Screening for Asymptomatic Coronary Artery Disease

 
Recommendation:
 
Clinicians should emphasize the primary prevention of 
coronary artery disease (CAD) by periodically screening for 
high blood pressure (see Chapter 3) and high serum 
cholesterol (Chapter 2) and by routinely investigating 
behavioral risk factors for CAD such as tobacco use 
(Chapter 48), dietary fat and cholesterol intake (Chapter 
50), and inadequate physical activity (Chapter 49). 
Secondary prevention of CAD (screening) by performing 
routine electrocardiography to screen asymptomatic persons 
is not recommended. It may be clinically prudent to perform 
screening electrocardiograms (ECGs) in certain high-risk 
groups (see Clinical Intervention). Routine resting or 
exercise ECG screening before entering athletic programs is 
not recommended for asymptomatic children, adolescents, or 
young adults.
 
Burden of Suffering
 
Coronary artery disease is the leading cause of death in 
the United States, accounting for about 1.5 million 
myocardial infarctions and 520,000 deaths each year.1,2 
Acute myocardial infarction is associated with high 
mortality despite recent advances in resuscitation and 
cardiac life support techniques; about 15% of patients who 
reach the hospital after acute myocardial infarction do not 
survive their hospitalization.3 In addition, CAD is 
responsible for significant morbidity and disability among 
those suffering from angina pectoris and the complications 
of myocardial infarction. Medical care and lost 
productivity for cardiovascular diseases cost the United 
States nearly $80 billion in 1986.2 Myocardial infarction 
and sudden death often occur without warning in persons 
without a history of angina pectoris or other clinical 
symptoms. The principal modifiable risk factors for CAD are 
cigarette smoking, hypertension, elevated serum 
cholesterol, and obesity. Age, sex, and family history are 
the principal nonmodifiable risk factors.
 
Efficacy of Screening Tests
 
There are two screening strategies to reduce morbidity and 
mortality from CAD. The first involves primary prevention 
by screening for cardiac risk factors, such as 
hypertension, elevated serum cholesterol, cigarette 
smoking, and physical inactivity. These topics are 
discussed in Chapters 2, 3, 48, and 49. The second strategy 
involves secondary prevention through early detection of 
coronary atherosclerotic disease. The principal tests 
considered for this form of screening include resting and 
exercise ECGs, which can provide evidence of previous 
silent myocardial infarctions. In addition, certain ECG 
findings may be useful in predicting the long-term risk of 
experiencing future coronary events. Prospective studies in 
asymptomatic persons suggest that Q-waves, ST-segment 
depression, T-wave inversion, left ventricular hypertrophy, 
and ventricular arrhythmias are associated with increased 
risk for coronary events and sudden death.4-12 However, 
there are important limitations to the sensitivity and 
specificity of electrocardiography when used as a screening 
test. A normal ECG does not rule out coronary disease; ECG 
changes often do not become apparent until atherosclerotic 
narrowing has become great enough to significantly impede 
coronary blood flow.13
  Conversely, an abnormal ECG cannot be relied on as 
conclusive evidence of underlying arterial disease. 
ST-segment changes, for example, occur commonly in the 
general population.14 Thus, routine ECG testing in 
asymptomatic persons, in whom the probability of having CAD 
is relatively low, generates a large proportion of 
false-positive results.15 Although precise data are lacking 
on the positive predictive value of the resting ECG, 
studies of exercise ECG (which has greater sensitivity and 
specificity than the resting ECG) indicate that most 
asymptomatic persons with abnormal results do not have 
underlying CAD. A series of reports have shown that 
angiographic evidence of significant stenosis (greater than 
50% narrowing) is present in only 30-43% of middle-aged 
asymptomatic persons with abnormal exercise tests.16-18 
Abnormal resting ECG findings, although often associated 
with increased long-term risk of developing symptomatic 
disease, are of limited prognostic value. Prospective 
studies lasting between 5 and 30 years have found that CAD 
develops in only 3-15% of asymptomatic persons with resting 
ECG abnormalities.4,5,9,12,19 An abnormal exercise test is 
of somewhat larger, but also limited, prognostic value in 
predicting CAD in asymptomatic persons.20 Longitudinal 
studies lasting 3-13 years have shown that, depending on 
the population being studied and the end points used to 
define cardiac events, between 5% and 46% (or an average of 
about 25%) of persons with exercise-induced ST-segment 
depression developed symptomatic coronary disease such as 
angina pectoris or myocardial infarction.21-30
 
