Left and right atrioventricular coupling: state-of-the-art review

The co-ordinated interaction between atria and ventricles, termed atrioventricular (AV) coupling, is essential for maintaining efficient cardiac performance. The left/right atrium (LA/RA) modulates left/right ventricular (LV/RV) filling through its reservoir, conduit, and booster pump functions, while the LV/RV in turn determines atrial pressures and compliance. Disruption of this finely balanced interplay leads to impaired filling dynamics, abnormal pressure-volume relationships, and progressive remodelling. Mechanisms of uncoupling include mechanical dysfunction from atrial dilatation and fibrosis, ventricular diastolic stiffness, and loss of atrial contractile reserve, as well as electromechanical desynchrony due to conduction abnormalities such as AV block or prolonged PR interval. The concept of quantifying AV coupling has been formalized through the left/right AV coupling index (LACI/RACI), defined as the ratio of LA/RA end-diastolic volume to LV/RV end-diastolic volume. LACI/RACI can be non-invasively derived across imaging modalities-including echocardiography, computed tomography, and cardiovascular magnetic resonance-without requiring specific acquisition protocols. First described in large population cohorts, LACI has demonstrated independent and incremental prognostic value for heart failure, atrial fibrillation and mortality, outperforming isolated atrial or ventricular parameters. Moreover, its ability to capture dynamic remodelling makes it a promising biomarker for risk stratification across a broad spectrum of cardiovascular diseases. This review synthesizes current knowledge on left and right AV coupling, outlines the physiological and pathophysiological mechanisms of uncoupling, and highlights the role of LACI/RACI as both a diagnostic and prognostic tool. Standardization of assessment strategies and reference values will be essential to facilitate clinical translation and precision cardiology.