Left Atrial Myopathy Across the Spectrum of Pediatric Heart Disease: Imaging, Mechanobiology, and Clinical Consequences.

Left atrial (LA) function has emerged as a critical determinant of cardiovascular performance and disease progression across the spectrum of pediatric heart disease. Traditionally viewed as a passive conduit, the left atrium is now increasingly recognized as a dynamic biomechanical chamber that modulates ventricular filling, pulmonary venous pressures, cardiac output, and neurohormonal signaling. In children with congenital and acquired heart disease, alterations in atrial structure and mechanics frequently precede overt ventricular dysfunction, making LA dysfunction an early and potentially reversible marker of cardiovascular injury. Advances in cardiac imaging, particularly speckle-tracking echocardiography and cardiac magnetic resonance imaging, have enabled detailed characterization of atrial reservoir, conduit, and contractile function in pediatric populations. Emerging evidence suggests that impaired left atrial strain is associated with adverse hemodynamics, exercise intolerance, arrhythmogenesis, pulmonary hypertension, Fontan failure, cardiomyopathy progression, and heart failure severity. Mechanobiological processes, including atrial stretch, fibrosis, extracellular matrix remodeling, inflammation, and altered atrioventricular coupling, contribute to the development of pediatric left atrial myopathy. These changes are increasingly recognized in congenital heart lesions, single-ventricle physiology, hypertrophic and dilated cardiomyopathies, Kawasaki disease, obesity-related cardiovascular dysfunction, and cardio-oncology populations. Despite growing interest, important gaps remain regarding normative pediatric reference values, age-related physiological variation, imaging standardization, and long-term prognostic significance. This narrative review summarizes current understanding of left atrial mechanobiology, multimodality imaging assessment, and clinical implications of LA dysfunction in pediatric heart disease. We also discuss emerging technologies, including artificial intelligence-based imaging analysis and future directions for integrating left atrial phenotyping into pediatric cardiovascular risk stratification and therapeutic decision-making.