***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  Graft Imaging to Improve Patency ( GRIIP ) , a single-center , r and omized blinded clinical trial , reported that intraoperative graft assessment with graft revision according to a priori criteria of transit time flowmetry ( TTF ) and intraoperative fluorescent angiography did not improve graft patency at one year after coronary artery bypass grafting ( CABG )  when compared with st and ard intraoperative management . The objective of this study is to investigate whether other TTF values are more predictive of the saphenous vein graft ( SVG ) failure and /or clinical outcomes . METHODS This is a case control retrospective study of 65 SVGs from 44 patients from GRIIP . Study outcomes were graft patency at 12 months and major adverse cardiac events ( MACE ; death , myocardial infa rct ion , repeat revascularization ) . RESULTS Twenty-two SVGs were occluded . In receiver operating characteristic curve analysis , TTF mean flow was significantly predictive of one-year SVG failure ( area under the curve = 0.698 , p < 0.01 ) , and 31 mL/min was the best cut-off value ( p = 0.017 , sensitivity 63.6 % , specificity 67.4 % ) . The risk of graft occlusion was 14/28 , 50 % for grafts with mean flow < 31 mL/min and 8/37 , 21.6 % for grafts with mean flow ≥ 31 mL/min . In logistic regression models , mean flow was a significant predictor of early SVG failure ( Odds Ratio 0.95 [ 0.91 - 0.99 ] per mL/min , p = 0.014 ) whereas other TTF values , patient comorbidities , and /or medication at discharge were not . However , TTF values were not predictive of MACE . CONCLUSIONS TTF can identify non-functional grafts during CABG , but is of question able value to improve one-year graft patency BACKGROUND Early coronary bypass graft failures may be preventable if identified intraoperatively . The purpose of this investigation was to compare the diagnostic accuracy of two intraoperative graft assessment techniques , transit-time ultrasound flow measurement and indocyanine green fluorescent-dye graft angiography . METHODS Patents undergoing isolated coronary artery bypass grafting with no contraindications for postoperative angiography were enrolled in the study . Patients were r and omly assigned to be evaluated with either indocyanine green angiography ( Novadaq Spy angiography system ; Novadaq Technologies Inc , Concord , Ontario , Canada ) and then transit-time ultrasonic flow measurement ( Medtronic Medi-Stim Butterfly Flowmeter TTF measurement system ; Medtronic Inc , Minneapolis , Minn ) or transit-time flow then indocyanine green angiography . Patients underwent x-ray angiography on postoperative day 4 . The primary end point of the trial was to determine the sensitivity and specificity of the two techniques versus reference st and ard x-ray angiography to detect graft occlusion or greater than 50 % stenosis in the graft or perianastomotic area . RESULTS Between February 2004 and March 2005 , 106 patients were enrolled and x-ray angiography was performed in 46 patients . In total , 139 grafts were review ed with all three techniques and 12 grafts ( 8.2 % ) were demonstrated to have greater than 50 % stenosis or occlusion by the reference st and ard . The sensitivity and specificity of indocyanine green angiography to detect greater than 50 % stenosis or occlusion was 83.3 % and 100 % , respectively . The sensitivity and specificity of transit-time ultrasonic flow measurement to detect greater than 50 % stenosis or occlusion was 25 % and 98.4 % , respectively . The P value for the overall comparison of sensitivity and specificity between indocyanine green angiography and transit-time flow ultrasonography was .011 . The difference between sensitivity for indocyanine green angiography and transit-time flow measurement was 58 % with a 95 % confidence interval of 30 % to 86 % , P = .023 . CONCLUSION Indocyanine green angiography provides better diagnostic accuracy for detecting clinical ly significant graft errors than does transit-time ultrasound flow measurement OBJECTIVE This study was undertaken to evaluate  transit-time flow ( TTF ) as a tool to detect technical errors in arterial bypass grafts intra-operatively and predict outcomes . METHODS TTF 's three parameters , pulsatility index ( PI , index of resistance ) , flow ( cc min(-1 ) ) and diastolic filling ( DF , proportion of diastole with coronary flow ) , were measured in 990/1000 ( 99 % ) of arterial grafts in 336 consecutive patients , prospect ively enrolled in a data base .  Grafts were revised when TTF findings supported the otherwise suspected graft malfunction . If no other signs/suspicion of graft malfunction existed ( normal electrocardiogram ( EKG ) , stable haemodynamics and unchanged ventricular function on trans-oesophageal echocardiography ( TEE ) ) , and the PI was > 5 , grafts were not revised . Major adverse cardiac events ( MACEs : recurrent angina , perioperative myocardial infa rct ion , postoperative angioplasty , re-operation and /or perioperative death ) were related to TTF measurements . RESULTS The average number of grafts per patient was 3.02 , of which 99 % were arterial . Satisfactory grafts were achieved in 916/990 ( 93 % ) of the grafts , with flows from 34 to 61 cc min(-1 ) , PI < or = 5 and DF of 62 - 85 % . Fourteen conduits , 20 grafts ( 2 % ) suspected to be problematic , were revised . Patients were divided into two groups : 277 ( 82 % ) with at least one graft with PI < or = 5 and 59 ( 18 % ) with a PI > 5 .  