Coronary Artery Calcification Scanning : Ethical Issues of a New Diagnostic Test
Sharron Cole
Issue 5, November 2001
"Radiation zap test too risky, says Heart Foundation" was a recent headline in the local evening newspaper. The first two paragraphs of the article described how the National Heart Foundation did not support the technique for checking patients' hearts because "the technique is expensive, has not been adequately studied and carries the risk of giving a radiation dose equivalent to up to 400 chest x-rays". In response, the test's provider claimed the radiation figures were scare mongering and that there was good evidence for the value of the scan. [1]
As Chair of a Regional Ethics Committee, I was interested because this sounded like an innovative procedure that should have come before the Ethics Committee for appraisal and approval. Ethics Committees are charged primarily with protecting research participants from harm and as innovative treatment is new or unconventional, it is, no less than health research is, human experimentation. Any application for ethical approval "must justify the use of the new procedure, provide reports from the literature if available, compare risks and benefits, demonstrate the experience and qualifications of the clinician and the training required for nurses and other staff, provide copies of information to be given to patients and discuss how informed consent is to be obtained." [2]
I am always concerned when medical "experts" disagree so publicly. While no one disputes that there should be healthy debate in medicine, the community-at-large becomes concerned and confused when those they look to for guidance on technical or very specialised medical matters appear to be at loggerheads. There is no better example of this in New Zealand than the "great cot death debate", a debate which has left parents and parents-to-be anxious about how best to protect their babies and has resulted in the reduction of money for cot death research in New Zealand.
Any new screening programme raises ethical issues that must be addressed and satisfied. What are these issues and why is there a difference between a patient who seeks help from a doctor for conventional diagnosis and treatment and those other patients whom the doctor seeks to identify as requiring his or her assistance? Thomas McKeown wrote:
"The position is ... different in screening, when a doctor or public medical authority takes the initiative in investigating the possibility of illness or disability in persons who have not complained of signs or symptoms. There is then a presumptive undertaking, not merely that abnormality will be identified if it is present, but that those affected will derive benefit from subsequent treatment or care.... No one should be expected to submit to the inconvenience of investigation or the anxieties of case finding without the prospect of medical benefit" [3]
He identifies obligations in screening which are to ensure:
a) that a screening programme is effective, and if it is
b) that it makes better use of limited resources than the available alternatives
c) that it reaches the entire at-risk population, and
d) how to manage the cases when they have been identified
Shortly after reading the article, a representative of the local cardiology community asked me to attend their meeting with the test's provider. This meeting was informative and evidence was produced to confirm that the test, Electron Beam Computed Tomography [EBCT], has been the subject of research throughout the 1990's. It also satisfactorily addressed some of the ethical issues, dispelling the notion that the test was an "innovative procedure" but it left others yet to be answered. It is useful to use the framework of McKeown's obligations to work through these issues.
