The role of the initial 12-lead ECG in risk stratification of patients with acute coronary syndrome

Abstract

This article reviews the prognostic significance of the initial 12 lead ECG in acute coronary syndrome (ACS). In patients with non ST segment elevation ACS, the initial ECG may vary from a normal one to an ECG which demonstrates T wave inversion and ST segment deviation. Patients, who present with either a normal ECG or T wave inversion in less than 5 leads, are considered to be at low risk. Those patients who have ST segment depression or a combination of ST segment depression and elevation have the highest incidence of cardiac death, re-infarction and recurrent chest pain. In patients with ST segment elevation ACS, the mortality and morbidity is mostly influenced by infarct size. The ECG findings which correlate with infarct size are 1) the degree and extent of ST segment elevation, 2) the infarct related coronary artery and 3) distortion of the terminal portion of the QRS complex. Patients with acute anterior wall myocardial infarction due to a proximal occlusion of the left anterior descending (LAD) coronary artery have the worst short and long-term prognosis. The ECG manifestation of a proximal left anterior descending artery occlusion is ST segment elevation in lead aVL and the precordial leads, combined with ST segment depression in the inferior leads. With regard to patients who have an acute inferior wall myocardial infarction, the patients at highest risk are those with a proximal right coronary artery (RCA) occlusion artery and posterolateral extension. The ECG findings in proximal right coronary artery occlusion are ST segment in the inferior leads and in V4R. Less frequently ST segment elevations may be present in lead V1 and V2. Patients with posterolateral wall extension can be identified by the presence of ST segment depression in the right precordial leads. Finally, distortion of the terminal portion of the QRS complex is an important indicator of poor outcome. (Fig. 3, Ref. 42.)