1. What are the contraindications for cardiac CT?
An inability to breath-hold or follow instructions are contraindications to cardiac computed tomographic angiography (CTA). A history of anaphylactic reaction to intravenous iodinated contrast is also considered a contraindication. Often, severe anaphylactic reactions can be confused with other, less severe contrast reactions. In the latter case, computed tomography (CT) is possible if the patient has been adequately premedicated (local premedication policies vary). According to the most recent appropriateness criteria, ongoing acute coronary syndrome is a contraindication to performing cardiac CTA.
2. Is it necessary to administer beta-blockers during acquisition?
With the advent of dual-source scanners and 320-detector scanners, we have witnessed a significant increase in temporal resolution and z-axis coverage, respectively. Thus, beta-blockers are no longer necessary before an acquisition on certain scanners (dual-source CT) but remain necessary on conventional single-source 64-slice scanners. In any case, a slower heart rate is still desirable because of increased image quality and lower radiation exposure when a prospective-triggered mode of acquisition is used. Target heart rates are typically 60 or below.
3. What are the three most challenging cardiac CT (CCT) artifacts?
Coronary artery motion artifact, especially at high heart rates, leads to blurring and potentially leads to the segment to be nondiagnostic for assessment of obstruction. The mid-right coronary artery is commonly affected. Low heart rates and scanners with fast temporal resolution help minimize the prevalence of motion artefact.
Calcium deposition within coronary arteries is most influenced by increasing age. Calcium usually results in a blooming artifact and may render segments of coronary arteries nonevaluable for underlying stenosis.
Other potential sources of image artifacts include slab artifacts from reconstruction kernels, respiratory motion artifacts, and cardiac motion secondary to heart rate variability or premature ventricular contractions (PVCs), as well as beam hardening artifact from pacer wires, implantable cardioverter defibrillators (ICDs), artificial valves, surgical clips,
4. What is the radiation dose of a standard cardiac CT examination?
The radiation dose of a standard cardiac CTA depends on a multitude of factors and can range from 1 mSv to as high as 30 mSv. To put things in perspective, the average dose from a nuclear perfusion stress test is 6 to 25 mSv (or as high as 40 mSv or more in thallium stress/ rest tests), and the average dose from a simple diagnostic coronary angiogram is approximately 5 mSv. Factors affecting the radiation dose of a cardiac CT include the type of scanner (single-source versus dual-source), the number of detectors (z-axis coverage), the body habitus of the patient and the selection of kVp and mAs, and the scan mode (triggered versus gated with or without tube modulation). General measures to reduce the radiation dose to the patient should be used whenever possible according to the as low as reasonably achievable (ALARA) principle. Tube modulation routinely should be applied if retrospective gating is selected, unless a specific reason prohibits its use. If only coronary anatomy is needed, prospective triggering is preferred if clinically feasible (low and regular heart rate).
5. What are volume-rendered three-dimensional (3D) images (VRT)? And are volume-rendered images diagnostically useful in the assessment of coronary artery disease?
Volume-rendered images are images that have been generated using a reconstruction algorithm to render a 3D volumetric image of the entire dataset. They are not suitable for an assessment of the severity of coronary artery disease. However, they are particularly useful in a rapid evaluation of course and number of coronary artery bypass grafts and the evaluation of coronary fistulas, collaterals, and coronary aneurysms. However, use of 3D VRT images does still require review of the two-dimensional (2D) dataset in axial and multiplanar modes.
6. Is there a calcium score above which a cardiac CT acquisition would be contraindicated?
There is no data demonstrating a clear calcium score cutoff above which a cardiac CT would be contraindicated. However, it is clear that the higher the calcium score, the higher the probability that one or more coronary artery segments might be rendered nonevaluable for stenosis exclusion secondary to blooming artifacts. A number often bandied around in the literature is an Agatston calcium score of 1000, but again many sites do not use any cutoff value that would preclude from acquiring a coronary CTA. Because of the limited prognostic value, performance of calcium scores on patients who have been previously revascularized (stents or bypass grafts) is not indicated.
7. Is a calcium score useful in a 67-year-old man who is a smoker with diabetes?
A calcium score is useful in a patient with an intermediate pretest probability of disease because it has been shown to be able to change the classification of such a patient and potentially affect therapy. This patient has a high pretest probability of disease (ATP III/ Framingham) and should be treated accordingly to current guidelines. The information from a calcium score CT would not have incremental value in this setting and should therefore be considered ‘‘not indicated.’’
