Principles of simple heart rate adjustment of ST segment depression during exercise electrocardiography.

Compared with standard test criteria, simple heart rate (HR) adjustment of ST depression during exercise electrocardiography can improve the identification and assessment of underlying coronary artery disease. Since heart rate during exercise drives progressive ST segment depression in the presence of coronary obstruction that limits flow reserve, the ST/HR index controls for the increasing metabolic severity of ischemia that accompanies exercise. Improvement of exercise test sensitivity with the ST/HR index results from reclassification of otherwise "equivocal" and even "negative" test responses, including increased identification of one and two-vessel disease in men and in women. In addition, in population studies of low and moderate risk subjects, the ST/HR index can increase the prognostic value of the exercise electrocardiogram for prediction of cardiac risk and mortality.