Download Chapter 6 Interpretation of Clinical Exercise Test Results

Chapter 6
Interpretation of
Clinical Exercise Test Results
Copyright © 2014 American College of Sports Medicine
Exercise Testing as a Screening Tool for
Coronary Artery Disease
• Bayes’ theorem
– Bayes’ theorem states that the posttest probability of
having a disease is determined by the disease
probability before the test and the probability that the
test will provide a true result.
–
The probability of a patient having a disease before
the test is most importantly related to the presence of
symptoms (particularly chest pain characteristics), in
addition to the patient’s age, sex, and the presence of
major CVD risk factors (see Table 2.2).
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Exercise Testing as a Screening Tool for
Coronary Artery Disease (cont.)
• Typical or definite angina
– Substernal chest discomfort that may
radiate to the back, jaw, or arms
– Symptoms provoked by exertion or
emotional stress and relieved by rest
and/or nitroglycerin
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Exercise Testing as a Screening Tool for
Coronary Artery Disease (cont.)
• Atypical angina
– Chest discomfort that lacks one of the
mentioned characteristics of typical
angina
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Exercise Testing as a Screening Tool for
Coronary Artery Disease (cont.)
• The use of exercise testing in asymptomatic individuals may be useful to
health/fitness and clinical exercise professionals given its ability to
–
reflect general health,
–
identify normal and abnormal physiologic responses to physical
exertion,
–
provide information to more precisely design the exercise
prescription (Ex Rx), and
–
provide prognostic insight, especially among those with multiple
CVD risk factors.
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Interpretation of Responses to Graded
Exercise Testing
• Assessing the diagnostic, prognostic, and therapeutic
applications of the test
– Hemodynamics: assessed by the heart rate and systolic
and diastolic blood pressure responses
– ECG waveforms: particularly ST-segment displacement
and supraventricular and ventricular dysrhythmias
– Limiting clinical signs or symptoms
– Ventilatory gas exchange responses
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Box 6.1 Electrocardiographic, Cardiorespiratory,
and Hemodynamic Responses to Exercise Testing
and Their Clinical Significance
(Variables and Their Clinical Significance)
ST-segment depression (ST ↓): An abnormal ECG response is defined
as ≥1 mm of horizontal or downsloping ST ↓ 60–80 ms beyond the J
point, suggesting myocardial ischemia.
ST-segment elevation (ST ↑): ST ↑ in leads displaying a previous Q
wave MI almost always reflects an aneurysm or wall motion
abnormality. In the absence of significant Q waves, exercise-induced ST
↑ often is associated with a fixed high-grade coronary stenosis.
Supraventricular dysrhythmias: Isolated atrial ectopic beats or short
runs of SVT commonly occur during exercise testing and do not appear
to have any diagnostic or prognostic significance for CVD.
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Box 6.1 Electrocardiographic, Cardiorespiratory,
and Hemodynamic Responses to Exercise Testing
and Their Clinical Significance (cont.)
(Variables and Their Clinical Significance)
Ventricular dysrhythmias: The suppression of resting ventricular
dysrhythmias during exercise does not exclude the presence of
underlying CVD; conversely, PVCs that increase in frequency,
complexity, or both do not necessarily signify underlying ischemic heart
disease. Complex ventricular ectopy, including paired or multiform PVCs,
and runs of ventricular tachycardia (≥3 successive beats) are likely to
be associated with significant CVD and/or a poor prognosis if they occur
in conjunction with signs and/or symptoms of myocardial ischemia in
patients with a history of sudden cardiac death, cardiomyopathy, or
valvular heart disease. Frequent ventricular ectopy during recovery has
been found to be a better predictor of mortality than ventricular ectopy
that occurs only during exercise.
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Box 6.1 Electrocardiographic, Cardiorespiratory,
and Hemodynamic Responses to Exercise Testing
and Their Clinical Significance (cont.)
