title: Septal flash and septal rebound stretch have different underlying mechanisms.
abstract: Abnormal left-right motion of the interventricular septum in early systole, known as septal flash (SF), is frequently observed in patients with left bundle branch block (LBBB). Transseptal pressure gradient and early active septal contraction have been proposed as explanations for SF. Similarities in timing (early systole) and location (septum) suggest that SF may be related to septal systolic rebound stretch (SRSsept). We aimed to clarify the mechanisms generating SF and SRSsept. The CircAdapt computer model was used to isolate the effects of timing of activation of the left ventricular free wall (LVFW), right ventricular free wall (RVFW), and septum on SF and SRSsept. LVFW and septal activation times were varied by ±80 ms relative to RVFW activation time. M-mode-derived wall motions and septal strains were computed and used to quantify SF and SRSsept, respectively. SF depended on early activation of the RVFW relative to the LVFW. SF and SRSsept occurred in LBBB-like simulations and against a rising transseptal pressure gradient. When the septum was activated before both LVFW and RVFW, no SF occurred despite the presence of SRSsept. Computer simulations therefore indicate that SF and SRSsept have different underlying mechanisms, even though both can occur in LBBB. The mechanism of leftward motion during SF is early RVFW contraction pulling on and straightening the septum when unopposed by the LVFW. SRSsept is caused by late LVFW contraction following early contraction of the septum. Changes in transseptal pressure gradient are not the main cause of SF in LBBB.
authors.affiliation: CARIM School for Cardiovascular Diseases, Maastricht University Medical Center, Maastricht, The Netherlands; and j.walmsley@maastrichtuniversity.nl.
authors.forename: John
authors.identifier: http://orcid.org/0000-0001-9171-7530
authors.initials: J
authors.lastname: Walmsley
authors.affiliation: CARIM School for Cardiovascular Diseases, Maastricht University Medical Center, Maastricht, The Netherlands; and L'Institut de Rythmologie et Modélisation Cardiaque (IHU-LIRYC), Université de Bordeaux, Pessac, France.
authors.forename: Peter R
authors.identifier: http://orcid.org/0000-0002-1845-6837
authors.initials: PR
authors.lastname: Huntjens
authors.affiliation: CARIM School for Cardiovascular Diseases, Maastricht University Medical Center, Maastricht, The Netherlands; and.
authors.forename: Frits W
authors.initials: FW
authors.lastname: Prinzen
authors.affiliation: CARIM School for Cardiovascular Diseases, Maastricht University Medical Center, Maastricht, The Netherlands; and.
authors.forename: Tammo
authors.identifier: http://orcid.org/0000-0001-6897-9700
authors.initials: T
authors.lastname: Delhaas
authors.affiliation: CARIM School for Cardiovascular Diseases, Maastricht University Medical Center, Maastricht, The Netherlands; and L'Institut de Rythmologie et Modélisation Cardiaque (IHU-LIRYC), Université de Bordeaux, Pessac, France.
authors.forename: Joost
authors.identifier: http://orcid.org/0000-0001-8129-7384
authors.initials: J
authors.lastname: Lumens
mesh_terms: D002037:Bundle-Branch Block / Q000503:physiopathology*; D003198:Computer Simulation; D004452:Echocardiography; D006801:Humans; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D013599:Systole; D054088:Ventricular Septum / Q000503:physiopathology*
keywords: cardiac mechanics; computer modeling; echocardiography; left bundle branch block; ventricular interaction