Background To differentiate effects of ventricular asynchrony from an underlying hypocontractile
cardiomyopathy this study aimed to enhance the understanding of functional impairment
and structural remodeling in idiopathic left bundle-branch block (LBBB). We hypothesize,
that functional asynchrony with septal flash volume effects alone might not entirely
explain the degree of functional impairment. Hence, we suggest the presence of a superimposed
contractile cardiomyopathy. Methods In this retrospective study, 53 patients with
idiopathic LBBB were identified and matched to controls with and without cardiovascular
risk factors. Cardiovascular magnetic resonance (CMR) was used to evaluate cardiac
function, volumes and myocardial fibrosis using native T1 mapping and late gadolinium
enhancement (LGE). Septal flash volume was assessed by CMR volumetric measurements
and allowed to stratify patients with systolic dysfunction solely due to isolated
ventricular asynchrony or superimposed contractile impairment. Results Reduced systolic
LV-function, increased LV-volumes and septal myocardial fibrosis were found in patients
with idiopathic LBBB compared to healthy controls. LV-volumes increased and systolic
LV-function declined with prolonged QRS duration. Fibrosis was typically located at
the right ventricular insertion points. Subgroups with superimposed contractile impairment
appeared with pronounced LV dilation and increased fibrotic remodeling compared to
individuals with isolated ventricular asynchrony. Conclusions The presence of superimposed
contractile impairment in idiopathic LBBB is crucial to identify patients with enhanced
structural remodeling. This finding suggests an underlying cardiomyopathy. Future
studies are needed to assess a possible prognostic impact of this entity and the development
of heart failure. Trial registration: This study was retrospectively registered.
