FDA Heart Attack diagram

Many people who have heart disease don't know it. They show no signs or symptoms. However, over time, the buildup of fat and other body chemicals clogs the arteries that feed the heart and increases the risk of a heart attack. So doctors, like cardiologist Samir Kapadia, take an inside look to assess the situation. "We typically do angiography, meaning we put catheters into the arteries and then inject dye to see if we can see different parts of the artery wall," Dr. Kapadia says.

But angiography is a costly, invasive procedure. An alternative - for some patients - is the cardiac CT-scan, which won approval from the U.S. Food and Drug Administration in 2004. Dr. Mario Garcia from the Cleveland Clinic Foundation and colleagues at eleven medical centers around the world studied the performance of what's called 16-detector scanners.

"The generation of scanners that we used for the study two years ago was the state of the art, and we used to obtain 16 images per each rotation of the scanner. A complete study will take anywhere from 30-45 seconds," he says.

Researchers compared CT-scans and invasive angiograms for almost 200 patients. The findings, published this week [July 26, 2006] in the Journal of the American Medical Association, are not an overwhelming endorsement. "If you have a positive result on a cardiac CT, the diagnosis could be in doubt," Dr. Garcia says, "but if the result is negative, you virtually exclude the possibility of having a blockage."

In other words, if the CT scan says you don't have a blockage, believe it. Dr. Garcia says if the scan indicates you do, it might not be right. "The results of our study would suggest that the use of 16-detector scanners should be used with caution or be very restricted because it could lead to false-positive interpretations."

But, the technology is evolving rapidly. Many centers are now investing in the more accurate 64-detector scanner.

Dr. Garcia says that the first generation, 16-detector machine is still a useful tool for people at low risk because it can correctly rule out blocked arteries. He says high-risk patients are better off having the invasive procedure.