Patterns of maximal spatial ST vector of S-T segment elevation in the right praecordial leads of the electrocardiogram in patients with acute inferior myocardial infarction.

Thirty patients with S-T segment elevation in the right praecordial leads during acute inferior myocardial infarction were studied by vectorcardiography. From the vectorcardiographic traces two types of maximal spatial ST vectors were seen. Their directions pointed either to: (1) the right-anterior-inferior, or (2) the right-posterior-inferior octant. This spatial ST vector could cause S-T segment elevation in the right praecordial leads in patients with acute inferior myocardial infarction in two ways. (1) The projection of the right-anterior-inferior maximal spatial ST vector on the horizontal plan pointing to right-anterior direction directly causes S-T segment elevation in the right praecordial leads--only a minority of patients (20%) show this. (2) The large magnitude of the right-posterior-inferior maximal spatial ST vector indirectly causes S-T segment elevation in the right praecordial leads adjacent to it. The majority of patients (80%) belong to this group. Therefore, the maximal S-T segment elevation in the electrocardiogram should be looked for in leads V5R to V8R. The direction of the vectors imply that in some patients there would be no S-T segment elevation in lead V4R. This study indicates that the use of S-T segment elevation in V4R, or several right praecordial leads, to claim that the maximal ST vector points to the right-anterior direction can be misleading. Without directional information, the use of single lead or several leads to detect the maximal spatial ST vector by a scalar electrocardiogram will give incomplete information.(ABSTRACT TRUNCATED AT 250 WORDS)