***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: AIMS The coronary collateral circulation has a beneficial role regarding all-cause and cardiac mortality .  Hitherto , the underlying mechanism has not been clarified . The aim of this prospect i ve study was to assess the effect of the coronary collateral circulation on  electrocardiogram ( ECG ) QTc time change during short-term myocardial ischaemia . METHODS AND RESULTS A total of 150 patients ( mean age 63 + /- 11 years , 38 women ) were prospect ively included in this study .  An ECG was recorded at baseline and during a st and ardized 1 min coronary balloon occlusion .  QT interval was measured before , during , and after balloon occlusion and was corrected for heart rate ( QTc ) . Simultaneously obtained collateral flow index ( CFI ) , expressing collateral flow relative to normal antero grade flow , was determined based on intracoronary pressure measurements . During occlusion of the left anterior descending coronary artery mean QTc interval increased from 422 + /- 33 to 439 + /- 36 ms ( P < 0.001 ) , left circumflex occlusion led to an increase from 414 + /- 32 to 427 + /- 27 ms ( P < 0.001 ) . QTc was not influenced by occlusion of the right coronary artery ( RCA ) ( 417 + /- 35 and 415 + /- 34 ms , respectively ; P = 0.863 ) . QTc change during occlusion of the left coronary artery was inversely correlated with CFI ( R(2 ) = 0.122 , P = 0.0002 ) . CONCLUSION Myocardial ischaemia leads to QT prolongation during a controlled 1 min occlusion of the left , but not the RCA . QT prolongation is inversely related to collateral function indicating a protective mechanism of human coronary collaterals against cardiac death Background —Native atherosclerosis and in-stent restenosis are focal and evolve independently . The endothelium controls local arterial responses by transduction of shear stress . Characterization of endothelial shear stress ( ESS ) may allow for prediction of progression of atherosclerosis and in-stent restenosis . Methods and Results —By using intracoronary ultrasound , biplane coronary angiography , and measurement of coronary blood flow , we represented the artery in accurate 3D space and determined detailed characteristics of ESS and arterial wall/plaque morphology . Patients who underwent stent implantation and who had another artery with luminal obstruction < 50 % underwent intravascular profiling  initially and after 6-month follow-up . Twelve arteries in 8 patients were studied : 6 native and 6 stented arteries . In native arteries , regions of abnormally low baseline ESS exhibited a significant increase in plaque thickness and enlargement of the outer vessel wall , such that lumen radius remained unchanged ( outward remodeling ) . Regions of physiological ESS showed little change . Regions with increased ESS exhibited outward remodeling with normalization of ESS . In stented arteries , there was an increase in intima-medial thickness , a decrease in lumen radius , and an increase in ESS at all levels of baseline ESS . Conclusions —The present study represents the first experience in humans relating ESS to subsequent outcomes in native and stented arteries . Regions of low ESS develop progressive atherosclerosis and outward remodeling , areas of physiological ESS remain quiescent , and areas of increased ESS exhibit outward remodeling . ESS may have a limited role in in-stent restenosis . This technology can predict areas of minor plaque likely to exhibit progression of atherosclerosis Background — The prognostic relevance of the collateral circulation is still controversial . The goal of this study was to assess the impact on survival of quantitatively obtained , recruitable coronary collateral flow in patients with stable coronary artery disease during 10 years of follow-up . Methods and Results — Eight-hundred forty-five individuals ( age , 62±11 years ) , 106 patients without coronary artery disease and 739 patients with chronic stable coronary artery disease , underwent a total of 1053 quantitative , coronary pressure – derived collateral measurements between March 1996 and April 2006 . All patients were prospect ively included in a collateral flow index ( CFI ) data base containing information on recruitable