8. What is the role of cardiac CT in patients presenting for noncoronary cardiac surgery?
A cardiac CT in this setting is quite useful for the assessment of coronary arteries for obstructive disease in young and middle-aged patients presenting for noncoronary cardiac surgery such as valve repair, resection of cardiac masses, and aortic surgery. Older patients, however, tend to have a higher calcium score, and up to 10% to 25% of studies in octogenarians may not allow definitive exclusion of obstructive coronary artery disease because of one or more nonevaluable segments (Fig. 10-1).
9. What is the diagnostic accuracy and clinical utility of plaque characterization by cardiac CT?
Cardiac CT is excellent for detection and quantification of calcified portions of coronary plaque (Agatston score) and for differentiation of calcified, mixed, and noncalcified plaques. However, when compared with the gold standard of intravascular ultrasound (IVUS), CT is only modestly accurate in the detection and quantification of the volume of noncalcified plaques (stable fibrous or potentially vulnerable lipid rich), and differentiation of the two subtypes is not reliably possible. Plaque characterization remains a work in progress, and currently there is no demonstrable utility of plaque characterization in prognosis or in directing medical therapy.
-1.jpg)
Figure 10-1. Cardiac gated CTA with curved multiplanar reconstructions of the right (top), left anterior descending (bottom left), and left circumflex (bottom right) coronary arteries show absence of coronary plaque or stenosis. A negative CT with good image quality has a very high negative predictive value and may spare a patient a diagnostic invasive angiogram.
10. Is cardiac CT safe and useful in patients presenting with newly diagnosed heart failure?
Coronary angiography is usually performed in patients with dilated cardiomyopathy and heart failure, in order to exclude multivessel coronary artery disease as a cause. Cardiac CTA has been shown to be safe and sensitive in excluding multivessel coronary artery disease in this group of patients, with a negative predictive value approaching 97% to 99%. In intermediate-risk to high-risk patients with chest pain or heart failure and a cardiac ultrasound demonstrating classic Tako-Tsubo features, a cardiac CT may be useful in excluding superimposed coronary artery disease.
11. Is cardiac CT useful in the assessment and management of asymptomatic postbypass patients?
Cardiac CT should not be performed in asymptomatic patients. However, it is excellent in assessing graft patency in symptomatic post-bypass patients, and it is useful for the assessment of native coronary artery disease progression and in the assessment of postoperative complications such as graft aneurysms, sternal integrity, and aortotomy dissections.
12. A 74-year-old diabetic, who underwent stenting of his second obtuse marginal artery with a 2.5-mm drug-eluting stent a year ago, has new-onset exertional chest pain. Is cardiac CT an appropriate modality for his initial evaluation?
Current scanner technology limits adequate evaluation of in-stent restenosis in stents that are smaller than 3 mm in diameter. Technical factors include metallic artifacts, calcium and motion artifacts, stent material, and strut design. However, cardiac CTA is useful in the assessment of stent patency, in the detection of other complications such as stent fractures, and in assessment of patients with large proximal stents (e.g., 3.5-mm left main stent).
13. What is the role of cardiac CT in patients with ST-segment elevation myocardial infarction (STEMI)?
Cardiac CTA is not indicated in patients with STEMI. However, because of its superior negative predictive value, it has been shown to be an excellent tool in the triage of patients in the emergency room whose presenting symptoms include chest pain, negative biomarkers, and a nondiagnostic ECG. Patients with a negative CT (in absence of substantial artifacts) can be safely discharged from the emergency room with no significant negative short-term outcomes after 30-day and 6-month follow-up.
14. Can cardiac CT be used to differentiate between a subacute and an old myocardial infarction?
An acute myocardial infarction appears as a hypoperfused, akinetic area of myocardium, with normal thickness. An old myocardial infarction is usually distinguished by wall thinning, aneurysm formation, fatty metaplasia, calcium deposition, and hyperenhancement on delayed imaging (Fig. 10-2). Functional evaluation may reveal normal contraction (if small nontransmural infarct is present), hypokinesis, or dyskinesis.
15. Should noncoronary structures be reviewed and reported on during cardiac CT examination?
The current consensus and standard of care is to include in the final report all significant findings noted in the acquired data set, using a wide field of view. Everything that is part of the originally acquired data set should be reviewed and reported on if potentially significant (Fig. 10-3).
