ST segment depression in exercise ECG

• diagnostic sensitivity is about 66% on average (higher in multi-vessel disease and lower in single-vessel disease).
• diagnostic specificity of no ST segment depression for the absence of coronary artery disease is about 80%.

These statistical factors mean that if an exercise test is applied to a population where there is a high prevalence of coronary heart disease then the number of false positive results will be small. However if a patient comes from a population where there is a low prevalence of ischaemic heart disease eg young women with non-specific chest pain, then the proportion of false positives may approach 50%. In light of these factors, specific tables, based on Bayesian statistics, have been calculated giving the probability of a 'positive' test given a certain degree of ST depression and taking into consideration the age, sex, and symptoms when the ST depression was recorded.