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Clinical "Calculators" Seriously Overrate Heart Attack Risk - Archived


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Most “risk calculators” used by clinicians to gauge a patient’s chances of suffering a heart attack and guide treatment decisions markedly overestimate the likelihood of an attack, according to results of a study by investigators at Johns Hopkins, the University of Louisville and other institutions.

Physicians commonly use standardized risk-assessment systems, or algorithms, to decide whether someone needs care with daily aspirin and cholesterol-lowering drugs or just watchful waiting and follow-up exams. These algorithms calculate heart attack probability using a combination of factors such as gender, age, smoking history, cholesterol levels, blood pressure and diabetes, among others.

The new findings, reported Feb. 17 in Annals of Internal Medicine, suggest four out of five widely used clinical calculators seriously overrate risk, including the most recent one unveiled in 2013 by the American Heart Association and the American College of Cardiology amid considerable controversy about its predictive accuracy.

The results of the study, the research team says, underscore the dangers of overreliance on standardized algorithms, and highlight the importance of individualized risk assessment factoring additional variables into a patient’s score, such as other medical conditions, family history of early heart disease, level of physical activity and the presence and amount of calcium buildup in the heart’s vessels.

“Our results reveal a concerning lack of predictive accuracy in risk calculators, highlighting an urgent need to reexamine and fine-tune our existing risk assessment techniques,” says senior investigator Michael Blaha, M.D., M.P.H., director of clinical research at the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease.

“The take-home message here is that as important as guidelines are, they are just a blueprint, a starting point for a conversation between patient and physician about the risks and benefits of different treatment or preventive strategies,” Blaha adds.

Those treatment and preventive strategies are impossible to develop without individualized consultation with patients, says Andrew DeFilippis, M.D., M.Sc., co-director of cardiovascular disease prevention and medical director of the Cardiovascular Intensive Care Unit at the University of Louisville, and a co-author of the study.  “What the data tell us is that current risk assessment algorithms provide the ‘jumping-off point’ for physicians to utilize in starting the process to determine a patient’s risk,” DeFilippis says. “Especially when these assessments indicate marginal or great risk, it is crucial for physicians to factor in other variables such as family medical history, calcium buildup in the vessels and lifestyle factors, among others, to obtain the truest picture of the patient’s condition. Only then can the physician develop prevention or treatment strategies that have the greatest chance of success.”

While prevention and treatment decisions are straightforward in some patients, many have borderline risk scores that leave them and their clinicians in a gray zone of uncertainty regarding therapy. Under the American Heart Association’s most recent guidelines, people who face a 7.5 percent risk of suffering a heart attack within 10 years are urged to consider preventive therapy with a cholesterol-lowering medication.

Risk overestimation could be particularly problematic for patients with marginal scores as it can artificially push a person with a relatively low risk profile into the “consider treatment” group. This is why patients with such borderline scores could benefit from further risk assessment including tests such as CT scans that visualize the degree of calcification in the arteries of the heart.

Additional testing could be a much-needed tie-breaker in all too common ‘to treat or not to treat’ dilemmas,” says study co-author Roger Blumenthal, M.D., professor of medicine and director of the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease. “Such testing should be considered in all patients with marginal risk scores — those in whom the decision to treat with long-term statin and aspirin remains unclear.”

To check the accuracy of each one of five risk calculators, the investigators compared the number of predicted versus actual heart attacks and strokes among a group of more than 4,200 patients, ages 50 to 74, followed over a decade. None of the patients had evidence of atherosclerotic heart disease at the beginning of the study. Atherosclerotic heart disease or atherosclerosis — a condition marked by the buildup of fatty plaque and calcium deposits inside the major blood vessels — is the main cause of heart attacks and strokes, claiming the lives of some 380,000 people in the United States each year.

Four out of five risk scores analyzed in the study overestimated risk by anywhere from 37 percent to 154 percent in men and 8 percent to 67 percent in women. The fifth, and least flawed, risk-scoring tool overestimated risk among men by only 9 percent, but underestimated it by 21 percent among women.

The new American Heart Association calculator overestimated risk by 86 percent in men and by 67 percent in women. Thus, a man with projected risk score of 10 percent, had, in fact, a 6 percent risk of suffering a heart attack within 10 years. In the group with a risk score between 7.5 to 10 percent — the threshold at which initiation of stain is recommended — the actual risk was 3 percent, well beyond the level at which statin use should be considered.

The least flawed prediction of heart attack risk was generated by the so-called Reynolds risk score calculator, which underestimated overall risk by 3 percent. In addition to age, gender, smoking, diabetes, cholesterol and blood pressure, the Reynolds score factors in levels of C-reactive protein — a marker of systemic and blood-vessel inflammation — and family history of early heart disease.

While not the subject of the current study, the researchers say they believe the overestimation of risk stems from the fact that all calculators, including the newest one, use as risk reference data obtained decades ago when more people were having heart attacks and strokes.

“The less-than-ideal predictive accuracy of these calculators may be a manifestation of the changing face of heart disease,” Blaha says. “Cardiac risk profiles have evolved in recent years with fewer people smoking, more people having early preventive treatment and fewer people having heart attacks or having them at an older age. In essence, baseline risk in these algorithms may be inflated.”
The Reynolds risk equation, for example, was based on data from a more recent group of patients compared with other calculators, which may explain its superior accuracy, the researchers say.

Other institutions involved in the study included University of Louisville, Kentucky; University of Washington, University of Colorado, the University of California-Los Angeles, and Baptist Medical Group in Miami.

The research was funded by the National Heart, Lung, and Blood Institute under grant numbers N01-HC-95159 and N01-HC-95169 and by the National Center for Research Resources under grants UL1-TR-000040 and UL1-TR-001079.

Related on the Web

Absence of Calcium Buildup in the Arteries Spells Low Risk for Heart Disease, Stroke Over 10 Years 

Publish date: 

Tuesday, March 24, 2015