Upsloping ST segments. Easy to measure, hard to agree upon.

In this issue of Circulation, Okin and coworkers1 present the results of an impressive project designed to demonstrate the effects of measuring ST segment amplitude at different times after the end of QRS on diagnostic accuracy of the exercise ECG for detection of ischemia. In all likelihood, this was prompted by a recent report critical of ST/HR types of analysis for improved detection of ischemia by Lachterman and coworkers.2 The background of this issue is the reasonable tendency of scientists and engineers to quantify an entity in terms of the strain provoked by a given degree of stress. When the subject is the heart, the relation is the amount of electrocardiographic abnormality provoked by a given degree of cardiac work. Heart rate is most often taken as the measure of cardiac stress to simplify the relation and bring it into workable terms. The measure of strain was taken to be the degree of depression of the ST segment, an indicator of the disparity between oxygen supply and demand of the working myocardium. The reasonableness of this concept has much to recommend it, and one would not have been surprised to find that this approach to interpretation of the exercise ECG yielded improved accuracy compared with conventional interpretation, but readers were surprised at the phenomenal accuracy of this method as found in early reports.3 4