Physiological Ventricular Pacing from the Right Side of the Septum by Engaging the Subendocardial Purkinje Network

Right ventricular (RV) pacing, particularly from the RV apex, causes bilateral ventricular dyssynchrony, reducing systolic and diastolic function, by delayed activation of the lateral left ventricle, resulting in a wide QRS with a left bundle branch block (LBBB) morphology. Alternative pacing strategies, such as His-bundle pacing and LBB area pacing, tend to be more physiological, avoiding this problem. The feasibility of attaining a narrow paced QRS from the RV septum has not been methodically examined. This study aimed to test the hypothesis that, through pacing at select RV septal sites by careful mapping, it is possible to achieve a narrow "paced QRS," facilitating physiological pacing. The underlying assumption is that a narrow paced QRS prevents long-term deterioration of cardiac function. During dual-chamber pacemaker implantation with standard active fixation leads, the RV septum was mapped carefully before fixing the lead. A characteristic spike potential was identified at some sites which, on stimulation, yielded a narrow paced QRS. The paced QRS duration was measured at different mapping sites; the narrowest paced complex was chosen for long-term pacing. Sixteen consecutive patients underwent pacemaker implantation using this mapping technique. A narrow paced QRS was achieved in 12 patients, whereas narrow paced complexes could not be achieved in 4 patients. Among the 12 narrow paced QRS patients (mean age, 81.5 ± 8.2 years), the indication for pacing was atrioventricular block in 6 patients and sick sinus syndrome in 6 patients. Two patients showed a negative paced QRS in leads 1 and aVL, suggesting an early left-sided septal activation. In the 12 narrow paced QRS patients, the post-pacing mean QRS duration (121.5 ± 14.9 ms) was not significantly different from the pre-pacing mean QRS duration (118.2 ± 23.5 ms) (P > .5); the QRS morphology was normal in seven patients, while four patients had LBBB and one patient had right bundle branch block. In all 12 patients, the narrowest paced complex was associated with a characteristic potential in the endocardial electrogram. Detailed RV septal mapping can yield a narrow paced QRS associated with a characteristic endocardial potential in the pre-pacing electrogram, suggesting possible direct native conduction system access.