ACSM’s Guidelines For Exercise Testing & Prescription

Interpretation Of Clinical Test DataInterpretation Of Clinical Test Data

World Health Organization World Health Organization ::

““The primary purpose of an exercise The primary purpose of an exercise test is to determine the responses of test is to determine the responses of the individual to [exercise] efforts the individual to [exercise] efforts at given levels and from this at given levels and from this information to estimate probable information to estimate probable performance in specific life and performance in specific life and occupational situations.”occupational situations.”

• Bayes TheoremBayes Theorem states : states : ““The post-test probability of a patient The post-test probability of a patient

having disease is determined by the having disease is determined by the disease probability before the test and by disease probability before the test and by the probability that the test will provide a the probability that the test will provide a true result.”true result.”

• Bayes Theorem speaks to the issue Bayes Theorem speaks to the issue that an exercise test must have two that an exercise test must have two qualities : sensitivity and specificity.qualities : sensitivity and specificity.

Sensitivity

• Sensitivity refers to the percent of Sensitivity refers to the percent of patients tested who have CAD patients tested who have CAD andand who who demonstrate a positive (abnormal) test demonstrate a positive (abnormal) test outcome - i.e. - how often the test will outcome - i.e. - how often the test will identify a sick individual (~ 70%).identify a sick individual (~ 70%).

Specificity

• Specificity refers to the percent of Specificity refers to the percent of healthy people without CAD who healthy people without CAD who alsoalso demonstrate a negative (normal) stress demonstrate a negative (normal) stress test - i.e. - how often the test is able to test - i.e. - how often the test is able to identify a healthy individual (~80%). identify a healthy individual (~80%).

False Negative Tests

• Failure to reach ischemic thresholdFailure to reach ischemic threshold

• Monitoring an insufficient # of leadsMonitoring an insufficient # of leads

• Failure to recognize non-EKG signs Failure to recognize non-EKG signs & symptoms associated w/ CAD& symptoms associated w/ CAD

• Collateralization that masks Collateralization that masks angiographically significant CADangiographically significant CAD

• Technical & observer errorTechnical & observer error

False Positive Tests

• Drugs - digitalis preparationsDrugs - digitalis preparations

• Wolff-Parkinson-White syndromeWolff-Parkinson-White syndrome

• Left Bundle Branch BlockLeft Bundle Branch Block

• Cardiac hypertrophyCardiac hypertrophy

• HypokalemiaHypokalemia

• Mitral valve prolapseMitral valve prolapse

• Coronary spasm - Prinzmetal anginaCoronary spasm - Prinzmetal angina

Predictive Value

• The predictive value of exercise The predictive value of exercise testing is a measure of how testing is a measure of how accurately a test result correctly accurately a test result correctly identifies the presence or absence of identifies the presence or absence of CAD in the test population.CAD in the test population.

• Using exercise tests to screen large Using exercise tests to screen large numbers of asymptomatic people is numbers of asymptomatic people is of questionable value. of questionable value.

• Testing individuals with symptoms is Testing individuals with symptoms is a much more practical reason for an a much more practical reason for an exercise test.exercise test.

• Symptoms which make Bayesian Symptoms which make Bayesian sensesense and which increase the and which increase the predictive value of an exercise test predictive value of an exercise test would be :would be :

• Angina, chest discomfort/pressureAngina, chest discomfort/pressure• Anginal equivalentsAnginal equivalents• Recurrent palpitations w/ exerciseRecurrent palpitations w/ exercise• SOB w/ exertion that is unexpectedSOB w/ exertion that is unexpected• Dizziness, syncope, vertigo, diplopia w/ ex.Dizziness, syncope, vertigo, diplopia w/ ex.

Imaging Stress Tests

• Generally speaking, Generally speaking, echocardiogaphicechocardiogaphic studies will slightly improve the studies will slightly improve the sensitivity & specificity of simple GXT’s sensitivity & specificity of simple GXT’s ..

• Exercise GXT’s with technetium-Exercise GXT’s with technetium-Tc99m sestamibi imaging or Tc99m sestamibi imaging or thallium chloride-201 imaging tend thallium chloride-201 imaging tend to improve the sensitivity and to improve the sensitivity and specificity of the test to ~ 85+%.specificity of the test to ~ 85+%.

• The sensitivity and specificity of any The sensitivity and specificity of any test is improved by the number of test is improved by the number of diseased vessels.diseased vessels.