16. Summarize the current consensus of indications for cardiac CT in the management of coronary artery disease.
Cardiac CT is indicated in intermediate-risk patients with symptoms suggestive of coronary artery disease who are unable to exercise, have an uninterpretable ECG, or have an equivocal stress test. It is also indicated in low-risk to intermediate-risk patients with acute chest pain being treated in an emergency room in the setting of negative biomarkers and a nondiagnostic ECG. Cardiac CT is the modality of choice in the evaluation of the origin and course of coronary anomalies and can accurately exclude coronary artery disease in patients with a left bundle branch block or a dilated cardiomyopathy with heart failure. It is also useful in the assessment of symptomatic postintervention patients (coronary artery bypass grafts [CABG] and stents), in preoperative assessment before repeat CABG, and in the assessment of pulmonary and coronary veins before or after electrophysiologic procedures.
17. In the evaluation of the pericardium, what are the advantages of cardiac CT when compared with cardiac magnetic resonance imaging (MRI) and cardiac ultrasound?
Cardiac CT is superior to the other modalities in the identification and delineation of the extent of calcium deposition within the pericardium and thus is useful in the detection of a patchy constrictive pericardial process. Moreover, it is useful in the delineation of accompanying findings such as a dilated inferior vena cava (IVC), dilated hepatic veins, ascites, and mottled enhancement of the hepatic parenchyma. MRI is superior for detection of pericardial enhancement/fibrosis and pericardial adhesions (tagged cine views).
18. What are the indications for performing cardiac CT after coronary angiography?
Cardiac CT is ideal in the delineation of the origin and course of coronary anomalies. It is also useful in the serial assessment of coronary artery aneurysms and aneurysms of the sinus of Valsalva. It is useful in the assessment of coronary, pulmonary, and systemic fistulas and collaterals (Fig. 10-4).
-2.jpg)
Figure 10-2. A, Cardiac gated axial CT shows apical myocardial thinning and deposition of subendocardial low attenuation material (arrows) measuring -15 Hounsfield units, indicating fatty metaplasia in a patient with remote left anterior descending myocardial infarction. B, Cardiac gated CT in left ventricular short axis shows inferolateral subendocardial hypoenhancement that measures 35HU (arrows) and normal myocardial wall thickness, representing a perfusion defect in a patient with acute left circumflex myocardial infarction.
-3.jpg)
Figure 10-3. Cardiac CT reveals spiculated 1.5-cm mass in the right upper lobe, suspicious for malignancy.
-4.jpg)
Figure 10-4. Volume-rendered 3D views: A, superior view; B, posterior view with atria removed; C, anterior view) of coronary CTA demonstrate LAD (white arrow) arising directly from left sinus of Valsalva. A benign left circumflex anomaly is present where the LCX arises from the right sinus of Valsalva and courses posterior to the aortic root toward the left (black arrowheads).
19. Would cardiac CT be an appropriate first modality in the assessment of a 29-year-old woman with suspected Turner’s syndrome with presenting symptoms of dyspnea, a murmur, and hypertension?
Patients with suspected Turner’s syndrome may have multiple congenital anomalies, including a bicuspid aortic valve, coarctation of the thoracic aorta, an atrial septal defect (ASD) or ventricular septal defect (VSD), or partial anomalous pulmonary venous return. A comprehensive cardiac CT examination is capable of identifying all these potential cardiac congenital anomalies in a single study (Figs 10-5 to 10-7).
-5.jpg)
Figure 10-5. Cardiac gated CT angiogram in (A) LV long-axis and (B) short-axis views shows a defect in the ventricular septum with contrast spilling from the opacified LV cavity across the septum into the otherwise nonopacified right ventricle (arrows). C, The volume-rendered image shows the contrast within the LV cavity and the small shunt volume (arrow) crossing into the nonopacified right ventricle.
-6.jpg)
Figure 10-6. Systolic frame of retrospectively gated cardiac CTA at aortic valve plane shows widely open bicuspid aortic valve. Note congenital fusion of left and right coronary cusps.
-7.jpg)
Figure 10-7. Volume-rendered 3D cardiac CT shows coarctation of the aorta with a focal narrowing distal to left subclavian artery (arrows).
