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'Calculators' Doctors Use May Overestimate Heart Risks, Study Says
Such assessments should only be starting points for predicting risk, researcher explains
By Amy Norton
TUESDAY, Feb. 17, 2015 (HealthDay News) -- The various "calculators" that doctors use to estimate patients' odds of future heart trouble often overestimate the risks, a new study suggests.
Researchers found that four of five widely used formulas may overestimate people's risk of heart attack, stroke or other related complications by as much as 154 percent in some cases.
That includes the most recently developed risk calculator, unveiled alongside new treatment guidelines in 2013 by the American College of Cardiology (ACC) and American Heart Association (AHA).
However, the findings do not mean the calculators should be tossed, experts stressed.
"I'm not calling for the [ACC/AHA] guidelines or the risk calculator to be dismantled," said lead researcher Dr. Michael Blaha, of the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, in Baltimore.
Instead, he said, any risk calculator should be seen as a first step in estimating patients' odds of a future heart attack.
"Are all risk scores, in general, limited? I'd say yes," Blaha said. "They should be seen as a starting point for a discussion."
That "discussion" is about whether a patient with no history of heart problems or stroke should start using preventive therapies, like a cholesterol-lowering statin or a daily aspirin.
According to the latest ACC/AHA guidelines, people should consider preventive therapies if their risk of suffering a heart attack or stroke over the next 10 years is at least 7.5 percent.
And how do you know what your odds are? Doctors have long used various risk calculators to get an estimate.
The calculators vary somewhat in the factors they consider, and the outcomes they try to predict. The ACC/AHA calculator estimates the risks of heart attack and stroke, while others focus on heart attack and still others try to forecast a bigger range of complications, including heart failure or invasive heart procedures.
To any doctor who has used the calculators, the findings will probably come as "no surprise," according to Blaha, who reported the results in the Feb. 17 issue of the Annals of Internal Medicine.
"I'm skeptical of calculators, in general," he said. "In practice, it's common to get a [risk estimate] for a patient and think, 'That just doesn't seem right.'"
One of the cardiologists who helped craft the ACC/AHA guidelines agreed that the calculator should not be the final word.
"We never expect that any risk calculator will be perfectly accurate," said Dr. Donald Lloyd-Jones.
Those guidelines and the accompanying calculator "were never intended to give a black-and-white demarcation for 'treat' or 'don't treat,'" said Lloyd-Jones, who chairs preventive medicine at Northwestern University Feinberg School of Medicine, in Chicago.
He agreed that calculator results are only a starting point. "But they're a good starting point," he added.
In general, risk calculators are developed by using data from large studies that follow people over time, looking at factors that are linked to heightened risks of suffering a heart attack or other cardiovascular trouble. But those studies include data from decades ago, when more people were having heart attack and strokes -- which may be why, according to Blaha's team, the calculators are prone to overestimating.
For the current study, the researchers tested five different calculators using data from a relatively recent heart study, begun in 2000. It included a racially diverse group of over 4,200 Americans who were aged 50 to 74 and free of heart disease at the outset of the study.
Blaha's team compared the calculators' risk predictions against study participants' actual rates of heart attack, stroke and other complications over 10 years.
It turned out that, on average, four of the five calculators overestimated people's risk by anywhere from 8 percent to 154 percent. The fifth calculator -- the Reynolds Risk Score -- overestimated the risk by only 9 percent in men; on the other hand, it underestimated women's risk by 21 percent.
The new ACC/AHA calculator overestimated risk by 86 percent in men and 67 percent in women, the researchers said.
None of that is actually news, Lloyd-Jones said. In developing the guidelines, the ACC and AHA tested their calculator in this same study group and saw similar effects, he noted.
The problem, according to Lloyd-Jones, is that this study group is not the best reflection of the U.S. public: They were closely followed, offered CT scans to detect calcium deposits in the heart arteries -- an early sign of heart trouble -- and most eventually ended up on a preventive therapy.
"They're not really a representation of the 'natural course' [of cardiovascular disease]," Lloyd-Jones said. "We're trying to predict what would happen if people don't get any preventive therapy."
The ACC/AHA calculator considers a handful of key factors: age, sex, race, cholesterol and blood pressure levels, and whether a person smokes or has diabetes. For some people, the resulting estimated risk will be quite low, and for others it will be high.
The real concern, Blaha said, is with the people who fall into the gray middle zone -- with a 10-year risk in the range of 7.5 percent to 10 percent. If the risk calculator is overblowing their odds, they may needlessly start a statin or aspirin.
Blaha said it's particularly important to consider additional factors in those gray-zone cases -- factors such as obesity or a strong family history of heart disease or stroke. Testing for calcium in the coronary arteries could also be an option, Blaha said.
Aspirin and statins can both have side effects, and should be used with caution, he pointed out.
"The decision to start these medications needs to be made very carefully," Blaha said. "If someone seems to be at intermediate risk, but comes from a family full of people who lived into their 90s, with no heart disease, I might not suggest medication -- just a healthy diet and exercise."
Lloyd-Jones agreed. He said the discussion between doctors and patients -- rather than the choice of risk calculator -- is the most important point.
"Cardiovascular disease is the number-one killer in this country," Lloyd-Jones said. "We know what to do to lower the risk, but we need to be talking about it more."
The ACC/AHA has more on understanding your cardiovascular risk.
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