The Next Generation of Cardiac Diagnostics:
David Marks, MD
Medical College of Wisconsin Interventional Cardiologist; Director, Cardiac Catheterization Laboratory
Named one of the "Best Doctors in America®" 2004 by Best Doctors, Inc.
In computed tomography (CT) scanning, x-rays obtain image data from different angles around the body and then a computer process that information to show a cross-section of body tissues and organs.And, although the technology is used to diagnose many different types of diseases, heart motion has historically made it challenging to achieve accurate CT images of blood vessels, also called coronary angiograms. But now, with the advent of the most advanced form of this imaging — the 64-slice CT — patients may experience a new type of less invasive angiography. Froedtert & Medical College of Wisconsin, the first in the world to receive this technology, is examining its application to the beating heart. David Marks, MD, discusses this new technology and how it may reduce or eliminate the need for more invasive procedures.
In industrial nations, coronary atherosclerosis is a very common disease. It’s the process in which deposits of fatty substances build up in the inner lining of an artery and impede blood flow to the heart muscle. When symptoms indicate there may be a blockage in a coronary artery, a physician will typically order a stress test. The test will look at blood flow to the heart muscle, but it doesn’t tell us anything about the anatomy of the inside of the artery. But we need that information to determine if the patient requires placement of a stent or bypass surgery to open the artery. Right now, there is only one commonly available method for looking at the anatomy of the arteries — heart catheterization. In this procedure, a thin plastic tube is inserted into an artery in the leg or arm and advanced into the coronary arteries. A dye is injected that helps image the blood flow to the arteries and the presence and location of a blockage.
Q. What tests are currently used to diagnose cardiovascular disease?
Heart catheterization is a very commonly performed test that is safe and provides very accurate information. But, it is still an invasive test, which is one reason why we are studying the use of CT scans to provide similar information.
Q. What type of information does the CT cardiovascular scan provide?With the advent of multi-slice detectors and high-powered computer programs, we’re able to reconstruct the anatomy of the heart arteries. We can look at the size of the arteries, see exactly where blood flows and determine if there is a blockage. The number of detectors is important because the heart, unlike other structures, is beating and moving in the chest. Froedtert & Medical College of Wisconsin was the first center in the world to have a true clinically operational 64-slice CT scanner. In just five seconds, this advanced scanner greatly increases our ability to get more information in as few of beats as possible. The quicker we obtain information and the more information we obtain per revolution of the CT scanner, the more accurate our study is going to be.
Now here’s the downside: Because this is brand new technology, we don’t know how accurate it is or where it is most useful. We know coronary CT scans have problems with certain situations. Patients who have heart disease typically develop calcification in the arteries and the presence of calcification makes the CT study potentially less accurate. And if the patient already has a stent in place, the CT scanner has a very hard time seeing inside the stent. The same is true for other types of metal artifacts, such as heart valves or pacemaker leads.
At the time of the procedure, we slow the patient’s heart rate with medication. The patient slides into the scanner tube and the CT scanner rapidly spins around the body, about four times a second. It sounds like a little jet engine, but the patient doesn’t see it because it’s contained within a case. It’s a very quick test — about 10 seconds — and the patient is in, out and done.
Q. How is the CT cardiovascular scan performed?
Q. What is being done to determine the accuracy of the 64-slice CT cardiovascular scan?
Froedtert & Medical College of Wisconsin is conducting a trial to help us understand the predictive power of this test. With the 16-slice and 32-slice CT scans, there was a lot of disagreement among physicians if the information we obtained was adequate for making a clinical decision. The reason that’s important is we don’t want to perform a CT scan and then end up having to do a heart catheterization to get the information we need. That would expose the patient to radiation and to dye and would be a waste of money. That’s why we need data to support the accuracy of the 64-slice CT scan and help us determine who are the most appropriate patients for this technology.
Currently, the 64-slice CT cardiovascular scan is available clinically for patients who we believe are at the lowest risk. It may be used in young patients to rule out a coronary anomaly or in someone who is at very low risk of having heart disease, but for some reason had an abnormal stress test. These types of patients are less likely to have calcification in their arteries, but they also represent a small number of patients. As we continue to collect data, what we really want to know is if someone comes in with chest pain and has an abnormal stress test, will the CT scan provide the accurate information we would get with a heart catheterization.