Significance of U wave polarities in previous anterior myocardial infarction

The significance of the polarity of U waves in left precordial leads was evaluated in relation to myocardial perfusion (T1 201 myocardial scintigraphy) and left ventricular function (99m Tc radionuclide ventriculography) in 63 patients with clinical and electrocardiographic evidence of a previous anterior myocardial infarction. Patients were divided into three groups according to the polarity of the U waves: positive U waves, flat U waves, and negative U waves. Twelve matched patients served as normal controls. The following parameters were analyzed: (1) total number of abnormal Q waves; (2) total myocardial perfusion index and regional myocardial perfusion index; (3) global ejection fraction; (4) regional ejection fraction; and (5) number of diseased coronary arteries. The total myocardial perfusion index values were 43.9 ± 1.0 in controls, 40.8 ± 3.4 in the positive U wave group, 33.4 ± 3.5 in the flat U wave group, and 30.3 ± 4.4 in the patients with negative U waves. Global ejection fractions in these groups were, respectively, 63.9 ± 8.6%, 65.0 ± 11.8%, 53.6 ± 8.1%, and 36.5 ± 13.6%. The sensitivity of negative U waves suggesting a global ejection fraction of less than 45% was 91.6%, and the specificity was 82.1%. Therefore the size of myocardial infarction increased and left ventricular function decreased, in order, from patients with positive U waves, to those with flat U waves, to those with negative U waves, with statistically significant differences. The regional myocardial perfusion index of apical and anterolateral segments tended to decrease, in successive order, from the patients with positive U waves, to those with flat U waves, to those with negative U waves; but no statistically significant difference was noted between the flat U wave and negative U wave groups. The regional ejection fraction in anteroseptal and apicoinferior segments decreased with significant differences in successive order from the groups with positive U waves, to those with flat U waves, to those with negative U waves. However, for the posterolateral segment only those with negative U waves revealed significantly lower values compared to the other three groups.