INTRODUCTION

Feline cardiomyopathy is a significant cause of morbidity and mortality in cats, with hypertrophic cardiomyopathy (HCM) being the most prevalent form [1, 2]. Conventional echocardiography remains the cornerstone of diagnosis, but it often fails to detect early or subtle myocardial dysfunction [3, 4]. Strain echocardiography, which uses speckle-tracking methods, enables quantitative evaluation of myocardial deformation and has been shown to detect subclinical changes before overt structural alterations [5–9]. In addition to the left ventricular (LV), the right ventricular (RV) plays a critical role in overall cardiac performance. In feline HCM, secondary pulmonary hypertension or interventricular interactions may compromise RV function [10, 11]. Assessment of right ventricular longitudinal strain (RVLS) provides a sensitive and reproducible indicator of systolic function and may reflect global myocardial disease burden [12]. Left atrial (LA) function also provides prognostic information, as it reflects LV filling pressures and diastolic compliance [13, 14]. Among left atrial strain components, the left atrial reservoir strain (LARS) represents the reservoir function during ventricular systole and offers incremental diagnostic value beyond standard volumetric measures [15–17].

Strain echocardiography allows simultaneous evaluation of LV, RV, and LA deformation throughout the cardiac cycle, providing a comprehensive overview of myocardial mechanics [18]. Myocardial strain imaging can be assessed using either tissue Doppler imaging (TDI) or speckle-tracking echocardiography (STE). TDI-derived strains are limited by angle dependence and susceptibility to artifacts, making them less reliable in small-animal patients. In contrast, STE is angle-independent and more robust and is therefore the preferred method in both research and clinical practice. STE evaluates myocardial deformation by tracking natural acoustic markers within the myocardium on two-dimensional echocardiographic images [19, 20]. These speckles are automatically identified and followed frame by frame throughout the cardiac cycle. The relative displacement of speckles provides quantitative information on myocardial shortening and lengthening, which is expressed as strain. Left ventricular global longitudinal strain (LVGLS) is a sensitive marker of early systolic dysfunction, whereas RVLS primarily reflects free-wall contractility. Strain echocardiography is strongly correlated with disease severity in feline and canine cardiomyopathies [21–23]. Accurate assessment of LV diastolic function and filling pressures remains challenging in cats due to the effects of preload and heart rate on traditional Doppler parameters (E/A ratio and tricuspid regurgitation velocity) [24]. LARS, measured by STE, quantifies atrial compliance and reservoir capacity and serves as a functional marker of LV diastolic performance [25, 26]. Reduced LARS was associated with increased LV wall thickness, impaired LV function, and a higher LA/Aorta (AO) ratio, which is consistent with impaired LV relaxation and elevated filling pressures. Studies in humans have shown that decreased LARS is associated with LV stiffness and diastolic dysfunction [27]. The incorporation of strain imaging into feline echocardiographic evaluation may enable early detection of diastolic impairment before LA enlargement develops [28]. Most feline studies have evaluated LV or LA strain independently, whereas integrated assessment of LV, RV, and LA deformation remains limited. Rather than serving as primary diagnostic tools, strain-derived indices may provide complementary functional information beyond conventional two-dimensional echocardiography, particularly in cats with borderline structural changes or early disease stages (B1–B2). Identifying phenotype- and stage-related differences in myocardial deformation may improve understanding of disease pathophysiology and support future investigations into their prognostic value.

Although conventional echocardiography remains the cornerstone of HCM diagnosis in cats, it often fails to detect early or subtle myocardial dysfunction. Previous studies have evaluated LV or LA strain independently, with limited integration of multi-chamber assessment. There is a clear need for a comprehensive evaluation that combines LVGLS, RVLS, LARS, and strain–volume curve analysis to better characterize hypertrophic phenotypes, distinguish subclinical dysfunction, and improve disease staging. The integration of these advanced strain parameters may provide additional functional information beyond conventional indices such as fractional shortening and LA/AO ratio, particularly in cats with borderline structural changes or early disease stages. Furthermore, the relationship between these strain-derived indices and disease progression, as well as their prognostic value, remains insufficiently explored in feline cardiology.

Accordingly, this study aimed to assess myocardial function in cats using strain echocardiography and to determine the diagnostic utility of LVGLS, RVLS, and LARS for distinguishing different cardiomyopathic patterns. We hypothesized that LARS and multi-chamber strain parameters provide additional functional information beyond conventional indices such as LA/AO ratio and fractional shortening, and may facilitate earlier recognition of myocardial dysfunction in feline HCM.