January 22, 2018, 02:14 pm Chris Crawford — On Jan. 16, the U.S. Preventive Services Task Force (USPSTF) released two draft recommendation statements and draft evidence reviews related to screening for cardiovascular disease (CVD): a draft recommendation statement and draft evidence review on screening for peripheral artery disease (PAD) and CVD risk assessment using the ankle-brachial index (ABI), and a draft recommendation statement and draft evidence review on risk assessment for CVD using nontraditional risk factors.
In each case, task force members concluded that the available evidence was insufficient to assess the balance of benefits and harms of the practice examined.
Patients with PAD experience reduced blood flow to the limbs, especially the legs, due to systemic atherosclerosis. This condition can cause leg and foot pain when resting or walking, poor wound healing, tissue damage, and even loss of limbs. In addition, patients with PAD are more likely to have a CVD event, such as a heart attack or stroke.
Resting ABI is the most commonly used test for detection of PAD in clinical settings, although results can vary based on the precise measurement protocol used. Calculated as the systolic blood pressure obtained at the ankle divided by that obtained at the brachial artery in a patient who is lying down, a ratio of less than 1 (typically defined as <0.9) is considered abnormal and is commonly used to define PAD.
According to the task force, however, although a low ABI value is frequently used as a surrogate marker for PAD in practice, its accuracy as a screening tool for PAD in asymptomatic primary care patient populations has not been well studied.
The task force examined current evidence to see whether screening asymptomatic patients with ABI helped reduce mortality or morbidity from CVD or PAD. Based on its review, the USPSTF found insufficient evidence to assess the balance of benefits and harms of screening for PAD and CVD using the ABI in adults -- an "I" statement.
"For people with symptoms of PAD, the ABI can be used for diagnosis," said USPSTF member and family physician Alex Krist, M.D., M.P.H., in a news release. "However, more evidence is needed to determine if the ABI can accurately identify PAD in people without signs or symptoms."
This draft recommendation statement updates and is consistent with the task force's 2013 final recommendation statement. The AAFP agreed with the USPSTF's 2013 recommendation in its own guidance at that time.
Jennifer Frost, M.D., medical director for the AAFP Health of the Public and Science Division, agreed that ABI is best used to diagnose PAD in patients with symptoms of the condition, not to screen those who show no signs or symptoms.
"By performing ABI in asymptomatic patients, and therefore diagnosing the condition early, the hope is to prevent progression of the disease and to prevent a cardiac event," she told AAFP News. "Unfortunately, there is not enough evidence to determine if screening has this effect."
Frost noted that in the USPSTF's evidence review, there were two studies that evaluated the benefit of treating screen-detected PAD, one with daily aspirin and the other with exercise. However, neither study showed any benefit.
"It's important to remember that the vast majority of patients with PAD have risk factors for heart disease: current smoking, high blood pressure, high cholesterol level or type 2 diabetes," she said. "Family physicians are already helping their patients to control these risk factors and promoting healthy lifestyle choices. A positive or negative ABI shouldn't change that."
The second USPSTF draft recommendation looked at whether adding certain nontraditional risk factors to traditional CVD risk models could improve risk assessment for CVD in asymptomatic adults.
Traditional CVD risk assessment tools used to inform treatment to prevent CVD events through risk factor modification, such as the Framingham Risk Score, the Pooled Cohort Equations or similar models, are based on age, race/ethnicity, gender, diabetes, smoking status, cholesterol levels and blood pressure.
The task force examined evidence regarding use of three nontraditional CVD risk factors -- the ABI, high-sensitivity C-reactive protein (hs-CRP) and coronary artery calcification (CAC) score -- ultimately concluding that the evidence was insufficient to assess the balance of benefits and harms of adding these three factors to traditional risk assessment for CVD in asymptomatic adults to prevent CVD events -- an "I" statement.
"While there is some evidence that ABI, CAC and hs-CRP can slightly improve clinicians' ability to define risk, the amount of improvement is not large or precise enough to help clinicians make better treatment or care decisions to prevent heart attack or stroke," said task force member Seth Landefeld, M.D., in the news release. "More research is needed to understand the benefits and harms of using these three nontraditional risk factors in addition to the traditional risk factors for assessing CVD risk."
This draft recommendation statement updates and is consistent with the USPSTF's 2009 final recommendation statement. At the time, the AAFP mirrored this guidance in its own recommendation.
Diagnosis and treatment of CVD is keenly important, according to Frost, because it's the leading cause of death in adults.
"While traditional risk factors help determine who is at increased risk, they are by no means perfect," she said. "The addition of other risk factors has the potential to more clearly define who is at risk, allowing clinicians to focus treatment on those at highest risk and avoid treatment and its potential harms in others.
"However, at this point, these nontraditional risk factors may offer a small improvement in the ability to identify patients at increased risk, but there is not currently evidence that this improves patient outcomes."
Frost said because these tests are being promoted to the public, family physicians need to be able to counsel their patients about any potential benefits and harms.
The USPSTF listed the primary potential harm of adding nontraditional risk factors to CVD risk assessment as low-dose radiation exposure from CAC score measurement. More general potential harms are false-positive test results and subsequent invasive diagnostic procedures, such as coronary angiography.
The USPSTF is inviting comments on its draft recommendation statement and draft evidence review on screening for PAD and CVD risk assessment with the ABI, as well as on its draft recommendation statement and draft evidence review on CVD risk assessment with nontraditional risk factors.
The public comment window for each of the draft recommendations and draft evidence reviews is open until 8 p.m. EST on Feb. 12. All comments received will be considered as the task force prepares its final recommendation.
The AAFP will review the USPSTF's draft recommendation statements and supporting evidence and provide comments to the task force. The Academy will release its own recommendation on the topic after the task force finalizes its guidance.