A Single Negative Cardiac Troponin Level in Conjunction With Electrocardiogram Data and Clinical Judgment May Safely Rule Out Acute Myocardial Infarction in Patients Presenting to the Emergency Department With Suspected Cardiac Chest Pain

EBM Focus - Volume 9, Issue 45

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Reference: Emerg Med J 2014 Nov;31(11):872 (level 2 [mid-level] evidence)

Myocardial infarction is a major cause of death and disability worldwide, but identifying myocardial infarction upon presentation to the emergency department can be difficult. Chest pain may result from many widely varying etiologies, ranging from cardiovascular disease to gastrointestinal disease to infection, and many patients with acute coronary syndrome present with atypical symptoms (Resuscitation 2010 Mar;81(3):281). Early exclusion of an acute coronary syndrome in patients presenting to the emergency department could avoid unnecessary and costly hospital admissions, but signs and symptoms alone have not been found to be sufficient to diagnose or rule out acute myocardial infarction (Br J Gen Pract 2008 Feb;58(547):105 and JAMA 2005 Nov 23-30;294(20):2623). A recent study from the United Kingdom investigated the ability of clinical judgment in combination with electrocardiographic (ECG) and cardiac troponin T data to safely rule out acute myocardial infarction in 458 patients (mean age 64 years and 59% men) presenting to the emergency department with suspected cardiac chest pain.

After reviewing ECG results and clinical information, physicians were asked to record their judgment about the likelihood of acute coronary syndrome using a 5-point Likert scale (“definitely not,” “probably not,” “not sure,” “probably,” and “definitely”). Physicians did not have access to cardiac troponin levels until after judgments were recorded. Blood samples taken at presentation and ≥ 12 hours after symptom onset were tested for cardiac troponin T and later retested using a high-sensitivity troponin T assay. Using the definition of acute myocardial infarction as a rise or fall of ≥ 20 ng/L in serial cardiac troponin testing with at least 1 measurement above the 99th percentile of the upper reference limit, 17.7% of patients received adjudicated diagnoses of acute myocardial infarction. Clinical judgment alone was insufficient to rule out acute myocardial infarction and safely discharge patients, with negative predictive values between 92% and 97%. By expanding the criteria for discharge to include normal high-sensitivity cardiac troponin levels and no ischemia on ECG in addition to clinical judgment, the negative predictive value increased to 100% (95% CI 95.7%-100%). Using high-sensitivity troponin assay results combined with the ECG and physician assessment of “definitely not”, “probably not”, or “not sure”, 41.7% of patients could be immediately discharged without missing a single acute myocardial infarction. With the use of standard cardiac troponin testing plus ECG and physician assessment of “definitely not” or “probably not” as requirements for discharge, the number of patients that could be safely discharged was 23.1%.

These results show that adding ECG and cardiac troponin T data to the clinical assessment allows physicians to rule out myocardial infarction and safely discharge patients. This study requires further validation, but could significantly reduce hospital admissions without missing any acute myocardial infarctions.

For more information, see the Acute coronary syndrome topics in DynaMed.