Effectiveness of Test
Research has shown a direct correlation between the amount of calcium in the coronary arteries and the likelihood of a future heart attack. EBCT takes a series of cross-sectional images of the heart, allowing the detection of even small amounts of calcium in the coronary arteries. The amount and density of the calcium allow the calculation of the calcium score. The score will show how an individual fits into various age and risk profiles and whether there is any likelihood of obstructive coronary artery disease in the future. For people at risk, their doctor will recommend an appropriate strategy to maintain cardiac health and may also recommend further testing. [4]
The American Heart Association is satisfied that "as EBCT has been shown to be sufficiently accurate for predicting the presence of angiographic stenoses (narrowings) somewhere in the coronary arteries and for predicting the likelihood of clinical end points in symptomatic patients, it can be used as part of a cardiological examination done under the supervision of a physician knowledgeable about the significance of scan results and the management of coronary heart disease." [5]
However, the Association remains quite cautious about EBCT. Unless the calcific area is greater than 2 mm, the reproducibility of coronary calcium detection with cardiac scanning appears to be insufficient for serial assessment of coronary calcium levels in individual patients. Presently the data are insufficient to recommend coronary artery calcium screening in lieu of stress testing for most patients with chest pain, except in those with atypical chest pain, for whom a negative study may be useful by itself or in addition to exercise testing. The role of EBCT as a screening tool in asymptomatic patients with conventional risk factors is not yet clearly defined. There is no role at present for application of the test to screen populations of young (less than 40 years old), healthy individuals with no risk factors. The importance of calcification in such individuals will have to await event data that are currently being obtained. [6]
A further limitation of calcium scoring is that although calcium deposition occurs relatively early in the atherosclerotic process, plaque material is not initially calcified. Therefore very early atherosclerosis may be undetected by this technique. This is important since early non-calcified plaque could potentially become unstable (plaque rupture) and cause symptoms (unstable angina or heart attack); if it is not accompanied by calcified plaque, a patient's calcium score could still be "zero." Consequently, any patient with typical chest pain should receive an appropriate evaluation, and calcium scoring at this time does not play a role in the evaluation of chest pain. [7]
In summary, research indicates that the test is effective at detecting the presence of atherosclerotic plaque. The greater the amount of calcification, the greater the likelihood of obstructive disease and high calcium score may be consistent with a moderate to high risk of a cardiovascular event within the next 2 to 5 years. Its use should be limited to areas of proven effectiveness and wider use should only be as part of well designed, scientific study.
Better use of Limited Resources
Heart and blood vessel diseases cause more than 41% of all deaths in New Zealand each year. At present rates, about one in three New Zealand men will die from a heart attack and one in five women. [8] For a number of apparently fit and healthy New Zealanders, the first indication that they have Coronary Artery Disease (CAD) is when they have a heart attack. EBCT is sensitive to the detection of early CAD, and extent of plaque burden. The detection of any degree of coronary calcium indicates that CAD is present. The calcium score provides a quantitative estimate of plaque burden and in general, the higher the score, the larger the plaque burden and the higher the risk of subsequent cardiac events. It is therefore a valuable "early warning system" for a potential heart attack.
Heart disease can be slowed, stabilised, and in some cases, reversed when a heart scan is done and detects early signs of calcium in the coronary arteries. EBCT therefore has the potential to reduce both the morbidity and mortality that arise from previously undetected CAD, the extent of which was previously unknown. But the clear limitations expressed by the American Heart Association should be heeded and EBCT should not be used where research has not proven its efficacy. EBCT is not adequate for the serial assessment of plaque levels, it should not replace stress testing in people with chest pain, it does not replace angiography as the most reliable technology to accurately assess luminal narrowing in the coronary circulation and that there is no evidence to support screening in people less than 40 with no risk factors. [9] To use it for these purposes would not be supported by the current evidence and would be termed a poor use of limited resources.
Reaching an Entire at-risk Population
Research indicates that EBCT is appropriate for both men and women, age 40 to 70, who have any of the following risk factors: family history of heart disease, high blood pressure, smoking, diabetes, overweight, sedentary lifestyle, high cholesterol or high stress level. The documentation of the presence of CAD would be expected to change or influence any therapy a doctor recommends and people with borderline lipid levels, or mild hypertension may benefit as their doctor could decide whether more aggressive secondary prevention therapies are appropriate.
Clearly there is a significant sector in the New Zealand population who could benefit from undergoing EBCT. However, the scan is only available through a private radiology service, at a cost of $560 per scan. This cost is not currently covered through health insurance. There is "direct-to-the-public" radio advertising, meaning the public at large is quickly becoming aware of what is conveyed in a 30 second sound bite as an important and potentially life saving test. The advertisement does mention that people would need to be referred by their doctor for the test but its intention is to market a product.
For obvious reasons of cost and limited access, the test cannot reach an entire at-risk population . In New Zealand, Māori and Pacific Island peoples are disproportionately represented in the at-risk group but as they are also over-represented in the low socio-economic grouping, they are the least likely people to undergo the test. There is an issue of equity, or rather, a lack of equity, when many of the people most likely to benefit from the test are unable to access it.
