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434 P A R T III / Assessment of Heart Disease
and those that increase myocardial oxygen demand by increasing
heart rate. The commonly used coronary vasodilators are adeno- PROGNOSIS
sine and dipyridamole (Persantine), whereas dobutamine is used
to increase myocardial oxygen demand. The vasodilators cause The exercise test has been shown to be of value for estimating
greatly increased endocardial and epicardial blood flow in normal prognosis in patients with a wide range of severity of cardiovascu-
coronary arteries but not in stenotic segments, whereas dobuta- lar diseases. 4,7,17,33–35,87–89 One of the most important clinical
mine can create an imbalance between myocardial oxygen supply applications of the exercise test is the identification oflow-risk pa-
and demand by increasing heart rate and contractility. These tients in whom catheterization (and revascularization) can be
drugs are administered intravenously and, when associated with safely deferred. There are several reasons why accurately establish-
an imaging technique such as thallium-201 scintigraphy, ses- ing prognosis is important. An estimate of prognosis provides an-
tamibi, or echocardiography, can provide important information swers to patients’ questions regarding the probable outcome of
about coronary artery stenosis. Comparisons between dipyri- their illness, which may be useful to the patient in planning return
damole and standard exercise testing have demonstrated dipyri- to work or making decisions regarding disability, recreational ac-
damole to have a diagnostic accuracy similar to or slightly better tivities, andfinances. A second reason to estimate prognosis is to
than that of standard exercise testing. 83,84 The disadvantages of identify patients for whom interventions might improve outcome.
dipyridamole and adenosine stress testing include side effects Combining clinical and exercise test information into scores has
(40% to 50% of patients have minor side effects) and lack of car- been shown to improve the estimation risk among men and
diovascular response (approximately 10% of patients). 85,86 women undergoing exercise testing. 33,44,90,91
Although there are many exercise test variables known to be of
value for estimating prognosis, including exercise capacity, maxi-
GAS EXCHANGE TECHNIQUES malheart rate, a hypotensive response, ST depression, and symp-
toms, the most powerfulpredictor of risk appears to be exercise
Because of the inaccuracies associated with estimating oxygen up- capacity. Recent studies from Duke University, the Mayo Clinic,
take and METs from work rate (i.e., treadmill speed and grade), the Cleveland Clinic, Boston University and the Veterans Admin-
many laboratories directly measure expired gases. The measure- istration have confirmed the value of including exercise capacity
ment of gas exchange and ventilatory responses provides an added in the risk paradigm among patients referredfor exercise test-
dimension to the exercise test by increasing the information ob- ing. 33,88,89,92,93 It has also been recently demonstrated that the
tained concerning a patient’s cardiopulmonary function. The di- rate in which heart rate recovers from exercise, long empirically as-
V
V
rect measurement of V ˙ o 2 has been shown to be more reliable and sociated withbetter cardiovascular health, is an important risk
reproducible than estimated values from treadmill or cycle er- marker among patients undergoing exercise testing. 94–96 For ex-
˙
gometer work rate. 29 Peak Vo 2 is the most accurate measurement ample, patients who fail to decrease heart rate more than
V
V
of functional capacity and is a useful reflection of overall car- 12 beats/min, 1 minute after completing the exercise test have
diopulmonary health. Measurement of expired gases is not con- four times the risk of mortality over the subsequent 6 years. 94
sidered necessary for all clinical exercise testing, but the additional
information provides important physiologic data. Heart and lung
diseases frequently manifest themselves through gas exchange ab- EXERCISE TESTING IN SPECIAL
normalities during exercise, and the information obtained is in- POPULATIONS
creasingly used in clinical trials to objectively assess the response
to interventions. Moreover, a growing body of literature suggests Women
that exercise capacity measured directly by gas exchange techniques
provides superior prognostic information relative to exercise time The interpretation of exercise testing results in women is more
or estimated METs. 7,29,87 Recent studies have demonstrated that challenging than that in men. 4,97,98 Exercise-induced ST-segment
˙
V
indices of ventilatory inefficiency (e.g., the VE/Vco 2 slope, oscilla- depression is less sensitive among women as compared to
V
tory breathing patterns, oxygen kinetics) are very powerful predic- men. 99,100 Test specificity is also thought to be lower among
tors of risk for adverse outcomes in patients with heart failure. 7,87 women, although there is a wide variation in the reported stud-
4
Situations in which gas exchange measurements are appropriate in- ies. Some of these differences may be explained by differences in
4,8
clude the following : the meaning of chest pain presentation between men and women,
although typical angina is as meaningful in women older than
1. When a precise response to a specific therapeutic intervention
60 years as it is in men. Nearly half the women with anginal
is needed for a particular patient
symptoms in the CASS (who were younger than 65 years) had
2. When a research question is being addressed 101
normal coronary arteries. Other possible explanations for the
3. When the cause of exercise limitation or dyspnea is uncertain
lower test accuracy in women include lower disease prevalence,
4. To evaluate exercise capacity in patients with heart failure to as-
higher incidence of mitral valve prolapse and syndrome X (chest
sist in the estimation of prognosis and assess the need for trans-
pain without coronary disease), differences in microvascular func-
plantation 4,102
tion, and possibly hormonal differences.
5. To assist in the development of an appropriate exercise pre-
The accuracy for diagnosing CAD in women has been shown to
scription for cardiac rehabilitation 103
be improved by the use of multivariate methods and by the addi-
The use of these techniques, however, requires added attention tion of nuclear or echocardiographic imaging techniques. 102,104,105
to detail and a working knowledge of the equipment and basic Thus, when exercise testing is performed in women, factors that may
physiology. This is particularly important given advances in au- affect test accuracy should be carefully considered; if the exercise test
tomation for the collection and calculation of expired gases. results are uncertain or when otherwise appropriate, a radionuclide