Who should be getting screened for CHD?

Coronary heart disease remains the leading cause of death among American men and women. An expert tells which tests should be used and when.

Your 48-year-old female patient asks what kind of coronary heart disease (CHD) screening tests she should have. She’s a nonsmoker with BP 135/85 mm Hg, total cholesterol 190 mg/dL, and LDL 130 mg/dL, giving her a 4% chance of having CHD in the next 10 years. However, she also reports strong family history of premature heart disease in several first-degree relatives.

What do you tell her?

For most primary-care practices, there’s no higher prevention priority than CHD. Despite a decrease in death rates over the past 20 years, CHD remains the leading cause of death among American men and women. Age, male gender, tobacco use, hypertension, hyperlipidemia, diabetes, and family history of CHD are the major identified risk factors. Using data from the Framingham Heart Study, risk-calculation tools1 have been developed that base their assessment on the chance of a coronary event in the next 10 years: <10% chance is low risk, 10%-20% chance is intermediate risk, and >20% chance is high risk.

The following noninvasive screening tests have been proposed for use in asymptomatic persons: resting ECG, exercise ECG, electron-beam CT (EBCT), carotid intimal thickness, and ankle-brachial index (ABI). Currently, however, no authoritative organizations or expert panels recommend routine screening for CHD in the asymptomatic general population.

In 2004, the U.S. Preventive Services Task Force (USPSTF) updated its guidelines on screening for CHD, recommending against routine screening with resting ECG, exercise ECG, or EBCT for coronary calcium, coronary artery stenosis, or prediction of CHD risk in asymptomatic adults at low risk. In addition, the USPSTF notes that “there is insufficient evidence to recommend for or against screening in adults at increased risk of CHD.”2 The Task Force finds fair evidence that ECG, exercise ECG, and EBCT can identify people at increased risk of CHD, but there is no indication that detection by screening results in better outcomes.

In the American College of Cardiology/American Heart Association (ACC/AHA) 2002 guidelines,3 exercise ECG testing to evaluate persons with multiple risk factors gets a “IIb” recommendation. (IIb means there is conflicting evidence or a divergence of opinion about the validity of the recommendation.) Exercise ECG testing for men older than 45 and women older than 55 years who plan to start vigorous exercise, or are involved in occupations in which impairment might affect public safety, or are at high risk for coronary artery disease because of other conditions (e.g., peripheral vascular disease and chronic renal failure), also gets a IIb rating.

The resting ECG is not very sensitive for predicting CHD in a low-prevalence asymptomatic population. While an ECG abnormality does indicate a significantly higher risk of having a coronary event, most people having a first coronary event will have had a previously normal resting ECG. An abnormal exercise ECG indicates a person is at higher risk of having a coronary event, but the test is not very sensitive or specific. The chance that an asymptomatic person with an abnormal stress test will have an angiographically significant stenosis (positive predictive value) ranges from 25% to 72%.4

No study of the sensitivity and specificity of EBCT calcium scores in asymptomatic persons has been done. However, in patients with symptoms of CHD, EBCT has a sensitivity of 80% and a specificity of 40% for detecting angiographically significant coronary artery stenosis. The sensitivity and specificity would be expected to be substantially lower in a low-prevalence asymptomatic population.

The recommendation to measure carotid-artery intimal thickness and the ABI reflects the fact that people with peripheral vascular disease (PVD) have a higher probability of having CHD. Most people with PVD will also have multiple risk factors for CHD. No studies have shown that screening asymptomatic people for carotid intimal thickness or ABI leads to better outcomes from CHD. Studies have also failed to show that knowledge of an abnormal screening result motivates patients to be more compliant with risk-factor reduction.5 And a normal result might falsely reassure patients with risk factors that they don’t need to aggressively pursue risk-factor reduction.

In my opinion, stress ECGs or EBCT should be considered for asymptomatic persons only if results will make a difference. The clinician should ask, “Will I do something different based on this test?” If the answer is “Yes,” screening may be reasonable. For example, in the 48-year-old woman at the beginning of this article, screening could make a difference. If EBCT showed a high coronary calcium score, I would recommend aggressive BP and lipid lowering in addition to low-dose aspirin. If the coronary calcium score were zero or low, I would be relatively reassured that she was still low-risk.

Dr. Frame is clinical professor of family medicine at the University of Rochester School of Medicine and Dentistry in Rochester, N.Y. He is also a former member of the U.S. Preventive Services Task Force.

References

1. Framingham risk calculator from the National Heart, Lung, and Blood Institute. Available at: hp2010.nhlbihin.net/atpiii/calculator.asp. Accessed April 17, 2007.

2. U.S. Preventive Services Task Force. Screening for coronary heart disease: recommendation statement. Ann Intern Med. 2004;140:569-572.

3. American College of Cardiology Foundation/American Heart Association. ACC/AHA Guideline Update for exercise testing. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Exercise Testing). Bethesda, Md.: American College of Cardiology Foundation; 2002. Available at www.acc.org /qualityandscience/ clinical/guidelines/exercise/exercise.pdf. Accessed April 17, 2007.

4. Greenland P, Gaziano JM. Selecting asymptomatic patients for coronary computed tomography or electrocardiographic exercise testing. N Engl J Med. 2003;349:465-473.

5. Greenland P. Improving risk of coronary heart disease: can a picture make the difference? JAMA. 2003;289:2270-2272.

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