(Variables and Their Clinical Significance)
Heart rate (HR): The normal HR response to progressive exercise is a relatively
linear increase, corresponding to 10 ± 2 beats ∙ MET−1 for physically inactive
subjects. Chronotropic incompetence may be signified by the following:
1. A peak exercise HR that is >2 SD (≈20 beats · min−1) below the age-predicted
HRmax or an inability to achieve ≥85% of the age-predicted HRmax for subjects
who are limited by volitional fatigue and are not taking β-blockers
2. A chronotropic index (CI) <0.8 (35); where CI is calculated as the percentage
of heart rate reserve to percent metabolic reserve achieved at any test stage
Heart rate recovery: An abnormal (slowed) HR recovery is associated with a
poor prognosis. HR recovery has frequently been defined as a decrease ≤12
beats ∙ min−1 at 1 min (walking in recovery), or ≤22 beats ∙ min−1 at 2 min
(supine position in recovery).
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Box 6.1 Electrocardiographic, Cardiorespiratory,
and Hemodynamic Responses to Exercise Testing
and Their Clinical Significance (cont.)
(Variables and Their Clinical Significance)
Systolic blood pressure (SBP): The normal response to exercise is a
progressive increase in SBP, typically 10 ± 2 mm Hg ∙ MET−1 with a
possible plateau at peak exercise. Exercise testing should be
discontinued with SBP values of >250 mm Hg. Exertional hypotension
(SBP that fails to rise or falls [>10 mm Hg]) may signify myocardial
ischemia and/or LV dysfunction. Maximal exercise SBP of <140 mm Hg
suggests a poor prognosis.
Diastolic blood pressure (DBP): The normal response to exercise is
no change or a decrease in DBP. A DBP of >115 mm Hg is considered an
endpoint for exercise testing.
Anginal symptoms: Can be graded on a scale of 1–4, corresponding to
perceptible but mild, moderate, moderately severe, and severe,
respectively. A rating of 3 (moderately severe) generally should be used
as an endpoint for exercise testing.
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Box 6.1 Electrocardiographic, Cardiorespiratory,
and Hemodynamic Responses to Exercise Testing
and Their Clinical Significance (cont.)
(Variables and Their Clinical Significance)
.
.
Cardiorespiratory fitness: Average values of VO2max /VO2peak
expressed as METs, expected in healthy sedentary men and women, can
be predicted from one of several regression equations (28).
.
Also, see Table 4.9 for age-specific VO2max norms. Recent meta-analysis
suggests each 1 MET increase in aerobic capacity equates to 13% and
15% decrease in all-cause mortality and cardiovascular events,
respectively (32).
.
.
Ventilatory efficiency: Normal VE/VCO2 slope value <30. Elevated
value is strongly prognostic in patients with heart failure and potentially
patients with pulmonary hypertension. Values of ~45 or more are
indicative of particularly poor prognosis in patients with heart failure.
Elevated values are clearly indicative of worsening ventilation perfusion
abnormalities in heart failure and pulmonary hypertension populations
and thus provide an accurate depiction of disease severity (8).
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Box 6.1 Electrocardiographic, Cardiorespiratory,
and Hemodynamic Responses to Exercise Testing
and Their Clinical Significance (cont.)
(Variables and Their Clinical Significance)
Partial pressure of end-tidal carbon dioxide (PETCO2): PETCO2 is
normally 36–42 mm Hg at rest; increases 3–8 mm Hg during exercise at
mild-to-moderate workloads and decreases at maximal exercise.
Abnormally low values at rest and during exercise reflective of
worsening ventilation perfusion abnormalities and in heart failure and
pulmonary hypertension populations, and thus provide an accurate
depiction of disease severity and indicate poor prognosis. Also appears
to reflect cardiac function in patients with heart failure (4,8).
CVD, cardiovascular disease; ECG, electrocardiographic; LV, left
ventricular; MET, metabolic equivalent; MI, myocardial infarction; PVC,
premature ventricular contraction;
SD, standard deviation;
SVT,
.
.
supraventricular tachycardia;
VE, minute ventilation; VCO
2, carbon
.
.
dioxide production; VO2max, maximal oxygen uptake; VO2peak, peak
oxygen uptake.
