Vector U loop in patients with old myocardial infarction.

The U loop of the vectorcardiogram was examined qualitatively and quantitatively in 100 normal subjects and 67 patients with old myocardial infarction, using a direct-writing vectorcardiograph with memory function. In the control group, the U loop was directed to the left, anteriorly and inferiorly, and it was inscribed counterclockwise in the horizontal plane. In patients with anterior myocardial infarction, the U loop tended to be displaced to the right, and in patients with inferior myocardial infarction to the right and superiorly. The shape of the U loop in patients was also different from that of normal subjects. The maximum U vector was significantly smaller in magnitude both in patients with anterior and inferior myocardial infarction than that of normal subjects (p less than 0.01). In patients with ventricular aneurysm, the magnitude of the maximum U vector was significantly smaller and its direction was displaced more to the right and posteriorly than those without aneurysm (p less than 0.01). In standard 12-lead electrocardiogram (ECG), observation of the U wave in patients with old myocardial infarction was difficult, especially in the limb lead, because of the small size of the U wave. Therefore, vectorcardiographic observation may be more useful than electrocardiographic observation for the analysis of the U wave in patients with old myocardial infarction.