ECHONOMY Tools for Echocardiographic Calculations Muhamed Saric, MD, PhD
New York University
demonstrate the impact of disease prevalence (pretest probability) on
positive and negative predictive values given the sensitivity and the
specificity of the test. Although the calculator is used in the context of
stress testing for coronary artery disease, basic principles apply to any
No matter how good an interpreting
physician is, some stress test results will be false positive and some false
negative. The primary determinant of the number of falsely read stress tests
is the prevalence of the coronary artery disease (CAD) in the test
(pretest probability of disease)
PPV: Proportion of all positive stress tests that are truly positive, i.e.
likelihood that a positive stress test is correct in identifying the
NPV: Proportion of all negative stress tests are truly negative; i.e.
likelihood that a negative stress test is correct in ruling out the disease.
Stress testing works best when the prevalence (pretest probability) of CAD
is moderate (10 - 30%). In low-risk populations, there is a large number of
false positives and only a few false negatives. In high-risk populations,
there is a large number of false negatives and a few false positives.