Divergence between left ventricular ejection fraction and global longitudinal strain by cardiac magnetic resonance as a new predictor of myocardial fibrosis burden in hypertrophic cardiomyopathy
Authors: Nguyen P C M 
Published: May 2024

Abstract

Funding Acknowledgements
None.

Background
Hypertrophic cardiomyopathy (HCM) is the most frequently diagnosed inherited cardiomyopathy as well as the leading cause of sudden death in young people. Despite that, prompt diagnosis and prognosis of this condition are still challenging due to subtle progression and preserved left ventricular ejection fraction (LVEF) in most stages. Latest studies showed that myocardial strains could be the earliest indicator of function impairment and a good trait suggesting underlying fibrosis development.

Purpose
By applying the cardiac magnetic resonance (CMR) feature-tracking technique, our aim is to evaluate whether the divergence between the LVEF and global strains, apart from the strains themselves, could help predict the burden of myocardial fibrosis in HCM patients.

Methods
In this retrospective, cross-sectional study from June 2022 to June 2023, we included 35 HCM patients and 16 healthy controls with 3T-CMR. LVEF, left ventricular global longitudinal (LVGLS), circumferential (LVGCS), and radial (LVGRS) strains were derived from short-axis Cine images. To assess the divergence, ratios of LVEF to LVGLS, LVGCS, and LVGRS absolute values (namely EF-GLS, EF-GCS, and EF-GRS, respectively) were calculated. The ratios helped emphasise that a persisting high/normal LVEF and/or a lower strain magnitude would produce a larger discrepancy between these two variables. Fibrosis was assessed by LGE amount (%LGE to LV mass, threshold of +5 SD). Two-sample t-Test, linear and binary logistic regression were the main statistical tests used.

Results
The global strain measures all expressed notable impairment in HCM groups compared to healthy controls (LVGLS [-12.04±3.9 vs -19.42±2%, p&lt;0.001]; LVGCS [-16.37±4.1 vs -19.3±2.1, p=0.002]; LVGRS [28.06±9.9 vs 33.8±6.5%, p=0.018] while sharing the same range of LVEF [59.09±9.9 vs 59.44±5.3, p=0.87). The ratios of EF-GLS, EF-GCS, and EF-GRS also showed statistically significant differences between the two groups. In the HCM group, LVGLS and EF-GLS ratio showed the strongest correlations with %LGE (r = 0.855 and r = 0.708, p&lt;0.001). A regression equation can also be derived to estimate the amount of LGE from the EF-GLS ratio: %LGE = 3.967 EF-GLS - 0.22.
To determine predictive power toward the severity of fibrosis, the EF-GLS ratio showed the best performance, in which a threshold of 4.96 had sensitivity and specificity of 73.7% and 93.8% to predict LGE ≥ 15% LV mass (Area Under the Curve [AUC]: 0.717; 95% CI: 0.521–0.913).

Conclusion
Our study demonstrated that the ratio of LVEF to LV global longitudinal strain exhibited a great capability to reflect LV dysfunction and predict myocardial fibrosis severity with good accuracy. Derived easily from the routine Cine-CMR image, this new deformation parameter has great potential to be used in clinical practice to better diagnose and manage hypertrophic cardiomyopathy.Clinical characteristics of groupsResults in graphs