The idea came from the morgue. Autopsies of 2,500 patients revealed a correlation between the amount of calcium in the coronary arteries and the total burden of atherosclerotic plaque. Moreover, patients who had died of coronary artery disease had two to five times as much calcium as those who had died from other causes.
Thus arose the clinical idea: antemortem assessment of calcium might identify patients at particular risk of coronary events. The earliest attempts to test the idea clinically yielded promising results, in that there was a correlation between the amount of coronary calcium detected fluoroscopically and the mortality rate at 5 or 6 years.
Measurement of coronary artery calcium became practical with the introduction of electron-beam computed tomography (EBCT), which made accurate quantification possible. The calcium burden was shown to parallel other measures of total plaque, with correlation coefficients of 0.75 to 0.93. In a series of almost 1,200 patients at St Francis Hospital in Roslyn, NY, the rate of cardiac events at 3.6 years was 0.007% in patients with calcium scores of 80 or less and 22% in those with scores above 300. Also, in patients with a score below 170, the worst stenosis was 22% and the average number of diseased coronary arteries was 0.7, whereas in those with scores of 170 or above, the worst stenosis averaged 67% and the average number of diseased vessels was 2.2.
So why is not every medical center doing coronary calcium scoring? Because the utility of the test still is not clear. Although the sensitivity of EBCT is excellent in detailing significant stenosis, as shown by a meta-analysis of 16 trials, the specificity is low, and there is a high false-positive rate (a patient with a large calcium burden but without significant stenosis). There are concerns that use of scoring will lead to unnecessary noninvasive and invasive work-ups. The test-retest reproducibility is variable. Most important, in the view of some commentators, is that the plaques that are most vulnerable to rupture and cause cardiac events often are not calcified. Because of these considerations, the American Heart Association (AHA)-American College of Cardiology (ACC) panel report on calcium scoring, scheduled for publication in Circulation in the spring of 2000, is expected not to recommend scanning as a routine screening test for coronary artery disease in asymptomatic individuals.
Despite the controversy, many medical centers are offering coronary calcium scoring to patients willing to pay for it. (Calcium scoring often is not covered by insurance.) The reasoning was summarized at this year’s AHA meeting by Alan D. Guerci, MD, of St Francis Hospital. “The calcified plaque is not necessarily the lesion of interest, but it is a marker for the lesion of interest,” he said. “EBCT cannot identify the lesion of interest, but it can identify the patient of interest.”
To learn about coronary calcium scoring programs, Decisions in Axis Imaging News talked to five practitioners who represent the entire spectrum of experience with the study. The University of Iowa, Iowa City, was one of the first institutions to purchase an EBCT scanner, and William Stanford, MD, and his colleagues have been involved in research and development of calcium scanning since the beginning. Heart CT, the coronary calcium program at the Center for Diagnostic Imaging (CDI) in Minneapolis and St Cloud, Minn, began accepting patients at the end of October and is now scanning eight to ten patients a day. We spoke with Elizabeth Klodas, MD, director of cardiac imaging, and Tom Rheineck, vice president, medical management, at CDI. The Ochsner Clinic in New Orleans plans to begin offering scans early in 2000, with an initial caseload of about 10 to 20 patients a month. Charles Matthews, MD, provided the viewpoint of this organization that is just getting started. Finally, Jeffrey Carr, MD, of the Department of Radiology and Public Health Sciences, Wake Forest University School of Medicine, Raleigh, NC, assisted in the development and evaluation of coronary calcium scoring on single and multislice helical CT scanners.
TECHNOLOGY AND PATIENTS
Although EBCT has become virtually synonymous with calcification scoring, it is not the only suitable method. Fast (500- or 750-millisecond) helical CT with cardiac triggering also can be used. The new multidetector-array scanners may additionally can be used. On the other hand, “if you try to do these scans with nongated helical CT or a conventional scanner, you are wasting your money,” Stanford specifies.
“Coronary calcification scanning should not be considered a mammogram for the heart,” Klodas stresses. “Until more data are available, it would be irresponsible to tell people, ‘You are 40 years old — you need a scan.’ ” Instead, all of the centers focus on high-risk patients, as defined by the AHA and the ACC: patients who smoke; who are overweight, diabetic, or hypertensive; or who have a family history of heart disease. Other possible candidates are patients with equivocal risk factors such as a borderline cholesterol value. In such cases, where the physician and patient are not certain whether aggressive treatment is needed, “a calcium scan can be useful in revealing problems early and encouraging patients to make lifestyle or treatment changes,” Klodas says.
