Electrocardiographic prediction of the development and site of acute myocardial infarction in patients with unstable angina.

BACKGROUND: ST-T changes on 12-lead electrocardiograms (ECGs) in patients with unstable angina (UA) have limited values for prediction of subsequent acute myocardial infarction (AMI). The aim of the present study is to obtain more useful ECG signs during UA in predicting the risk and the site of AMI.

METHODS: ECGs were recorded from 238 consecutive patients with UA; 149 developed AMI, whereas 89 did not in the following 60 days after the UA episodes. P, ST-T and U wave changes in these AMI and non-AMI patients were analyzed retrospectively. Three groups of ECG leads were referred to reflect ischemic changes of anterior (V1-V5), lateral (I, aVL and V6) and inferior (II, III, and aVF) left ventricular walls. To explore the site-dependent predictors, the 149 AMI patients were divided into two groups; group A/L with anterior, antero-septal, apical or lateral AMI, versus group I/P with inferior or posterior AMI.

RESULTS: ST depression > or =1 mm and abnormal T wave or U wave changes and P wave abnormalities were observed more frequently in AMI patients than non-AMI patients. On multivariate analysis, an independent ECG finding of the development of AMI was a biphasic U wave (odds ratio (OR) 5.4, 95% confidence interval (CI), 1.9-15.6, P=0.002) in the anterior leads. An inverted T wave (OR 5.1, 95%CI, 1.7-15.5, P=0.0036) and a biphasic U wave (OR 6.0, 95%CI, 2.2-16.1, P=0.0004) in the anterior leads were independent predictors of AMI in group A/L. There was no independent ECG predictor of group I/P.

CONCLUSIONS: Biphasic U wave in anterior leads during UA is a useful ECG observation in the risk stratification of subsequent AMI. The independent ECG predictors of antero-lateral MI are inverted T wave and biphasic U wave.