P5259Evaluation of functional impairment and cardiac remodelling in isolated left branch bundle block using magnetic resonance imaging
Authors: Salatzki J , Fischer T , Ochs M , Fortner P , Hirschberg K , Andre F , Katus H , Riffel J 
Published: October 2019

Abstract

Introduction
Left bundle-branch block (LBBB) is associated with underlying cardiovascular abnormalities, such as dilated cardiomyopathy and coronary heart disease. However, an isolated LBBB can be found in individuals without detectable cardiovascular disease. Echocardiographic studies demonstrated a reduced left ventricular (LV) ejection fraction (EF) and an increased LV cavity volume and mass in patients with isolated LBBB. Recent studies have shown larger cavity volumes (end-diastolic volume – EDV; end-systolic volume – ESV) and lower LVEF using CMR. However, there is still limited data on cardiac function, volumes and mass and the correlation between the parameters and the QRS duration (QRS) in patients with isolated LBBB.

Purpose
In this retrospective study LV function, volume, mass, T1-values and myocardial strain were measured and correlation between QRS duration in patients with isolated LBBB was identified using CMR.

Methods
Potential cases were identified from our local database, who underwent CMR during 2015–2018. We excluded patients with echocardiographic abnormalities besides abnormal septal motion or greater than a mild valve disease, known cardiovascular disease (coronary artery disease, cardiomyopathy or arrhythmia), history of potential cardiotoxic chemotherapy. We could identify 26 adults, who underwent CMR in a 1.5- or 3-Tesla scanner. LBBB was confirmed by ECG prior to CMR by a cardiologist. T1-values (MOLLI) were available in 19 patients. Myocardial strain (tissue tracking) could be performed in 23 patients. Associations were tested using Pearson's correlation analysis.

Results
26 patients (age 61.5±9.6 years, 19 women, BMI 25.4 (18.2–38.1)) with isolated LBBB were included (QRS duration: 138±12ms). CMR results in the cohort revealed a reduced LVEF (53.4±3,8%) and slightly enlarged LV cavity when corrected to body-surface area (BSA) (LV-EDV/BSA: 83.7±13.8ml/m2; LV-ESV/BSA: 39.3±8.6ml/m2), when compared to normal values from the study center. There is a negative correlation between LVEF and QRS duration (r=−0.550, p<0.05) and a positive correlation between QRS duration and LV-EDV/BSA (r=0.627, p<0.05) as well as between QRS and LV-ESV/BSA (r=0.661, p<0.05). In addition, there is a positive correlation between QRS duration and myocardial mass (r=0.645, p<0.05), septal myocardial thickness (r=0.405, p<0.05) and lateral wall thickness (r=0.495, p<0.05). In addition, there is a positive correlation between LV longitudinal strain and QRS (r=0.449, p<0.05). T1-values were in normal range. There is no correlation between QRS and T1-values.

Conclusion
Using CMR a negative correlation between LV function and QRS duration and the positive correlation between LV volumes and QRS duration in patients with isolated LBBB could be identified. The absence of significant myocardial fibrosis with normal T1-values indicates an electromechanical dissociation rather than an underlying myocardial abnormality as an explanation for the reduced LVEF.