Usefulness of the QTc interval in predicting myocardial ischemia in patients undergoing exercise stress testing

Most recently, there has been great interest in the role of QT dispersion, a measure of interlead variations of the QT interval duration in the surface electrocardiogram. These variations are believed to reflect regional differences in repolarization heterogeneity and thus may provide an indirect marker of the potential for arrhythmia.(1,2) However, more basic contributions to changes in PR segments or QT intervals during ischemia are less well characterized. Nonetheless, it seems reasonable to propose the use of the QT interval as a possible candidate for the assessment of ischemia, because it reflects, within limits, the duration of depolarization and repolarization. Furthermore, ischemia is known to prolong the QT interval due to its relation to the calcium flux during the cardiac action potential.(3) Accordingly, in this study we sought to address variations in the QTc segment in patients undergoing exercise stress testing for the diagnosis of coronary artery disease in an attempt to assess the sensitivity and specificity of this electrocardiographic variable in the detection of ischemia.