Robert D. Glatter, MD

Disclosures

April 02, 2009

Question

Should triple rule-out CTA be the study of choice for patients with acute chest pain in the emergency department?

Response from Robert D. Glatter, MD
Attending Physician, Department of Emergency Medicine, Lenox Hill Hospital, New York, NY

Response

Each year, approximately 6 million patients in the United States present to the emergency department (ED) with acute chest pain.[1] Emergency physicians must rapidly and accurately determine whether a patient is suffering from an emergency medical condition such as acute coronary syndrome (ACS), aortic dissection (AD), or pulmonary embolism (PE).

The emergency physician may be presented with several challenges while diagnosing the cause of the pain. Initial cardiac biomarkers and D-dimer may be elevated in patients with ACS, PE, or AD, adding to the physician's difficulty in distinguishing between the 3 entities.[2,3,4] In addition, the sensitivity of a screening chest x-ray to diagnose AD or PE is low, and the ability of the electrocardiogram to detect ACS, PE, or AD is quite limited as well.[5,6,7,8,9]

Alternatively, coronary computed tomography angiography (CCTA) offers great potential as a diagnostic modality in the triage of patients with acute chest pain.[10] In addition to the demonstrated reliability of CT angiography for the diagnosis of AD and PE, CCTA has recently been shown to be highly sensitive and accurate in diagnosing significant coronary artery stenosis.[11,12,13,14,15,16] Data also suggest that CCTA is reliable for the triage of appropriately selected chest pain patients for early discharge or additional inpatient evaluation.[11,12,13,14,15,16] Patients with a low-to-intermediate pretest likelihood of coronary artery disease, negative cardiac markers, and normal electrocardiograms are best suited for CCTA-based triage.

Although 16-slice scanners have allowed for the adequate evaluation of coronary arteries, they are not fast enough to provide a high-quality scan of the entire chest cavity in addition to a gated scan of the heart and coronary arteries. Newer, state-of-the-art, 64-slice scanners (as well as higher-generation 128- and 256-slice scanners) can scan the entire coronary circulation in approximately 5 seconds or less. A scan through the chest can be completed in approximately 10-15 seconds, even with high-resolution slices.[17]

Concerns about radiation exposure should limit unrestricted use of 64-slice scanner triple rule-out protocols. Compared with the usual radiation dose of a standard 64-slice CCTA (10-23 mSv), the effective radiation dose of a "triple rule-out" scan is often increased by 50% (25-40 mSv) -- the equivalent of 240-300 chest x-rays.[10] By comparison, nuclear stress tests typically involve exposures in the range of 8-16 mSv, while doses from diagnostic angiography with percutaneous transluminal coronary angioplasty/stent placement range from 5-13 mSv.[10] Moreover, among patients who undergo CCTA as a primary triage test in the ED, there is a subset that may require a noninvasive stress test, often a nuclear stress test. In particular clinical scenarios, the stress test may be followed by diagnostic and interventional invasive angiographic procedures. This combined radiation dose is a reason for concern, particularly in younger female patients due to radiosensitivity of breast tissue.

Newer imaging protocols that require heart rate control with administration of beta-blockers along with various gating protocols can significantly reduce radiation exposure to less than 5 mSv. However, many of these techniques are difficult to apply in ED patients. It has also been observed that the incidence of occult PE or AD without suggestive signs or symptoms is very low in patients with acute chest pain.

In a recent study by Rogg and colleagues,[18] nearly 24% of ED chest pain patients received at least 1 diagnostic test for 1 of the 3 main chest pain syndromes (ACS, PE, or AD). Of these patients, 22% received tests aimed at 2 or more diagnoses. The most common combined diagnostic workup was for ACS and PE, which accounted for 19% of all workups and 87% of all multiple workups. This study found that the "triple workup" for ACS, PE, and AD is relatively uncommon, occurring in only 0.6% of patient encounters in which at least 1 of these 3 diseases was evaluated.[18] The diagnostic yields demonstrated for ACS, PE, and AD varied from 6% to 8%. Therefore, unless there is a high degree of suspicion of AD or PE (in addition to ACS), the emergency physician should limit the use of the triple rule-out protocol. It should be noted that the entire thoracic aorta up to the aortic arch and the lower two thirds of the lungs are within the field of view during a standard CCTA, revealing the majority of dissections and central-vessel pulmonary emboli without additional radiation.

Conclusion

Technological advances over the past decade have made highly detailed images of the coronary arteries, thoracic aorta, and pulmonary arteries available from a single CT scan protocol. Although this triple-rule out technique may exclude deadly causes of chest pain from 3 different anatomic vascular locations, the higher radiation dose delivered with current techniques is a valid clinical concern Therefore, the triple rule-out protocol should be limited to selected patients in which there is "weighted" support for the diagnosis of either PE or AD, as well as suspicion for ACS.

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