Electrical characteristics of deep septal vs. left bundle branch (area) pacing. (25th November 2020) - Heckman, L.I.B
Abstract: Background/Introduction: Recent studies have described transvenous left bundle branch (LBB) pacing as a new conduction system pacing strategy. However, information on effect of pacing depth within the septum and the additional effect of LBB capture is unknown. Purpose: To investigate the relation of electrocardographic characteristics with transseptal LV lead implantation depth and LBB capture. Methods: 20 consecutive patients referred for pacemaker implantation were enrolled. The right atrial (RA) lead was positioned according to routine practice. The LV septal pacing lead (Medtronic 3830) was transvenously positioned against the right side of the interventricular septum and advanced in small steps of 1–2mm towards the left side of the septum. At each depth in the septum 12-lead ECG's were recorded during pacing, from which vectorcardiograms (VCG) were calculated. QRS duration and QRS area were measured, the latter being the integral of the QRSarea in X, Y and Z directions. Successful LBB capture was defined as paced right bundle branch block (RBBB) morphology, stable and short stimulus to LV activation time (LVAT; R in V5) and recorded LBB potential. Differences were compared among pacing conditions using repeated measures ANOVA with Bonferroni multiple comparisons procedure applied to pairwise comparisons. Statistical significance was assumed at p<0.05. Results: LV septal lead implantation was successful in all patients. Left bundle branch capture was achieved in 10/20 patients (50%). Post-procedural LV pacing threshold, impedance and sensing was 0.7±0.1 V at 0.5 ms pulse width, 658±5 Ω and 13±10 mV, respectively. Compared to intrinsic rhythm, QRS duration was significantly increased by both RV septum (RVS; 124±5 vs. 161±3 ms) and LV septum pacing (LVS; 142±3 ms). QRS area increased significantly during RVS pacing as compared to intrinsic rhythm but decreased when moving from RVS to LVS to values close to intrinsic rhythm (panel A & B). LVS-pacing derived QRS area was significantly lower in patients with LBB capture (36±6 mV*ms) compared to patients without LBB capture (deep septal pacing; 46±12 mV*ms). The reduction in QRS area between RVS and LVS pacing coincided with normalization of the QRS vector in the transverse plane (panel C), which is characterized electrocardiographically by predominantly negative-to-positive inversion of the QRS complex in the precordial leads (V1-V3). Conclusions: Compared to RV septal pacing, LV septal pacing restores ventricular electrical synchrony, as determined by QRS area, and normalizes the activation vector in the transverse plane to a level comparable to intrinsic rhythm. Differences in resynchronization between left bundle branch pacing and deep septal pacing are small. Funding Acknowledgement: Type of funding source: None