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Archived Issues of Radiology Rounds
MGH Department of Radiology Website
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Coronary CTA
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- Coronary angiography remains the “gold-standard” for evaluating coronary artery disease
- Coronary CTA is a non-invasive alternative to angiography for some patients
- The clinical indications for coronary CTA are not completely established but patients most likely
to benefit are those who have atypical symptoms and are at intermediate coronary risk
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The
current “gold standard” to assess stenosis in diseased coronary
arteries is selective catheter-based angiography. CT-based coronary
angiography is a new, non-invasive alternative for some patients, made
possible by the development of high-speed multi-detector CT (MDCT)
scanners. MDCT scanners have an array of detectors that collect data
from 4-64 slices with one revolution of the CT gantry. These scanners
acquire imaging data extremely rapidly, which allows selective imaging
of the heart in a specific phase of the cardiac cycle while a bolus of
contrast agent passes through the arteries. Cardiac gating and short
breath-holds ensure that the images are free from motion artifacts.
After data processing, images can be viewed as cross-sections of the
heart, 3-D reconstructions of the heart and coronary arteries, and 3-D
reconstructions that appear as planar images along the length of the
arteries.
Clinical studies have shown that coronary
CTA is reliable for the non-invasive assessment of stenoses in the
proximal and mid regions of the coronary arteries, where the majority
of stenoses are found. Both the sensitivity and specificity for the
detection of clinically significant stenoses are about 90%.
Coronary CTA does have some advantages over catheter-based angiography.
First, coronary CTA can image blood vessel walls and the anatomy of the
heart and can, therefore, be used to assess the pericardium, cardiac
chamber size and shape, and to detect ventricular aneurysms. Secondly,
it can also be used to map the pulmonary veins prior to pulmonary vein
ablation for atrial fibrillation or biventricular
pacemaker placement. In addition, both calcified and non-calcified
atherosclerotic plaques can be seen in coronary CTA images and,
therefore, it is possible to assess a patient’s total calcified and
non-calcified plaque burden as high, medium or low. However, it is not
yet possible to reliably distinguish between lipid-rich and fibrous
plaques, and predict which lesions are more likely to rupture and cause
an acute cardiac event. |
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Volume rendered 3-D coronary CTA showing a stenosis in the left anterior descending artery.
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indications for Coronary CTA
At
this time, the clinical indications for coronary CTA are not completely
established. However, patients who are most likely to benefit from
coronary CTA are those who have atypical symptoms and are of
intermediate risk for coronary artery disease. A nuclear cardiology
stress test is more appropriate to define myocardial ischemia. In
patients with typical angina, conventional angiography may be more
suitable, as this procedure can be followed by an intervention.
However, in rare cases, poor perfusion of the myocardium is missed
during a nuclear cardiology test because of multiple blockages in all
the coronary arteries. If the nuclear cardiology examination is
negative but there is reason to think that perfusion is poor,
non-invasive coronary CTA can show whether there are stenoses present.
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Advantages |
Disadvantages |
| Coronary CTA |
Non-invasive
Can rule out coronary stenoses with high accuracy
Can establish patency of by-pass grafts and stented arteries
Can visualize cardiac and coronary venous anatomy
Can assess calcified and non-calcified plaque burden
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Not suitable for patients with irregular heart beat or those who are pregnant
Need ß-blocker to lower HR to < 65
Difficult to assess in-stent re-stenosis
Patients must hold breath 15-20 sec, 3-4 times
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| Coronary Angiography |
Well established “gold standard”
Can perform interventions (e.g. angioplasty, stent placement)
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No visualization of wall structures
Cannot detect early disease before lumen narrowing
Risk of groin hematoma, pseudoaneurysm, or A/V fistula, 1-3%
Risk of heart attack or stroke, 0.1%
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A. Image from the same patient as that on p. 1, showing 3-D reconstruction that flattens the artery into a single plane. B. Catheter-based angiography confirms the presence of the stenosis, indicated by arrows.
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Tomographic image from Coronary CTA, showing the coronary atery as it leaves the aorta.
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Patient Preparation and Procedures
In
order for coronary CTA imaging to be successful, the heart rate must be
less than 65. Therefore, if a patient’s heart rate is more than 70, he
or she must take a ß-blocker the evening before and the morning of the
scan. If the heart rate is too high immediately before the scan,
intravenous ß-blockers may be administered. No food or drinks should be
consumed in the last 4 hours before the scan. As a precaution when
using contrast agents, (see the October 2004 issue of Radiology Rounds
on Minimizing Adverse Reactions to Contrast Agents,
for more information) all patients must have a recent measure of their
serum creatinine level. Pregnant patients and those with poor renal
function, multiple myeloma, or a history of anaphylactoid reactions to
iodinated contrast agents may be excluded. Patients may take their
regular medication, with the exception of metformin (Glucophage), which
should be discontinued for at least 48 hours after the scan.
The
coronary CTA scan takes 10-15 minutes to perform. As the heart is
scanned, 80-100 ml of non-ionic iodinated contrast agent is injected
the patient through an IV line at a rate of 3-5 ml/s to maintain
homogeneous vascular contrast throughout the scan. During the scan, the
patient will be asked to hold his or her breath 3-4 times for
approximately 15-20 seconds. The images will be displayed as volume
rendered 3-D images of the heart and coronary vessels and flattened
images showing the full length of the coronary arteries, as well as
standard tomographic images. Radiology reports will be available within
24 hours.
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Scheduling
Coronary
CTA examinations may be scheduled online through Radiology Order Entry
(ROE) or by calling the CT Operations Manager, 617-724-8519.
Most insurance carriers cover coronary CTA (but not cardiac CT for calcium scoring).
Further Information
For
further questions on coronary CTA, please contact Cardiac Radiologist Suhny Abbara, M.D., 617-726-0796 or Cardiologist Ik-Kyung Jang, M.D., Ph.D., , 617-726-9226.
This article provided useful information about the appropriate use of imaging studies:
 
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References
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Achenbach S, Giesler T, Ropers D, et al. (2001) Detection of coronary artery stenoses by contrast-enhanced, retrospectively ECG-gated, multi-slice spiral CT. Circulation 103:2535-2538
Herzog, C, Dogan, S, Diebold, T, Khan, MF, et al. (2003) Multi-detector
row CT versus coronary angiography: preoperative evaluation before
totally endoscopic coronary artery bypass grafting. Radiology 229: 200-8
Nieman K, Oudkerk M, Rensing BJ, et al. (2001) Coronary angiography with multi-slice computed tomography. Lancet 357:599-603
Nieman K, Cademartiri F, Lemos PA, et al. (2002) Reliable noninvasive coronary angiography with fast submillimeter multislice spiral computed tomography. Circulation 106:2051-2054
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Rodenwaldt, J.(2003) Multislice computed tomography of the coronary arteries. Eur Radiol 13: 748-57.
Ropers D, Baum U, Pohle K, et al. (2003) Detection
of coronary artery stenoses with thin-slice multi-detector row spiral
computed tomography and multiplanar reconstruction. Circulation 107:664-666
Schoenhagen, P, Halliburton, SS, Stillman, AE, Kuzmiak, SA, et al. (2004) Noninvasive imaging of coronary arteries: current and future role of multi-detector row CT. Radiology 232: 7-17
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