ACC/AHA guidelines explained, defended at AHA 2013

DALLAS — Leaders of the teams that developed the recently released American College of Cardiology/American Heart Association joint clinical practice guidelines for the prevention of CVD defended their work from criticism but promised evidence-based refinements, if necessary, during a forum at AHA 2013.

In particular, Donald M. Lloyd-Jones, MD, PhD, co-chair of the work group that developed a new CVD risk score, and Neil J. Stone, MD, chair of the work group that wrote new guidelines for cholesterol treatment, responded to an editorial in The Lancet alleging that the risk prediction algorithm overestimates risk by 75% to 150%.

Questioning risk estimation

That editorial, written by Paul M. Ridker, MD, and Nancy R. Cook, ScD, both of Brigham & Women’s Hospital, stated that the new algorithm overstated 10-year risk in three large-scale primary prevention cohorts by 75% to 150%, and that the new risk score could lead to significant overprescription of statins.

“It is possible that as many as 40% to 50% of the 33 million middle-aged Americans targeted by the new ACC/AHA guidelines for statin therapy that do not actually have risk thresholds that exceed the 7.5% threshold suggested for treatment,” Ridker and Cook wrote. “Miscalibration to this extent should be reconciled and addressed in additional external validation cohorts before these new prescription models are widely implemented.”

During the forum at AHA, Lloyd-Jones, of Northwestern University Feinberg School of Medicine, said he is “eager to look at their data and understand it more,” but he questioned the cohorts used in the editorial — the Women’s Health Initiative Observational Study, Women’s Health Study and Physicians’ Health Study.

“Because they’re clinical trial populations … they’re really not representative of the broad US population,” he said. “They are substantially healthier. The Women’s Health Initiative screening population … has extraordinarily low event rates, much lower than the rest of the US population. The other ones … were also remarkably healthy populations with very low rates of smoking, nowhere near what’s present in the US population.”

Another potential factor in the applicability of those cohorts, Lloyd-Jones said, is that risk factors were self-reported, and in particular, BP levels were reported in a broad range.

“I’m not at all surprised that our equations, which are representative of the broad US population, would overpredict in a group like that,” Lloyd-Jones said. “Of course they would. Let’s look at the data, though. Let’s figure it out. I’d be eager to figure out if we can tweak these things and improve them if it looks like that’s the appropriate thing to do. We’ve got more work to do, and that’s what the guidelines process is all about: continuing to marginally improve these things … so we can get the best information possible for our patients.”

Physician-patient discussion

Stone, of Northwestern University Feinberg School of Medicine, said the point of the new cholesterol guideline is not to prescribe a statin to everyone with a 10-year risk score for CVD of 7.5% or more, but to prompt discussion between physicians and patients about CVD risk that leads to better prevention and treatment.

“This isn’t some gimmick designed to push medicines on people,” he said. “This is a patient-centered approach. It’s designed to allow the physician his or her judgment, and [incorporate] the patient’s preferences once the physician can show them the factors that may make a difference, and try to decide what path is best for them. I’d like to see more guidelines do that, as opposed to one-size-fits-all. It’s the start of the risk conversation, not the end.”

For example, Lloyd-Jones said, a 65-year-old man with very few risk factors is going to have a risk score of at least 5% because of age, but “he’s probably not going to be one of the 7.5 men out of 100 who’s going to have a heart attack, so maybe he shouldn’t use a statin.”

Lloyd-Jones said the panel that devised the risk score wanted to incorporate HF as an endpoint, in addition to CHD and stroke, but could not for several reasons.

“The [HF] diagnostic criteria across different studies are sometimes widely variable,” he said. “When we put HF as an endpoint in the model, the relationship to the risk factors was quite different with HF than they were with the atherosclerotic endpoints. We are not at all trying to say that HF is not important. Of course it is. Unfortunately, it requires a little bit different approach.”

The reason why the cholesterol panel chose a 7.5% risk factor for CVD as a threshold for consideration of statin therapy, lower than that for any other guideline around the world, is because it is the only guideline to incorporate stroke into the risk equation, Stone said.

“Remember, this is not the same as Framingham, which only looks at CHD; this is CHD plus stroke,” he said. “It’s a little different from the numbers other people are using. But … we’re not going to allow treatment based on a single number. We’ve got to sit down and look at the patient characteristics.” – by Erik Swain

For more information:

Lloyd-Jones DM and Stone NJ. Clinical practice guidelines for prevention: Next steps. Presented at: the American Heart Association Scientific Sessions; Nov. 16-20, 2013; Dallas.

Ridker PM. Lancet. 2013;doi:10.1016/S0140-6736(13)62388-0.

Disclosure: Ridker reports financial ties to Amgen, AstraZeneca, Novartis, Pfizer and Siemens. Cook, Lloyd-Jones and Stone report no relevant financial disclosures.