2022 use of coronary computed tomographic angiography for patients presenting with acute chest pain to the emergency department: An expert consensus document of the Society of cardiovascular computed tomography (SCCT)

In the ED setting, the high accuracy of coronary CTA is driven by its high sensitivity and negative predictive value for detecting or excluding obstructive coronary artery disease, particularly among patients with low-to-intermediate pretest risk for ACS.^{,  ,  ,}  In the Perfusion Imaging and CT-Understanding Relative Efficacy (PICTURE) trial, coronary CTA demonstrated per-patient sensitivity of 92% and specificity of 87% for significant coronary stenosis using invasive catheter angiography (ICA) as a reference standard, compared with stress myocardial perfusion imaging (per-patient sensitivity of 55% and specificity of 78%).

Over the past decade, coronary CTA has established itself as a first-line imaging strategy for rapid triage of patients with low-to-intermediate risk ACP in the ED.^{,  ,  ,  ,  ,  ,,  ,  ,} In the multicenter randomized-controlled CT-STAT trial, 699 patients with TIMI risk scores ≤4 were randomized to coronary CTA (n ​= ​361) or rest-stress myocardial perfusion imaging (MPI) (n = 338) and demonstrated a significant reduction in time-to-diagnosis with a coronary CTA approach (2.9 hours vs 6.2 hours, p ​< ​0.0001) and a low rate of major adverse cardiovascular events (MACE) in patients with a normal coronary CTA. Similar results were observed in ACRIN PA, a randomized-controlled trial to compare coronary CTA in the ED to standard care, in which 30-day MACE was 0% among subjects discharged from the ED with a negative coronary CTA (95% confidence interval, 0 to 0.57). In the 2012 ROMICAT II trial, 1000 low-to-intermediate risk subjects were randomized 1:1 to coronary CTA or standard care, and demonstrated a significant reduction in ED length-of-stay among patients in the CTA arm (23.2 hours vs 30.8 hours, p ​< ​0.001). Further, there were more direct-from-ED discharges in the CTA arm (47% vs 12%, p ​< ​0.001) with comparable safety (28-day MACE 0.4% for CTA vs 1.2% for standard care, p ​= ​0.18), confirming improved efficiency of coronary CTA without a compromise in patient outcomes.

More recently, the CT-COMPARE trial randomized low-to-intermediate risk patients with acute chest pain to coronary CTA (n ​= ​322) or exercise ECG (n ​= ​240). Coronary CTA was associated with 20% reduction in hospital costs, and a 34% reduction in length-of-stay (13.5 hrs vs 20.7 hrs, p ​< ​0.0001). The long-term clinical value of coronary CTA in the ED was evaluated in the 2013 CATCH trial, which randomized 600 patients 1:1 to coronary CTA or functional testing and followed patients for a median duration of 18.7 months. Over this interval, the composite endpoint for MACE (including cardiac death, myocardial infarction, hospitalization for unstable angina, and late symptom-driven revascularization) was less frequent in the coronary CTA arm compared to functional testing (5 vs 14 events, p ​= ​0.04).

Detecting early myocardial injury with high sensitivity troponin (hs-cTn) assays has become more common throughout the U.S. and internationally. High-sensitivity troponins are preferred over prior generations of conventional cardiac troponin (cTn) tests because they enable faster detection or exclusion of myocardial injury and increase diagnostic accuracy for ACS.^, However, false positive results and borderline results are a concern as many other cardiac and non-cardiac etiologies can account for elevated hs-cTn measurements beyond epicardial CAD, including myocarditis, arrhythmia, cardiotoxicity, chronic kidney disease, heart failure, sepsis, rhabdomyolysis, chronic obstructive pulmonary disease, and pulmonary embolism.

