Abstract 20414: Cardiac Resynchronization Therapy Reduces Septal Contribution to Right Ventricular Work

Abstract

Introduction: During left bundle branch block (LBBB) there is abnormal motion of the interventricular septum (IVS) with early systolic beaking into the left ventricle (LV), followed by rebound stretch into the right ventricle (RV). Hypothesis: We hypothesize that septal rebound stretch contributes to RV function, and therefore cardiac resynchronization therapy (CRT) which removes rebound stretch, may have a negative effect on RV systolic performance. Methods: In 6 anesthetized dogs, LBBB was induced by radio frequency ablation. CRT was applied with electrodes on the IVS and the LV lateral wall. RV pressure (RVP) was measured by a micromanometer, and septum-to-RV free wall diameter and RV free wall long axis segment length by sonomicrometry. RV short-axis work was calculated as the area of RVP-diameter loop and long-axis work as area of the RVP-segment length loop. Results: Induction of LBBB increased RV short axis work from 36 ± 20 to 62 ± 18 mmHg*mm (± SD, p<0.05), but decreased RV long-axis work from 40 ± 13 to 30 ± 14 mmHg*mm (p<0.05). With CRT these changes were reversed; RV short-axis work decreased to 35 ± 21 (p<0.05) and long-axis work increased to 41 ± 15 mmHg*mm (p<0.05). This was associated with an increase in RV dP/dt max (p<0.05). Conclusions: Application of CRT during LBBB caused a marked reduction in RV short-axis work, indicating reduced septal contribution to RV work. This was compensated by an increase in RV free wall long-axis work, and RV dP/dt max increased. Thus, a non-failing RV has the ability to compensate and even increase its function during CRT, but emphases the importance of RV function to achieve response of CRT treatment.