Left Atrioventricular Coupling Index: A Comprehensive Review of the Literature.

Traditional cardiovascular assessment has historically focused on the isolated evaluation of either atrial or ventricular structure and function. However, the left atrioventricular coupling index (LACI) represents a paradigm shift by moving beyond single-chamber metrics to quantify the dynamic interaction between the left atrium and left ventricle. Defined as the ratio of left atrial end-diastolic volume to left ventricular end-diastolic volume, LACI integrates structural and functional aspects of cardiac performance. This comprehensive review examines the physiological basis of how the left atrium and ventricle operate as an integrated hemodynamic unit. We detail current measurement methodologies, including two- and three-dimensional echocardiography, cardiac computed tomography, and cardiac magnetic resonance imaging, which serves as the reference standard. Furthermore, the review explores the pathophysiological mechanisms driving atrioventricular uncoupling, specifically mechanical dysfunction, electromechanical desynchrony, and hemodynamic alterations. Extensive clinical evidence demonstrates LACI's robust independent prognostic value across diverse cardiovascular conditions, such as heart failure, myocardial infarction, cardiomyopathies, and atrial fibrillation. Observational data suggest that LACI provides a promising prognostic value beyond established risk assessment tools by combining the assessment of both chambers' interdependence. Finally, we outline future directions for clinical translation, highlighting the necessity for standardized measurement protocols, the integration of artificial intelligence, and the potential of LACI as a target for personalized therapeutic strategies.