Copyright © 2014 American College of Sports Medicine
Heart Rate Response
• Maximal heart rate (HRmax) may be predicted
from age using any of several published
equations (see Chapter 7).
• The relationship between age and HRmax for
a large sample of subjects is well
established; however, interindividual
variability is high (±12 beats · min−1).
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Heart Rate Response (cont.)
• There is potential for considerable error in
the use of methods that extrapolate
submaximal test data to an age-predicted
Hrmax.
• Using the 220 – age equation, failure to
achieve an age-predicted HRmax ≥85% in the
presence of maximal effort (chronotropic
incompetence) is an ominous prognostic
marker.
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Heart Rate Response (cont.)
• Failure to achieve an age-predicted HRmax >80% (chronotropic
incompetence), using the equation
{[HRpeak – HRrest]/[(220 – age) – HRrest]},
is also an indicator of increased risk for adverse events.
• A delayed decrease in HR early in recovery after a symptom-limited
maximal exercise test (≤12 beats · min−1 decrease after the first minute
in recovery) is also a powerful independent predictor of overall mortality
and should therefore be included in the exercise test assessment.
• Achievement of age-predicted HRmax should not be used as an absolute
test endpoint or as an indication that effort has been maximal because
of its high intersubject variability.
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Blood Pressure Response
The normal BP response to dynamic upright
exercise consists of:
• A progressive increase in SBP
• No change or a slight decrease in DBP
• A widening of the pulse pressure
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Blood Pressure Response (cont.)
• A drop in SBP (≥10 mm Hg decrease in SBP with an increase in
workload), or failure of SBP to increase with increased workload, is
considered an abnormal test response.
• The normal postexercise response is a progressive decline in SBP.
• In patients on vasodilators, calcium channel blockers, angiotensinconverting enzyme inhibitors, and α- and β-adrenergic blockers, the BP
response to exercise is variably attenuated and cannot be accurately
predicted in the absence of clinical test data (see Appendix A).
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Blood Pressure Response (cont.)
• Although HRmax is comparable for men and women, men
generally have higher SBPs (~20 ± 5 mm Hg) during
maximal treadmill testing.
• The sex difference is no longer apparent after 70 yr.
• The rate pressure product, or double product (SBP  HR), is
an indicator of myocardial oxygen demand.
• Maximal double product values during exercise testing are
typically between 25,000 (10th percentile) and 40,000 (90th
percentile).
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Electrocardiograph Waveforms
• The normal ECG response to exercise includes
the following:
– Minor and insignificant changes in P wave
morphology
– Superimposition of the P and T waves of
successive beats
– Increases in septal Q wave amplitude
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Electrocardiograph Waveforms (cont.)
– Slight decreases in R wave amplitude
– Increases in T wave amplitude (although
wide variability exists among
clients/patients)
– Minimal shortening of the QRS duration
– Depression of the J point
– Rate-related shortening of the QT interval
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ST-Segment Elevation
• ST-segment elevation (early repolarization) may be seen in the
normal resting ECG in various patterns.
• Data suggest that an early repolarization pattern in the inferior
leads may indicate an increased risk of cardiac mortality in
middle-aged individuals.
• Benign early repolarization can be common in the ECG of
athletes and is typically localized to the chest leads V2–V5.
• Early repolarization exclusively observed in the anterolateral left
precordial leads is not thought to be associated with increased
risk for sustained ventricular arrhythmias, whereas global early
repolarization (limb and precordial leads) appears to indicate a
higher risk.
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ST-Segment Elevation (cont.)
• Exercise-induced ST-segment elevation in leads with Q
waves consistent with a prior myocardial infarction may
be indicative of wall motion abnormalities, ischemia, or
both.
• Exercise-induced ST-segment elevation on an otherwise
normal ECG (except in augmented voltage right [aVR] or
chest leads V1 and V2) generally indicates significant
myocardial ischemia and localizes the ischemia to a
specific area of myocardium.
• This response may also be associated with ventricular
arrhythmias and myocardial injury.
