Multivessel disease and decreased left ventricular ejection fraction (LVEF) are believed to be significant predictors of the outcome in patients with acute inferior myocardial infarction (AIMI). We attempted to determine new electrocardiographic (ECG) markers for detecting concomitant left anterior descending (LAD) disease and/or decreased left ventricular function in patients with AIMI. Eighty patients with AIMI were evaluated within 6 h of the onset of symptoms and grouped according to the presence (Group 1) or absence (Group 2) of concomitant LAD disease. All of the patients underwent coronary angiography and left ventriculography 4-6 weeks from the onset of their infarction. We studied the validity of two new ECG markers: S-T depression deeper in lead V5 than in V4 (S-T decreases V5 > V4) and negative U waves (NUs) > 0.5 mm (50 muV) in leads V4-6. The sensitivity and specificity of S-T decreases V5 > V4, NUs in V4-6, or both, in detecting concomitant LAD disease were 56% and 83%, 59% and 87%, and 35% and 98%, respectively. LAD lesions in patients who showed either of these new markers (74% of those with S-T decreases V5 > V4 and 80% of those with NUs in V4-6) were mostly in the proximal segments (AHA segments #6 or #7). Patients with either S-T decreases V5 > V4 or NUs in V4-6 tended to have asynergy in the anterolateral segment, while there was a strong correlation between the asynergy of the anterolateral and septal segments in patients who showed both ECG markers.(ABSTRACT TRUNCATED AT 250 WORDS)