False-positive electrocardiography results are undesirable 
for several reasons. Persons with abnormal results often 
subsequently receive diagnostic procedures such as thallium 
scintigraphy and, if this is also positive, coronary 
angiography before it can be determined that the ECG is 
falsely positive. The initial abnormal ECG as well as the 
serial tests that follow may produce considerable anxiety 
among patients. Both the extent and precision of diagnostic 
testing can be modified to some extent by performing 
work-ups in accordance with a Bayesian model:31 testing can 
be targeted to high-risk groups, such as men with a family 
history of premature CAD or those persons whose calculated 
pretest probability of developing CAD is greater than 10%. 
Nonetheless, even the initial abnormal ECG tracing may 
disqualify some patients from jobs, insurance eligibility, 
and other opportunities, although precise data on the 
magnitude of these problems are lacking.
 

Effectiveness of Early Detection
 
Although there is evidence from case-control and cohort 
studies that asymptomatic persons with selected ECG 
findings are at increased risk of cardiac death, myocardial 
infarction, and sudden death,21,29,30,32-35 there is little 
evidence that the identification of these individuals 
through ECG screening and the treatment of their 
asymptomatic CAD can reduce the incidence of these 
outcomes. Studies have shown that antianginal drugs such as 
nitroglycerin, beta-adrenergic blockers, and calcium 
antagonists can reduce the frequency and the duration of 
silent ischemic episodes,36-38 but there is no evidence 
that this treatment results in lowered incidence of cardiac 
events in persons with no history of angina or myocardial 
infarction. Other, more invasive treatment options such as 
coronary artery bypass grafting and angioplasty may be of 
benefit to asymptomatic persons with left main coronary or 
three-vessel disease.39 For example, three-vessel disease 
accounts for about 25% of abnormal angiograms in 
asymptomatic middle-aged men.40 However, it is unclear from 
current evidence that the detection of such individuals 
provides sufficient justification for routine screening of 
large asymptomatic populations.
 
Some argue that a screening ECG is valuable as a baseline'' 
to help interpret changes in subsequent ECGs.41 Such ECG 
records are clinically useful on occasion, and changes in 
serial ECGs may help predict future coronary events,11 but 
studies indicate that in actual practice, most baseline 
tracings are either unavailable or do not provide 
information that affects treatment decisions.42 Even when 
important differences are noted between the baseline ECG 
and a subsequent tracing, it is often difficult to 
determine when during the interval the change occurred. 
Another argument for electrocardiography screening is that 
the early identification of persons at increased risk for 
CAD on the basis of ECG findings may help to modify other 
important cardiac risk factors such as cigarette smoking, 
hypertension, and high blood cholesterol.41 While the 
efficacy of these behavioral changes is well established, 
these interventions are recommended independently of the 
ECG, and there is little evidence to suggest that patients 
who are aware of their ECG findings are more likely to 
change behavior or to experience a better outcome than 
those who do not obtain ECG results.
 

Periodic ECG screening has also been advocated for persons 
who might endanger public safety were they to experience 
myocardial infarction or sudden death at work (e.g., 
airline pilots, bus and truck drivers, railroad 
engineers).43 Cardiac events in such individuals are more 
likely to affect the safety of a large number of persons, 
and clinical intervention, either through medical treatment 
or counseling to change job status, might prevent such 
catastrophes. There are no available data to confirm the 
efficacy of these measures, however.
 
Preliminary exercise ECG testing has been advocated for 
sedentary persons planning to begin vigorous exercise 
programs. There is evidence that strenuous exertion may 
increase the risk of sudden cardiac death,44,45 usually as 
a result of underlying hypertrophic cardiomyopathy or 
congenital coronary anomalies in young persons46 or CAD in 
older persons.45 Cardiac events during exercise in persons 
without overt heart disease are relatively uncommon, 
however, and thus the number of cases that are preventable 
through preexercise testing of asymptomatic persons is 
limited. In addition, it has not been proved that 
restricted exertion in asymptomatic persons at risk for 
heart disease can prevent the occurrence of subsequent 
cardiac events. In populations at low risk for heart 
disease, such as healthy young persons engaged in athletic 
programs or recreational sports, the limited benefits of 
screening may be outweighed by the harmful effects of 
labeling and exercise restrictions for the large proportion 
of persons whose positive ECG results will be falsely 
positive.
 

