Correlation Between Conduction Times and Electrode Distance in CRT Patients

Abstract

Introduction: Positioning of the LV lead in the latest activated area is associated with maximizing the hemodynamic and clinical benefits of CRT. Maximizing RVLV lead separation is also often used during lead implantation in an attempt to achieve optimal outcomes. The correlation between RV-LV lead separation and the inter-ventricular delay measured by the conduction time between the two leads (RV-LV delay) has not been previously studied. We examined this relationship in CRT patients with the Quartet quadripolar lead (St Jude Medical, Sylmar CA). Methods: A total of 26 CRTD patients were included in the analysis. Baseline clinical parameters such as LVEF, QRS duration and NYHA class, were obtained. Interpolar conduction times were measured from RV tip to each LV lead electrode at the time of implant during RV pacing. These measurements were compared to the distances measured in mm between the RV tip to each LV electrode and cardiac dimensions on the PA chest X-ray. The ratio of RV-LV electrode distance over conduction time was calculated for each LV electrode and used as a surrogate marker for intracardiac conduction velocity. Results: The longest distance was from the RV to the distal LV electrode (57.4621.9 mm), while the longest conduction time was from the RV to the proximal LV pole (165.1632.0 msec). Therefore, the slowest conduction velocity was to the distal LV electrode (0.37 60.13 mm/msec). Higher baseline NYHA class (P50.05), female gender (P50.05) and smaller cardiac diameter (P50.01) were associated with higher D1V values. Conclusions: Utilizing the Quartet TM lead, we demonstrated that conduction from the RV tip electrode to the LV lead electrode with the greatest RV-LV physical separation had the shortest conduction time. Therefore, maximizing radiographic RV-LV separation at implant may not correspond to sites with delayed RV-LV activation, likely due to anisotropic conduction properties. Conduction to the distal LV electrode had the fastest conduction velocity. Factors predicting conduction velocity to the LV distal electrode correspond to previously identified predictors of CRT response and may explain an underlying mechanism for CRT that requires further investigation in a larger cohort of patients.