Electrocardiogram risk stratification of non–ST-elevation acute coronary syndromes

Abstract

During acute myocardial ischemia and after reperfusion, various changes in the QRS complexes, ST segments, and the T waves can be detected on the 12-lead electrocardiogram (ECG) (Fig. 1). The standard badmission Q or benrollment Q 12-lead ECG is only a snapshot that may miss some of the transient ischemic changes that can be detected with continuous ECG recording, especially in patients with non–ST-elevation acute coronary syndromes (NSTEACS). Nevertheless, there have been attempts to use this badmissionQ or benrollmentQ ECG for risk stratification and triage of patients with NSTEACS. Most studies have concentrated on the ST segment. Some have also assessed the significance of T-wave inversion. Although acute ischemia may also affect the QRS complexes (QRS duration; Q-wave, R-wave, and S-wave amplitude; and QRS axis), except of the general notion that presence of abnormal Q waves on admission may be associated with lower myocardial reserves and poorer outcome, this spectrum of ischemic ECG changes has been less investigated. Several different approaches have been used to try to quantify all these ECG changes. One approach is to concentrate on 1 variable and to compare patients with and without such ECG changes (eg, patients with and without T-wave inversion) or to use simple correlation or linear regression models (eg, sum of ST depression, number of leads with ST depression, etc). However, the initial assumption underlying this approach is inaccurate. The heart is not a sphere and the various ECG leads are not bsamplingQ identical portions of the heart. Therefore, ischemic myocardial areas of similar size may cause different absolute amount of ST depression in different number of leads depending on the exact location of ischemic zone (anterior vs lateral vs inferior). Moreover, because the