***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 no-reflow phenomenon is associated with poor functional and clinical outcomes for patients with acute myocardial infa rct ion ( AMI ) . In the era of primary intervention , accurately identifying lesions at high risk of no reflow is of crucial importance . At present , no study into the relationship between lesion morphology and no reflow has been performed . The aim of this study was to investigate the relationship between preintervention intravascular ultrasound ( IVUS ) lesion morphology and the no-reflow phenomenon . Methods and Results —This study comprised 100 consecutive patients with AMI who underwent preintervention IVUS and were successfully recanalized with primary balloon angioplasty or stenting .  IVUS was again performed to identify and exclude any mechanical vessel obstruction in cases of thrombolysis in myocardial infa rct ion flow grade 0 , 1 , or 2 after intervention in the absence of angiographic stenosis . Angiographic no reflow was seen in 13 patients ( 13 % ) . Univariate analysis indicated that hypercholesterolemia , fissure and dissection , lipid pool – like image , lesion , and reference external elastic membrane cross-sectional area correlate with the no-reflow phenomenon . Multivariate logistic regression analysis showed that lipid pool – like image ( P < 0.05 ; odds ratio 118 ; 95 % CI , 1.28 to 11 008 ) and lesion elastic membrane cross-sectional area ( P < 0.05 ; odds ratio 1.55 ; 95 % CI 1.01 to 2.38 ) are independent predictive factors of no-reflow phenomenon after reperfusion for AMI . Conclusions —Large vessels with lipid pool – like image are at high risk for no reflow after primary intervention for AMI . Also , plaque content may play a role in damage to the microcirculation after primary intervention for AMI OBJECTIVES The aim of this study was to underst and the impact of attenuated plaque on distal embolization during stent implantation in patients with acute myocardial infa rct ion ( AMI ) . BACKGROUND Attenuated plaques identified by grayscale intravascular ultrasound ( IVUS ) might predict transient deterioration in coronary flow and /or no-reflow during percutaneous coronary intervention ( PCI ) . METHODS We analyzed clinical , angiographic , and IVUS data from 364 patients ( n = 364 infa rct -related arteries ) enrolled in the r and omized HORIZONS-AMI ( Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infa rct ion ) trial . No-reflow was final Thrombolysis In Myocardial Infa rct ion ( TIMI ) flow grade ≤2 in the absence of mechanical obstruction . Attenuated plaque was hypoechoic or mixed atheroma with ultrasound attenuation without calcification . A mean attenuation score was created by measuring the angle of attenuation each 1 mm , scoring the angle as 1 to 4 ( corresponding to < 90 ° , 90 ° to 180 ° , 180 ° to 270 ° , or 270 ° to 360 ° , respectively ) , summing the scores , and normalizing for analysis length . RESULTS Overall , 284 ( 78.0 % ) patients had attenuated plaques ; no-reflow occurred in 37 ( 10.2 % ) . Patients with no-reflow had a higher mean attenuation score ( median [ interquartile range ] 2.2 [ 0.0 to 2.8 ] vs. 1.3 [ 0.7 to 1.8 ] , p < 0.001 ) , lower baseline left ventricular ejection fraction ( 52.8 % [ 43.2 % to 61.5 % ] vs. 61.4 % [ 52.2 % to 68.1 % ] , p = 0.002 ) , and more baseline angiographic thrombus ( 89.2 % vs. 74.1 % , p = 0.043 ) with no differences in post-PCI stent expansion versus patients without no-reflow . Multivariate analysis indicated that mean attenuation score was the strongest predictor of no-reflow . The mean attenuation score that best predicted no-reflow was ≥2 points ( 90 ° to 180 ° , sensitivity of 81.5 % , and specificity of 80.5 % ) . CONCLUSIONS Attenuated plaque was present in three-quarters of patients with AMI . The amount of attenuated plaque strongly correlated with no-reflow ; the larger the attenuated plaque , the greater the likelihood of no-reflow . ( Dual Arm Factorial R and omized Trial in