Toward a Prospective Definition of Atrial Fibrillation-induced Cardiomyopathy.

AF can mediate left ventricular systolic dysfunction (LVSD) through a tachycardia-mediated cardiomyopathic process that may reverse with rate control alone. However, additional mechanisms contribute to AF-induced cardiomyopathy (AIC) that require rhythm control therapies. AIC can currently only be diagnosed retrospectively, as these component mechanisms are difficult to distinguish from each other and from other causes of LVSD prospectively. This narrative review considers the different potential mechanisms through which AF can impair ventricular function: rapid ventricular rate; irregularity of the ventricular rhythm; and impaired atrial contraction. How these features may exploit underlying structural vulnerability are considered and additional imaging-based parameters such as late gadolinium enhancement on cardiac MRI and contractile reserve during stress echocardiography are discussed. The limitations of existing parameters are discussed and a novel, non-parametric marker of ventricular rate with consideration of the inherent irregularity of AF - the Restitution Threshold Index (RTI) - is reviewed. Integrating RTI with these imaging-based measures may enhance clinical decision-making by more accurately identifying patients who would benefit from timely rhythm control. Further prospective validation is essential to develop accessible tools and an open-access RTI calculator has been made available (https://restitutionthreshold.com) to facilitate reproducibility and wider application.