Cardiac Imaging: Coronary CTA

Last Editorial Review: 9/23/2005

WebMD Live Events Transcript

New imaging techniques are giving doctors a clearer picture of the heart and allowing them to better manage heart disease. A Coronary CTA is a heart-imaging test to determine if either fatty deposits or calcium deposits have built up in the coronary arteries, which supply blood to the heart muscle. We discussed the latest noninvasive cardiac imaging techniques with Richard White, MD, and Mario Garcia, MD, from the Cleveland Clinic Heart Center. They joined us on Aug. 16, 2005.

The opinions expressed herein are the guests' alone and have not been reviewed by a WebMD physician. If you have questions about your health, you should consult your personal physician. This event is meant for informational purposes only.

MODERATOR:
Welcome to WebMD Live, Dr. White and Dr. Garcia. Thank you for joining us today.

GARCIA:
Thank you. It's a pleasure to join you.

WHITE:
Thank you for the invitation to be here.

MODERATOR:
Please explain the role of imaging in diagnosing heart disease.

GARCIA:
There are different tests that we have to do in order to characterize the nature of a patient's symptom or the likelihood of that patient having a cardiac problem based on their reflectors. The most common imaging tests that we use in cardiovascular medicine are echocardiography or ultrasound of the heart, nuclear profusion imaging, cardiac magnetic resonance, or MRI, and most recently, cardiac CT, computer tomography.

WHITE:
Imaging could be said to have begun even with an X-ray of the chest, and the fundamental purpose is to get some direction as to the key problem at hand and then add on with more sophisticated or more targeted diagnostic imaging to delve further into it. And in many ways, it's to give the user who might be a surgeon -- or whoever is administering care to the patient -- something in their mind's eye which has direct benefits, such as reduced exploratory surgeries.

MODERATOR:
Let's talk about the advantages and disadvantages of noninvasive heart procedures for diagnosis.

WHITE:
The one disadvantage of the noninvasive imaging techniques is they do not provide the opportunity of a measurement of a pressure or to sample the blood directly, so we are not provided direct measures of the ability of the blood to carry oxygen or the pressure generated by a pumping chamber, although we can surmise some of these things indirectly through noninvasive imaging. The advantage is in the title; it is noninvasive.

GARCIA:
The invasive diagnostic methods in many cases are more accurate. Nevertheless, they do carry a significantly higher cost and in general, a higher risk to the patient.

MODERATOR:
When would you decide to use noninvasive vs. invasive procedures?

GARCIA:
Depends on the information that we are trying to achieve but in general, we like to use noninvasive diagnostic methods as a start and only recur to invasive methods when we need additional information.

MEMBER QUESTION:
Are there times when you would go straight to the cath lab to see what is going on?

WHITE:
Yes. Certainly catheterization of the heart is the backbone of understanding coronary disease and indicating its treatment, whether it be by a catheter based or a surgery, so I think it's expected a patient would go directly there if there is a high suspicion of a narrowing of the arteries which would need such intervention, but the suspicion may be preceded by a noninvasive indicator.

MODERATOR:
Can you please explain how coronary CTA works?

WHITE:
The basic principles of CT involve a rotating X-ray beam with the detection, on the other side of the patient, of the ability of the different tissues to absorb the X-ray. And because it's viewing the body from multiple different angles and can be done over a long portion of the body, you end up with a three-dimensional column of information that can be viewed in multiple directions.

MODERATOR:
What is involved from a patient's perspective?

GARCIA:
The patient can have this procedure done in the hospital setting or in an outpatient setting. The preparation required is minimal. An intravenous catheter is placed in a vein in the arm. A drug is typically used to control or slow down the heart rate, and contrast is injected into the vein. Then the procedure is performed typically over a few seconds. The patient can get dressed and drive back home immediately, practically after the procedure.

MODERATOR:
How long does it take to get results?

WHITE:
From start to finish the cardiac CT examination takes approximately 10 minutes. The information is made available to the noninvasive imager immediately. Depending on the presence or absence of disease and the extent of disease, the interpretation might take anywhere from five minutes to 15 minutes.

MODERATOR:
What specifically are you looking for with this CT?

GARCIA:
Interpretation of this study requires specialized training. A cardiovascular imaging specialist from radiology or cardiology usually performs this. In the best circumstances, it's a combined effort from both the specialties.

MEMBER QUESTION:
Is this available in most hospitals? Has it been around for a while or is it new?

WHITE:
Versions of this technology have been available in a select few major centers over the past five years. As the technology has improved, the value of the CT for the heart has been more and more appreciated and now you're seeing it in most major centers and we're starting to see it propagating out in the community.

GARCIA:
Even though the technology is rapidly becoming available, the number of adequately trained physicians who interpret this image is still limited and patients should inquire about the expertise and training of the doctors performing this test.

MEMBER QUESTION:
How accurate is this test?

WHITE:
I think the experience to date would support the idea that it is accurate, especially accurate in excluding significant disease. It is highly accurate in detecting the presence of significant narrowing in major arteries but limited in its ability to grade the degree of narrowing.

GARCIA:
Even though occasionally it's difficult to differentiate a moderate from a severe narrowing, this technique is unique to actually identify the presence of plaques that are potentially vulnerable to precipitate a future cardiac event. Currently there is no other noninvasive test that could provide this type of information.

MEMBER QUESTION:
Is it possible to detect blockage of small branches such as D1 or D2 branches of LAD?

WHITE:
It is possible, but it would be asking a lot of the technology to consistently do that at this point.

GARCIA:
To some extent, the accuracy depends on the caliber or diameter of the vessel and it is accepted that vessels that are smaller than 1 and-a-half or 2 millimeters in diameter, whether they're branches or main vessels, are more difficult to characterize by CT.