The 2016 BEACON trial aimed to compare a strategy of early coronary CTA versus standard care for suspected ACS following hs-cTn testing. Five hundred patients were randomized 1:1 to coronary CTA or standard care, and followed for the primary endpoint of 30-day rate of obstructive CAD requiring revascularization. While the primary endpoint was similar in both study arms (9% coronary CTA vs 7% standard care, p ​= ​0.40), CTA was associated with less outpatient testing (4% vs 10%, p ​< ​0.01) and lower direct medical costs (€337 vs. €511, p ​< ​0.01). Further, there were nonsignificant trends toward fewer repeat ED visits (5% vs 8%), and repeat hospitalizations (3% vs 6%) among patients in the CTA arm. A secondary analysis of ROMICAT II data demonstrated that hs-cTn and advanced CTA features (including stenosis ≥50% and the presence of high-risk plaque) had a significant improvement in accuracy for ACS when compared to conventional cardiac troponin testing. High-risk plaque features on coronary CTA allowed for more accurate risk stratification, particularly among patients with intermediate hs-cTn levels below the 99th percentile. In the PRECISE-CTCA trial, patients who presented to the ED with acute chest pain and intermediate hs-cTn concentrations (between 5 ng/L and the sex-specific 99th percentile) were 3× more likely to have CAD compared to those with low hs-cTn concentrations, suggesting further testing with coronary CTA in this population could aid in higher precision risk-stratification. Collectively, these data suggest hs-cTn and coronary CTA likely have complementary roles, and together may offer a superior chest pain triage strategy compared to any test used in isolation.

Recent evidence suggests an expanded role of coronary CTA for patients at higher pretest risk for ACS, including select patients with non-ST elevation myocardial infarction (NSTEMI) when a non-invasive strategy is preferred (e.g. bleeding risk, vascular access issues, patient preference). Potential benefits of coronary CTA within this higher-risk population include 1) rapid and accurate exclusion of obstructive CAD, 2) identification of high-risk plaque and atherosclerosis burden to improve future risk prediction, and 3) reduction in costs and resource utilization for cases where ICA can be safely avoided. An observational component of the randomized-controlled VERDICT trial examined the accuracy of coronary CTA in 1023 patients with documented non-ST elevation ACS, and determined CTA maintains high accuracy to rule out clinically significant CAD (stenosis ≥50%) with a per-patient negative predictive value 91% and positive predictive value 88%. In addition, 33% of patients with non-ST elevation ACS had no clinically significant CAD (stenosis <50%), suggesting an opportunity for coronary CTA to safely defer ICA in nearly 1/3 of high-risk patients. In a follow-up study evaluating long-term outcomes after a median follow-up time of 4.2 years, coronary CTA was equivalent to ICA for the assessment of long-term risk.

Similar results were observed in CARMENTA, a single-center, prospective, randomized-controlled trial designed to investigate whether cardiac magnetic resonance imaging (CMR) or coronary CTA could serve as an effective gatekeeper for ICA in NSTEMI patients presenting to the ED. Early coronary CTA safely reduced referrals for invasive coronary angiography by 34% compared to routine clinical care, with no increase in MACE after 1 year. More recently, in the RAPID-CTCA prospective multi-center randomized-controlled trial,^, 1748 patients at intermediate-to-high risk for ACS were randomized to coronary CTA with standard care versus standard care alone. Pretest risk was established on the basis of prior CAD, abnormal ECG, or elevated cardiac biomarkers. While the primary outcome of all-cause death or MI at 1 year was similar in both arms (5.8% in the CTA group vs 6.1% in standard care), coronary CTA significantly reduced referrals for invasive coronary angiography (HR 0.81, 95% CI 0.72–0.92), underscoring a potential role as a gatekeeper among higher risk patients.

CT-based fractional flow reserve (FFR-CT) and stress myocardial CT perfusion (CTP) are established techniques for evaluating the hemodynamic significance of coronary stenosis.^{,,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,}  Both strategies offer incremental value over coronary CTA, improving its diagnostic accuracy by increasing specificity and positive predictive value.^,, They are most appropriate in situations where the presence or absence of ischemia may guide patient management, as with an intermediate-grade stenosis on coronary CTA (i.e. 40-80% stenosis).^, While the clinical utility of these strategies in the ED setting is not fully recognized, there is evidence both FFR-CT and CTP offer more comprehensive evaluation of coronary anatomy and physiology, potentially eliminating unnecessary invasive coronary angiograms.

Large-scale clinical outcomes data have related plaque burden on coronary CTA to adverse CAD outcomes. Data from the CONFIRM registry^, demonstrated that absence of CAD on coronary CTA is associated with a very favorable prognosis, and as coronary plaque burden increases, so does the risk of MACE and all-cause mortality. In a cohort of 3242 patients followed over a median duration of 3.6 years, a greater extent of coronary plaque on CTA conferred higher risk of MACE independent of stenosis. Patients with non-obstructive plaque and extensive plaque burden (defined by a segment involvement score >4) had a similar adjusted hazard ratio for MACE as did patients with obstructive CAD and lower plaque burden (segment involvement score ≤4).