There has been considerable discussion in the medical literature about the difficulties diagnosing coronary artery disease in women in a timely fashion. Calcification scoring performs as well in women as in men if one important fact is kept in mind, Klodas believes.
“In general, atherosclerosis is delayed about 10 years in women,” Klodas points out. “We accept men over the age of 35 for scanning. However, with women, we usually wait until they are at least 45.”
There are groups of patients in whom it is generally agreed that scanning is not appropriate. For example, a 40-year-old patient without risk factors probably has little to gain.
“If such a patient asks for a scan, we would tell him or her that we do not think it is appropriate,” Klodas says. “We encourage a discussion with the family physician. If the person insists, we will do a scan, but only after he or she signs a waiver confirming that we have explained that the scan is not indicated.”
Klodas identified another group of patients in whom a scan is not indicated: those with overwhelming risk factors for coronary disease or those with known coronary artery disease.
“These patients should be treated aggressively anyway,” she points out. “I am not sure the scan results would have much impact on their care.”
At present, calcium scanning also is not indicated for routine follow-up of individual patients.
“Initial studies indicate that in groups of patients, you can measure progression, and probably regression, of at least one component of coronary atherosclerosis with calcium scanning,” Carr observes. “However, in any given individual, we still have difficulty because of the variability of the calcium score with existing technology. With the introduction of volume scoring and acquisitions and with further improvements in CT systems, both electron beam and helical, the reproducibility of coronary calcium measures should improve. Then we will be able to determine better exactly what changes in calcium scores mean and how large an impact this may have on reducing heart disease.
INTERPRETING THE RESULTS
“Knowing what to do with the results of a coronary calcium scan is more complicated than simply giving the patient the score,” Carr states. “Making sense of the results requires putting them in the context of our knowledge of atherosclerosis and the patient’s other cardiovascular risk factors. And there remain significant gaps in our understanding. It is less clear, for example, what scores in, say, African-American women or Hispanic men mean in terms of the likelihood of a heart attack or stroke.”
The three possible outcomes of a scan were explained by Stanford as they would be discussed with a patient.
“One scenario is ‘You do not have calcification, which is good, but this result does not exclude the presence of soft plaque.’ ” he explains. “The second scenario is ‘You have calcium commensurate with your age.’ The third scenario is the most important: ‘You have more calcium than is expected for your age, and we recommend that you see your physician for further evaluation and reassessment of risk factors.’
“We make no specific recommendations for further tests or medical therapy,” Stanford stresses.
To help ensure proper follow-up, Heart CT offers patient education that Klodas believes is one of the most important parts of its program. Every patient receives a pamphlet that explains the development of coronary atherosclerosis, the risk factors for the disease, and how the patient can reduce his or her risk. The CDI can put patients in touch with needed resources such as smoking cessation programs or diet advisors. In other words, if you are a Heart CT patient, “You do not leave here with just a calcium score,” Klodas emphasizes. “You leave with education to make you more proactive about your health.”
Indeed, all of the experts we talked to stressed that a calcium score is the beginning of care, not the end.
“If you simply open up a center to provide the scan to everyone who comes in, you may be doing a disservice,” Carr believes. “The results must be placed within a framework of cardiovascular care. Just getting a score is not helpful by itself. The benefit of the test is helping patients and their health care providers institute appropriate preventive measures.”
There is a risk that some patients will use the results to make unwise decisions.
“You may have some patients who want to use the scan to rationalize a less than ideal lifestyle,” Carr notes wryly. “They will say, ‘I am overweight, and smoke and do not want to exercise, so I will get a calcium scan to see if I have to.’ Coronary calcium is only one piece of the complex puzzle of cardiovascular disease.”
Some radiologists have expressed concerns about the legal issues implicit in screening of asymptomatic patients in a test using radiation. However, as Stanford points out, scanning for coronary calcification takes only 30 seconds, uses a very small amount of radiation, and involves no contrast medium.
Rheineck does not believe there are any unusual legal issues. “There are abundant data to show the value of early detection of heart disease and considerable evidence of the accuracy of coronary calcium scoring in identifying significant disease,” he asserts. “We have board-certified physicians score the examinations. Also, as part of the self-referral waiver needed for a radiation examination, there is a requirement for the name of a physician contact to whom the results will be sent. Even if there were no such requirement, our internal policy is that positive findings will be communicated to a physician, and we tell patients this. If they do not have a primary care physician, we will work with them to find one.”
