Heart Risk Prediction May Improve with Calcium CT Scan
Using a computed tomography (CT) test to measure calcium in coronary arteries helps predict a person's future heart disease, a new study finds.
Still in question, however, is whether or not it is worth the cost and risk due to radiation exposure.
"This kind of evidence gives encouragement to go on and do additional testing, but it shouldn't convince us that this test should be done routinely," says Dr. Philip Greenland, at Northwestern University in Chicago and a co-author on a report in the Journal of the American Medical Association (JAMA).
CT uses x-rays to get a detailed picture of heart structure. Some experts are concerned about using it to diagnose heart disease because x-ray exposure may increase the risk of cancer.
The new study of nearly 6,000 healthy Americans was done to see whether the technique could provide extra help to physicians assessing risk. This would be in addition to looking at known risk factors such as high blood pressure, high cholesterol, and obesity.
The study began in July 2000 and ran through May 2008. It used two models to predict the five-year risk of a heart attack, resuscitated cardiac arrest, or death from coronary heart disease: the traditional risk factors or those risk factors plus the coronary artery calcium score.
At nearly six years, the participants had experienced 209 coronary heart disease problems and 122 "major events" - heart attacks, deaths from coronary heart disease, or cardiac arrest followed by resuscitation.
The second model, which used the regular risk factors plus the calcium CT, was able to predict an additional 23 percent of participants who would go on to experience a harmful cardiovascular event.
But, the question remains if added predictive power makes a difference in terms of saving lives and reducing unnecessary treatment.
Dr. Greenland says, "What we can say here is that additional testing looks like it improves prediction. Whether it improves clinical outcome requires a different kind of study."
The first steps toward such a study have been taken. Dr. Greenland is discussing a possible new study with the National Heart, Lung, and Blood Institute (NHLBI).
This could involve tens of thousands of people and cost millions of dollars, says Dr. Andrew J. Einstein, director of cardiac computed tomography research at Columbia University Medical Center in New York City.
The study would aim at finding whether more intensive treatment of traditional risk factors would improve survival of people classified as high risk by the coronary artery calcium score.
"No study has compared patients who had intensive preventive therapy with those who didn't and see if it makes a difference in terms of the number of heart attacks people have," explains Dr. Einstein. "That study would be the ideal."
Cancer risk and cost are also parts of the equation. Dr. Greenland says a well-controlled computed tomography scan gives about twice the radiation exposure as a mammogram.
A new large-scale trial could show whether the added risk is justified by the number of lives saved, and the same is true of the cost, estimated to run between $200 and $600 per scan.
Always consult your physician for more information.
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Computed tomography (CT scan) is a non-invasive, diagnostic imaging procedure that uses x-rays and computer technology to produce cross-sectional images (often called slices) of the body.
A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than standard x-rays.
In standard x-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle, and other tissue.
While a lot can be learned from a standard x-ray, a lot of detail about internal organs and other structures is not available.
In CT, the x-ray beam moves in a circle around the body. This allows many different views of the same organ or structure.
The x-ray information is sent to a computer that interprets the x-ray data and displays it in a two-dimensional (2D) form on a monitor.
CT scans of the chest can provide more detailed information about organs and structures inside the chest than standard x-rays of the chest, thus providing more information related to injuries and/or diseases of the chest organs.
The calcium CT scan can be used to look for calcium buildup in the walls of the coronary arteries. Calcium in the coronary arteries may be an early sign of coronary heart disease, where a fatty substance called plaque narrows the coronary (heart) arteries and limits blood flow to the heart.
If contrast dye is used during cardiac CT, it helps highlight the coronary arteries on the x-ray pictures. This can show whether the coronary arteries are narrowed or blocked (which may cause chest pain or a heart attack).
The CT scan can also find problems with heart function and heart valves. Physicians may recommend cardiac CT instead of echocardiography or cardiac MRI (magnetic resonance imaging) for some people.
Always consult your physician for more information.
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