Coronary CTA can detect high-risk plaque features associated with greater risk of plaque rupture and ACS, independent of stenosis severity.^{,  ,  ,  ,}  This is particularly important in the ED setting, as most precursors of ACS and culprit lesions are non-obstructive.^, High-risk plaque features include positive remodeling, low attenuation (<30 Hounsfield Units), napkin ring sign, and spotty calcification. In a post hoc analysis of ROMICAT II data, high-risk features on CTA increased the likelihood of ACS with a relative risk of 32.0, and this increased risk was independent of stenosis severity and clinical risk assessment. In the ICONIC trial, a nested case-control study from the CONFIRM registry, quantitative coronary plaque evaluation, including assessment of high-risk plaque and plaque composition, identified high-risk patients at risk for ACS above and beyond stenosis severity and aggregate plaque burden. Further, results from the CREDENCE trial demonstrated that comprehensive plaque measures on coronary CTA improved prediction of vessel-specific coronary physiology more so than stress-induced myocardial perfusion defects, among patients referred for nonemergent invasive coronary angiography. In light of this evidence, a recent expert consensus document was developed by the SCCT for the reporting atherosclerosis on coronary CTA.

Numerous professional societies have embraced coronary CTA as a first-line triage strategy for chest pain in select patients. In the 2015 Multi-Society Appropriate Utilization of Cardiovascular Imaging in Emergency Department Patients with Chest Pain document, coronary CTA was designated “appropriate” in ACP patients with low or intermediate pretest likelihood of ACS, and for patients with equivocal initial diagnosis of NSTEMI where initial troponin is equivocal or elevated without additional evidence of ACS. In 2016, the National Institute for Health and Clinical Excellence within the United Kingdom updated their chest pain guidelines, recommending that all patients with typical or atypical angina without STEMI be referred directly for coronary CTA as a first-line test, reserving functional testing as a second-order test for patients with non-diagnostic or inconclusive CT exams. However, it should be noted that the updated NICE guidelines excluded patients with acute chest pain.

In the 2020 European Society of Cardiology guidelines for the management of ACS in patients without persistent ST-segment elevation, coronary CTA received a “Class I” endorsement (“Level A″ quality of evidence) for early triage of patients with low-to-intermediate risk chest pain with normal ECG and negative troponins, and in patients with inconclusive or equivocal troponins. The evidence also prompted inclusion of coronary CTA as a usually appropriate initial imaging strategy in the American College of Radiology Appropriateness Criteria on acute nonspecific chest pain with low probability of coronary artery disease.

Most recently, updated chest pain guidelines from the American College of Cardiology and the American Heart Association elevated the role of coronary CTA for the non-invasive assessment of patients with either acute or stable chest pain. Coronary CTA is the only non-invasive testing modality issued a “Class I” endorsement by the ACC/AHA for patients with acute or stable chest pain, supported by “Level A” quality of evidence. Other modalities also received a Class I endorsement, but “Level B” quality of evidence.

A preliminary needs assessment should be undertaken prior to initiating a new coronary CTA program for the evaluation of ACP patients. This assessment should be conducted jointly by representatives from Emergency Medicine, Radiology, and Cardiology, and as applicable, the medical center administration. There also should be evidence that sufficient case volume and multi-departmental buy in will be likely to maintain performance and interpretation expertise, and that the resources are available to achieve rapid, high-quality studies, and interpretations available during sufficient service hours to benefit patients.

CT scanner equipment should include multi-detector scanners with a minimum of 64 detector-rows and appropriate cardiac software. Modern CT scanners provide higher temporal resolution (ranging from 66 to 150 msec), allowing for coronary CTA imaging with less contrast, lower radiation, and fewer artifacts. Patient-specific tube potential and current adjustment should be available. Patient safety equipment including advanced cardiovascular life support (ACLS) equipment should be present in the patient preparation and scanner areas. Scanners should be equipped to perform prospectively triggered axial scanning with ECG-gated tube current modulation. Low dose acquisition modes such as volumetric acquisition or high-pitch scan mode are advantageous and should be utilized if available and appropriate. The use of iterative or model-based reconstruction to facilitate radiation dose reduction is also strongly recommended. Periodic review of the site's radiation levels and comparison with published references should be performed at least twice a year. Image interpretation should be performed with 3D post-processing software capable of displaying reconstructed axial data, multi-planar reconstructions (MPRs) including curved MPRs and maximum intensity projections (MIPs).

