***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 Before any new diagnostic test is accepted in clinical practice , such a test should be compared with established diagnostic tools in an appropriately large series of patients encompassing the complete spectrum of challenges to which the test is exposed . The aim of the present study was to assess the relative diagnostic and prognostic accuracies of high-dose dipyridamole echocardiography ( two-dimensional echocardiographic monitoring during dipyridamole infusion up to 0.84 mg/kg over 10 hours ) versus maximal symptom-limited bicycle exercise ECG test in patients with angina . METHODS AND RESULTS We studied 429 consecutive in-hospital patients who met the following inclusion criteria : history of chest pain , off antianginal therapy for at least 2 days ( 1 week for beta-blockers ) , no previous myocardial infa rct ion and /or obvious regional left ventricular dyssynergy of contraction ( akinesis or dyskinesis ) at baseline , and acceptable acoustic window under resting conditions . All patients underwent dipyridamole echocardiography and exercise ECG -- on different days and in r and om order -- within 1 week of coronary angiography ( which was performed independent of test results ) and were followed up for 37.8 + /- 14 months ( range , 1 to 73 months ) . Criteria of positivity were for dipyridamole echocardiography , a transient regional dyssynergy absent in the baseline examination ; for exercise ECG , an ST-segment shift of > or = 0.1 mV from baseline ; and for coronary angiography , a luminal reduction of > or = 75 % in at least one major coronary vessel ( 50 % for left main ) . There were 183 patients without and 246 with coronary artery disease ; 132 had one- , 70 had two- , and 44 had three- and /or left main vessel disease . The specificity was higher for dipyridamole echocardiography than for exercise ECG ( 90 % versus 51 % , P < .001 ) . The overall sensitivity of dipyridamole echocardiography  was similar to that of  exercise ECG  ( 75 % versus 74 % , P = NS ) , with no significant differences in the subset with one- ( 67 % versus 69 % , P = NS ) , two- ( 79 % versus 77 % , P = NS ) , or three- ( 93 % versus 86 % , P = NS ) vessel disease . During the follow-up , there were 20 deaths , 13 nonfatal myocardial infa rct ions , and 126 revascularization procedures . In the univariate analysis , dipyridamole result ed in higher chi 2 values than did exercise stress testing . A Cox forward stepwise survival analysis identified the  dipyridamole time as the most powerful prognostic predictor of death ( chi 2 = 19.4 , P < .0001 ) of all invasive and noninvasive parameters . The dipyridamole time also provided independent and additional prognostic information when it was adjusted for age , diabetes , resting ECG , and exercise stress test according to a modified , interactive stepwise procedure . This is true when death only , death and myocardial infa rct ion , and death , myocardial infa rct ion , and revascularization procedures were considered end points . CONCLUSIONS In patients with no previous myocardial infa rct ion and good resting left ventricular function , compared with exercise ECG , dipyridamole echocardiography has a similar sensitivity and a higher specificity for the noninvasive detection of angiographically assessed coronary artery disease . Dipyridamole echocardiography also provides information in addition to that provided by exercise ECG for predicting death , infa rct ion , and all events when the presence as well as the timing , severity , and extension of  dipyridamole-induced wall motion abnormalities are considered Because of numerous reports of false positive results with thallium-201 ( Tl-201 ) stress testing in patients with left bundle branch block , the authors decided to evaluate another mode of coronary vasodilatation , dipyridamole , for the diagnosis of coronary atheromatosis . Nine patients were prospect ively studied with stress and dipyridamole Tl-201 scintigraphy ; both tests were performed within three to 79 days of one another . Five of the patients also had coronary angiograms ( four within one year , one five years earlier ) . Four of the patients had normal results with both tests ( two normal angiograms , two not performed ) ; two had reversible septal defects with stress-induced coronary vasodilatation but normal dipyridamole studies ( only one had an angiogram , which was normal ) ; one patient had a fully reversible septal defect with stress and a fixed defect with dipyridamole ( normal angiogram ) ; one had a partially reversible septal stress defect which was fixed with dipyridamole ; and one had a normal stress study but a reversible septal defect with dipyridamole ( an angiogram performed five years earlier showed 30 to 40 % stenosis