Unusual QRS morphology associated with transvenous pacemakers. The pseudo RBBB pattern.

Eleven patients with implanted pervenous pacemakers were found to have unusual QRS morphology resembling right bundle branch block (RBBB) on the 12-lead electrocardiogram. In nine patients, the tip of the electrode catheter was established with certainty to be in the right ventricular apex. In eight of the nine, the standard leads showed a left bundle branch block pattern (LBBB), whereas only the precordial leads V1 and V2 resembled RBBB. In only one of the nine was the RBBB pattern also seen in the standard leads. In all nine, recording the precordial leads one intercostal space below the usual space eliminated the RBBB pattern in V1-V2 and resulted in inscription of a QS complex, whereas recording the leads one space higher than usual enhanced the height of the R wave. This is explained by the marked superior and slight anterior orientation of the main QRS complex in right ventricular pacing. It is suggested that the pattern of RBBB in V1-V2 + LBBB in lead 1 be named pseudo RBBB pattern since it does not represent left prior to right ventricular activation.