Left atrial minimum volume index predicts durable reverse remodeling following cardiac resynchronisation therapy

Background Cardiac resynchronization therapy (CRT) remains limited by significant non-response rates, particularly in patients with advanced ventricular remodeling. While myocardial scar assessment provides important prognostic information, biomarkers that specifically capture the residual capacity for reverse remodeling are lacking. Objectives This study aimed to evaluate the prognostic value of cardiac magnetic resonance (CMR)-derived metrics for predicting durable CRT response in a dedicated cohort with complete left bundle branch block (LBBB). Methods Consecutive patients with non-ischemic cardiomyopathy, complete LBBB, and reduced ejection fraction who underwent CMR prior to CRT implantation were prospectively enrolled. Echocardiographic response was assessed at 6 and 12 months. Multivariable regression and Receiver operating characteristic analyses were performed. Results Among 118 patients, left atrial minimal volume index (LAVImin) demonstrated independent predictive value for both 6-month (adjusted OR: 0.962) and 12-month (adjusted OR: 0.884) CRT response after adjusting for myocardial tissue characteristic and pacing modality. A combined stratification model using LAVImin <27.1 mL/m2 and late gadolinium enhancement (LGE) <2.2% identified a favorable substrate group with 0% non-response at 12 months. Conversely, patients with both parameters elevated had 57.1% non-response, rising to 72.2% with biventricular pacing. All patients with preserved substrate (LAVImin < 43.6 mL/m2 or LGE <2.2%) achieved response with left bundle branch pacing. Conclusion LAVimin maintained independent predictive value at both 6-month and 12-month follow-ups, even after adjustment for late gadolinium enhancement percentage or extracellular volume fraction. Second, preprocedural stratification combining both LAVimin and LGE demonstrated strong discriminatory capacity. In the favorable substrate group, defined by left atrial minimum volume index below 27.1 mL/m2 and late gadolinium enhancement below 2.2%, no patients were non-responders at 12 months. The simplified three-tier classification using left atrial minimum volume index alone also showed substantial prognostic utility, with 93.9% response rate in the low-risk tier versus 57.1% non-response in the high-risk tier, particularly in 90.9% non-response rate with BiVP. Importantly, all patients with preserved substrate (LAVImin < 43.6 mL/m2 or LGE < 2.2%) presented as response/super response following LBBP-CRT at 12-month follow-up. Collectively, these findings support the clinical implementation of left atrial minimum volume index as a practical biomarker for identifying patients most likely to achieve durable cardiac resynchronization therapy response, particularly with left bundle branch pacing, while also flagging high-risk candidates who may require alternative therapeutic strategies or intensified follow-up.LVEF changes following CRT.