Assessment of left ventricular systolic function and pathological changes using layer-specific strain in rats with myocardial hypertrophy at various disease stages.

Purpose: Although layer-specific strains are effective for assessing cardiac function, their application in rat models at different stages of myocardial hypertrophy (MH) is immature, and their relationship with MH and myocardial fibrosis (MF) is unclear. This study aimed to investigate changes in layer-specific strains across different disease stages and analyze their association with pathological changes.

Methods: A progressive MH rat model was established using isoproterenol injection and categorized into baseline, 1-week, 2-week, 3-week, and 4-week groups. Echocardiographic indices and pathological differences between the five groups were assessed. The correlation between layer-specific strain parameters and cardiomyocyte hypertrophy and MF was analyzed.

Results: As the disease progressed, the left ventricular (LV) dilated, with the LV wall thickening and then thinning. The left ventricular ejection fraction declined significantly in the fourth week. The endo-myocardial, mid-myocardium and epi-myocardial global longitudinal strain, along with endo-myocardial global circumferential strain (GCS) and the transmural gradient, significantly decreased in the first week, the mid-myocardium GCS in the second week, and continued to decrease as the disease progressed. The epi-myocardial GCS increased in the first week, but then decreased, becoming significantly lower than the baseline group in the third week. The degrees of MH and MF were correlated with the layer-specific strain parameters.

Conclusion: Layer-specific strains maybe are valuable for early and effective monitoring of LV systolic function and pathological changes in rats with MH. Longitudinal strain is more sensitive to functional changes; endomyocardial strain reflects early LV remodeling and circumferential strain perhaps indicates disease progression and severity.