The guideline defines 4 categories of patients to be considered for treatment: (1) patients with known cardiovascular disease, (2) patients with LDL cholesterol ≥ 190 mg/dL, (3) patients with diabetes aged 40 to 75 years and LDL cholesterol ≥ 70 mg/dL, and (4) patients aged 40 to 75 years with LDL cholesterol ≥ 70 mg/dL and an estimated 10-year risk of a cardiovascular event of ≥ 7.5%. The guidelines call for patients in groups 1 and 2 to receive high-intensity statins (rosuvastatin 20 to 40 mg, atorvastatin 40 to 80 mg), although patients with known cardiovascular disease > 75 years of age can receive moderate-intensity statins. Group 3 should receive high-intensity statins if their 10-year risk is ≥ 7.5%; if otherwise, they can receive a moderate-intensity statin. Group 4 should receive a moderate-to high-intensity statin. As with most guidelines, the guidelines offer the caveat that physicians should take an informed consent approach regarding treatment and make decisions in consultation with their patients.
The publicity surrounding the new guidelines was heightened by the controversy that emerged regarding the new Pooled Cohort Risk Equation developed by the guideline committee [4] for determining 10-year risk. Using data from 5 well-known cohort studies (over 24,000 participants), they created the new risk calculator because of what they viewed as limitations of existing risk calculators: (1) the lack of racial diversity in samples used to derive them, (2) the lack of use of stroke as a cardiovascular outcome, and (3) the use of some subjective outcomes, such as coronary revascularization, angina, and congestive heart failure. Critics have suggested that the new risk calculator is poorly calibrated to more recent cohorts and that the threshold for treatment (≥ 7.5% 10-year risk) is too low and should be 10% or higher [6,7].
Physicians have long used risk calculators to help guide treatment. As an example, the Framingham Heart Study risk score was endorsed by the ATP III guideline. However, all risk scores have limitations, as clearly articulated by the developers of the ACC/AHA risk calculator:
This process is admittedly imperfect; no one has 10% or 20% of a heart attack during a 10-year period. Individuals with the same estimated risk will either have or not have the event of interest, and only those patients who are destined to have an event can have their event prevented by therapy. The criticism of the risk estimation approach to treatment-decision making also applies to the alternative, and much less efficient approach, of checking the patient’s characteristics against numerous and complex inclusion and exclusion criteria for a potentially large number of pertinent trials [4].
No matter how well calibrated or thoughtful, all calculators will be flawed. But guidelines are meant to be just that—guides rather than a prescription for treatment.
Applications for Clinical Practice
The ACC and AHA have promised a 2014 update to their guideline, which may come with adjustments to the risk calculator. Perhaps calibration of the calculator in newer cohorts will improve and the threshold for treatment will change. In the meantime, the guidelines and the accompanying calculator have an important role in helping physicians decide whom to treat for primary prevention of cardiovascular disease. Physicians should consider applying the new guidelines, while having an informed consent discussion with their patients about the risks and benefits of treatment.