Patients w/ST Segment Elevation AMI to Compare the Results of Using Anticoagulation With Either Unfractionated Heparin + Routine GP IIb/IIIa Inhibition or Bivalirudin + Bail-out GP IIb/IIIa Inhibition ; and Primary Angioplasty with stent implantation with Either a Slow Rate-release Paclitaxel-eluting Stent [ TAXUS ™ ] or Uncoated Bare Metal Stent [ EXPRESS2 ™ ] ; NCT00433966 ) OBJECTIVES We aim ed to predict the high-risk plaque of distal embolization after stent deployment in patients with acute ST-segment elevation myocardial infa rct ion ( STEMI ) with Virtual Histology intravascular ultrasound ( VH-IVUS ) ( Volcano Therapeutics , Inc. , Rancho Cordova , California ) . BACKGROUND Distal embolization during primary percutaneous coronary intervention ( PCI ) carries a poor prognosis in patients with STEMI . However , it is unclear which plaque characteristics cause distal embolization after stent deployment . METHODS A total of 71 patients with STEMI were included prospect ively . All patients underwent primary PCI within 12 h of symptom onset . After crossing the lesion with a guidewire and performing thrombectomy with an aspiration catheter , VH-IVUS of the infa rct -related vessel was performed . Stent deployment was then undertaken without embolic protection . ST-segment re-elevation ( STR ) was used to evaluate distal embolization . Correlations among plaque characteristics , morphology , and distal embolization were analyzed . RESULTS The STR after stent deployment was observed in 11 patients ( STR group , 15.5 % ) . Necrotic core volume was significantly higher in the STR group than in the non-STR group ( 32.9 + /- 14.1 mm3 vs. 20.4 + /- 19.1 mm3 , p < 0.05 ) . Total plaque volume was similar in both groups . On receiver-operating characteristic analysis , necrotic core volume clearly predicted STR after stent deployment as compared with fibrous , fibro-lipid , dense calcium , and total plaque volumes . The necrotic core volume that was best predictive for STR was 33.4 mm3 , with a sensitivity of 81.7 % and a specificity of 63.6 % . CONCLUSIONS Virtual Histology IVUS is a useful means of predicting the risk of distal embolization after primary stent deployment in patients with STEMI OBJECTIVES We evaluated the clinical significance of attenuated plaque ( hypoechoic plaque with deep ultrasound attenuation ) . BACKGROUND Attenuated plaques are unusual intravascular ultrasound ( IVUS ) findings in patients with acute coronary syndrome ( ACS ) . METHODS We review ed clinical presentations and angiographic and pre-intervention IVUS findings in 293 ACS patients undergoing percutaneous coronary intervention ( PCI ) without a distal protection device : 187 with non-ST-segment elevation myocardial infa rct ion ( NSTEMI ) and 106 with ST-segment elevation myocardial infa rct ion ( STEMI ) . RESULTS Attenuated plaque was observed in 75 patients ( 25.6 % ) : 39.6 % of STEMI versus 17.6 % of NSTEMI ( p < 0.001 ) . ( We also review ed 100 r and omly selected patients with stable angina and pre-intervention IVUS ; none had attenuated plaque . ) Overall , in ACS patients with attenuated plaques : 1 ) the level of C-reactive protein was higher ; 2 ) angiographic thrombus and initial coronary flow Thrombolysis In Myocardial Infa rct ion flow grade < 2 were more common ; and 3 ) IVUS lesion site plaque burden and remodeling index were significantly greater , lesion site luminal dimensions significantly smaller , and thrombus , positive remodeling , and plaque rupture were more common . No-reflow ( 26.7 % vs. 4.6 % , p < 0.001 ) and deteriorated post-PCI coronary blood flow ( 8.0 % vs. 2.8 % , p = 0.001 ) were higher . In ACS patients with normal coronary blood flow at baseline , deterioration in the coronary blood flow post-PCI was more common in lesions with attenuated plaque . CONCLUSIONS Attenuated plaque was more common in ACS patients with STEMI than NSTEMI . Attenuated plaque in ACS patients was associated with a higher C-reactive protein level , more severe and