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ST-Segment Depression
• ST-segment depression (depression of the J point
and the slope at 80 ms past the J point) is the most
common manifestation of exercise-induced
myocardial ischemia.
• Horizontal or downsloping ST-segment depression is
more indicative of myocardial ischemia than is
upsloping depression.
• The standard criterion for a positive test is ≥1.0 mm
(0.1 mV) of horizontal or downsloping ST-segment at
the J point extending for 60–80 ms.
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ST-Segment Depression (cont.)
• Slowly upsloping ST-segment depression should be
considered a borderline response, and added emphasis
should be placed on other clinical and exercise variables.
• ST-segment depression does not localize ischemia to a
specific area of myocardium.
• The more leads with (apparent) ischemic ST-segment
shifts, the more severe the disease.
• Significant ST-segment depression occurring only in
recovery likely represents a true positive response and
should be considered an important diagnostic finding.
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ST-Segment Depression (cont.)
• Adjustment of the ST-segment relative to the HR may provide additional
diagnostic information.
– The ST/HR index is the ratio of the maximal ST-segment change
(µV) to the maximal change in HR from rest to peak exercise (beats
· min−1).
– An ST/HR index of >1.6 µV ∙ beats−1 ∙ min−1 is defined as abnormal.
– The ST/HR slope reflects the maximal slope relating the amount of
the ST-segment depression (µV) to HR (beats ∙ min-1) during
exercise.
– An ST/HR slope of ≥2.4 µV ∙ beats−1 ∙ min−1 is defined as abnormal.
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ST-Segment Normalization or
Absence of Change
• Ischemia may be manifested by
normalization of resting ST-segments.
• ECG abnormalities at rest including
T-wave inversion and ST-segment
depression may return to normal during
anginal symptoms and during exercise in
some patients.
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Dysrhythmias
• Exercise-associated dysrhythmias occur in
healthy people as well as patients with CVD.
Increased sympathetic drive and changes in
extracellular and intracellular electrolytes,
pH, and oxygen tension contribute to
disturbances in myocardial and conducting
tissue automaticity and reentry, which are
major mechanisms of dysrhythmias.
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Dysrhythmias (cont.)
• Supraventricular dysrhythmias
– Atrial flutter or atrial fibrillation may occur in
organic heart disease or may reflect endocrine,
metabolic, or medication effects.
– Sustained supraventricular tachycardia (SVT)
occasionally is induced by exercise and may
require pharmacologic treatment or
electroconversion if discontinuation of exercise
fails to abolish the rhythm.
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Dysrhythmias (cont.)
• Ventricular dysrhythmias
–
The suppression of PVCs that are present at rest with exercise
testing does not exclude the presence of CVD, and PVCs that
increase in frequency, complexity, or both do not necessarily
signify underlying ischemic heart disease.
–
Serious forms of ventricular ectopy include paired or multiform
PVCs or runs of ventricular tachycardia (≥3 PVCs in succession).
–
These dysrhythmias are likely to be associated with significant
CVD, a poor prognosis, or both, if they occur in conjunction with
signs or symptoms of myocardial ischemia, or in patients with a
history of resuscitated sudden cardiac death, cardiomyopathy, or
valvular heart disease.
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Dysrhythmias (cont.)
• Criteria for terminating exercise tests based
on ventricular ectopy include sustained
ventricular tachycardia, multifocal PVCs, and
short runs of ventricular tachycardia.
• The decision to terminate an exercise test
should also be influenced by simultaneous
evidence of myocardial ischemia and/or
adverse signs or symptoms (see Box 5.2).
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Limiting Signs and Symptoms
• All of the following criteria for maximal effort can be
subjective and therefore possess limitations to varying
degrees:
– Failure of HR to increase with further increases in
exercise intensity.
– A plateau in oxygen uptake (or failure to increase
oxygen uptake by 150 mL · min−1) with increased
workload (this criterion has fallen into disfavor because
a plateau is inconsistently seen during continuous
graded exercise tests and is confused by various
definitions and how data are sampled during exercise).
