title: The association between pretest probability of coronary artery disease and stress test utilization and outcomes in a chest pain observation unit.
abstract: OBJECTIVE
  Cardiology consensus guidelines recommend use of the Diamond and Forrester (D&F) score to augment the decision to pursue stress testing. However, recent work has reported no association between pretest probability of coronary artery disease (CAD) as measured by D&F and physician discretion in stress test utilization for inpatients. The author hypothesized that D&F pretest probability would predict the likelihood of acute coronary syndrome (ACS) and a positive stress test and that there would be limited yield to diagnostic testing of patients categorized as low pretest probability by D&F score who are admitted to a chest pain observation unit (CPU).
  
  
  METHODS
  This was a prospective observational cohort study of consecutively admitted CPU patients in a large-volume academic urban emergency department (ED). Cardiologists rounded on all patients and stress test utilization was driven by their recommendations. Inclusion criteria were as follows: age>18 years, American Heart Association (AHA) low/intermediate risk, nondynamic electrocardiograms (ECGs), and normal initial troponin I. Exclusion criteria were as follows: age older than 75 years with a history of CAD. A D&F score for likelihood of CAD was calculated on each patient independent of patient care. Based on the D&F score, patients were assigned a priori to low-, intermediate-, and high-risk groups (<10, 10 to 90, and >90%, respectively). ACS was defined by ischemia on stress test, coronary artery occlusion of ≥70% in at least one vessel, or elevations in troponin I consistent with consensus guidelines. A true-positive stress test was defined by evidence of reversible ischemia and subsequent angiographic evidence of critical stenosis or a discharge diagnosis of ACS. An estimated 3,500 patients would be necessary to have 1% precision around a potential 0.3% event rate in low-pretest-probability patients. Categorical comparisons were made using Pearson chi-square testing.
  
  
  RESULTS
  A total of 3,552 patients with index visits were enrolled over a 29-month period. The mean (±standard deviation [SD]) age was 51.3 (±9.3) years. Forty-nine percent of patients received stress testing. Pretest probability based on D&F score was associated with stress test utilization (p<0.01), risk of ACS (p<0.01), and true-positive stress tests (p=0.03). No patients with low pretest probability were subsequently diagnosed with ACS (95% CI=0 to 0.66%) or had a true-positive stress test (95% CI=0 to 1.6%).
  
  
  CONCLUSIONS
  Physician discretionary decision-making regarding stress test use is associated with pretest probability of CAD. However, based on the D&F score, low-pretest-probability patients who meet CPU admission criteria are very unlikely to have a true-positive stress test or eventually receive a diagnosis of ACS, such that observation and stress test utilization may be obviated.
authors.affiliation: The Department of Emergency Medicine, Warren Alpert Medical School of Brown University, Providence, RI.
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Napoli
mesh_terms: D054058:Acute Coronary Syndrome / Q000150:complications / Q000175:diagnosis*; D000328:Adult; D000368:Aged; D002637:Chest Pain / Q000209:etiology*; D016009:Chi-Square Distribution; D003324:Coronary Artery Disease / Q000150:complications / Q000175:diagnosis*; D003661:Decision Support Techniques; D004636:Emergency Service, Hospital; D005080:Exercise Test / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011336:Probability; D011446:Prospective Studies; D012237:Rhode Island; D019564:Unnecessary Procedures / Q000706:statistics & numerical data*