# The Vectorcardiogram Characteristic and Its Predictive Value for Reduced Left Ventricular Ejection Fraction of Children with Duchenne Muscular Dystrophy

## TL;DR

This study explores how vectorcardiogram (VCG) readings can predict heart issues in children with Duchenne muscular dystrophy (DMD) before symptoms appear.

## Contribution

The study is the first to report VCG characteristics and their predictive value for reduced left ventricular ejection fraction in children with DMD.

## Key findings

- DMD patients show distinct VCG patterns, including higher heart rate and QRS loop percentages in specific quadrants.
- The sagittal quadrant IV QRS loop percentage at 7.57% is a predictive cutoff for reduced LVEF with 53.3% sensitivity and 88.3% specificity.
- Abnormal VCG readings can be detected in DMD boys as young as under 5 years old.

## Abstract

The prognosis of Duchenne muscular dystrophy (DMD)
is poor once it develops to the stage of cardiac impairment. Recent studies have
demonstrated that electrocardiogram (ECG), which consists of general ECG and
vectorcardiogram (VCG), retains an extremely powerful role in the assessment of
patients with reduced left ventricular (LV) systolic dysfunction. However, data
regarding VCG recordings in DMD and its prognostic value for reduced left
ventricular ejection fraction (LVEF) of DMD have never been reported. This study
aims to describe the characteristics of VCG in children with DMD and to explore
the predictive value of VCG for reduced LVEF in children with DMD.

A total of 306 patients with a known diagnosis of DMD confirmed
by the genetic test were retrospectively enrolled at our hospital between August
2018 and August 2022. This resulted in a total study group of 486 VCG recordings.
Among them, 75 DMD patients who underwent
cardiac magnetic resonance (CMR) later after
one year follow-up were prospectively enrolled. The trend of VCG parameters of
DMD patients across the different age span were compared with age-matched normal
children. Concordance statistic analysis was further performed to assess the
validity of VCG parameters in predicting the occurrence of reduced LVEF in
patients with DMD.

DMD patients have a significantly higher
heart rate, R waves in V1, QRS loop percentage in the right anterior quadrant in
the horizontal plane (horizontal quadrant II) and QRS loop percentage in the
anterior superior quadrant in the sagittal plane (sagittal quadrant IV) than
normal children. Concordance statistic (C-statistic) showed an area under the curve of quadrant IV in the
sagittal plane of baseline was 0.704. The receiver operating characteristic (ROC)
curve shows that quadrant IV in the sagittal plane of 7.57% was the optimal
cutoff with a sensitivity of 53.3% and a specificity of 88.3% for predicting
reduced LVEF in DMD patients.

Our study firstly showed that
QRS loop percentage in the right anterior quadrant in the horizontal plane
(horizontal quadrant II) and QRS loop percentage in the anterior superior
quadrant in the sagittal plane (sagittal quadrant IV) could be abnormal in DMD
boys as early as before 5 years old. Evaluation of the myocardium by VCG in the
early age to predict possible cardiac systolic dysfunction may have important
implications for the ongoing management of DMD boys.