , repeat operation , hospital stay , and survival . There were 5 ( 4.6 % ) , 3 ( 2.8 % ) , and 12 ( 11 % ) postoperative cerebral ischemic events for group A at time points of < 24 hours , 24 hours to 3 months , and > 3 months , respectively ; for group B patients , 3 ( 3.9 % ) , 2 ( 2.6 % ) , and 9 ( 11.8 % ) events were seen during the same respective time periods . There were no statistically significant differences for ischemic events during any of these time periods for the 2 groups . Bleeding complications occurred in 10 ( 9.2 % ) group A 
    Output:
    
Conclusions In a meta‐ analysis of r and omised and observational studies of VKA versus AP/no treatment in patients undergoing bioprosthetic valve implantation , there was no benefit of adding a VKA regarding thromboembolism or mortality .
However , use of a VKA was associated with increased risk of major bleeding