Recommendations of Others
 
In 1977, a task force sponsored by the American College of 
Cardiology (ACC) recommended that all adults receive a 
baseline 12-lead ECG at an unspecified age, followed by 
periodic ECG testing every five years, or annually in 
high-risk persons.47 The American Heart Association (AHA) 
recommends baseline electrocardiography at age 20 followed 
by repeated tracings at ages 40 and 60 in normotensive 
persons.48 The Institute of Medicine has recommended 
obtaining a baseline ECG at age 40 or 45.49 Recommendations 
against routine electrocardiography have been issued by the 
Canadian Task Force50 and a number of reviewers.51-53 The 
ACC and AHA recommend exercise electrocardiography testing 
of asymptomatic males over age 40 under the following 
circumstances: (a) occupations affecting public safety 
(e.g., airline pilots, firemen, police officers, bus or 
truck drivers, railroad engineers); (b) two or more cardiac 
risk factors (serum cholesterol over 240 mg/dL [6.20 
mmol/L], blood pressure greater than 160/90 mm Hg, 
cigarette smoking, diabetes mellitus, family history of CAD 
onset before age 55); or (c) sedentary persons planning to 
begin a vigorous exercise program.43 The American College 
of Sports Medicine recommends preliminary exercise54
 

Discussion
 
CAD is the leading cause of death in the United States, and 
thus even preventive interventions of only modest benefit 
may have large public health implications. The screening 
ECG has this potential due to its ability to detect 
previously unrecognized atherosclerotic heart disease and 
its prognostic value in predicting subsequent illness.
 
However, the ECG is an imperfect screening test. 
False-positive ECG results are not uncommon in healthy 
persons, especially when screening is performed routinely 
in low-risk asymptomatic populations. In these groups, the 
large majority of persons with abnormal ECG results do not 
have CAD and are unlikely to develop the disease in the 
near future. To minimize the physical, psychological, and 
economic effects of false-positive labeling, ECG screening 
should be targeted to individuals at increased risk for CAD 
and to those whose sudden death or incapacitation would 
endanger the safety of others.
 

There are major costs associated with the widespread 
performance of periodic resting ECG on large numbers of 
asymptomatic persons. Exercise testing is an even more 
expensive procedure. These expenses would be justified if 
the incidence of CAD could be significantly lowered in the 
process, but such evidence is not yet available. Further 
research is necessary to demonstrate whether early 
detection and treatment of asymptomatic CAD is effective in 
lowering morbidity and mortality. In the meantime, the most 
effective proven means of preventing CAD are the 
identification and control of major cardiac risk factors 
such as hypertension, elevated serum cholesterol, and 
cigarette smoking.
 
Clinical Intervention
 
Clinicians should emphasize primary prevention of CAD by 
periodically screening for hypertension (see Chapter 3) and 
high serum cholesterol (Chapter 2) and by routinely 
investigating behavioral risk factors for CAD such as 
tobacco use (Chapter 48), dietary fat and cholesterol 
intake (Chapter 50), and inadequate physical activity 
(Chapter 49). Secondary prevention (screening) by 
performing routine electrocardiography in asymptomatic 
persons is not recommended as an effective strategy to 
reduce the risk of CAD. It may be clinically prudent to 
perform screening ECGs on asymptomatic males over age 40 
with two or more cardiac risk factors 
(hypercholesterolemia, hypertension, cigarette smoking, 
diabetes mellitus, or family history of early-onset CAD); 
on those who would endanger public safety were they to 
experience sudden cardiac events (e.g., commercial airline 
pilots); and as exercise tests for sedentary or high-risk 
males over age 40 who are planning to begin a vigorous 
exercise program. Due to the lack of data on the 
effectiveness of the screening ECG, the optimal interval 
for such testing is uncertain and is left to clinical 
discretion. The exercise ECG is a more sensitive and 
specific screening test than the resting ECG. Routine 
resting or exercise ECG screening to enter athletic 
programs is not recommended for children, adolescents, or 
young adults with no evidence of heart disease.
 

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