When using intracardiac electrocardiography to guide pacing catheters in acute myocardial infarction, both ST segment elevation and a large S wave are required to confirm right ventricular apical placement and avoid misinterpreting coronary venous placement.
Intracardiac electrocardiography has been reported to be the most reliable of the techniques used for guiding placement of transvenous pacing catheters. When a catheter electrode is in contact with the right ventricular apical endocardium, the intracardiac electrogram demonstrates marked ST segment elevation and, usually, a very large S wave. The case presented indicates that both of these features of the intracardiac electrogram should be sought since ST segment elevation alone may represent epicardial recording of an acute myocardial infarction when the catheter electrode is in the coronary venous system.
Wallace et al. (1979) studied this question.