Triple-rule-out CT (TRO CT) is angiography with triple exclusion. TRO CT may be ordered in the setting of acute chest pain to examine the thoracic aorta and the coronary and pulmonary arteries. TRO protocol helps exclude life-threatening causes of acute chest pain, especially if atypical, or if alternative causes to acute coronary syndrome (ACS) are being entertained (i.e. the patient is thought to be at a low to intermediate risk for ACS).
Causes of acute chest pain to be ruled out using this protocol include:
- aortic dissection
- pulmonary embolism (PE)
- coronary artery disease (CAD)
- non-vascular chest disease
All patients with acute coronary syndrome – ACS require hospitalization, and many will benefit from rapid triage to cardiac catheterization and intervention.
On the other hand, when the patient’s condition clearly suggests a non-cardiac diagnosis, coronary assessment is not necessary and is not cost-effective. Patients suspected of having acute coronary syndrome must be clearly classified as patients without this diagnosis prior to discharge. Given the potentially life-threatening consequences of a lack of ACS diagnosis, discharge of patients with possible undiagnosed ACS is highly critical.
Triple-rule-out CT angiography for evaluation of acute chest pain and possible acute coronary syndrome
TRO CT examination can be a powerful tool for assessment and triage of patients with low to moderate risk of acute coronary syndrome in whom diagnostic catheterization is not indicated. However, unlike most CT studies that a radiologist can perform using a simple protocol, TRO CT studies require more individual attention.
Careful consideration of patient selection, patient preparation, and technicqe of contrast agent injection and CT imaging will result in high-quality TRO CT studies to assess the aorta, coronary circulation, pulmonary arteries, and adjacent intrathoracic conditions.
Compared to conventional treatment of acute chest pain in the emergency department, appropriate application of TRO CT can:
- reduce patient triage time
- number of diagnostic tests required
- radiation exposure
At the Pulse Cardiology Center, a Tripple rule out – TRO CT is performed, as a diagnostic examination for the assessment of acute chest pain and possible acute coronary syndrome. Within the Center for Chest Pain, our experts diagnose, monitor and treat all cardiovascular diseases according to world standards and protocols. Within the Pulse Cardiology, a department for the observation of patients with chest pain has been specially established, so each patient is treated with special care and individual approach.
Scan protocol for TRO – Tripple rule out
The TRO exam is essentially an extended coronary CT angiogram:
- patient preparation is the same as for cardiac CTA, including administration of an intravenous β-blocker and sublingual nitroglycerin, unless contraindicated
- the scan should include the thoracic aorta and lungs
- the scan can begin from 1 cm above the aortic arch, excluding the lung apices for the sake of minimizing radiation exposure, as apical emboli are both rare and virtually undetectable at CT angiography
- biphasic contrast injection has been shown to give a more homogeneous enhancement profile compared with monophasic injection
- during the first phase, undiluted contrast material is injected for opacifying the left heart, commencing at the plateau phase of peak aortic and coronary enhancement
- following this, diluted contrast material (1:1) is injected at the same rate for opacifying the right heart
- contrast material quantities and rates differ between CT machines
The primary goal of the triple exclusion test – TRO CT
A CT scan with intravenous (IV) contrast can combine imaging of the coronary arteries, ascending aorta, and pulmonary arteries; this allows assessment of coronary artery disease (CAD), pulmonary embolism, and disease of the thoracic aorta (dissection) with a single study. This type of evaluation has been called the “triple rule out (TRO).” Technical aspects of this type of study differ from that of CCTA, owing to a wider field of view and a different protocol for the administration of IV contrast.
The primary goal of CT with a triple rule out (TRO) in the emergency department is to enable the safe and rapid discharge of patients who are estimated to have a low to moderate risk of acute coronary syndrome.
Detection of non-coronary lesions that explain the presented complaint is a great advantage of TRO CT examination over nuclear stress testing.
TRO studies are most appropriate and cost-effective when acute coronary syndrome is suspected, along with other diagnoses, such as pulmonary embolism, acute aortic syndrome, or nonvascular disease in the chest.
The optimized TRO protocol provides excellent image quality for the assessment of the aorta, coronary and pulmonary arteries, while minimizing the dose of contrast and radiation exposure.
Attention to detail on patient preparation, contrast administration, and scan time is key to high-quality TRO studies.
Why a quick assessment of chest pain is important
Assessment of acute chest pain and related symptoms is always one of the most common reasons for visiting the emergency department. Suspicion of heart disease and chest pain were the most common reasons for direct admission to the hospital.