complex lesion morphology , reduced coronary blood flow before PCI , and especially no-reflow after PCI BACKGROUND Atherosclerotic plaques that lead to acute coronary syndromes often occur at sites of angiographically mild coronary-artery stenosis . Lesion-related risk factors for such events are poorly understood . METHODS In a prospect i ve study , 697 patients with acute coronary syndromes underwent  three-vessel coronary angiography and gray-scale and radiofrequency intravascular ultrasonographic imaging after percutaneous coronary intervention . Subsequent major adverse cardiovascular events ( death from cardiac causes , cardiac arrest , myocardial infa rct ion , or rehospitalization due to unstable or progressive angina ) were adjudicated to be related to either originally treated ( culprit ) lesions or untreated ( nonculprit ) lesions . The median follow-up period was 3.4 years . RESULTS The 3-year cumulative rate of major adverse cardiovascular events was 20.4 % . Events were adjudicated to be related to culprit lesions in 12.9 % of patients and to nonculprit lesions in 11.6 % . Most nonculprit lesions responsible for follow-up events were angiographically mild at baseline ( mean [ ±SD ] diameter stenosis , 32.3±20.6 % ) . However , on multivariate analysis , nonculprit lesions associated with recurrent events were more likely than those not associated with recurrent events to be characterized by a plaque burden of 70 % or greater ( hazard ratio , 5.03 ; 95 % confidence interval [ CI ] , 2.51 to 10.11 ; P<0.001 ) or a minimal luminal area of 4.0 mm(2 ) or less ( hazard ratio , 3.21 ; 95 % CI , 1.61 to 6.42 ; P=0.001 ) or to be classified on the basis of radiofrequency intravascular ultrasonography as thin-cap fibroatheromas ( hazard ratio , 3.35 ; 95 % CI , 1.77 to 6.36 ; P<0.001 ) . CONCLUSIONS In patients who presented with an acute coronary syndrome and underwent percutaneous coronary intervention , major adverse cardiovascular events occurring during follow-up were equally attributable to recurrence at the site of culprit lesions and to nonculprit lesions . Although nonculprit lesions that were responsible for unanticipated events were frequently angiographically mild , most were thin-cap fibroatheromas or were characterized by a large plaque burden , a small luminal area , or some combination of these characteristics , as determined by gray-scale and radiofrequency intravascular ultrasonography . ( Funded by Abbott Vascular and Volcano ; Clinical Trials.gov number , NCT00180466 . ) OBJECTIVES We investigated attenuated plaque ( hypoechoic plaque with deep ultrasonic attenuation despite absence of bright calcium ) in nonculprit lesions . BACKGROUND Recent intravascular ultrasound ( IVUS ) studies describe acoustic shadowing behind large , echolucent , acute culprit lesion sites in the absence of bright calcium . Such " attenuated plaque " is considered a characteristic of high-risk lesions , but its prevalence in stable nonculprit lesions is incompletely known . METHODS We review ed  IVUS pullback data from nonculprit vessels in 159 patients from the ASTEROID ( A Study to Evaluate the Effect of Rosuvastatin on Intravascular Ultrasound-Derived Coronary Atheroma Burden ) trial . We identified attenuated plaque and compared volumetric IVUS data in the segments with and without attenuation . In addition , we described plaque morphology in segments with attenuation at baseline and follow-up . RESULTS Attenuated plaque was found in 17 of 159 patients ( 10.7 % , 95 % confidence interval : 6 % to 17 % ) . At baseline , there were no significant differences in clinical presentation and cardiovascular risk factors between patients with and without attenuation . Other than a greater plaque eccentricity index ( p = 0.008 ) , 
    Output:
    
Our study presents the evidence that plaque with ultrasound signal attenuation would induce slow/no reflow phenomenon and distal embolization during PCI , but this appearance has no impact on MACE rates within three years