Mechanical Effects on Right Ventricular Function From Left Bundle Branch Block and Cardiac Resynchronization Therapy

Abstract

Background: Right ventricular (RV) function influences prognosis in patients with left bundle branch block (LBBB) and cardiac resynchronization therapy (CRT). There is, however, limited insight into how LBBB and CRT affect RV function. Objective: To study how LBBB and CRT modify RV free wall function by direct ventricular interaction. Methods: In 24 LBBB patients with non-ischemic cardiomyopathy, RV and left ventricular (LV) strain by speckle-tracking echocardiography was measured before and after CRT. Underlying mechanisms were studied in 16 anesthetized dogs with ultrasonic dimension crystals and micromanometers. Results: LBBB patients demonstrated distinct early systolic shortening in the RV free wall, which coincided with the typical abnormal early systolic septal shortening. In animals, it was demonstrated that this RV free wall contraction pattern resulted in reduced myocardial work as a large portion of the shortening occurred against low pressure during early systole, coinciding with abnormal leftward septal motion. RV systolic function was maintained by vigorous contraction in the late-activated LV lateral wall which pushed the septum towards the RV. CRT reduced abnormal septal motion and increased RV free wall work as there was less inefficient shortening against low pressure. Conclusions: LBBB reduces workload on the RV free wall due to abnormal septal motion and delayed activation of the LV lateral wall. Restoring septal and LV function by CRT increases workload in RV free wall and may explain why patients with RV failure respond poorly to CRT.

Right ventricular‐arterial coupling – A new perspective for right ventricle evaluation in heart failure patients undergoing cardiac resynchronization therapy

“…Nevertheless, in the CARE HF study CRT improved LV but not RV structure and function with little evidence of an interaction with TAPSE 17 . A possible explanation for the lack of CRT response in patients with RV failure is proposed by two recent studies by Storsten 22 and Lumens 23 . The study by Storsten et al gathers animal experimental data with human measurements in patients with non‐ischemic dilated cardiomyopathy and investigated how LBBB and treatment by CRT modify RV wall motion 22 .…”

Ratio between Right Ventricular Longitudinal Strain and Pulmonary Arterial Systolic Pressure: Novel Prognostic Parameter in Patients Undergoing Cardiac Resynchronization Therapy

“…The role of analyzing RV strain in CRT patients may have more potential, as very recent data show that in patients with LV systolic dysfunction and LBBB, there is abnormal contraction of the interventricular septum (IVS) with marked early systolic shortening and leftward motion that also affect RV contraction [ 17 ]. Storsten et al investigated how LBBB and CRT modify RV free wall motion.…”

“…Storsten et al investigated how LBBB and CRT modify RV free wall motion. The work gathers animal experimental data with human measurements in patients with non-ischemic cardiomyopathy, LBBB and a normal RV function [ 17 ] The study revealed an abnormal early systolic premature shortening of the RV free wall visible with the echocardiographic longitudinal strain analysis. Interestingly, in this study, CRT reduced or abolished this abnormal RV shortening, therefore increasing the RV workload [ 17 ].…”

“…The work gathers animal experimental data with human measurements in patients with non-ischemic cardiomyopathy, LBBB and a normal RV function [ 17 ] The study revealed an abnormal early systolic premature shortening of the RV free wall visible with the echocardiographic longitudinal strain analysis. Interestingly, in this study, CRT reduced or abolished this abnormal RV shortening, therefore increasing the RV workload [ 17 ]. Lumens et al analyzed the mechanics of a failing heart with LBBB and treatment with CRT, using computer simulations with models of artificial hearts [ 18 ].…”

“…This may be explained mostly by the lack of significant decrease in PASP one year after CRT ( Table 2 ). The contradictory results of the effect of CRT upon RV function [ 19 , 20 ] may be due to the fact that the RV workload seems to be increased by CRT [ 17 ], and therefore the RV evolution in time may differ among CRT patients depending on the RV function at baseline.…”