Changes of Q wave amplitude during exercise for the prediction of coronary artery disease.

We have examined the changes of Q wave amplitude during exercise in 156 patients with chest pain with a view to improving the accuracy of stress testing for the diagnosis of coronary artery disease. Coronary arteriography showed significant disease in 127 patients and normal arteries or minimal disease in 29. The Q wave amplitude was measured in lead CM5 from the computer-derived average of 25 consecutive beats immediately before and at the peak of maximal treadmill exercise. The amplitude was greater in the normal subjects at rest and increased with exercise, but the reverse occurred in those with coronary disease. Using the criterion of decrease or no change of Q wave amplitude during exercise as indicating a positive test, the discriminative capacity of Q wave changes was equivalent to that of ST segment depression and was maintained when patients with myocardial infarction were excluded. Using either an abnormal Q wave or ST segment response to exercise improved the test's sensitivity with a loss of specificity but no change of predictive value. In 42% of patients with coronary disease when both the Q wave and ST segment exercise responses were abnormal coronary disease was predicted with an accuracy of 91%. Analysis of subgroups of patients with coronary artery disease suggested a possible explanation for the observed changes in Q wave amplitude, measurement of which can improve the stress test's accuracy for predicting obstructive coronary artery disease.