Diagnosing Coronary Artery Disease in the 21st CenturyCoronary artery disease is the single leading cause of death in America today. Unfortunately, accurately diagnosing coronary artery disease — the first step toward intervention — has always been an invasive procedure. Until now.
In 2005, Froedtert & the Medical College of Wisconsin became one of the first medical centers in the world to explore the use of a new technology to detect coronary artery disease: the 64-slice Volume Computed Tomography, or VCT. VCT scanning is an updated version of CT scanning. Like a CT scan, it’s a non-invasive procedure. However, unlike traditional CT scans, the VCT is able to quickly capture incredibly sharp images of the moving heart, including the coronary arteries. Researchers at Froedtert & the Medical College of Wisconsin are putting this new technology to the test, comparing VCT scanning with cardiac catheterization, the current “gold standard” in detecting coronary artery disease.
Diagnosing an Arresting Problem “We’re trying to evaluate whether we can use VCT scanning to replace heart catheterization in a percentage of patients,” David Marks, MD, Medical College of Wisconsin interventional cardiologist and director of the Cardiac Catheterization Laboratory at Froedtert & the Medical College of Wisconsin said. “We’re currently conducting a study to evaluate the accuracy of the VCT scanner compared with coronary angiography.”
The clinical study has the potential to revolutionize cardiac care. In essence, researchers are looking for a better way to diagnose coronary artery disease — the buildup of fatty substances in the blood vessels supplying the heart. Currently, the only definitive diagnostic test for coronary artery disease is a cardiac catheterization. Stress tests can indicate a possible disturbance in blood flow to the heart, but cannot determine the severity or location of a blockage. Cardiac catheterization reveals that information by tracking the flow of blood through the coronary arteries.
Cardiac catheterization is a highly accurate, but invasive test. A thin, flexible tube is inserted into an artery in the leg or arm and advanced into the coronary arteries. Dye is injected and images are taken as the dye flows through the arteries. Although cardiac catheterization is a very safe procedure, it “does entail some degree of risk, to the vessels to the brain and vessels to your heart,” W. Dennis Foley, MD, Medical College of Wisconsin radiologist and director of Digital Imaging said. There is also a risk of infection or bleeding, not to mention possible discomfort from the procedure itself or the hours of bed rest required afterwards.
The Promise of VCTBut what if physicians were able to non-invasively visualize the coronary arteries? Until recently, that was impossible. While CT scanning provides highly detailed images of internal body structures, scanning the moving heart has always presented a challenge.
The 64-slice VCT scanner is the first to provide clear images of the coronary arteries.
“With the VCT, pictures are taken very rapidly during the circulation of a contrast medium (x-ray dye) through the heart,” Dr. Foley explained. “Then, we can reconstruct the anatomy in three dimensions to define the coronary arteries, the chambers and the valves of the heart. We time acquisition of images to the cardiac rhythm to obtain the clearest pictures.” In just five seconds, the VCT scanner can obtain images that reveal the size of the arteries, location of any blockages and the flow of blood through the arteries — all non-invasively.
For patients, a VCT scan is much more comfortable than a cardiac catheterization. Instead of a catheter threading its way to the coronary arteries, a small amount of dye is injected through a vein at the front of the elbow. Medication slows the patient’s heart rate, and the patient slides into the scanner tube while the CT scanner spins rapidly around the body. The entire process generally takes less than 15 minutes. And because it’s non-invasive, patients are able to avoid sedation and hours of bed rest that accompany a cardiac catheterization.
Establishing AccuracyWhile the VCT scanner shows incredible promise, “the accuracy still needs to be evaluated. It’s also not clear right now for which patients it’s appropriate,” Dr. Marks said. The current clinical trial will help answer those questions.
“Everyone in the study has already been scheduled to have a heart catheterization,” Dr. Marks said. Participants have at least one symptom of coronary artery disease and catheterization is required to confirm the diagnosis. But as part of the research, “they also get a state-of-the-art CT scan” within 48 hours, Dr. Marks said. The researchers then compare test results. “What we really want to know is if someone comes in with chest pain and has an abnormal stress test, will the VCT scan provide the accurate information we would get with a heart catheterization?”
More than 50 patients have already been scanned as part of the study. More participants are needed, though, to complete the trial. “Iif people are excited about new technology they might consider enrolling in a clinical trial. Truly, the only way to answer these questions is by doing a study. You need clinical trials to show that new innovations are safe and effective. And that’s what we try to do,” Dr. Marks said.
21st Century Cardiac CareWhile VCT scanning is not for everyone — the scanner cannot accurately image highly calcified areas, for instance — physicians are excited about the potential of VCT.
“We think this test might be good for patients with somewhat atypical symptoms, such as a low-risk profile but a positive stress test,” Dr. Marks said. “The other subset of patients who might benefit are those who present to the emergency room with chest pain. There are many other causes for chest pain other than just heart disease, so the VCT scanner may be a very effective diagnostic tool in that circumstance.”
If the study proves the accuracy of the scanner, VCT scanning may eventually be used to diagnose asymptomatic coronary artery disease. “The CT images have better contrast than heart catheterization, so you can look at differences in tissue,” Dr. Foley said. “That lets us see what’s in the vessel wall. In particular, we can look at plaque which is non-calcified, called ‘vulnerable plaque.’ From 30 percent to 50 percent of patients who have an acute myocardial infarct (heart attack) have had no preceding symptoms, and it is thought this is the factor that causes them.” Patients found to have ‘vulnerable plaque’ may then be advised to begin medical therapy to decrease the very real risk of a future heart attack.
Leading the WayFroedtert & the Medical College of Wisconsin were the first to participate in this important study, and Froedtert Hospital remains the core laboratory. “Cardiac services are going to change and eventually become more non-invasive, and we need to be prepared to go that direction,” Dana Bode, RN, director of Cardiac Services said. “The VCT scanner and research study certainly keep us in the forefront.”
Source: Froedtert Today
Date: June 2006
|Medical Reviewer: ||David Marks, MD|
|Medical College of Wisconsin interventional cardiologist|
|Director, Cardiac Catheterization Laboratory||