ED programs should be initiated only at sites with sufficient experience and case volume, with an expected minimum of 200 coronary CTA cases within the previous year or additional outside support for training the local staff and implementation of the program. At least one technologist with prior experience of at least 100 coronary CTA scans is recommended to initiate the program. Properly trained ACLS certified nursing or similar qualified staff should supervise premedication of patients, consistent with institutional policy. A rapid response team and/or an ACLS certified physician should be readily available for prompt response to urgent or emergent complications. The scanner and staffing service hours must satisfy ED minimum requirements.

All coronary CTA exams should be performed and interpreted by physicians adequately trained in cardiac CT, who have achieved at least Independent Practitioner status as defined in recent training guidelines issued by SCCT. This includes at least 250 mentored coronary CTA exams, among other criteria. Radiologists interpreting coronary CTA exams should also follow American College of Radiology (ACR) training standards. Due to the severe consequences of missed ACS, additional physician experience is recommended for physicians reading ED coronary CTA scans. Interpreting physicians should be promptly available in person or by phone for consultation about patient preparation and scan protocoling. A qualified physician should also interpret the non-cardiac anatomy on all scans either as the primary reader or as a collaborating physician.

A quality assurance program is recommended with quality targets, including: a diagnostic-quality scan rate of ≥95%, a quarterly median radiation dose rate within the reference level (dose-length product 110-338 mGy-cm) and a quarterly comparative review of cases with both coronary CTA and invasive angiography that demonstrates a median accuracy of at least 75% per-patient.

Developing an algorithm for the appropriate triage of ACP patients into well-established clinical pathways is critical for successful program implementation. For example, a five-tiered chest pain pathway can be utilized for patients with no known CAD, as depicted in Table 2a. All patients and all imaging strategies should be included in the algorithm that should be understood and agreed upon by stakeholders including ED physicians, radiologists, cardiologists, nursing, hospitalists, and medical center administration.

Patient selection is primarily guided by the patient's history, clinical presentation, ECG and initial biomarker assessment (Fig. 1). Clinically appropriate patients should have reasonable clinical suspicion of ACS. A careful history and physical examination should precede any cardiac testing, to exclude alternative non-coronary diagnoses and to help define the pre-test likelihood of ACS. ECG should be acquired and reviewed for STEMI within 10 minutes of arrival to the ED. Cardiac troponin or hs-cTn should be measured as soon as possible. High sensitivity troponin assays are preferred for establishing a diagnosis of acute myocardial infarction due to their improved performance over contemporary cTn.^, Clinicians should be familiar with 99th percentile upper reference limit for the hs-cTn or conventional cTn assay used at their local institution.

Risk stratification tools for ACS can help categorize patients into low-, intermediate- and high-risk. Commonly used tools in Emergency Medicine include the HEART pathway, EDACS, and ADAPT (based on the TIMI risk score), which incorporate the results of troponin testing and have established value in clinical practice (Table 1). Risk stratification should be performed in parallel with serial troponin measurements to exclude myocardial injury. For hs-cTn assays, baseline sample collection should be obtained followed by a repeat measurement in 1–3 hours, unless the baseline test is below the limit of detection in a low-risk patient. . For conventional troponin assays, repeat sample collections are generally advised between 3 and 6 hours (see Table 2a).

STEMI should be managed according to recent guidelines, with prompt ICA as the only appropriate imaging study. Patients with documented NSTEMI should also follow guidelines-directed management, with consideration of early coronary CTA in limited scenarios.

Clinical scenarios are provided in Table 2 to illustrate a sample diagnostic pathway that integrates appropriate coronary CTA utilization for patients with suspected or definite ACS. Institutional practices will vary, and all management decisions should be tailored to individual patients based on clinical judgment. In selecting the optimal diagnostic test for a patient, it is important to recognize that coronary CTA provides information about coronary atherosclerosis burden, plaque morphology, and stenosis severity. CT may also permit evaluation of regional and global ventricular function and wall motion at low radiation doses, which adds incremental value for the diagnosis of ACS beyond evaluation of coronary anatomy. By contrast, functional testing (including ECG-only stress testing and stress testing with the use of imaging such as echocardiography or SPECT MPI) evaluates for regional myocardial ischemia due to inadequate coronary flow reserve. There are advantages and disadvantages to each approach.

