St-qR pattern: New sign for diagnosis of anterior myocardial infarction during right ventricular pacing

In 4 patients with recent anterior wall myocardial infarction involving the ventricular septum, bipolar right ventricular apical stimulation resulted in small negative deflections preceding larger R waves (St-qR pattern) in leads I, aVL, and (except for Case 3) V6. Abnormal ST segment elevation after St-qR pattern was noted in only 2 cases. The presence or absence of repolarization changes probably reflected the stage of infarction during which electrocardiograms were obtained. The mechanisms of these changes are similar to those responsible for the qR morphology in left bundle branch block complicated by septal infarction, as shown by the case in which both patterns were seen during spontaneous left bundle-branch block as well as during right ventricular stimulation. The St-qR pattern may not be recorded when the ventricular complexes are distorted by large spikes (as when unipolar pacing is used) or when stimulation is performed from the upper portion of the right septal surface, an area to which the infarction does not extend.