Mechanism of Abnormal Septal Motion in Left Bundle Branch Block

Abstract

Objectives: This study sought to investigate how regional left ventricular (LV) function modifies septal motion in left bundle branch block (LBBB). Background: In LBBB the interventricular septum often has marked pre-ejection shortening, followed by immediate re-lengthening (rebound stretch). This motion, often referred to as septal flash, is associated with positive response to cardiac resynchronization therapy (CRT). Methods: In 10 anesthetized dogs we induced LBBB by radiofrequency ablation and occluded the circumflex (CX) (n=10) and left anterior descending (LAD) (n=6) coronary arteries, respectively. Myocardial dimensions were measured by sonomicrometry and myocardial work by pressure-segment length analysis. In 40 heart failure patients with LBBB, including 20 with post-infarct scar and 20 with non-ischemic cardiomyopathy, myocardial strain was measured by speckle-tracking echocardiography and myocardial work by pressurestrain analysis. Scar was assessed by cardiac magnetic resonance imaging with late gadolinium enhancement. Results: During LBBB each animal showed typical septal flash with pre-ejection shortening and rebound stretch, and reduced septal systolic shortening (p<0.01). CX occlusion caused LV lateral wall dysfunction and abolished septal flash due to loss of rebound stretch (p<0.0001). Furthermore, CX occlusion restored septal systolic shortening to similar level as before induction of LBBB and substantially improved septal work (p<0.001). LAD occlusion, however, accentuated septal flash by increasing rebound stretch (p<0.05). Consistent with the experimental findings, septal flash was absent in patients with LV lateral wall scar due to lack of rebound stretch (p<0.001), and septal systolic shortening and septal work far exceeded values in non-ischemic cardiomyopathy (p<0.0001). Septal flash was present in most patients with anteroseptal scar. Conclusions: LV lateral wall dysfunction and scar abolished septal flash and markedly improved septal function in LBBB. Therefore, function and scar in the LV lateral wall should be taken into account when using septal motion to evaluate dyssynchrony.

Acute redistribution of regional left ventricular work by cardiac resynchronization therapy determines long-term remodelling

“…less "wasted" work) implies also, that the potential to improve septal function is A c c e p t e d m a n u s c r i p t reduced. At the same time, the lateral wall is exposed to less pre-stretch and performs therefore less work, which explains that here the potential for unloading by CRT is lower 18,19 .…”

“…Adding information on ischemic aetiology to myocardial work mattered only before CRT, which indicates that work heterogeneity found before CRT is not only the result of loading differences which can be treated by resynchronization, but has likely also an ischemic component. Indeed, total myocardial scar burden has been shown before to be associated with non-response to CRT 23 , and a LBBB-pattern of work distribution may be mimicked by a septal scar, which also reduces septal work 19 . In such hearts, successful redistribution of myocardial work may not be possible by means of CRT which, however, becomes only overt after CRT-implantation if scar is not recognized.…”

Tracking Early Systolic Motion for Assessing Acute Response to Cardiac Resynchronization Therapy in Real Time

“…Our group has performed several studies on LBBB and CRT where sonomicrometric crystals have been implanted which allows analysis of SF ( Gjesdal et al, 2011 ; Aalen et al, 2019 ; Andersen et al, 2021 ). This study was therefore a combination of retrospective analysis of previously performed experiments ( n = 4) and a prospective study where EM tracking sensors were implanted ( n = 22).…”

“…The motion may be small or absent in the presence of septal scar, impaired global or right ventricular (RV) contractility or RV volume overload ( Remme et al, 2016 ). However, SF assessed by echocardiography or other imaging technologies has been shown to be a reliable predictor of CRT response ( De Boeck et al, 2009 ; Sohal et al, 2014 ; Risum et al, 2015 ; Aalen et al, 2019 ). The correction of this abnormal septal motion by CRT indicates an increased likelihood of LV volumetric reverse remodeling ( Jansen et al, 2007 ; Parsai et al, 2009 ; Stankovic et al, 2016 ) and some studies have shown ability to predict long term response ( Menet et al, 2017 ).…”

Radiofrequency catheter ablation for improving myocardial work in patients with ventricular pre-excitation

“…Myocardial work is an alternative tool for studying LV function through incorporating deformation and LV pressure into its analysis (5). A growing amount of evidence supports the use of myocardial work to detect early-stage heart diseases, aid prognostication, and predict therapeutic responses (6)(7)(8)(9)(10)(11)(12)(13)(14). However, myocardial work has not been studied in a ventricular pre-excitation setting.…”