CJ Gunther for The New York Times
Dr. Peter Libby, the chief of cardiovascular medicine at Brigham and Women's Hospital, at his office in Boston in 2007. "The disease of atherosclerosis is changing before our eyes," he said.
This week, cardiologists learned that a new online calculator meant to help them determine a patient's suitability for cholesterol treatment was flawed, doubling the estimated risk of heart attack or stroke for the average patient. But fixing it would not be easy, because it is based on older data, and heart attack and stroke rates today are much lower than in decades past, meaning that people are at less risk than might be expected from historical extrapolations.
Yet the outdated risk figures are the only ones available for researchers to use as assessment tools, cardiologists say, and that raises real problems for the new risk calculator, which the American Heart Association and the American College of Cardiology posted online last week as part of a radical new set of guidelines for treating high cholesterol. The guidelines, which are supposed to shape the way doctors prescribe cholesterol-lowering statins, recommend looking beyond a patient's cholesterol readings.
"The disease of atherosclerosis is changing before our eyes," said Dr. Peter Libby, the chief of cardiovascular medicine at Brigham and Women's Hospital in Boston. The reasons for the changes, he said, are only partly understood.
The problem of using longitudinal health studies from previous decades to assess health risks today arose unexpectedly last weekend at the annual meeting of the American Heart Association. Two Harvard researchers, Dr. Paul M. Ridker and Dr. Nancy Cook, revealed that the new calculator released with fanfare last week exaggerated the true risk of a heart attack or stroke by an average of 100 percent. Moreover, they said, the committee that developed the calculator knew that the online tool was inaccurate yet told doctors to use it in deciding whom to treat.
The data that was used to build the calculator was 20 years old, the researchers said, and a lot has happened since then. Many fewer people have heart attacks and strokes. Those who have them do so at older ages. Women are now nearly as susceptible as men.
But there also is another issue, said Dr. H. Gilbert Welch, a medical professor at Dartmouth. The calculator, like many others used in medicine, is based on a mathematical model that assumes that risk rises in a straight line. As levels of blood pressure rise, for example, the chances of a heart attack or stroke rise in concert, the calculator assumes. In reality, Dr. Welch said, that line is far from straight.
"The model suggests that lowering systolic blood pressure from 130 to 100 is nearly as important as from 180 to 150," he said. "I doubt there is a cardiologist in the country that believes that."
When the guidelines were being developed, several outside reviewers, including the two Harvard researchers and Dr. Roger Blumenthal from Johns Hopkins University, pointed out that the tool seemed to exaggerate risk. The calculator, Dr. Blumenthal said, "was clearly not satisfactory."
In response, he said, the guidelines committee added a tiebreaker for doctors to use with patients whose risk score was equivocal. Those patients could have other tests, such as a heart scan for coronary calcium, which can determine if they have plaque in their arteries, and a blood test for a protein, C.R.P., that is associated with increased risk.
But the heart groups do not plan to change or eliminate the calculator, in part because there is no good alternative. Prescribing statins is often a judgment call, doctors say, except for patients whose chance of a heart attack or stroke is extremely high, like those who have already had a heart attack or who have diabetes.
Previous treatment guidelines, which were released in 2004, also included a risk calculator, but researchers recently discovered that it, too, overestimates risk.
In fact, said Dr. Michael Blaha of Johns Hopkins, the old calculator overestimated risk much greater than the new one, mainly because it was based on data from the 1980s and from the largely white male population of Framingham, Mass.
"The new risk calculator is actually better," Dr. Blaha said. "People did not appreciate the problems with the Framingham calculator."
Dr. Blaha and his colleagues discovered the flaws of the calculator based on the Framingham Heart Study a couple of years ago but did not publish their results because they were waiting for the new calculator to appear. They thought any issues with the old calculator would soon be moot.
"It's a touchy subject," Dr. Blaha said of the old calculator's problems.
Many doctors never used the Framingham calculator anyway, said Dr. Benjamin Ansell of the University of California, Los Angeles. Instead, they mostly offered statins to people with very high cholesterol levels, ignoring the fact that those who have lower cholesterol levels but other risk factors, like smoking or high blood pressure, often benefited.
But others used the Framingham calculator to prod patients to take statins. Dr. Lisa Schwartz and Dr. Steven Woloshin at Dartmouth, for example, said they would show patients their risk percentage and then recalculate what it would be if they were under treatment.
Dr. Ansell said he feared that the problems with the new calculator would make doctors and patients skeptical of the new guidelines in general, even though most of the advice on how to prevent heart attacks and stroke — such as through weight control, diet, exercise and smoking cessation — has nothing to do with the calculator.
"It will be that much more challenging to implement this or subsequent guidelines," Dr. Ansell said. "It's a definite setback."
Dr. Michael Pignone of the University of North Carolina said it was time to take another look at the new calculator. The guideline committee members are experts, he said, but "getting it right is really hard."
Dr. Welch went further.
"It should be fixed," he said. "And before we launch it on the public, we should launch it on the skeptical doctors. This matters to millions of people."
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