Nov. 26, 2008 -- Newer CT scans are pretty good at detecting clogs in arteries -- but they aren't ready for prime time, a new study suggests.
The gold standard for finding clogged arteries is the angiogram. This requires inserting a thin catheter into an artery in the groin and running it up into the arteries near the heart. It takes 30 to 45 minutes plus another hour of recovery; complications, though rare, include heart attack and stroke.
CT scans take just a few seconds, and no blood is shed. The downside is that they expose patients to relatively high levels of radiation. A 2007 study linked up to 2% of all U.S. cancers to CT radiation.
When obtaining pictures of the heart, CT scanners with a higher number of detectors provide more detailed images in a shorter amount of time. So the newer CT scanners, which use "64-row" technology, give much better images than the older "16-row" machines.
But are they good enough for routine use?
To find out, Johns Hopkins researchers Julie M. Miller, MD; Joao A.C. Lima, MD; and colleagues at nine centers in seven nations performed 64-row CT scans on 291 patients suspected of having blocked arteries. After getting the CT scans, all the patients underwent angiography.
As it turned out, 56% of the patients did indeed have angiogram-demonstrated coronary artery disease. And the CT scans worked pretty well. They detected blocked arteries 85% of the time, and 90% of the arteries they said were blocked actually had blockages.
On the other hand, the CT scans misclassified 13% of patients.
"CT angiography cannot replace conventional coronary angiography in this population of patients at present," Miller and colleagues conclude.
However, the researchers suggest that the scans are "an alternative diagnostic tool" that can help doctors "rule in or rule out" blocked arteries when patients aren't able to undergo other indirect tests, such as stress tests.
Not so, suggests an editorial by Rita F. Redberg, MD, director of women's cardiovascular services, and Judith Walsh, MD, MPH, of the University of California, San Francisco.
Although the current study was carefully done, Redberg and Walsh note, "It does not advance our knowledge of the appropriate use and possible benefits of the technology."
As the authors conclude that CT scans still can't replace traditional angiograms, Redberg and Walsh say the study "adds to the body of research failing to prove a benefit of the new procedure."
"Without such evidence, a high-resolution cardiac CT angiographic image of the heart is just another pretty picture," Redberg and Walsh write. Research regarding the prognostic implications and downstream effects of heart CT scans will be required to better define the role of this technology in patient care.
The Miller study was funded by Toshiba, which makes one of the 64-row CT devices used in the study. Miller, Lima, and other study authors report grant support from Toshiba; Lima and other study authors report receiving speaker fees from Toshiba.
The Miller study and the Redberg/Walsh editorial appear in the Nov. 27 issue of the New England Journal of Medicine.