Left Atrioventricular Coupling Index in Feline Hypertrophic Cardiomyopathy: Association with Disease Severity and Arterial Thromboembolism

HCM is the most prevalent cardiac disease in cats and is associated with substantial morbidity and mortality. Among its complications, FATE represents a major adverse clinical outcome. Conventional echocardiographic indices typically assess atrial or ventricular parameters separately and may not fully capture the structural relationship between the LA and LV. The left atrioventricular coupling index (LACI) is a volumetric ratio that combines LA remodeling and LV chamber size at end-diastole into a single structural index. This retrospective, cross-sectional observational study included 91 cats, classified according to ACVIM guidelines into healthy controls (n = 33), asymptomatic HCM (stage B1, n = 14; stage B2, n = 16), symptomatic HCM (stage C, n = 15), and cats with FATE (n = 13). Conventional and two-dimensional speckle-tracking echocardiography were performed, and LACI-ED was calculated as the ratio of LA end-diastolic volume to LV end-diastolic volume. LACI-ED increased progressively with disease severity (p < 0.001), showing the highest values in symptomatic HCM and FATE cases. It correlated positively with LA size and volume (p < 0.01) and inversely with LV GLS (p < 0.01). Exploratory ROC analysis for FATE status yielded limited discriminatory performance for LACI-ED > 150% (AUC = 0.575; 95% CI: 0.402–0.736; sensitivity 46.2%; specificity 84.4%). Although LACI-ED > 150% was associated with higher odds of prevalent FATE (OR = 4.65; 95% CI: 1.405–29.215; p = 0.020), this finding should be interpreted with caution. Pairwise comparisons of ROC curve areas between LACI-ED and conventional echocardiographic parameters (LA/Ao ratio, LA diameter, and LV GLS) revealed no statistically significant differences (all p > 0.05). Although LACI-ED > 150% was associated with higher odds of prevalent FATE (OR = 6.8; p < 0.05), this finding should be interpreted with caution. This cross-sectional study evaluates associations with disease stage and thromboembolic status at the time of examination. The findings suggest that LACI-ED reflects disease severity in feline HCM, whereas its utility for thromboembolic risk assessment appears limited.