A Double-Blind Evaluation of Its Use in the Diagnosis of Angina Pectoris

IN AN EFFORT to confirm the diagnosis of angina pectoris by objective evidence, Master devised a standardized two-step exercise electrocardiographic test that has become widely employed, especially in the presence of a normal resting electrocardiogram. A number of other investigators have pointed out various limitations of the test and have questioned its validity, criteria, and diagnostic reliability.'13 On the other hand, Master has reported numerous studies over the past 20 years on the basis of which he has consistently claimed an accuracy of 95 per cent for the two-step exercise electrocardiogram in detecting or excluding angina pectoris caused by ischemic heart disease.4-6 As a result of these reports, many physicians have come to place such faith in the diagnostic accuracy of the test that a negative test has been interpreted to exclude angina pectoris and a positive test to indicate the presence of significant coronary disease, regardless of the clinical diagnosis. If such a degree of reliability could be established, the two-step exercise test should virtually eliminate any diagnostic problem in regard to angina pectoris. We have been surprised, however, by the frequency with which patients without angina pectoris have shown a positive two-step test, according to Master's criteria, whereas others with unequivocal angina pectoris have presented negative tests. In our experience the test has sometimes been negative at one performance and positive several days later, although the technic was unaltered and there was no discernible cause for this change. We have also noted the failure of published reports to emphasize the fre-