MACE occurred in 25 ( 7.4 % ) patients --15/277 patients with a PI < or = 5 ( 5.4 % ) and 10/59 with a PI > 5 ( 17 % , p=0.005 ) . Mortality following non-emergent surgery was significantly higher in patients with a PI > 5 ( 5/54 , 9 % ) than in patients with a PI < or = 5 ( 5/250 , 2 % , p=0.02 ) . Flow and DF were not predictive of outcomes . CONCLUSION A high PI predicts technically inadequate arterial grafts during surgery -- even if all other intra-operative assessment s indicate good grafts ; it also predicts outcomes , particularly mortality OBJECTIVE Transit-time flow measurement ( TTFM ) is the most widely used method for intra-operative graft quality control in coronary artery bypass surgery . Although it may provide the opportunity for the surgeon to promptly revise the graft before the patient is discharged from the operating room , controlled clinical data on the ultimate usefulness of the TTFM are scarce . Clear cut-off values for when to revise grafts have not been set . METHODS A total of 204 consecutive grafts ( left internal mammary artery ( n=46 ) , vein graft ( n=155 ) , and radial artery ( n=3 ) ) underwent TTFM in 75 elective coronary artery bypass grafting ( CABG ) patients . The following parameters were recorded : mean graft flow ( MGF ) , pulsatility index ( PI ) , and insufficiency ratio ( IR ) . After a mean follow-up of 199 ± 42 days , coronary angiography was performed for assessment of graft patency . RESULTS A total of 166 grafts were found to be patent ( 85 % ) , and 29 ( 15 % ) were completely occluded . The median and interquartile range ( IQR ) of MGF for the occluded grafts at the time of surgery was 38 ml min(-1 ) ( IQR , 2549 ml min(-1 ) ) and for the patent grafts 45 ml min(-1 ) ( IQR , 31 - 71 ml min(-1 ) ; p = ns ] . The corresponding PI values were 3.3 ( IQR , 2.8 - 5.0 ) and 2.2 ( IQR , 1.7 - 3.2 ; p=0.003 ) , and the IR values were 1.6 ( IQR , 0.6 - 6.1 ) and 0.2 ( IQR , 0 - 2.2 ; p=0.03 ) . By receiver operating characteristic ( ROC ) analysis , the highest sensitivity ( 72 % ) and specificity ( 70 % ) were associated with a PI value>3.0 . However , 49 out of 70 such grafts ( 70 % ) were found to be patent . Furthermore , 10 out of 16 ( 63 % ) grafts , that had a combination of low flow ( MGF<15 ml min(-1 ) ) and high PI ( > 3.0 ) , were patent at control angiography . CONCLUSIONS TTFM predicts graft failure within the 6 months after CABG . However , specific cut-off recommendations for when to revise a graft can not be set on the basis of TTFM . The cut-off values suggested in the literature lead to unnecessary graft revisions in the majority of cases , and , on the other h and , many technical defects probably remain unnoticed . Better methods to assess the quality of coronary artery bypass grafts are needed OBJECTIVE To determine whether coronary graft patency can be predicted by  transit time flow measurement ( TTFM ) . METHODS From May 1 1997 to December 31 1998 , TTFM was prospect ively evaluated in 409 patients undergoing coronary artery bypass grafting ( CABG ) without cardiopulmonary bypass ( CPB ) .  All grafts ( 1145 ) were tested with TTFM . RESULTS Thirty-seven out of 1145 grafts ( 3.2 % ) were revised in 33 patients ( 7.6 % ) . In six cases ( 18.1 % ) use of CPB was necessary during revision due to hemodynamic instability . The remaining patients underwent revision off-pump . Thirty-four grafts ( 91.9 % ) were revised for both low flow and abnormal flow curve patterns . Findings at revision included : thrombosis of the anastomosis ( n=6 ) , stenosis at the toe or heel of the anastomosis ( n=8 ) , coronary flap or dissection ( n=5 ) , dissection of the internal mammary artery ( n=5 ) , graft kinking ( n=4 ) , flap at proximal anastomosis ( n=1 ) , coronary stenosis distal to the graft ( n=3 ) , and no findings ( n=2 ) . After revision all flow values and flow patterns improved . Although three additional grafts ( 8.1 % ) were revised for low flow ( < 7 ml/min ) despite normal flow patterns , there were no findings at revision and flow values and curves remained unchanged after revision . Postoperatively , one patient developed a stroke ( 3 % ) , one had an acute myocardial infa rct ion ( MI ) ( 3 % ) , one had a sternal wound infection ( 3 % ) , and one required prolonged ventilatory support ( 3 % ) . CONCLUSION Evaluation of TTFM is valuable in determining the status of a coronary graft after CABG . Correct interpretation of flow patterns allows for correction of abnormalities prior to chest closure BACKGROUND Intraoperative graft patency assessment during coronary artery bypass grafting enables detection and immediate correction of graft failure . Currently transit-time flowmetry is used to assess graft patency on the basis of mean graft flow and derived values , such as the pulsatility index . Intraoperative fluorescence imaging , based on the fluorescence of indocyanine green dye , provides direct visual images to confirm graft patency . METHODS We performed a prospect i ve observational study to assess intraoperative graft patency in patients undergoing coronary artery bypass grafting , by using an intraoperative fluorescence imaging system ( SPY ) and transit-time flowmetry ( BF 2004 ) . Poor flow with the intraoperative fluorescence imaging system was defined if there was an absence of fluorescence or if it did not appear within 15 seconds in the graft . A persistent mean graft flow value less than 5 mL/min and a pulsatility index greater than 5 with transit-time flowmetry were considered unacceptable and prompted graft revision . RESULTS We assessed the intraoperative patency of 266 grafts in 100 coronary artery bypass grafting patients . Intraoperative fluorescence imaging and transit-time flowmetry confirmed adequate flow in 241 ( 91 % ) grafts in 75 patients ( 75 % ) . Transient poor flow was detected with both intraoperative fluorescence imaging and transit-time flowmetry in 7 ( 2.6 % ) grafts in 7 ( 7 % ) patients . This subsequently proved to be adequ 
    Output:
    
This systematic review and meta- analysis showed that TTFM could improve CABG procedures .