Differential diagnosis of chest pain is a complex problem for an emergency physician. The diagnosis of acute coronary syndrome (ACS) includes unstable angina pectoris, myocardial infarction without ST elevation and myocardial infarction with ST elevation. From the patients with ACS symptoms, only 25% eventually have a confirmed diagnosis of ACS at the time of discharge.
Patients who are misdiagnosed with ACS are usually younger and have an atypical presentation and a non-diagnostic electrocardiogram (ECG). Uncertainty in the diagnosis of ACS gives rise to an increased number of diagnostic tests and hospital admissions. The costs of negative hospital cardiac examinations are huge.
In current practice, TRO-CTA has performed very well in appropriately selected patients. Improved scanning hardware and imaging algorithms have the potential to reduce radiation exposure without compromising the accuracy of the data obtained.
Who is a candidate for the tripple rule out test?
Patients who are likely to have a high burden of calcified coronary plaque because they have had coronary heart disease (including patients with previous myocardial infarction, chronic angina, or stents, and patients who have undergone bypass) are less likely to benefit from coronary imaging performed using TRO CT, although the TRO study may still be useful in relation to the aorta, pulmonary arteries, and other intrathoracic conditions. The degree of coronary heart disease is often overestimated in these patients due to the flowering of calcified plaque, so it is impossible to exclude clinically significant coronary disease.
Elderly patients with multiple cardiac risk factors are more likely to have extensive coronary calcification. Indeterminate coronary CT assessment is much more likely in patients with elevated calcium (score> 400–1000). In such patients, a calcium scoring study may be useful prior to TRO CT to define whether the patient is a candidate for TRO CT.
Symptoms that may cause you to undergo Tripple rule out testing
An acceptable clinical history of TRO CT includes a complex of symptoms that raises suspicion of ACS, including symptoms such as chest pain, shortness of breath, syncope, or pain in the neck, shoulder, back, or arm that do not appear to be musculoskeletal in nature. Patients should be negative for initial cardiac biomarkers (myoglobin and troponin-I) and should not have new ECG changes indicating myocardial ischemia. Ideally, these patients should have signs, symptoms, and laboratory data that could be interpreted as consistent with ACS or other causes of chest pain, including pulmonary embolism and acute aortic syndrome.
In selected patients who test positive for low biomarkers, TRO CT may be appropriate when the clinical impression is in favor of pulmonary embolism or acute aortic syndrome or when there is a need to exclude ACS, but there is no immediate intention to send the patient for catheterization.
When the clinical suspicion is really limited to ACS, a dedicated coronary CT angiogram is preferred, because it will include less contrast material and expose the patient to a lower radiation dose. Age, sex, and clinical picture are well-validated parameters that can be used to define a population with a possible ACS that would correspond to TRO CT. While traditional cardiac risk factors, such as family history of coronary heart disease, hypercholesterolemia, hypertension, and other clinical parameters, may be important long-term prognostic markers, such risk factors have limited clinical value in the diagnosis of ACS.
The presence of cardiac arrhythmia is a challenge for recording coronary arteries with an ECG, but it is no longer an absolute contraindication. Sinus bradycardia is the preferred heart rhythm for TRO CT. In the absence of a clinical contraindication, a b-blocker should be used before TRO CT. Heart rate and ectopy decrease after treatment with intravenous b-blocker.
The new CT technology provides improved timing resolution, with the ability to scan the entire heartbeat in one to two heartbeats (compared to four to five beats for most 64-section scanners). This new technology has reduced the necessary phase window for diagnostic imaging of coronary arteries and the effects of heart rate variability on coronary image quality.
Contraindications for the use of Tripple rule out – TRO CT
Contrast material allergies and renal failure are relative contraindications for the use of iodinated contrast material for TRO studies. The presence of asthma, acute heart failure, severe cardiomyopathy, or hypotension may limit the use of b-blockers to control heart rate and thus may reduce the quality of TRO CT images.
The decision on whether a patient should be excluded from TRO CT due to cardiac arrhythmia must be based on an assessment of the size of the arrhythmia and the specific capabilities of the scanner which be used for the examination. The usual heart rate of up to 80 beats per minute is no longer a contraindication for many new scanners, including dual-source scanners and single-source scanners with portal rotation times faster than 300 msec. Irregular tachyarrhythmia is a more serious problem, but the degree of contraindication depends on the frequency of ectopic beats.
A history of recent cocaine use or a positive cocaine test is also a relative contraindication to the use of b-blockers for scanning, although this contraindication remains controversial. The recent use of phosphodiesterase inhibitors is a relative contraindication to the use of nitroglycerin for coronary vasodilation during CT, but it is not a contraindication for TRO CT.