MEMBER QUESTION:
Can this technology be used in patients with stents placed in coronary arteries?

GARCIA:
In most cases the technology -- as it exists today -- cannot accurately identify the presence of a narrowing inside a stent, unless the stent is completely occluded. Therefore, we do not recommend this test to evaluate for stenosis after stent procedures in the heart.

MODERATOR:
What kind of research are you doing at The Cleveland Clinic with coronary CT and other types of cardiac imaging?

WHITE:
We have a special focus on the use of the CT angiogram to look at early changes in the coronary arterial wall that might indicate more or less likelihood of rupture down the road. And that involves comparison with the current gold standard, which is intravascular coronary ultrasound.

GARCIA:
We are also performing studies to determine whether this technology can obviate the need for catheterization in patients who have mechanical or artificial heart valve, in patients who require surveillance catheterization -- such as patients with heart transplant -- and in patients who have a cardiomyopathy of unknown cause.

MEMBER QUESTION:
How much more accurate is the CT compared to the standard echocardiogram?

GARCIA:
They measure different things. The echocardiogram is a great test to visualize the cardiac chambers, the function of the heart muscle, and the status or the condition of the heart valve, whereas the most important value of cardiac CT will be its unique ability of visualizing the coronary arteries.

MODERATOR:
We have a 3-D image of the heart made by coronary CT.

GARCIA:
It's a 3-D image of the heart that has been obtained in a patient that had symptoms of chest pain and had a negative stress test. The arrow points at a severe narrowing and one of the main coronary arteries, the left anterior descending.

MODERATOR:
Before coronary CT, what kind of testing would this patient have faced to determine this blockage?

GARCIA:
Before cardio CT this patient would have continued with symptoms of chest pain or possibly experienced a heart attack until an invasive cardiac catheterization would be performed.

MODERATOR:
It is really quite extraordinary to see the heart in this way.

MEMBER QUESTION:
Who is a good candidate for coronary CT? And aside from those with stents, who is not a good candidate?

WHITE:
Although there's quite a bit of debate about that very issue, we believe that a patient who already has a high likelihood of having stenotic coronary artery disease, in other words, disease with significant narrowing, should undergo a heart catheterization and strong indicators include classic chest pain with exercise, positive stress examinations, symptomatic patients of advanced age, to a large extent, and patients with known coronary disease and have had prior bypass or grafting.

We do not feel the CT is a replacement for a needed catheterization, but in approximately 30% of patients that undergo catheterization there is a lower suspicion and it is simply used to rule out the disease process; those are the patients where we think the CT is warranted because the narrowing can be ruled out and there can be a greater appreciation for the amount of early disease which may lead to future events (roughly 30%).

MEMBER QUESTION:
Is this still considered an experimental procedure? Or is it established enough that many insurance companies and Medicare will pay for it?

GARCIA:
There is accepted consensus from experts in the field that this technology is no longer experimental for diagnosing coronary artery disease. The reimbursement already exists for patients who have symptoms of chest pain; nevertheless, it is not yet available for patients who are not experiencing any chest pain symptoms or shortness of breath.

WHITE:
I don't think the experimental and reimbursement to be mutually exclusive. At this point we do not regard the technique to be experimental, but it has not undergone rigorous assessment with multicenter studies and large patient population data analysis to convince the insurers that it's fully established. One thing that has been problematic is the rapid advancement in the technology, which makes it difficult to reflect in such studies the current state-of-the-art.

MEMBER QUESTION:
Can the CT help with A-Fib or give more info and how to treat it differently?

WHITE:
It is commonplace for us to use the CT in the evaluation of patients with atrial fibrillation, but it is used once it has been decided that the patient needs interventional treatment with pulmonary vein isolation. We rely on it to show the anatomy of the pulmonary veins in order to direct the therapy and then used quite often after the therapy to evaluate for any possible complications. But it does not tend to tell us about the nature of the atrial fibrillation.

SLIDESHOW

Heart Disease: Causes of a Heart Attack See Slideshow

GARCIA:
Pulmonary isolation is a catheter-based procedure that is gaining popularity and has been shown in many patients that it can correct or improve the symptoms of atrial fibrillation.

MODERATOR:
What do you see in the future for cardiac imaging? What new technologies are on the horizon?

WHITE:
I believe we are entering somewhat of a "what's it all mean" stage, and I think there is an expectation for us to start to weigh the current technologies against each other and assess their value for "what they bring to the table," so to speak. The basic needs of patient diagnosis and care aren't changing so much but the approaches to answering those key questions. I think we are seeing more and more direct cross-referencing between the imaging types including the fusion of images -- the actual creation of images off scanners that have combined capabilities. This will allow us to better assess where we might need to go in the future. I think the key breakthroughs will probably be in pharmaceuticals, such as different kinds of contrast agents that target the tissues and we already have the ability to scan for that.

GARCIA:
One of the challenges we are facing is how to continue to deliver the best possible care to the patient and at the same time, control the rapidly growing costs. In that regard, physicians who are currently involved in the use of imaging diagnostic tests will have to become very familiar with all the available technologies and choose wisely which are most likely to benefit a patient while controlling costs.

MODERATOR:
Gentlemen, we are almost out of time. Before we wrap things up for today, do you have any final comments for us?

GARCIA:
Specific information about this and other imaging tests is available through The Cleveland Clinic web site.

MODERATOR:
We are out of time. Thanks to Richard White, MD and Mario Garcia, MD for joining us today. For more information, please visit The Cleveland Clinic Heart Center online at www.clevelandclinic.org/heartcenter.

©1996-2005 WebMD Inc. All rights reserved.

Health Solutions From Our Sponsors