Clinical significance of QRS complex during ventricular pacing: a non-invasive study

Fifty-seven patients with artificial pacemakers were studied from electrocardiograms (ECGs), vectorcardiograms, echocardiograms, and non-invasive techniques of systolic time intervals. Thirty-nine patients demonstrated a left bundle branch block (LBBB) pattern induced by transvenous right ventricular (RV) pacing, and 9 patients demonstrated a right bundle branch block (RBBB) pattern also induced by transvenous RV pacing. Perforation of the right ventricle or malpositioning of the catheter electrode was not recognized. Eight patients with epicardial left ventricular (LV) pacemakers showed a RBBB pattern and one showed a LBBB pattern. The maximal QRS vector of a RBBB pattern produced by RV pacing was directed leftwards and anteriorly, whereas that of a RBBB pattern produced by LV pacing was oriented rightwards and posteriorly. A rapid initial posterior motion of the left side of the interventricular septum (IVS) during early systole and/or anterior or flat motion of the IVS during the ejection period was almost exclusively indicative of RV pacing, regardless of the ECG wave form. There was one exceptional case in LV pacing, which showed a LBBB pattern with the same septal motion as that in RV pacing. However, the direction of the maximal QRS vector in this case was directed inferiorly, which is in sharp contrast to that in the RV pacing which was directed superiorly. There was no significant differences in systolic time intervals between a LBBB pattern and a RBBB pattern in RV pacing. Based on the hypothesis that the ECG wave form induced by epicardial LV pacing might be equivalent to that in a case of perforated right ventricle, the following conclusions can be drawn from the present study. (1) A RBBB pattern in RV pacing could be differentiated from perforation of the right ventricle. The following findings may suggest uncomplicated RV pacing: (a) the left and anterior orientation of the maximal QRS vector, and (b) a rapid initial posterior septal motion during the early systole and/or a paradoxical anterior septal motion during the ejection period. (2) A RBBB pattern in uncomplicated RV pacing does not require the repositioning of the catheter electrode. (3) A LBBB pattern with inferior orientation of the maximal QRS vector would suggest perforation of the right ventricle.