Dyssynchrony without dysfunction: Left bundle branch block does not acutely reduce cardiac output.

Authors

Carola Kruthoff, Jonathan Krauß, Jorge Sánchez, Tobias Gerach, Cristian Barrios Espinosa, Jan-Erik Duhme, Axel Loewe

Published in

The Journal of physiology. Oct 06, 2026. Epub Oct 06, 2026.

Abstract

Left bundle branch block (LBBB) describes a disruption or delay in electrical conduction through the left bundle branch of the His-Purkinje system (HPS). While new-onset LBBB commonly emerges in individuals with a history of hypertension, cardiomegaly or coronary artery disease, it can also occur in the absence of other cardiovascular abnormalities. Whether LBBB is a cause or a consequence of heart failure remains unclear. In this work, we used six different electromechanical in silico heart models with an integrated HPS to simulate both a healthy control and a pure LBBB case for each geometry, affecting only the HPS in the absence of other cardiovascular pathologies. We compared electrophysiological, mechanical and haemodynamic metrics between both cases. Despite exhibiting a severe delay of up to 87 ms in left ventricular activation, all six virtual patients showed almost no acute change in ejection fraction (EF) due to LBBB. However, an absolute increase in septal flash of 1.4 mm to 2.7 mm indicated mechanical dyssynchrony. Furthermore, we observed a relative strain increase of 12.3-30% in the left ventricular free wall across all models. The load imbalance marked by the strain increase could drive LBBB-induced remodelling, leading to a major reduction in EF over time. Regardless of variations in heart geometry, this study shows that electrical dyssynchrony immediately affects mechanics more than haemodynamics. In line with clinical data, our findings suggest that patients with LBBB might benefit from an earlier application of cardiac resynchronization therapy to prevent strain-induced remodelling and preserve cardiac output. KEY POINTS: Left bundle branch block (LBBB) describes an impairment of electrical conduction in the left bundle branch of the His-Purkinje system, causing a delay in left ventricular activation. While LBBB has been discussed as a risk factor for the progression of heart failure, the exact relationship of acute and chronic effects of LBBB in heart failure is not fully understood. In this study, we simulated both a healthy and a pure and acute LBBB scenario in six different electromechanical in silico heart models. Pure LBBB induced mechanical dyssynchrony, increasing septal flash and left ventricular free wall strain, while the ejection fraction remained virtually unchanged. The strain-induced load imbalance may cause long-term remodelling, reducing ejection fraction over time. In line with clinical data, our results suggest an early application of cardiac resynchronization therapy in patients with LBBB to prevent remodelling and sustain cardiac output.

PMID:
42837421
Bibliographic data and abstract were imported from PubMed on 07 Oct 2026.

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