of the anterior descending artery ) . Because it seems that dipyridamole produces fewer false positive results , it should be used instead of stress testing to induce coronary vasodilatation in patients with left bundle branch block BACKGROUND The prognostic value of tomographic myocardial perfusion imaging with dipyridamole or adenosine in patients with left bundle-branch block has not been established . METHODS AND RESULTS The study group consisted of 245 patients with left bundle-branch block who underwent tomographic ( single photon emission tomography ) myocardial perfusion imaging with thallium-201 ( n=173 ) or technetium-99 m sestamibi ( n=72 ) and either dipyridamole ( n=153 ) or adenosine ( n=92 ) stress .  Patients were prospect ively classified into two groups . Patients were classified as " high risk " if they had ( 1 ) a large severe fixed defect ( n=28 ) , ( 2 ) a large reversible defect ( n=36 ) , or ( 3 ) cardiac enlargement and either increased pulmonary uptake ( thallium ) or a decreased resting ejection fraction ( sestamibi ) ( n=20 ) . The remaining 161 patients ( 66 % of the study group ) were at " low risk . " Follow-up was 99 % complete at 3+/-1.4 years . Three-year overall survival was 57 % in the high-risk group compared with 87 % in the low-risk group ( P<.0001 ) . Survival free of cardiac death/nonfatal myocardial infa rct ion/cardiac transplantation was 55 % in the high-risk group and 93 % in the low-risk group ( P<.0001 ) . The presence of a high-risk scan had significant incremental prognostic value after adjustment for age , sex , diabetes , and previous myocardial infa rct ion ( P<.0001 ) . Patients with a low-risk scan had an overall survival that was not significantly different from that of a US age-matched population ( P=.86 ) . CONCLUSIONS Tomographic myocardial perfusion imaging with adenosine or dipyridamole stress provides important prognostic information in patients with left bundle-branch block , which is incremental to clinical assessment This article is the first of two papers about the care of patients with chronic stable angina . The second paper , which deals with the treatment of patients with chronic stable angina , will be published in a future issue . Both articles have been adapted from material s created by the Committee on Guidelines for Chronic Stable Angina sponsored by the American College of Cardiology ( ACC ) , the American Heart Association ( AHA ) , and the American College of PhysiciansAmerican Society of Internal Medicine ( ACPASIM ) ( 1 - 3 ) . The adaptations in these articles are intended to make the information more useful for clinicians who do not specialize in the care of patients with heart disease . The committee created the original material s after review ing published reports identified in part through MEDLINE search es of the English literature from 1975 through 1998 . The weight of the evidence was ranked high and given a grade of A if the data were derived from multiple r and omized clinical trials involving many patients . The weight of the evidence was ranked intermediate and given a grade of B if the data were derived from a few r and omized trials involving small numbers of patients , nonr and omized studies , or observational registries . A lower rank and a grade of C were given when an expert consensus was the primary basis for the recommendation . We used the following classification system for final recommendations . Class I referred to conditions for which there is evidence or general agreement that a given procedure or treatment is useful and effective ; class II referred to conditions for which there is conflicting evidence or a divergence of opinion about the usefulness or efficacy of a procedure or treatment ; class IIa referred to conditions for which the weight of evidence or opinion is in favor of usefulness or efficacy of a procedure or treatment ; class IIb referred to conditions for which usefulness or efficacy of a procedure or treatment is less well established by evidence or opinion ; and class III referred to conditions for which there is evidence or general agreement that the procedure or treatment is not useful or effective and in some cases may be harmful . For the sake of brevity , we have combined some original recommendations and omitted others , especially those that affect fewer patients , are based on weaker evidence , or recommend that interventions not be done . Scope of the Guidelines These recommendations are intended for adult patients with stable chest pain syndromes and known or suspected ischemic heart disease and patients who have ischemic equivalents , such as dyspnea or arm pain with exertion . Also , some recommendations about follow-up apply to patients who become asymptomatic during therapy . These guidelines are not