Left atrial stiffness as a novel echocardiographic parameter of atrial dysfunction in cats with hypertrophic cardiomyopathy: A two-dimensional speckle-tracking study

Background and Aim: Hypertrophic cardiomyopathy (HCM) is the most common form of cardiomyopathy in cats and is often linked with diastolic dysfunction and progressive remodeling of the left atrium (LA). While LA strain analysis has been utilized to measure atrial function, LA stiffness (LASt), a load-adjusted marker that combines diastolic filling pressures and atrial deformation (E:E’/εS), has not yet been studied in feline patients. This study aimed to compare LASt between normal cats and those with HCM and to assess its correlation with traditional echocardiographic parameters of LA and left ventricular (LV) function. Materials and Methods: This retrospective cross-sectional study included client-owned cats evaluated at a university teaching hospital between August 2021 and August 2022. Cats were classified as normal or HCM based on LV wall thickness (≤5 mm vs. ≥6 mm). Standard echocardiographic parameters, doppler indices, tissue Doppler imaging (TDI) values, and two-dimensional speckle-tracking echocardiography (STE)–derived LA strain variables (reservoir, conduit, and active strain) were measured. LASt was calculated as E:E’/εS. Group comparisons were performed using t-tests or Mann–Whitney U tests, and correlations were assessed using Pearson’s coefficient. Results: Thirty-seven cats met the inclusion criteria (12 with HCM and 25 normal). Cats with HCM showed significantly higher LASt values compared to normal cats (median 2.26 vs. 0.30; p < 0.001), representing approximately a sevenfold increase. Reservoir strain (εS), conduit strain (εE), and active strain (εA) were all significantly lower in the HCM group (p < 0.001). LASt showed strong positive correlations with LA diameter and LA:Ao ratio (r ≥ 0.85; p < 0.001), and moderate-to-strong correlations with Doppler and TDI markers of diastolic dysfunction, including E:A ratio, MV A velocity, MV E’, and MV S’. Conclusion: LASt, measured by STE, provides a sensitive, load-inclusive index of LA mechanical dysfunction in cats with HCM and may detect atrial remodeling earlier than strain alone. Its strong association with established markers of diastolic impairment supports its potential clinical utility for identifying subclinical atrial dysfunction. Larger longitudinal studies are warranted to validate LASt as a prognostic biomarker and to define clinically relevant thresholds for disease staging and monitoring. Keywords: diastolic dysfunction, feline cardiology, hypertrophic cardiomyopathy, left atrial function, left atrial stiffness, speckle-tracking echocardiography.