Nowadays, fast scanner technology combined with heart-rate-reducing medication has made it possible to image the coronary arteries without motion artifacts in most patients. Indeed, state-of-the-art scanners acquire 64–320 cross-sections per rotation, depicting vascular details with a spatial resolution of <0.5 mm. ECG-synchronized, contrast-enhanced images of the heart and coronary arteries can be acquired in one to five heart cycles. The diagnostic performance of coronary CTA has been investigated extensively in patients with stable coronary artery disease (CAD). Using invasive angiography as a reference, coronary CTA is more sensitive (98–100%) than any other noninvasive technique [30]. Because of its high negative predictive value (99–100%), coronary CTA is recommended in patients with a low to intermediate probability of CAD and in patients with an inconclusive functional test [31]. A normal cardiac CT examination is associated with a low adverse cardiac event rate in the following years [32] The reported perpatient specificity (∼85%) is lower because stenosis severity is overestimated, often due to the presence of calcifications, but it is not inferior to that of other noninvasive techniques. In addition, radiation exposure has decreased dramatically over the past years, such that doses of <5 mSv are now common practice using state-of-the-art technology; moreover, very recent innovations permit doses under 1 mSv in selected patients [33]. Given the practical limitations of functional testing in the ED setting and the relatively low prevalence of CAD in patients visiting EDs, direct coronary visualization by CTA offers an attractive diagnostic alternative for the early triage of ACS patients.

CTA of the thorax and abdomen is a well-established imaging technique for many acute abnormalities of the aorta. Even without the use of ECG gating, CTA of the aorta has high sensitivity and specificity for the detection of acute thoracic aortic diseases and it has largely replaced conventional diagnostic angiography [34]. However, over the last decade it has become clear that the spectrum of acute aortic abnormalities also includes subtle yet important aortic lesions that evade nearly all cross-sectional imaging techniques, including non-gated CTA. Conversely, using ECG-gated CTA, the aortic root, coronary arteries, and valve apparatus can be accurately assessed preoperatively Finally, modern endovascular treatment options require much higher degrees of accuracy in the delineation of pathology and treatment planning: both the exact size and location of a primary intimai tear and the branching pattern of the aortic arch are affected by cardiac pulsation artifacts, and their suppression is highly desirable.

The CT techniques used for the assessment of CAD are different from those used in patients with acute aortic diseases; thus, selection of the correct protocol is the first step in any CT imaging procedure and is based on clinical judgment by ED physicians.

While the potential diagnostic value of cardiac CT in the ED seems evident, there are practical obstacles that interfere with its widespread implementation. CT equipment with sufficient cardiac imaging capabilities (minimally a single-source 64-slice system), fully-trained technologists, and experienced cardiac CT readers are essential. Not all patients are eligible for cardiac CTA, including those with known CAD, cardiac arrhythmia, tachycardia, or severe obesity (typically BMI >40 kg/m²). CTA is associated with risks due to radiation exposure, although doses have decreased substantially over the past decade. The use of iodine-containing contrast media is contraindicated in patients with renal dysfunction or related allergies. The guidelines emphasize that the choice of test, whether CT or another modality, should be based on local expertise and the individual characteristics of the patient that affect eligibility [36]. More advanced CT technology, i.e., dual-source CT systems or wider detector arrays, can improve image quality in somewhat less suitable patients. Presently, few centers have a sufficient number of experienced personnel to offer cardiac CT around the clock. Current published guidelines on the practice of cardiac CT in the ED specify the requirements for and maintenance of certification for imaging centers, interpreting physicians, and medical staff [36].

The following sections provide guidance based on professional society standards and encourage the use of the recommended practices [36]. Cardiac CT should be performed and interpreted in accordance with best practice standards as delineated in the imaging guidelines of the Society of Cardiovascular Computed Tomography (SCCT), using at least 64-slice technology and interpreted by physicians at least Core Cardiology Training Symposium (COCATS) level 2 or equivalent, SCCT level 2, or certified by the Certification Board of Computed Cardiovascular Tomography (CBCCT) [29]. Below is a summary of the standards that should be considered at every institution:

The absence of plaque on CTA excludes ACS (sensitivity 100%), while obstructive CAD (>50% stenosis) does not (sensitivity 77%); only half of the patients with obstructive CAD on CTA have acute coronary disease. Several randomized controlled trials have investigated the safety and economic performance of cardiac CT in acute chest pain (Table 3) [37–39]. Taken together, the three trials comprised more than 3000 patients. Follow-up analysis demonstrated that, based on the CTA results, not a single patient was discharged with a missed diagnosis of ACS. These trials demonstrated the efficiency of CTA compared to the standard of care (SOC) as evidenced by a reduction in length of stay, hospital admissions, and ED cost, while overall hospital costs remained similar to those of the SOC, driven by a higher rate of invasive angiography and revascularizations. Across the trials, patients randomized to CTA more often underwent cardiac catheterization (8.4% vs. 6.3%) and percutaneous coronary intervention (4.6% vs. 2.6%). Unfortunately, the trials were not powered to prove that higher sensitivity for the detection of obstructive CAD by CTA, with subsequently increased revascularization rates, also results in a better clinical outcome. Additionally, radiation exposure will be higher for CTA when the SOC consists of exercise tests and stress echocardiography. In summary, these trials have established cardiac CT as a viable alternative to functional testing in the triage of low-risk patients with acute chest pain. Several studies demonstrated that CTA findings of plaque, stenosis, and ventricular function accurately predict adverse cardiac events over the next 6 months to 2 years. While patients without CAD remain virtually event-free, those with non-obstructive CAD have a slightly increased risk, and those with obstructive CAD are at the highest risk [32].