intended for patients with acute ischemic syndromes , patients with chest pain after cardiac transplantation , patients with chest pain within 6 months of revascularization by percutaneous techniques or coronary artery bypass grafting ( CABG ) , patients with coronary artery disease ( CAD ) detected without symptoms , patients with nonanginal chest pain , or pediatric patients . The Initial Evaluation The initial evaluation of patients presenting with chest pain includes a detailed history , a focused physical examination , and performance of a few tests and procedures that are useful for estimating the probability of significant CAD ( Figure 1 ) . Significant CAD is defined as an obstruction of at least one major epicardial artery that occupies at least 70 % of the artery 's cross-sectional diameter or an obstruction of the left main coronary artery that occupies at least 50 % of its diameter . Figure 1 . Diagnosis of chest pain . Comorbid conditions and patient preferences . The history should elicit specific information about chest pain because accurate characterization helps determine whether CAD is the cause of angina . Angina usually occurs in patients with CAD , but it can occur in patients with unobstructed coronary arteries who have myocardial ischemia related to an arterial spasm or endothelial dysfunction . It also can occur in patients with other cardiovascular problems , such as aortic stenosis , hypertrophic cardiomyopathy , or uncontrolled hypertension . Symptoms that mimic angina can also occur in patients with noncardiac conditions involving the chest wall , esophagus , or lung . The following characteristics of chest pain should be determined : quality , location , duration , and the presence of factors that provoke and relieve the pain . Angina is characterized by a substernal pain or discomfort , although it may radiate to the neck , jaw , epigastrium , or arms . Patients often describe the quality of angina with characteristic terms , such as squeezing , grip-like , pressure-like , suffocating , or heavy . Angina usually lasts for minutes . Exertion or emotional stress provokes it , and rest or nitroglycerin relieves it , typically within 30 seconds to several minutes . After the history is obtained , the clinician should classify the chest pain . Typical angina has the following characteristics : 1 ) substernal chest discomfort with a characteristic quality and duration that is 2 ) provoked by exertion or emotional stress and 3 ) relieved by rest or nitroglycerin . Atypical angina has two of the three characteristics of typical angina , while noncardiac chest pain has one or none of the characteristics of typical angina . The term noncardiac chest pain means that the probability of CAD is low . The term nonspecific chest pain more accurately describes this situation , but tradition prevents its use . In patients with angina , the severity of pain should be grade d according to the Canadian Cardiovascular Society ( CCS ) classification system ( Table 1 ) ( 6 ) . Although grading chest pain is less useful for establishing a diagnosis or estimating risk , it is essential for evaluating the effects of therapy . Table 1 . Grading of Angina by the Canadian Cardiovascular Society Classification System In patients with angina , the stability of pain should be assessed . Patients have unstable angina if the pain started recently ; is more easily provoked ; or occurs with increased frequency , severity , or duration ( 7 ) . Some patients with unstable angina have a measurable risk for short-term death ( 8) . Those characterized as high risk have a 1.7 % probability of dying within 30 days , and those characterized as moderate risk have a 1.2 % probability . These patients have  pain at rest , nocturnal pain , signs or symptoms of heart failure , or new or ischemic changes on resting electrocardiography  ( ECG ) . They should be evaluated in the inpatient setting . However , patients with unstable angina whose pain has been present for at least 2 weeks and who lack any of angina 's more worrisome clinical features , including ECG changes , can be evaluated in an outpatient setting because their probability of death or myocardial infa rct ion within 30 days is indistinguishable from zero . The initial history should also include information about the risk factors for CAD , such as smoking , hyperlipidemia , diabetes , hypertension , and a family 
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Since these cutoff points are not absolute , there is no definite threshold of risk below which no further work-up is warranted .
The probabilities for nonanginal chest pain and atypical angina are larger in primary care practice .
For risk stratification in a patient with chronic stable angina who has a history of documented MI or Q waves on