Heart-Type Fatty Acid–Binding Protein as a Marker of Subclinical Cardiac Dysfunction and Cardiorenal Interaction in Autosomal Dominant Polycystic Kidney Disease

(1) Background: Cardiovascular disease represents the leading cause of morbidity and mortality in patients with autosomal dominant polycystic kidney disease (ADPKD), often developing early in the disease course, even in the presence of preserved renal function. We aimed to evaluate circulating heart-type fatty acid–binding protein (H-FABP) as a marker of subclinical cardiac involvement and cardiorenal interaction in ADPKD. (2) Methods: In this single-center observational study, 80 adult patients with ADPKD receiving tolvaptan therapy were evaluated using echocardiography, renal function parameters, and circulating H-FABP levels. Associations between H-FABP and echocardiographic indices of cardiac structure and function, as well as renal parameters, were assessed using linear regression models. In addition, a composite severity score integrating CKD stage and H-FABP levels was constructed to assess the combined cardiorenal burden. (3) Results: Higher H-FABP concentrations were significantly associated with echocardiographic markers suggestive of subclinical cardiac involvement, particularly parameters related to impaired myocardial relaxation, including lower E/A ratio and reduced tissue Doppler e′ velocities. These associations remained significant after adjustment for renal function and relevant clinical covariates. In parallel, H-FABP levels were also associated with markers of renal disease severity, including lower baseline eGFR and greater total kidney volume. The composite severity score showed a graded association with echocardiographic parameters, with a progressive trend toward less favorable diastolic indices as risk categories increased. These findings suggest a potential complementary role for H-FABP in the integrated evaluation of cardiorenal involvement in ADPKD. Given the cross-sectional design and single-centre setting, these results should be considered hypothesis-generating and require prospective validation in larger, independent cohorts.