collateral flow parameters obtained during a 1-minute coronary balloon occlusion . CFI was calculated as follows : where Poccl is mean coronary occlusive pressure , Pao is mean aortic pressure , and CVP is central venous pressure . Patients were divided into groups with poorly developed ( CFI < 0.25 ) or well-grown collateral vessels ( CFI ≥0.25 ) . Follow-up information on the occurrence of all-cause mortality and major adverse cardiac events after study inclusion was collected . Cumulative 10-year survival rates in relation to all-cause deaths and cardiac deaths were 71 % and 88 % , respectively , in patients with low CFI and 89 % and 97 % in the group with high CFI ( P=0.0395 , P=0.0109 ) . Through the use of Cox proportional hazards analysis , the following variables independently predicted elevated cardiac mortality : age , low CFI ( as a continuous variable ) , and current smoking . Conclusions — A well-functioning coronary collateral circulation saves lives in patients with chronic stable coronary artery disease . Depending on the exact amount of collateral flow recruitable during a brief coronary occlusion , long-term cardiac mortality is reduced to one fourth compared with the situation without collateral supply Background — Rapid loss of collateral support has been reported after  percutaneous coronary intervention ( PCI )  , leaving the myocardium susceptible to subsequent infa rct ion . However , well-developed collaterals have been found in normal hearts , suggesting that collaterals exist even in the absence of an ischemic stimulus . We assessed the plasticity and determinants of collateral supply after PCI . Methods and Results — Collateral flow index ( CFI ) was calculated in 60 patients as (Pw−Pv)/(Pa−Pv ) by measurement of aortic ( Pa ) , central venous ( Pv ) , and coronary wedge ( Pw ) pressures . CFI was reassessed during transient balloon occlusion 5 minutes and 24 hours after PCI in the first 29 patients and at 6 months in the subsequent 25 patients . We also evaluated the relationship between collateral supply , lesion characteristics , and circulating hemopoietic cells numbers before and after successful PCI . CFI at baseline was 0.23±0.10 , with no change 5 minutes and 1 day later ( 0.21±0.12 , P=0.62 ; and 0.22±0.11 , P=0.96 , respectively ) . At 6 months , CFI was 0.14±0.07 or 63±27 % of the baseline value ( P<0.001 ) . CFI was proportional to severity of the coronary lesion at baseline ( r=0.63 , P<0.0001 ) but not 6 months after PCI ( r=−0.04 , P=0.87 ) . The number of circulating CD133 + and CD34 + cells was associated with CFI 6 months after PCI ( CD133 , r=0.59 , P=0.035 ; CD34 , r=0.63 , P=0.037 ) . Conclusions — Coronary collateral flow remains undiminished for at least 24 hours after successful PCI  . Functional collateral support subsequently declines but does not regress completely Objective : To evaluate whether a well developed collateral circulation predisposes to restenosis after  percutaneous coronary intervention ( PCI ) . Design : Prospect i ve observational study . Patients and setting : 58 patients undergoing elective single vessel PCI in a tertiary referral interventional cardiac unit in the UK . Methods : Collateral flow index ( CFI ) was calculated as ( Pw − Pv)/(Pa − Pv ) , where Pa , Pw , and Pv are aortic , coronary wedge , and right atrial pressures during maximum hyperaemia . Collateral supply was considered poor ( CFI < 0.25 ) or good ( CFI ⩾ 0.25 ) . Main outcome measures : In-stent restenosis six months after PCI , classified as neointimal volume ⩾ 25 % stent volume on intravascular ultrasound ( IVUS ) , or minimum lumen area ⩽ 50 % stent area on IVUS , or minimum lumen diameter ⩽ 50 % reference vessel diameter on quantitative coronary angiography . Results : Patients with good collaterals had more severe coronary stenoses at baseline ( 90 (11)% v 75 (16)% , p < 0.001 ) . Restenosis rates were similar in poor and good collateral groups ( 35 % v 43 % , p = 0.76 for diameter restenosis , 27 % v 45 % , p = 0.34 for area restenosis , and 23 % v 24 % , p = 0.84 for volumetric restenosis ) . CFI was not correlated with diameter , area , or volumetric restenosis ( r2 < 0.1 for each ) . By multivariate analysis , stent diameter , stent length , > 10 % residual stenosis , and smoking history were predictive of restenosis . Conclusion : A well developed collateral circulation does not predict an increased risk of restenosis after PCI OBJECTIVES The objectives of the study were to evaluate the effect of angiographic follow-up on revascularization rates in the TAXUS-IV trial and to determine whether the relative benefit of paclitaxel-eluting stent implantation compared with bare metal stent implantation was modified by angiographic follow-up . BACKGROUND Although several clinical trials have demonstrated that drug-eluting stents ( DES ) reduce restenosis compared with bare-metal stents ( BMS ) , virtually all of these studies have incorporated angiographic follow-up . METHODS In the TAXUS-IV trial , 1,314 percutaneous coronary intervention patients were r and omized to receive paclitaxel-eluting stents ( PES ) ( n = 662 ) or identical-appearing BMS ( n = 652 ) . Clinical outcomes were compared , stratified by assignment to angiographic follow-up or clinical follow-up alone . RESULTS Compared with clinical follow-up alone , angiographic follow-up patients had a significantly higher rate of target vessel revascularization ( TVR ) at 1 year ( adjusted hazard ratio [ HR ] 1.46 ; p = 0.04 ) , with similar relative increases in PES and BMS patients . Because PES reduced TVR by approximately 60 % regardless of type of follow-up , assignment to angiographic follow-up tended to overestimate the absolute benefit of PES relative to clinical follow-up alone . In contrast , assessment of end points immediately before the time of follow-up angiography led to substantial underestimation of the absolute benefit of PES implantation . CONCLUSIONS Performance of m and atory angiographic follow-up increases rates of TVR among patients receiving both BMS and PES and overestimates the absolute clinical benefits of PES relative to clinical follow-up alone . Nonetheless , PES substantially reduces TVR regardless of assignment to m and atory angiographic follow-up or not . Future studies design ed to determine the true clinical benefits of DES should either forgo routine angiographic follow-up or separate the time of repeat angiography from the primary clinical end point by as long as possible Accelerated progression of atherosclerosis is known to occur in surgically bypassed coronary arteries in which the preoperative stenosis was greater than 50 per cent . To assess the effect of coronary bypass on vessels with lesser degrees of stenosis , we studied 85 men who had undergone coronary bypass surgery .  In this group we identified bypass grafts placed in 37 arteries with minimal atherosclerosis , which was defined as less than 50 per cent stenosis of the vessel diameter . In the same 85 men there were 93 coronary vessels with minimal atherosclerosis for which a bypass graft had not been placed . Progression of atherosclerosis , defined as further loss of at least 25 per cent of the lumen , during an average follow-up period of 37 months was more than 10 times as frequent ( 38 per cent vs. 3 per cent ) in bypassed arteries with minimal atherosclerosis as in comparable arteries that were not bypassed . These findings support the view that minimally diseased coronary arteries should not be bypassed BACKGROUND Balloon-exp and able coronary-artery stents were developed to prevent coronary restenosis after coronary angioplasty . These devices hold coronary vessels open at sites that have been dilated . However , it is unknown whether stenting improves long-term angiographic and clinical outcomes as compared with st and ard balloon angioplasty . METHODS A total of 520 patients with stable angina and a single coronary-artery lesion were r and omly assigned to either stent implantation ( 262 patients ) or st and ard balloon angioplasty ( 258 patients ) . The primary clinical end points were death , the occurrence of a cerebrovascular accident , myocardial infa rct ion , the need for coronary-artery bypass surgery , or a second percutaneous intervention involving the previously treated lesion , either at the time of the initial 
    Output:
    
Conclusions The risk of restenosis after percutaneous coronary intervention ( PCI ) is increased in patients with good coronary collateralization .