Called cardiac calcium scoring, the test uses a special x-ray called a CT scan to show the location and extent of calcified plaque in a person's coronary arteries. "Calcium does not deposit in healthy arteries; it deposits in arteries which already have plaque," says Dr. Mike Mounir, a Lafayette cardiologist. "This new technology is making it very easy for us to know if someone is starting to have atherosclerosis [fatty material deposited along the walls of the arteries]. I use this technology to know how aggressive I need to be in treating different patients."
The coronary arteries are the vessels that carry blood to the heart wall. The main cause of heart disease is build-up of plaque, which includes fat and calcium, in the arteries of the heart. When the arteries narrow, the heart muscle doesn't get enough oxygen-containing blood, and a heart attack can occur. The plaque can also break away from the artery walls and cause blockage.
Available in this market for several years, this calcium scoring test is non-invasive, uses no dye or needles and exposes a patient to minimal radiation.
The CT's sub-second scanning capability takes 70 to 90 images of the patient's coronary arteries to derive a calcium score. The entire process takes less than 10 minutes. A fully clothed patient simply lies down on the table attached to the CT scanner while a technologist places a few EKG leads on his chest. The table slides through the opening in the scanner while a cylinder around the opening rotates around his body, and the electrodes ' which are also attached to a machine that records the electrical activity of the heart ' make it possible to record CT scans when the heart is not actively contracting. The patient holds his breath for periods of 20 to 30 seconds while the images are recorded ' and the test is over.
Radiologists like Dr. Henry McLemore of the Acadiana Radiology Group at Our Lady of Lourdes read the results using high tech software that shows the cross-sections, or slices, of the areas of interest and calculate the calcium score. They provide an evaluation within 48 hours.
"We've had some people that took the test and they had calcium, so we checked the other risk factors," McLemore says. "If they'd have kept on, they might have had a heart attack and required more extensive surgery than just a stent."
"The test is most beneficial in middle-aged people, 45 to 50 and above, because young people could have plaques and blockage without calcium deposit," Mounir says. The test also does not detect soft plaque, the earliest form of coronary artery disease.
"If the calcium score is zero in a middle-aged person, that means this person has a 95 percent chance of not having any blockages," the cardiologist continues. While zero means no buildup, a score above 400 indicates significant buildup and plaque ' most likely obstruction of one of the coronary arteries. "If a calcium score is high, that means indirectly that the plaque burden is high also."
The calcium scoring test doesn't indicate if the plaque is obstructive, but a score in the 1,000 to 2,000 range is a likely sign of obstruction, and the patient typically will undergo coronary angiography. This invasive procedure is more risky and much more expensive. Considered the "gold standard" for detecting coronary artery stenosis (the narrowing or obstruction of the heart's aortic valve), it uses dye injected through a thin catheter in the groin or arm to enhance x-ray images of the heart. The tip of the tube is positioned either in the heart or at the beginning of the arteries supplying the heart. The pictures that are obtained are called angiograms, and the physician is able to correct problems during the procedure.
If a person's calcium score is between 100 and 400, other factors must be weighed before additional tests are ordered. "If he does not have chest pain or an abnormal stress test, then he does not need to have any further testing, just starting him on cholesterol medication and aspirin," Mounir says. If the patient is having some chest discomfort and the stress test is inconclusive, the physician may recommend a cardiac CT angiogram, which uses the same calcium scoring CT technology but includes a dye contrast administered intravenously in the arm.
Though vastly improved in terms of the number of slices it produces in a single rotation to create a 3-D image of the heart, cardiac CT angiography still is not sufficient to replace the traditional catheter-based coronary angiography, Mounir says. For example, he says it doesn't produce clear images in an overweight person.
If the calcium scoring reveals a high chance of having heart disease, a person should also take steps such as eating better, quitting smoking and getting more exercise ' lifestyle adjustments similar to those a doctor would recommend after looking at a person's health history, physical health, and any lab tests, such as a cholesterol test.
McLemore has personally undergone the test twice, the second revealing a calcium score of 19 (only a minimal risk), so he simply increased his exercise regimen and continued taking a mild medication for his elevated cholesterol.
The struggle to fight America's No. 1 killer is far from over, but Lafayette's medical community believes early diagnosis through this revolutionary and affordable CT imaging is going a long way toward better managing the crisis. "It not only detects calcium in the arteries; I have seen enlarged hearts, pericardial effusions [fluid around the heart], calcification of the heart valve and evaluations of the aorta," says McLemore. "It's a screening test, but you get a good idea of what the heart and everything else [around it] looks like."
McLemore, however, cautions against leaning on a single test for determining a person's chances of developing coronary artery disease. He says all other risk factors ' high cholesterol, high blood pressure, smoking and diabetes ' must be weighed. "This is a screening test. It should not take the place of a physical exam for detection of your risk factors," the doctor says.
For now in Lafayette a physician has to request the test, but Mounir believes that may soon change ' it has in other states. "I do expect in the future it could be done without a physician order," he says. Mounir's only fear is the test could lead to unnecessary procedures, meaning a higher number of coronary angiograms. "That is why it should be done with the knowledge of a physician who will interpret the test according to the whole clinical picture," he says.