Background and aim: The study was undertaken to assess the predictive role of myocardial contractile reserve for functional mitral regurgitation (FMR) improvement after cardiac resynchronisation therapy (CRT), and to define other predictors of FMR improvement (FMRI) and the impact of FMRI on left ventricular (LV) reverse remodelling.

Methods and results: Among 90 patients in whom echocardiography was performed one day before and six weeks after CRT implantation, 66 with at least FMR(2+) in a four-point scale (mean age 64 ± 10 years, mean LV ejection fraction [LVEF] 25.7 ± 6%, ischaemic aetiology 48%) were included. FMRI was defined as the reduction of the FMR severity by at least one grade. The patients were divided into groups: A with FMRI (n = 30) and B without FMRI (n = 36). Contractile reserve was evaluated using low-dose dobutamine stress-echo before CRT implantation and was defined as a relative improvement in LVEF of more than 20% and segmental contractility improvement. Reverse remodelling was defined as the reduction of the LV end-systolic volume (LVESV) by at least 15%. Cox regression multivariate analysis revealed the following predictors for FMRI: contractile reserve preserved in more than three segments with an OR = 5.7 (95% CI 1.81–17.97, p = 0.005, sensitivity 65.5%, specificity 72.2%, AUC = 0.727) and LV end-diastolic diameter ≤ 74 mm with an OR = 2.09 (95% CI 0.75–5.78, p < 0.05, sensitivity 80.0%, specificity 47.2%, AUC = 0.632). FMRI was associated with greater reduction of LVESV (p = 0.002), greater increase in LVEF (p < 0.001) and higher incidence of the LV reverse remodelling (p < 0.001).

Conclusions: Preserved contractile reserve and lesser degree of LV dilation were predictive factors of short-term FMR improvement after CRT implantation. FMR improvement was associated with higher incidence of the LV reverse remodelling early, already in the six weeks after CRT implantation.