MATERIALS AND METHODS

Ethical approval

The study protocol was reviewed and approved by the Animal Care and Use Committee of Kasetsart University, Thailand (approval no. ACKU-65-VET-077). This retrospective observational study used clinical and echocardiographic data obtained from client-owned cats presented to Kasetsart University Animal Teaching Hospital between May 2024 and May 2025. All procedures were performed as part of routine clinical cardiac evaluation and did not involve any experimental intervention beyond standard diagnostic care.

Written informed consent was obtained from the owners or legal custodians of all cats before clinical examination and use of anonymized medical data for research purposes. Patient confidentiality was maintained throughout the study by removing all owner-identifying information and using anonymized clinical records for data analysis. No animals or people are identifiable in this manuscript. All procedures were conducted in accordance with institutional animal ethics guidelines and accepted standards for retrospective veterinary clinical research.

Study period and location

Echocardiographic examinations were performed between May 2024 and May 2025. Clinical data were obtained from the Kasetsart University Animal Teaching Hospital, Faculty of Veterinary Medicine, Kasetsart University, Kamphaeng Saen, Nakhon Pathom, Thailand.

Study design and case enrollment

A retrospective observational study was conducted from May 2022 to May 2025. Forty client-owned cats were recruited for cardiac evaluation. The inclusion criteria were a sinus rhythm, fractional shortening greater than 25%, and the availability of complete echocardiographic datasets, including three-dimensional full-volume acquisitions. Cats with poor image quality and unclear speckle-tracking were excluded. Cats were classified into the following groups on the basis of their clinical history and echocardiographic findings: healthy controls (Group 1), characterized by the absence of clinical or echocardiographic evidence of heart disease; cardiomyopathy with a normal LA/AO ratio (Group 2), characterized by increased myocardial thickening without LA enlargement; and cardiomyopathy (Group 3), characterized by myocardial hypertrophy and LA dilation. Hypertrophic phenotype is defined as IVSd and/or LV posterior wall thickness at end-diastole (LVPWd) ≥6 mm in diastole and increased LA size with LA/AO >1.5. In addition, secondary causes of myocardial hypertrophy, such as hyperthyroidism and systemic hypertension, were excluded through clinical evaluation.

Echocardiography

An echocardiographic examination was performed by an experienced cardiologist using a Vivid E95 ultrasound system (GE Healthcare, Horten, Norway) equipped with a 2–8 MHz phased-array transducer. Cats were scanned in right and left lateral recumbency without sedation. Standard two-dimensional, M-mode, and Doppler echocardiography were performed in accordance with American College of Veterinary Internal Medicine (ACVIM) guidelines [29]. Images for strain evaluation were obtained from the three apical views, ensuring adequate endocardial border definition. Images were acquired by an experienced operator and analyzed offline using vendor-provided software (EchoPac AFI; GE Healthcare, version 206).

Strain and myocardial work analysis

Global longitudinal strain of the LV (LVGLS) was calculated from three apical planes. Circumferential, radial, right ventricular strain, and LA strain (reservoir) were also obtained. Strain curves were constructed by plotting strain values against end-diastolic and end-systolic volumes throughout the cardiac cycle. Strain–volume curves were generated by synchronizing speckle-tracking-derived strain values with left ventricular volume changes throughout the cardiac cycle, allowing visualization of deformation–volume relationships. The technique in the present study was adapted from human and canine cardiology. Myocardial work was integrated with the blood pressure values and global longitudinal strain (GLS) by time alignment. Echocardiographic acquisition parameters were applied at a frame rate (≥100 fps) for speckle-tracking analysis. The standardized imaging views were evaluated as follows, with manual contour adjustments made as needed to ensure tracking quality. LVGLS was evaluated from apical 4-, 2-, and 3-chamber views, RVLS was evaluated from an RV-focused apical 4-chamber view, and LARS was evaluated from an apical 4-chamber view optimized for LA. However, intra-observer variability analysis was reported as correlation coefficients.

Statistical analysis

Continuous data were expressed as mean ± standard deviation (SD). Group comparisons were performed using one-way analysis of variance with Tukey post hoc analysis or Student’s t-test as appropriate. Correlations between strain parameters and left ventricular volumes were assessed with Spearman’s correlation coefficient. A p < 0.05 was considered statistically significant. Multiple comparisons were tested using the Bonferroni method, and the Shapiro–Wilk test was used to assess normality. Statistical analyses were conducted using GraphPad Prism 10 (GraphPad Software, San Diego, CA, USA).