Estimation of the probability of exercise-induced ischemia by quantitative ECG analysis

In order to improve the value of exercise tests for the detection of coronary artery disease (CAD) a system for on-line computer processing of the Frank lead exercise ECG was developed. Data were analyzed from 95 patients with CAD and 129 ostensibly healthy men. All subjects had a normal ECG at rest. Visual ECG interpretation during exercise yielded a sensitivity of 50% and a specificity of 95%. A large number of QRS and ST measurements were compared by discriminant function analysis in a group of 86 normal subjects and 52 patients (designated training group). Best results were obtained with a combination of two ST amplitudes from lead X: sensitivity, 85%, specificity, 90%. This was confirmed in a test group of 43 patients and 43 normal subjects. The results of the discriminant function were expressed as the likelihood ratio for an abnormal or normal ST segment at a given heart rate, a figure which provides a quantitative assessment of the degree of exercise-induces ischemia. This is a more realistic approach than classification into normal or abnormal since persons with and without CAD fall along the same continuous spectrum.