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Limiting Signs and Symptoms (cont.)
– A respiratory exchange ratio (RER) ≥1.10 is a
minimal threshold that may be obtained in most
individuals putting forth a maximal effort, although
there may be considerable interindividual variability
with an RER ≥1.10.
– Various postexercise venous lactic acid
concentrations (e.g., 8–10 mmol · L−1) have been
used; however, there is also significant interindividual
variability in this response.
– A rating of perceived exertion >17 on the 6–20 scale
or >9 on the 0–10 scale.
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Ventilatory Expired Gas Responses to
Exercise
• Direct measurement of ventilatory expired gas during exercise
provides a more precise assessment of exercise capacity and
prognosis and helps to distinguish causes of exercise intolerance.
• The combination of this technology with standard GXT
procedures is typically referred to as cardiopulmonary exercise
testing (CPX).
.
• Maximal volume of oxygen
consumed per unit time (VO2max) or
.
peak oxygen uptake (VO2peak) provides important information
about cardiorespiratory fitness and is a powerful marker of
prognosis.
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Ventilatory Expired Gas Responses to
Exercise (cont.)
. .
• The assessment of ventilatory efficiency (i.e., VE/VCO2 slope and partial
pressure of end-tidal carbon dioxide [PETCO2]) provides robust prognostic
and/or diagnostic information in patients with congestive heart failure (CHF) and
pulmonary hypertension.
• Ventilatory expired gas responses often are used in clinical settings as an
estimation of the point at which lactate accumulation in the blood occurs,
sometimes referred to as the lactate or anaerobic threshold. Assessment of this
physiologic phenomenon through ventilatory expired gas is typically referred to
as ventilatory threshold (VT).
• It should be remembered that VT provides only an estimation, and the concept
of anaerobic threshold during exercise is controversial.
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Ventilatory Expired Gas Responses to
Exercise (cont.)
• In addition to estimating when
. blood lactate values begin to increase,
maximal minute ventilation (VEmax) can be used in conjunction with the
maximal voluntary ventilation (MVV) to assist in determining if there is a
ventilatory limitation to maximal exercise.
.
• The relationship between VEmax and MVV, typically referred to as the
ventilatory reserve, traditionally is defined
. as the percentage of the MVV
achieved at maximal exercise (i.e., the VEmax/MVV ratio).
.
• In most normal healthy people, the VEmax/MVV ratio is ≤0.80. Values
surpassing this threshold are indicative of a reduced ventilatory reserve
and a possible pulmonary limitation to exercise.
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Ventilatory Expired Gas Responses to
Exercise (cont.)
• Pulse oximetry should also be assessed when CPX is used to assess possible
pulmonary limitations to exercise. A decrease in pulse oximeter saturation >5%
during exercise also indicates a pulmonary limitation.
• Most currently available ventilatory expired gas systems also possess
capabilities for pulmonary function testing. Obstructive or restrictive patterns on
baseline pulmonary function testing provide insight into the mechanism of
limitations to exercise.
• A >15% decrease in FEV1.0 and/or peak expiratory flow following CPX compared
to baseline values is indicative of exercise-induced bronchospasm.
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Diagnostic Value of Exercise Testing
• Sensitivity
– The percentage of patients tested with
known CVD who demonstrate significant STsegment (i.e., positive) changes.
• Specificity
– The percentage of patients without CVD who
demonstrate nonsignificant (i.e., negative)
ST-segment changes.
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Diagnostic Value of Exercise Testing (cont.)
• Sensitivity
– A true positive exercise test reveals
horizontal or downsloping ST-segment
depression of ≥1.0 mm or more and
correctly identifies a patient with CVD.
– False negative test results show no or
nondiagnostic ECG changes and fail to
identify patients with underlying CVD.
