A new international study found that while a new generation of faster computed tomography (CT) scanners easily and correctly identified people with blocked arteries, they were not accurate enough compared to the conventional coronary angiography.
The study was led by senior investigator and cardiologist Dr João Lima, who is a professor of medicine and radiology at The Johns Hopkins University School of Medicine and its Heart and Vascular Institute in Baltimore, Maryland, USA, and was published in the 27 November online issue of the New England Journal of Medicine, NEJM. Altogether, researchers from nine medical centers in the US, Brazil, Germany, Japan, Canada, Singapore and the Netherlands worked on the study.
Lima and colleagues concluded that while conventional catheterization was still the gold standard for diagnosing coronary artery blockages, the newer more powerful 64-row CT scanner is proving to be a close second. The study may well allay fears that CT scanners are a costly tool for this type of diagnosis.
The researchers said that although the new and faster 64-row CT scanners were only 93 per cent as precise as cardiac catheterization at pinpointing blocked arteries, they were 100 per cent accurate at identifying which people had them and which did not.
Blocked coronary arteries put people at high risk of heart attack because they can restrict blood flow. Once diagnosed, patients can then have cardiac bypass surgery or angioplasty (where the artery is widened using a small balloon that is inflated after being inserted in the affected blood vessel) to restore their blood flow.
Over 250,000 people have a coronary bypass in the US every year, and another 1.2 million undergo angioplasty.
Lima and colleagues compared the results of CT scans and catheterization, and found they were equally useful at predicting the need for bypass surgery and angioplasty in patients who had shown heart attack symptoms, for instance shortness of breath and pains in the chest. The CT scans predicted 84 per cent and the catheterization predicted 82 per cent of the invasive procedures performed.
While not advocating that the new 64-CT replaces catheterization as a diagnostic tool, Lima pointed out that it takes only 5 to 10 seconds to carry out a scan, making it a useful alternative to help doctors “rule in or rule out” coronary blockages, when other tests, such as the cardiac stress test, might be unclear or unsafe for certain patients.
Catheterization, where a catheter is inserted into an artery in the patient’s groin (usually under local anasthetic) and manipulated up toward the heart where the function of heart valves and muscles can be examined using X-rays, usually takes between 30 and 45 minutes, with over an hour for patient recovery. Being an invasive procedure it also carries the usual risks of infection, heart attack, stroke, although these are rare.
The CT scanner also uses X-rays which pass through the body from the outside at different angles and a computer produces a 3D image on the screen.
Lima estimated that the new 64-CT scans could reduce by as much as 20 per cent the 1.3 million cardiac catheterizations that show no blockages that are carried out each year in the US. Also, although not covered by many private health plans, CT scanning could be a viable alternative to cardiac stress testing for weak and elderly patients who can’t perform the strenuous exercise it requires.
Previous studies on using CT scans were using older technology based on 16-CT which is slower and less powerful said Lima, and have only a quarter to one third of the precision of the newer 64-CT machines.
“Our latest findings weigh heavily in favor of the more advanced 64-CT scans,” said Lima, adding that they had four times the strength of the more widely available 16-CT scanner. The new 64-CT technology gave the team their:
“First real view of the whole picture of what is going on in the artery, precisely where the blockage is, even if it is only partially obstructed,” explained Lima.
Lead author and interventional cardiologist Dr Julie Miller, who is leader of angiographic research and an assistant professor at Johns Hopkins University School of Medicine, said that the advanced scanners are so good that for the first time doctors can see blockages in blood vessels 1.5 mm in diameter. The older scanners were more suited to blood vessels bigger than 2 mm in diameter, she added.
For the study, Lima, Miller and colleagues recruited 291 men and women over the age of 40 who were already scheduled to undergo cardiac catheterization to check for blocked arteries. Each patient also had a 64-CT scan before their procedure and had regular check ups afterwards. The study began in 2005 and follow up will continue until 2009 to see who develops heart problems, and how many may have needed bypass surgery or angioplasty.
The results showed that the 64-CT scans identified 90 per cent of the patients who were subsequently found to have a major blockage when they underwent conventional cardiac catheterization.
There are disadvantages to using 64-CT said Miller, and these include radiation exposure and in rare cases patients can have allergic reactions or develop kidney problems from the contrast dyes that are injected into them to enhance the CT images.
Miller said that CT technology had come a long way in the last decade. Radiation exposure has been cut and the time to complete a scan has come down. There is also a 320-CT scanner that takes less than a second to perform a scan.
“Diagnostic Performance of Coronary Angiography by 64-Row CT.”
Miller, Julie M., Rochitte, Carlos E., Dewey, Marc, Arbab-Zadeh, Armin, Niinuma, Hiroyuki, Gottlieb, Ilan, Paul, Narinder, Clouse, Melvin E., Shapiro, Edward P., Hoe, John, Lardo, Albert C., Bush, David E., de Roos, Albert, Cox, Christopher, Brinker, Jeffery, Lima, Joao A.C.
N Engl J Med, Volume 359, Number 22, pp 2324-2336, November 27, 2008.
Sources: Journal Abstract, Johns Hopkins Medical Institutions .
Written by: Catharine Paddock, PhD