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What is cardiac computed tomography angiography?
Cardiac computed tomography angiography (CCTA) is an imaging method that uses a computed tomography (CT) scanner to look at the structures and blood vessels of the heart.
These scanners have been used to image blood vessels in other parts of the body for many years. The heart vessels (coronary arteries), however, are more difficult to view because they are small and move quite fast with the heartbeat. CT scanners are now fast enough and can image with enough detail to see the small moving coronary arteries very well.
Prior to CCTA, to directly look at the blood vessels of the heart, one would have to undergo an invasive (inside the body) procedure called cardiac catheterization. CCTA is a non-invasive (outside the body) way to evaluate the blood vessels of the heart. In some situations a CCTA can be done instead of, or in addition to, a stress test.
How is a CCTA the same as or different from a stress test?
Both CCTA and a stress test may be used when more information about the heart is needed. Both can help tell whether a symptom is likely related to heart disease. The two tests, however give somewhat different information.
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Stress tests look at the electrical activity of the heart and the heart’s muscle function or blood flow patterns while the heart is under stress from exercise or medications. In this way, stress tests find areas of reduced blood flow to the heart, which imply a blockage of the coronary artery feeding blood to that area.
A CCTA, on the other hand, “looks” directly at the coronary arteries and can estimate the amount of blockage. Using this information, a large blockage of a coronary artery likely indicates an area of ischemia (limited blood supply.) In some cases, both tests may be used.
How is a CCTA the same as or different from a cardiac catheterization?
CCTA and cardiac catheterization have a lot in common. Both tests use X-rays and imaging contrast to look at the heart vessels to understand their structure.
Cardiac catheterization uses thin plastic catheters that pass from an artery in the leg up to the heart and inject imaging contrast directly into the coronary arteries. This allows for very precise pictures of the arteries – but also has a small, but real, risk of injury during the procedure.
CCTA uses imaging contrast injected through a vein in the arm and takes pictures of the heart vessels from outside the body. The images produced by cardiac catheterization are more finely detailed. However, the images from a CCTA are detailed enough for doctors to make decisions that are 95-99 percent accurate in patients without severe disease.
What other information can a CCTA provide?
Unlike coronary catheterization or stress testing, CCTA sees into the wall of the coronary artery and can estimate the extent of coronary disease. Physicians can measure the amount of calcium in the wall of the coronary arteries to help predict the risk of heart attacks and cardiac death. The extent of calcium may help doctors decide how aggressively to treat a patients’ risk factors for heart disease. This possibility is being actively researched at the UW and around the world.
CCTA can also create complex 3-dimensional models of the heart and related structures. These can help doctors understand the anatomy of a heart that developed abnormally at birth. The data can also be used by cardiologists that specialize in the heart’s electrical system, to build a 3-D computer model of the atria and cardiac veins to help with procedures involving these structures.
Who is a good candidate for CCTA?
- Patients with symptoms that could be due to ischemia (including chest discomfort, shortness of breath with activity, a sudden decrease in the ability to do physical activities) who cannot undergo optimal stress testing due to the inability to exercise or due to an abnormal resting electrocardiogram (ECG)
- In addition, those patients who have had a stress test that could not rule out or in a problem with blood flow to the heart may also be candidates
- Those born with possible or known structural defects of the heart, coronary arteries, or the major blood vessels coming from the heart may benefit from CCTA to define the precise anatomy
- Patients with a newly diagnosed cardiomyopathy (weak heart muscle), who need an evaluation of the coronary arteries
- Patients with suspected masses or pericardial (covering around the heart) abnormalities without good enough images from an echocardiogram or MRI
- A patient planning an atrial ablation procedure or placement of a pacemaker lead in the cardiac veins that needs anatomic mapping before the procedure
- Patients with an acute onset of possible cardiac symptoms, who need to know if there is coronary disease (usually in the emergency room)
Who is not a good candidate for CCTA?
The following may not be good candidates:
- Those patients for whom it would be unsafe to have imaging contrast or X-rays: mainly women who are pregnant and patients with abnormal kidney function
- CCTA requires a slow regular heart rate; so those patients with irregular heart rhythms or who have fast heart rates and are unable to take medications that slow the heart are unlikely to have accurate images
- Patients who are not able to lie flat, follow voice instructions, or hold their breath for up to 20 seconds
Are there any dangers?
As stated above, the imaging contrast can be irritating or cause injury to the kidneys; however this is very unlikely in patients with normal kidney function. In addition, some people can have allergic reaction to imaging contrast. In patients who have not had problems with contrast in the past, this is also unlikely. For patients who have had reactions to contrast in the past, medications can be given before the test to protect from repeat reactions.
Other problems are possible, but not likely – such as significant bleeding or infection at the IV site. In addition, if there is a problem with the IV, the contrast can be injected into the skin instead of the vein which can be mildly irritating. Lastly, as we give medicines to slow the heart, the heart could slow too much. We follow carefully developed guidelines and monitor heart rates at all times to help avoid this.
Are there specific instructions prior to testing?
Prior to a CCTA, patients should have nothing to eat four hours prior to the test. Patients can and should drink water four hours prior to the test. We encourage drinking extra water up to test completion as it helps flush the kidneys.
Patients should skip morning diuretic medicines (water pills) until the test is over. Patients taking medicines for diabetes should speak with the nurse in the CCTA preparation (prep) area before the test for instructions.
Medicines that slow the heart rate should be taken normally prior to the CCTA. The most common medicines in this category are metoprolol, atenolol, carvedilol, verapamil, diltiazem and others in the classes of beta-blockers or calcium channel blockers.
How is CCTA performed?
CCTA is performed in both the inpatient and outpatient settings. Outpatients arrive about an hour and a half before the scan to a prep area. In the prep area, patients are connected to a cardiac monitor, and a nurse will place an intravenous (IV) line into a vein in the arm. Medicine is given by mouth and IV as necessary to slow the heart rate.
The patient then goes to the CT scanner room and the following steps are taken:
- The patient is made comfortable on the CT table and the IV is connected to the contrast injector
- Initial pictures of the chest are taken for positioning
- Heart pictures without contrast are taken for a calcium evaluation
- A small dose of imaging contrast is injected and the time it takes for the contrast to get to the heart is measured
- The imaging dose of contrast is injected and CCTA pictures are taken
How long does it take?
From arrival to, and departure from, the prep area, the total time is about two hours. The time of the CCTA itself is 10-20 minutes. The actual time the scanner takes to make the final heart pictures is 5-7 seconds.
How do I get my test results?
In all cases, the results of the CCTA will be sent to the physician who ordered the test. In many cases, we will be able to give you initial results after the test.