• presence of acute coronary syndromes (ACS) [ Time Frame: six months ] [ Designated as safety issue: No ]
  

The acute coronary syndromes (ACS), which encompass unstable angina (UA) and both ST elevation and non-ST elevation myocardial infarction (STEMI and non-STEMI), are the leading cause of death in the United States. In addition, they account for a significant number of hospital admissions (300,000 per year for STEMI, >1,000,000 per year for non-ST elevation ACS). Differentiation of patients with ACS from those with chest pain due to other causes, as well as risk stratification of those within the ACS group, are critically important.

In the Emergency Department, the ECG is initially used to distinguish patients with STEMI from those with non-STEMI and other ACS. Subsequent workup in non-STEMI patients is aimed at rapidly distinguishing those who require admission and possible intervention or intensive medical therapy, from those who can be safely discharged. However, because of the frequent inability to determine whether symptoms are related to an ACS during this initial ED visit, further evaluation is often needed, resulting in an estimated 5,000,000 admissions per year.

Currently, a variety of modalities are used in this process of risk stratification, with resting myocardial perfusion imaging (MPI) often assuming a central role. This modality has an overall sensitivity of 80% and an excellent negative predictive value (95-97%). Resting MPI therefore enables clinicians to safely triage low risk patients to delayed stress testing or discharge. However, as with any test, this technique has limitations, including an increased incidence of equivocal findings in obese patients, lower sensitivity in patients without ongoing symptoms, and unsuitability in patients with previous myocardial damage. Perhaps most importantly, alternative diagnoses such as aortic dissection or pulmonary embolism cannot be evaluated with myocardial perfusion imaging.

If coronary CT angiography (CTA) could be shown to be a robust technique in the clinical setting, it could become a powerful tool in the triage of patients with ACS. CT of the chest is currently considered the gold standard for evaluation of the two most common serious alternative chest pain diagnoses - aortic dissection and pulmonary embolism. A single, rapid comprehensive imaging study that could reliably diagnose or exclude coronary artery disease, aortic dissection, and pulmonary embolism would allow quicker and more appropriate triage of this acutely ill population.

However, in keeping with the principles of evidence-based medicine, before comprehensive gated chest CT angiography can be recommended in preference to existing techniques, systematic comparative studies should be performed. In this study, the results of the CTA will be compared with those of the resting MPI, which is part of the standard ED evaluation of chest pain at this institution. In addition, a majority of these patients subsequently undergo stress MPI. It is therefore anticipated that the stress MPI results will also be compared with the CTA findings.