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Box 6.2 Sensitivity, Specificity, and
Predictive Value of Diagnostic
Graded Exercise Testing
sensitivity = TP/(TP + FN) = the percentage of patients with CVD who
have a positive test
specificity = TN/(TN + FP) = the percentage of patients without CVD
who have a negative test
predictive value (positive test) = TP/(TP + FP) = the percentage of
patients with a positive test result who have CVD
predictive value (negative test) = TN/(TN + FN) = the percentage of
patients with a negative test who do not have CVD
CVD, cardiovascular disease; FN, false negative (negative exercise test
and CVD); FP, false positive (positive exercise test and no CVD); TN,
true negative (negative exercise test and no CVD); TP, true positive
(positive exercise test and CVD).
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Box 6.3 Causes of False Negative Test Results
• Failure to reach an ischemic threshold
• Monitoring an insufficient number of leads to detect ECG
changes
• Failure to recognize non-ECG signs and symptoms that may be
associated with underlying CVD (e.g., exertional hypotension)
• Angiographically significant CVD compensated by collateral
circulation
• Musculoskeletal limitations to exercise preceding cardiac
abnormalities
• Technical or observer error
CVD, cardiovascular disease; ECG, electrocardiographic.
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Box 6.4 Causes of Abnormal ST-Segment
Changes in the Absence of
Obstructive Cardiovascular Diseasea
• Resting repolarization abnormalities (e.g., left bundlebranch block)
• Cardiac hypertrophy
• Accelerated conduction defects (e.g., Wolff-ParkinsonWhite syndrome)
• Digitalis
• Nonischemic cardiomyopathy
• Hypokalemia
• Vasoregulatory abnormalities
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Box 6.4 Causes of Abnormal ST-Segment
Changes in the Absence of
Obstructive Cardiovascular Diseasea (cont.)
• Mitral valve prolapsed
• Pericardial disorders
• Technical or observer error
• Coronary spasm in the absence of significant coronary
artery disease
• Anemia
• Being a woman
aSelected
variables simply may be associated with rather
than be causes of abnormal test results.
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Diagnostic Value of Exercise Testing (cont.)
• Predictive value
– A measure of how accurately a test result
(positive or negative) correctly identifies the
presence or absence of CVD in tested patients
– Cannot be estimated directly from a test’s
specificity or sensitivity because it depends on
the prevalence of disease in the population
being tested
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Prognostic Applications of the
Exercise Test
• Several clinical factors contribute to patient outcome
including
– severity and stability of symptoms,
– left ventricular function,
– angiographic extent and severity of CVD,
– electrical stability of the myocardium, and
– the presence of other comorbid conditions.
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FIGURE 6.2. Duke nomogram uses five steps to estimate prognosis for a given individual from the parameters of the
Duke score. First, the observed amount of ST depression is marked on the ST-segment deviation line. Second, the
observed degree of angina is marked on the line for angina, and these two points are connected. Third, the point where
this line intersects the ischemia reading line is noted. Fourth, the observed exercise tolerance is marked on the line for
exercise capacity. Finally, the mark on the ischemia reading line is connected to the mark on the exercise capacity line,
and the estimated 5-yr survival or average annual mortality rate is read from the point at which this line intersects the
prognosis scale (40).
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The Bottom Line
• Interpreting the results of a clinical exercise test requires a multivariable
approach.
• The HR, hemodynamic, and ECG response to exercise are key objective
parameters that require intricate assessment from an experienced clinician. In
addition, the subjective symptoms including RPE, angina, and dyspnea are
important components of exercise test interpretation.
• When ventilatory expired gas is assessed during the clinical exercise test, a highly
accurate determination of aerobic capacity is possible in addition to a potentially
more accurate quatification of exercise effort (i.e., peak RER) and assessment of
submaximal exercise performance and ventilatory efficiency.
• Clinical exercise testing assists in the diagnosis of CVD as well as the physiologic
mechanisms for abnormal functional limitations such as unexplained exertional
dyspnea.
• The diagnostic accuracy of clinical exercise testing depends on the characteristics
of the patient who is undergoing the assessment and the quality of the test.
• Clinical exercise testing data, and in particular aerobic capacity, provide valuable
prognostic information in virtually all individuals undergoing this procedure.
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