Advances & Insights: Heart Health
January 31, 2009
What the news means for you
Mushabbar A. Syed, MD
Newer technology is changing practice
The Johns Hopkins study is important because previous research with the 64-slice CT scan has been done only at single centers led by people who are at the forefront of this technology. The results obviously have been good, but they don't apply to day-to-day use. Multicenter trials are more reflective of the real world; you're pooling practical experience.
CT angiography . . . can replace a stress test because it is more accurate, and in some cases it can replace a traditional angiogram because it is noninvasive.”
Also, in the Johns Hopkins study, researchers tried to be more inclusive of the patient population. They wanted to reflect that imaging can be done in a wider variety of patients, not just a selected few, which was primarily what single-center studies.
The fact that they excluded patients with high calcium scores (more than 600) is a bit controversial. However, calcium in the arteries obscures the visualization of the lumen, so sometimes you cannot tell whether there is blockage under that calcium.
Risks of both procedures
It's important that we evaluate this new technology with a balanced perspective. It is a noninvasive angiography that can be completed on an outpatient basis in about half an hour. Conventional angiograms take longer and require more recovery time. There is also a small risk (1 to 2 percent) of bleeding and infection because this is an invasive procedure in which a catheter is inserted. There ís an even smaller risk of heart attack or stroke.
“Radiation in the newer scanners can be manipulated and decreased by 40 to 60 percent.”
The risks in CT are related to the dye, which can cause reactions in some patients. Radiation exposure in CT scans is slightly higher than in coronary angiography but fairly comparable to that in a nuclear stress test. However, radiation in the newer scanners can be manipulated and decreased by 40 to 60 percent. The Advanced Cardiovascular Imaging Center in the UK Gill Heart Institute uses these low-radiation scanning techniques.
As for the cost, the conventional test is more expensive. It requires more equipment and more staff, and more procedures are involved. In a CT scan, there is a CT technologist, a physician and possibly a nurse. The equipment is also less expensive than it is for the conventional angiogram.
As a newer technology, CT scanning has generated some controversy. There are some very strong proponents who say it should be used more routinely in a larger patient population, but the studies aren't there to back up this claim. There's also a push from the industry making these scanners. That hurts the field and limits the scientific growth. As a result, some people have become reluctant to use CT scanning.
Where a CT scan is appropriate
At UK, we have adopted an evidence-based approach to this issue. We try to follow the American College of Cardiology guidelines for appropriate indications and use CT angiography in the following instances:
1. Patients with chest pain and an unclear stress test.
2. Patients with recurrent chest pain and normal stress test.
3. Evaluation of suspected coronary anomalies.
4. Evaluation of patients with chest pain who have intermediate pretest probability of CAD and normal or borderline abnormal electrocardiogram.
5. Evaluation of coronary arteries in patients with new onset failure to assess the cause of failure.
6. Other uncommon indications include:
- Patients with technically limited images from echocardiogram, MRI or TEE.
- Pulmonary vein imaging prior to ablation.
- Coronary vein mapping prior to biventricular pacemaker.
- Coronary arterial mapping prior to repeat cardiac bypass surgery.
I believe CT angiography is a very good technology if used appropriately. In many cases it can replace a stress test because it is more accurate, and in some cases it can replace a traditional angiogram because it is noninvasive. Some data even suggests CT angiography decreases the utilization of other resources. For example, further cardiac testing can be avoided if CT angiography is normal.
However, it's a relatively new field so there's not a great deal of data available. Future research should further identify the best patient population and appropriate clinical circumstances for using this technology.
Additionally, we know more about possible patient outcomes after a conventional angiogram or a stress test. If a person has normal results on these tests, his or her chances of having a heart attack within the next 12 months are considered low. On the other hand, the prognostic value of CT angiography is still evolving, but the early results are very good.
Dr. Syed is director of cardiovascular CT and MR imaging at the UK Gill Heart Institute and associate professor of medicine in the UK College of Medicine.
Can noninvasive CT scans replace conventional coronary angiography?
Coronary artery disease (CAD), a blockage of arteries that carry blood to the heart, is the leading cause of death for both men and women in the United States, killing more than 650,000 people a year, according to the Centers for Disease Control and Prevention. In patients suffering chest pain and those whose EKG or stress tests suggest CAD, a swift and accurate diagnosis is crucial. Typically, physicians have used coronary angiography for diagnosing heart disease in these instances. More recently, many are turning to a newer test ñ CT scans that display 3-D images of the heart.
In the conventional angiogram, dye and X-rays are used to see inside coronary arteries. A catheter is put into a blood vessel in the arm or groin. The tube is then threaded into the coronary arteries, and the dye is injected. Special X-rays are taken while the dye is flowing through the coronary arteries.
In a CT angiogram, X-rays and computers create images that show three-dimensional cross-sections, or slices, of the heart. Because the dye is injected into a vein in the arm rather than into a coronary artery, as in traditional angiography, and a catheter is not used, CT angiography is considered noninvasive.
Research so far has shown that newer CT scans can be as useful as the older, traditional angiography in selected patients; however, more research is needed before this technology becomes routine clinical practice.
CT vs. conventional angiography
Researchers at Johns Hopkins University set out in 2005 to assess the accuracy of the CT test in the first multicenter study of multidetector CT angiography. They looked at 291 patients at nine hospitals in seven countries. Participants were age 40 or older, had suspected symptomatic coronary artery disease, and had been referred for conventional coronary angiography. They underwent calcium scoring and a 64-row CT scan before having a conventional angiogram.
“Researchers concluded that CT angiography cannot yet replace conventional coronary angiography in symptomatic patients with high probability of CAD.”
The researchers found that the newer test had a reliable accuracy for diagnosing CAD, and disease severity detected by both tests was similar. However, they concluded that CT angiography cannot yet replace conventional coronary angiography in symptomatic patients with high probability of CAD because of the number of false negatives it yielded in this patient population.
The strengths of the study include the large number of patients, multicenter design, broad spectrum of clinical characteristics of the patients and use of independent labs for data analysis.
What some say about CT scans
Medicare pays for CT scans, which cost around $700. Conventional angiograms cost about $1,500, according to Johns Hopkins. But while the newer technology is widely used, it does have its detractors.
In an editorial appearing in the same issue of the New England Journal of Medicine as the Johns Hopkins study, Drs. Rita Redberg and Judith Walsh described CT angiography as bombarding patients with radiation many orders of magnitude greater than traditional radiographs.
Aside from the risk of radiation, the authors argue that CT angiography may lead to greater incidental findings, which in turn can lead to additional, often unnecessary procedures such as biopsies, revascularizations and additional diagnostic tests.
Nevertheless, they point out two benefits of CT angiography: It's much faster than the conventional test, taking only 10 minutes; and it produces higher-resolution photos, color, and 3-D images of the heart and vessels.
For more information, see:
- Diagnostic performance of coronary angiography by 64-row CT,New England Journal of Medicine , v. 359, no. 22 Nov. 27, 2008
- Pay now, benefits may follow - The case of cardiac computed tomographic angiography,New England Journal of Medicine , v. 359, no. 22, Nov. 27, 2008.
- Newer heart test may not be better, CNN.com, Nov. 27, 2008
- Coronary angiography, MedlinePlus, National Library of Medicine
- CT angiography, RadiologyInfo, Radiological Society of North America
UK HealthCare cardiac resources - UK Gill Heart Institute
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