Aims: Patients with severe aortic stenosis (AS) and normal ejection fraction (EF) can paradoxically present low-transaortic flow and worse prognosis. The role of co-existing mitral regurgitation (MR) in determining this haemodynamic inconsistency has never been quantitatively explored. The hypothesis is that MR influences forward stroke volume and characterizes the low-flow AS pattern.

Methods and results: Consecutive patients with indexed aortic valve area (AVA) ≤0.6 cm2/m2 and EF > 50% formed the study population. Complete echocardiographic data were collected, and mitral effective regurgitant orifice area (ERO) and regurgitant volume were obtained with proximal isovelocity surface area method. Patients were divided into subgroups according to indexed stroke volume (SV index). Included patients were 273 [age 79 ± 10 years, 53% female, EF 65 ± 7%, indexed AVA 0.47 ± 0.09 cm2/m2, mean transaortic gradient (MG) 32 ± 17 mmHg]. Mitral regurgitation was present in 89 (32%); ERO was 0.12 ± 0.08 cm2 (range 0.02–0.49 cm2). A low-flow state (SV index ≤35 mL/m2) was diagnosed in 41 (15%) patients. The prevalence of MR was higher in with low-flow vs. normal-flow group (56 vs. 28%, P = 0.03). Effective regurgitant orifice was associated to low-flow state univariately (OR: 1.75 [1.59–2.60]; P = 0.004) and after comprehensive adjustment (OR:1.76 [1.12–2.75]; P = 0.01). When MG was forced in the model, ERO remained significant (P < 0.009). On average, there was a 6 mL reduction in forward SV appeared per each 0.1 cm2 of ERO. Conclusion In patients with severely reduced AVA and preserved EF, MR is a major determinant of the low-flow condition. Furthermore, MR quantification by ERO predicts the presence of reduced flow independently of chamber volumes, systolic function, and transaortic gradient.