The principal safety considerations for coronary CTA include radiation exposure, allergic reactions to iodinated contrast agents, and contrast-induced nephropathy. The risk of contrast-induced nephropathy is very low, and recent guidelines from the American College of Radiology (ACR) recommend limiting eGFR screening prior to iodinated contrast administration to patients who are older than 60 years, history of renal disease, history of hypertension and taking antihypertensive medication, and diabetes mellitus. The use of any exposure to radiation should always be weighed against the potential risk of cancer, according to the “as low as reasonably achievable” principle. For example, increased radiation sensitivity in pre-menopausal women or younger patients or patient characteristics known to impair image quality (i.e., inability to take beta-blockers, lack of cooperation, or high body mass index) may favor alternative test strategies. Although high body mass index adversely affects coronary CTA image quality, that is also true for alternative modalities, and ultimately clinical judgment by the referring clinician is required for optimal test selection.

Chest pain pathways should be patient-centric, with patients included in shared decision-making. Patients should be provided the risks and benefits of different diagnostic strategies, including radiation exposure, costs, and alternative testing options. A sample decision aid is provided to guide this discussion (Supplement A). Provider cultural competency training is also recommended to encourage best outcomes in patients of diverse racial and ethnic backgrounds. Translation services should be utilized to address potential language barriers with patients for whom English may not be their primary language.

The majority of randomized-controlled trial evidence supporting coronary CTA in the ED enrolled patients within the low-to-intermediate risk category risk.^,,,,, in this group of patients coronary CTA is most efficient; approximately 5–15% of patients will have obstructive CAD warranting further evaluation with invasive coronary angiography, while the majority of patients can be safely discharged from the ED with normal or nonobstructive disease.

• 5.
  Very Low Risk for ACS: This category refers to patients who are considered low-risk by risk stratification tools, with normal or nonischemic ECG, and normal baseline hs-cTn. Within this patient population, the 30-day risk of MACE is less than 1%.

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  For many of these patients, further diagnostic testing for CAD is not necessary as the yield would likely be low. However, coronary CTA may be appropriate in some very low risk patients to confidently exclude CAD and provide risk stratification; for example, patients with recurrent ED visits for chest pain who desire further testing to confidently rule-out CAD. Testing during the index ED visit could expedite a more thorough coronary evaluation, including the presence of non-obstructive plaque and also evaluate for other potential sources of chest pain. Further, coronary CTA is considered appropriate in the 2015 multi-society appropriate use criteria for ED cardiac imaging in very low risk patients, defined by TIMI risk score zero and negative early hs-cTn.

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  Shared decision making cannot be overemphasized in this patient population, so patients are well informed of the potential risks and benefits of additional testing.

Coronary artery calcium (CAC) testing with non-contrast CT is rarely appropriate as a stand-alone test for the evaluation of ACP in the ED. While there is established utility for CAC testing in asymptomatic patients with intermediate risk of CAD, there is limited data on CAC as a stand-alone test for symptomatic patients in whom ACS is a leading differential diagnosis. When CAC ​= ​0, the rate of obstructive CAD is low (less than 1%) and long-term prognosis is favorable.^, However, CAC ​= ​0 cannot exclude ACS, which can occur in 1–3% of patients who have noncalcified plaque.^, However, obtaining CAC prior to coronary CTA can be useful as an opportunity to quantify coronary plaque burden and modify the CTA protocol when heavy plaque burden is detected (i.e., use of sharp reconstruction filter, iterative reconstruction, increased acquisition time, and/or retrospective technique). However, the decision to perform a non-contrast CT scan for CAC scoring prior to coronary CTA should be made by each institution, based on their workflow and patient population.

The addition of FFR-CT^,,, or stress myocardial CTP^,, to coronary CTA may be appropriate in situations where the determination of lesion specific ischemia or myocardial ischemia would be helpful to guide management, including the following scenarios:

• •
  Coronary artery stenosis of unknown hemodynamic significance (40–70%)
• •
  Severe coronary calcification

Coronary CTA is appropriate for the early triage of symptomatic patients with known CAD and prior PCI, provided: 1) the coronary stent is ​≥ ​3-mm in diameter and within a proximal coronary segment; 2) the ECG is normal or nonischemic; and 3) the baseline cTn or hs-cTn is normal or equivocal. In some scenarios it may be appropriate to perform coronary CTA in patients with stents less than 3-mm, particularly in patients known to have thin stent struts (<100-μm) in proximal, non-bifurcation locations.

