Predicting heart attacks — the government study the media ignored
Most heart disease occurs in healthy people without traditional risk factors and who aren’t considered to be at risk. That has led healthy people without symptoms to feel vulnerable to this ‘silent killer’ and seek ways to see if they could be at risk. The biggest growth industry of preventive health screenings are tests for an array of “emerging” cardiac risk factors. While these tests are heavily marketed to the public and millions of people are lining up for them, do they have any credibility?
The results of a massive systematic review of the evidence for these nontraditional heart disease risk factors were released last week by the U.S. Preventive Services Task Force. This major government review — involving 42 years of published studies and 212 citations — as well as its recommendations for clinical practice, has extensive ramifications in preventive care for all Americans, as well as the clinical practice of medical professionals. These results should have been widely reported, offering information to help everyone make more informed decisions about preventive screenings. But, did you hear anything?
This is another example of mainstream media failing to report science that is politically incorrect. Amidst today’s popular “preventive wellness” movement, how many news stories reported this far-reaching government review last week?
There’s a good chance that you, like most people, missed them.
Emerging cardiac risk factors
You’ve seen the advertisements for scans to measure calcium scores, carotid intima-media thickness (CIMT) and other measures, claiming to be able to identify people who need treatment and to prevent heart attacks or sudden death. Offered by hospital radiology departments, for-profit heart hospitals and mobile test units in communities, they also claim that 90,000 deaths could be prevented and $21.5 billion of healthccare costs could be saved every year if people were screened.
As JFS readers have followed, clinical research has found that CIMT is not a measure of atherosclerosis or predictive of people who will have cardiovascular events, heart attacks or premature death. It is a measure of, and most closely related to, age, not to plaque or stenosis formation. As Dr. Jerome P. Kassirer, M.D., professor at Tufts University School of Medicine and former editor-in-chief of the New England Journal of Medicine, said, what appears to be behind the heavy promotion of these screenings, despite the fact even major professional organizations oppose them and no sound evidence supports their use, is a profit motive.
The U.S. Preventive Services Task Force had earlier found no credible evidence to support screenings for coronary heart disease. In fact, it specifically “recommend[ed] against routine screening with resting electrocardiography (ECG), exercise treadmill test, or electron-beam computerized tomography (CT) scanning for coronary calcium for either the presence of severe coronary artery stenosis or the prediction of coronary heart disease events in adults at low risk for coronary heart disease events.” It also found insufficient evidence to recommend routine screening “in adults at increased risk for coronary heart disease events.” Carotid artery screenings received a D recommendation by USPSTF, meaning they should be actively discouraged.
Despite what might seems intuitive, it found no evidence that these screenings improve health outcomes for most adults, but instead, that false-positive test results are likely to cause harm, “including unnecessary invasive procedures, over-treatment, and labeling, the USPSTF concluded that the potential harms of routine screening for CHD in this population exceed the potential benefits.”
Another increasingly promoted new risk factor is C-reactive protein (CRP) levels, but that correlation has also already been shown to not have a causal role in heart disease. Even so, based on the results of the JUPITER study (covered here), CPR is being marketed as another screening test which could increase statin sales to $14 billion a year for the study’s sponsor, AstraZeneca.
In this newly-released systematic review, USPSTF examined the evidence for nine such novel risk factors: CRP, coronary artery calcium score as measured by electron-beam computed tomography, lipoprotein(a) level, homocysteine level, leukocyte count, fasting blood glucose, periodontal disease, ankle–brachial index, and carotid intima–media thickness. Specifically, the researchers investigated the merits of these risk factors among people classified as being at intermediate risk using traditional risk factors (the Framingham Risk Model). This describes 23 million adults in the United States, who are told they have a 10% to 20% chance of having a heart attack or cardiac death over the next decade. Proponents have proposed that by adding these new risk factors doctors would be able to identify those people who could be reclassified as high-risk, and targeted for more aggressive interventions.
As the authors noted, more than one hundred emerging risk factors have been proposed to improve the predictive ability of risk assessments. Consensus conferences in 1998 and 2002, however, have recommended against them because of a lack of evidence to support their ability to predict cardiovascular events. For a new risk factor to be credible and have value, the authors pointed out, it must independently predict major heart disease events and be clinically useful for reclassifying intermediate-risk patients so that their clinical treatment would change. It must also offer a convenience, availability, cost and safety benefit over traditional risk factors with similar prognostic ability.
As the methodology of systematic reviews have been covered before, we’ll get right to the findings. The USPSTF reviewers found the evidence for these nine emerging risk factors lacking. Good-quality studies were sparse or the body of studies did not consistently find that the factor independently predicted major CHD events. Even while an index, such as CRP, may be associated with cardiovascular disease, there was insufficient evidence that changing the levels reduced cardiovascular events.
The USPSTF concluded: “The current evidence does not support the routine use of any of the nine risk factors for further risk stratification of intermediate-risk persons.”
The authors went on to remind us:
As Lloyd-Jones and colleagues recently pointed out, “assessments of new prognostic testsshould not rely solely on associations measured by relative risks.” Our results illustrate the importance of considering multiple criteria to evaluate whether a new risk factor should be incorporated into guidelines for coronary risk assessment in primary care.
But few of us heard about this study. Instead, we read hundreds of news stories marketing these preventive screenings and claiming, based on no or poor-quality evidence, that heart disease is preventable and that our risks can be measured and known ahead of time. Science isn’t what they're selling.
© 2009 Sandy Szwarc