How to manage cases when they have been identified
EBCT is advertised as a test for which a doctor's referral is necessary and people undergoing it must fit the risk profile. Test results are mailed out to both the individual and their General Practitioner. It is essential that full information is given before the test so that the individual is aware of the nature of the test including an explanation of the calcium score, the likely benefits and risks, costs and alternative tests including the possibility of no testing.
Having undergone the test, the issue then becomes one of interpretation and management. As the test results go to the General Practitioner, it is up to him/her to discuss the results with the individual and to decide the best course of action. There will need to be continuing medical education provided for General Practitioners so that they are knowledgeable about both the test and its results in order to implement or recommend an effective treatment programme or make the appropriate referrals. Reducing the risk factors is a sensible course of action even though it is not easy to change a person's lifestyle. This often requires considerable support from both family and community groups, meaning more resources would need to be provided for primary, community-based health and support groups.
The presence of any detectable coronary calcium implies the presence of coronary artery disease but this does not mean a heart attack is imminent or that the person must be referred to secondary cardiology services. Indiscriminate referral would soon result in an overburdening of already stretched cardiology services and would mean delays in people being seen. This might not matter for those who are at little risk but could have tragic consequences for high-risk people.
Detectable coronary calcium may affect patient management by providing impetus for more aggressive hypertension control, lipid lowering, and low-dose aspirin therapy. Investigators have also noted that individuals, when informed of their score, or shown actual images, have displayed much more willingness to undertake healthy lifestyle changes. Since patients with very high scores (over 400) have a high likelihood of harbouring a significant narrowing, they should probably undergo stress testing. Patients with intermediate scores may require further testing based upon other factors such as age and other risk factors. [10]
All these management options, including General Practitioner and patient education, drugs, support for lifestyle changes, secondary care referral and further diagnostic testing, have resource implications that the EBCT provider has no professional responsibility, apart from informed consent obligations, to either consider or to ensure these are in place. This raises the ethical issue of a private provider introducing and profiting from what is in essence a private screening programme with significant resource implications for the public sector but does not and is not required to satisfy the obligations identified by McKeown or the WHO Criteria for appraising the viability, effectiveness and appropriateness of a screening programme. [11]
Conclusion
There is little doubt that Coronary Artery Calcification Scanning or EBCT is able to detect Coronary Artery Disease and provided the right treatment and/or lifestyle changes occur, morbidity and mortality can be reduced. Few would see this as anything but "a good thing" and worth pursuing. However, it is not as simple as providing "up-to-the-minute" technology that might save lives. Technology is not to be used indiscriminately and it would be a waste of limited resources to use it where research has not shown it to be efficacious. Almost certainly, cost and inaccessibility would deny the test to large numbers of people most at risk and this would be inequitable. Finally, having identified a condition in an otherwise well person, the health service providers have a responsibility to provide education, treatment and support to ensure there is medical benefit.
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[1] Evening Post, 17 August 2001
[2] Skinner, Anna & Gillett, Grant "A Review of Innovative treatment" in Otago Bioethics Report, Vol 7 No 1, March 1998, p. 14
[3] McKeown, Thomas 'Validation of Screening Procedures' in Screening and Medical Care, OUP 1968
[4] Robert J. Optican "Coronary Artery Calcification Scanning; Its Time Has Arrived" http://www.msit.com/news3.htm
[5] A Statement for Health Professionals From the American Heart Association "Coronary Artery Calcification: Pathophysiology, Epidemiology, Imaging Methods, and Clinical Implications" http://www.americanheart.org/Scientific/statements/1996/0903.html
[6] ibid
[7] Optican, op cit
[8] National Heart Foundation http://www.nhf.org.nz/index.html
[9] Optican, op cit
[10] Optican, op cit
[11] World Health Organisation Report on Criteria for Appraising the Viability, Effectiveness and Appropriateness of a Screening Programme 1996
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Sharron Cole is Chair of the Wellington Ethics Committee and National Chair of the Ethics Committees in New Zealand.
©
2001