SETTING UP A PROGRAM
“If you plan to become involved in calcification scanning, the first thing you need to do is to get the support of the cardiologists in the community,” Stanford says. “You also need to start talking to the referring physicians about what coronary calcium means and what the test can and cannot tell you. Third, you need to learn what types of patients in your community might benefit from the scan and establish procedures for reaching them.”
Carr likewise stressed the importance of a multidisciplinary effort. “Cardiology, primary care, and imaging must collaborate,” he says. “Also, calcium scanning must fit in with the organization’s overall goals, because once you have the score, the patients need to have someone help them figure out what to do with the information.”
Significant training also is necessary. “Doing the scan is relatively trivial,” Carr says. “The people who are interpreting the results need to understand several unique aspects of cardiac physiology and anatomy. Most health care professionals do not have the necessary knowledge of cross-sectional coronary anatomy. For example, you have to be able to identify calcium in relation to the position of the vessels and distinguish it from calcification of the mitral or aortic valves.” He suggests that certain people specialize in doing coronary calcification scans to improve the quality of the work.
Matthews spoke of three types of training. First, there is the collection of information about the arguments for and against the test and the use of the information. He obtained these data both from published papers and from speaking with practitioners. Second, there is the need to master the scoring software the department will use, with training provided by the vendor. Finally, there is the interpretation of the results. To learn how to do that, he advises radiologists to undergo training from experienced practitioners.
MARKETING THE SCAN
The Heart CT program sees itself as having two audiences for its advertising: primary care physicians and consumers.
“As an imaging services company, our main constituency is referral physicians,” Rheineck says. “As we started our program, we paid particular attention to educating primary care physicians about which patients were appropriate candidates for this procedure and what information it could provide.
“We also address consumers. We believe that more health care is moving to an open model in which consumers obtain education about their health and make choices. When you demonstrate a value to consumers, they will make decisions with their own dollars, because they are willing to put their money into a preventive measure they believe is valid.” Approximately 75% of the patients who come to Heart CT for calcium scans are self-referred.
The Heart CT program uses several channels for marketing to consumers. Not unexpectedly, CDI makes use of radio and newspapers. A focus of these advertisements is the organization’s Web site (www.heartct.com), which provides education about the scan and access to scheduling, as well as hyperlinks to other relevant sites such as that of the AHA. Heart CT also has placed informational packets in physicians’ offices.
For all this effort, the most effective advertising may be free. “Many friends and coworkers of our patients come in for scans,” Klodas reports. “One of our most effective sources of clients is word-of-mouth advertising.”
The Ochsner Clinic is in a different situation and thus has a different approach. The principal audience for information about calcium scanning is the 450 physicians within the clinic. Later, Matthews says, the clinic will approach family physicians within the community. He also expects self-referrals.
“We constantly receive calls from people who have heard about a new medical procedure in the lay press and want to know if they can obtain it at Ochsner,” he reports.
GUIDANCE FROM THE PIONEERS
All of the people we spoke with agreed that the success of mammography has paved the way for calcium scoring and resolved numerous issues that might otherwise have to be confronted. Examples are self-referral for an examination involving radiation, confidentiality, the importance of guidelines on who should be imaged, the need for patients to take responsibility for their own care, and communication of positive findings to a physician. However, as Carr remarks, calcium studies are in approximately the same position mammography was 20 to 25 years ago.
“For mammography, we have eight randomized trials that prove a 33% reduction in breast cancer mortality with imaging of women older than 50,” Carr notes. “We do not have any randomized trials of the impact of calcium scoring.”
He also emphasized the need for standardization and quality control of the equipment and the measurement technique and for continued research to define the correlation of scores with long-term outcomes.
“Although it may seem strange given all the work on coronary calcium, I believe that we are still very much in the infancy of figuring out what coronary calcium means and how this test can best be used to reduce heart attacks,” he says. Although several trials are in progress, such as the National Heart, Lung and Blood Institute’s MESA (Multi-Ethnic Study of Atherosclerosis), which will follow 18,000 patients, the results will not be available for some time.
“Everybody, myself included, wants the answers now,” Carr notes. “Unfortunately, those answers are not available.”
A remark from Klodas summarizes the thinking of all experts regarding the role of calcium scoring. “Be realistic about the test,” she advises. “A coronary calcium score is not a replacement for common sense.”
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SUGGESTED READING
Stanford W, Thompson BH. Imaging of coronary artery calcification: its importance in assessing atherosclerotic disease. Radiol Clin North Am. 1999;37:257-272.
Judith Gunn Bronson, MS, is a contributing writer to Decisions in Axis Imaging News.
