New ACCF/ACC guidelines for coronary artery calcium scanning in asymptomatic adults
There are compelling reasons to screen for coronary artery disease. It is the leading cause of death and chronic illness in men and women. A new coronary event occurs, on average, every 25 seconds in the US, and about once per minute someone dies of one.
The most feared consequence of CAD, sudden cardiac death, occurs without any prior premonitory symptoms or prior cardiac diagnosis in at least half of its instances. Yet, we have excellent therapies that can prevent unnecessary events. The long premonitory phase before CAD becomes clinically evident represents an opportunity for early intervention to slow the progression of this disease, if we can identify the patient at risk. Currently, however, there is no national consensus on how to best screen for heart disease.
Recently, the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines released new guidelines for assessment of CV risk in asymptomatic adults. All potential modes of screening were considered. Contained in the report were new guidelines for using coronary artery calcium (CAC) scanning to screen for CAD. Based on evidence from a very large number of manuscripts reporting consistent results of the strong prognostic information of CAC scanning in more than 100,000 patients, the new guidelines, which are characteristically conservative, contain two NYHA Class IIa indications, with NYHA Class IIa indications defined as those for which [t]he weight of evidence or opinion is in favor of the procedure or treatment.
This represents the first time that CAC scanning has received a NYHA Class IIa indication. Class IIa indications are for asymptomatic patients with an intermediate (10% to 20%) 10-year risk of cardiac events based on the Framingham risk score (FRS) or other global risk algorithm, and for asymptomatic patients 40 years and older with diabetes mellitus.
Because the number of US adults with an intermediate FRS and/or diabetes is substantial, these guidelines mean that many may benefit from CAC scanning. What do clinicians need to know about these new guidelines?
CAC as a prognostic predictor
The presence of CAC is a specific marker of atherosclerosis. Evidence indicates a proportional relationship between CAC score measurements and the frequency of subsequent cardiac events among men and women and across all ethnicities. A zero CAC score is a strong predictor of low risk, with a 10-year event rate of only about 1%. A zero CAC score is also associated with low risk among patients with diabetes. Importantly, about 30% of adult diabetics have a zero CAC score, indicating that diabetes is not necessarily a CAD equivalent.
It is also important to note that although early prognostic studies commonly assessed the prognostic accuracy of CAC scanning in isolation to clinical data, a number of recent studies have compared how global risk scores alone vs. combining global risk and CAC scores predicts the actual observed occurrence of clinical events. These studies demonstrate that the addition of CAC scores results in substantial improved risk prediction for events when both scores are considered together. Notably, a measurement that quantifies this improvement termed the net reclassification improvement is consistently highest in those patients with intermediate global risk scores.
A note on clinical management
Current trends call for assessing cardiac tests according to their ability to lead to direct improvement in clinical management, as evidenced by improved CAD risk profiles, more judicious downstream uses of tests and procedures, and reduction in clinical events. Study of CAC scanning and other noninvasive tests relative to these considerations is currently scant. However, new evidence indicates aggressive physician use of medications to control CAD risk factors when CAC scans indicate atherosclerosis. Although such medication use can reduce CAD risk profiles, it is not yet known whether CAC scanning is also an effective motivational tool for spurring improvement in patients health behaviors.
Importantly, data based on patients undergoing both CAC scanning and stress-rest myocardial perfusion single-photon emission CT demonstrate a threshold relationship between CAC magnitude and myocardial ischemia, with CAC scores less than 400 generally being associated with a low frequency of inducible myocardial ischemia. These findings suggest a use for CAC scanning beyond screening to triage which patients with suspected CAD may be suitable for referral for cardiac stress tests. The use of stress SPECT or PET myocardial perfusion imaging or stress echo is considered appropriate in recent Appropriate Use Criteria of the ACCF in patients with CAC scores of more than 400. Consistent with this, new data from the Early Identification of Subclinical Atherosclerosis by Noninvasive Imaging Research (EISNER) study indicate that physicians are limiting cardiac stress testing in patients with low CAC scores and ordering stress tests with high frequency in patients with high CAC scores.
The selection of which patients deserve CAC scanning is predicated on the assumption that the FRS accurately reflects baseline risk. Substantial data, however, now question the accuracy of the FRS in women because the FRS is frequently low among women with elevated CAC scores. Recognizing these limitations, the new guidelines also gave a recommendation, although less strong (Class IIb), for CAC scanning of patients with a 6% to 9% FRS score.
In addition, physicians must be mindful that the FRS score does not consider the important CAD risk factors of family history, obesity and poor physical fitness, or the chronicity of CAD risk factors. Thus, consideration of such data may temper the decision to rely on the FRS as a guide for the need for CAC scanning in individual patients. Most notably, emerging data suggest that atherosclerotic burden may be substantially elevated in asymptomatic patients vs. asymptomatic individuals merely seeking to assess their future risk for CAD. Accordingly, a study is needed to determine whether a different metric should be applied for determining when CAC scanning is useful in patients as opposed to screening the public.
The new ACCF/ACC guidelines for CAC scanning calls for CAC scan consideration among asymptomatic individuals with intermediate global risk scores and for diabetics older than the age of 40 years. An abnormal CAC scan establishes the presence of underlying CAD and signals the need for aggressive risk factor management. The risk for future events increases in direct proportion to CAC score elevation. Patients with high CAC scores may be candidates for cardiac stress testing, to rule out the presence of silent myocardial ischemia. Application of these newly published guidelines may represent a true breakthrough in our nations attempt to eliminate unnecessary myocardial infarction and coronary deaths due to unrecognized heart disease.
Alan Rozanski, MD, is a cardiologist at the New York Cardiac Diagnostic Center and professor of medicine at the Columbia University College of Physicians and Surgeons in New York. Daniel S. Berman, MD, is chief of cardiac imaging and nuclear cardiology at the S. Mark Taper Foundation Imaging Center at Cedars-Sinai Medical Center in Los Angeles, and is a member of the Cardiology Today Editorial Board.
For more information:
- Blaha M. JACC Cardiovasc Imaging. 2009;2:692-700.
- Elias-Smale S. J Am Coll Cardiol. 2010;56:1407-1414.
- Erbel R. J Am Coll Cardiol. 2010;56:1397-1406.
- Greenland P. J Am Coll Cardiol. 2010;56:2182-2199.
- Lloyd-Jones D. Circulation. 2009;119:480-486.
- Polonsky T. JAMA. 2010;303:1610-1616.
- Shaw LJ. J Am Coll Cardiol. 2009:54:1258-1267.