Measures to improve the accuracy of stent imaging are encouraged, including strict heart rate control (goal <60 bpm), iterative or model-based reconstruction, sharp kernel reconstruction, and mono-energetic reconstructions (when available). Protocols to optimize stent imaging should be locally developed and followed.

Coronary CTA is also appropriate in select patients with known CAD who have had prior coronary artery bypass grafting (CABG), particularly if the primary objective is to evaluate graft patency. These patients should have a normal or nonischemic ECG and normal or equivocal baseline cTn or hs-cTn.

Patients should be evaluated by staff (for example a CT technologist or patient nurse), to ensure that no absolute contraindications exist to the examination. If uncertain, staff should confer with the attending physician. It should be clear that the patient understands the nature of the examination and can cooperate with breath-holding instructions. Baseline vital signs should be used to design a pre-scan medication protocol to achieve heart rate targets based on the scanner model to be used. Staff should ascertain the patient's previous medications. If the baseline heart rate is within target range, a mild stress, e.g., 30 seconds of hard hand-grip on a towel, may be considered to ensure heart rate does not rise unduly.

Patients should be fully informed about the nature of the examination, its objectives, possible risks including radiation dose, their required cooperation and the sensations they are likely to feel. This is a critical component of shared decision-making. It is suggested that radiation dose be compared to annual background dose (approximately 3 mSv in the United States). Patients should be given a chance to request an alternative diagnostic strategy if they feel unable or unwilling to proceed. This educational process should be repeated after premedication, just before scanning, to ensure patients remember instructions on breath-holding and are prepared for the sensations likely to occur from nitroglycerin and contrast administration.

The majority of patients referred for coronary CTA require pre-medication with beta-blockers to establish heart rate control and reduce heart rate variability. SCCT guidelines for the performance and acquisition of coronary CTA should be followed. Generally, a target heart rate of 60 beats per minute or less is usually appropriate. A detailed example of pre-medication orders is listed in Table 3. Institutional protocols will vary depending on target heart rates required by the scanner model to be used; preferably a set of standardized orders should be made available to staff.

Oral metoprolol administration is the usual practice, with 50–100 mg by mouth 1 hour prior to imaging. Slow-release formulations of oral metoprolol should not be used. At the time of scanning, supplementation with IV metoprolol can be used to achieve target heart rates (5 mg IV, followed by repeated 5 mg doses as necessary, typically up to 20–25mg total).

Ivabradine, a direct I(f) current inhibitor, can be used in addition to or in lieu of beta-blockers for heart rate control prior to coronary CTA. It is available in oral and IV formulations and can lower heart rate without affecting myocardial contractility or blood pressure. This makes ivabradine an attractive alternative to metoprolol in patients with low blood pressure. A sample protocol is 15 mg orally 60–75 minutes prior to scanning. Ivabradine may be more effective than metoprolol in patients treated with chronic beta-blockers. However, it is ineffective in patients who are not in sinus rhythm, as it acts through direct inhibition of the sinoatrial node.

Scenarios when coronary CTA may be difficult or nondiagnostic are presented in Table 5, along with strategies to improve quality. Scenarios when the risks associated with coronary CTA may not outweigh the benefits are presented in Table 6, with strategies to improve safety.

Relative contraindications to coronary CTA in the ED include:

• •
  History of allergic reaction to iodinated contrast after adequate steroid/antihistamine preparation.
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  Estimated GFR<30 unless on chronic dialysis, or evidence of acute kidney injury.
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  Patient factors leading to potentially non-diagnostic scans, which will vary with scanner technology and site capabilities, including HR ​> ​site maximum for reliably diagnostic scans after pre-medication, markedly irregular rhythm, high coronary calcium burden, and large body size.
• •
  Inability to cooperate and follow commands during the CT acquisition
• •
  Pregnancy or uncertain pregnancy status in pre-menopausal women. Coronary CTA may be useful to exclude spontaneous coronary artery dissection (SCAD) which predominantly occurs in young women without traditional CAD risk factors.

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Patient-specific scan protocoling is recommended to minimize radiation dose while still achieving diagnostic quality. This results in modification of scan length, timing and infusion rate of the contrast bolus, and alteration of tube potential and tube current based on patient characteristics. A sample protocol selection guide is presented in Table 4.