Low-flow severe aortic stenosis with preserved ejection fraction, N-terminal pro-brain natriuretic peptide (NT-proBNP) and cardiovascular remodeling.

Background And Aim Of The Study: Severe aortic stenosis (AS) with preserved systolic function may coexist with 'low flow' and a lower stroke volume (SV). As the mechanisms of this phenomenon are not fully understood, the study aim was to assess the cardiac and vascular mechanisms of 'low-flow' severe AS with a preserved left ventricular ejection fraction (LVEF).

Methods: Forty-four consecutive patients (mean age 69.7 +/- 7.6 years) with severe degenerative AS [mean effective orifice area (EOA) 0.7 +/- 0.3 cm2] and preserved LVEF (> 50%) were enrolled into the study, and allocated to two groups depending on their stroke volume index (SVI) (< 35 and > or = 35 ml/m2, respectively). The clinical data, N-terminal pro-brain natriuretic peptide (NT-proBNP) serum levels and ultrasound assessment of LV geometry and function [stroke work (SW), relative wall thickness (RWT)], AS severity, indices of systemic arterial hemodynamics [systemic arterial compliance (SAC), systemic vascular resistance (SVR)] and remodeling [flow-mediated dilatation (FMD), pulse wave velocity (PWV)], as well as valvuloarterial impedance (Z(va)) were analyzed for all study patients.

Results: Twenty-four patients (56%; 13 females, 11 males) had low-flow LV output, and 20 (44%; four females, 16 males) had a normal LV output. The mean NT-proBNP serum levels were comparable between the study groups. An analysis of LV remodeling and function revealed a lower LV end-diastolic volume (LVEDV; 85.5 +/- 24.1 versus 160.4 +/- 60.9 ml, p = 0.001), LV end-systolic volume (LVESV; 40.3 +/- 18.5 versus 66.8 +/- 44.2 ml, p = 0.03), LV mass index (LVMI; 150.1 +/- 53.4 versus 183.7 +/- 57.5 g/m2, p = 0.07) and SW (95.6 +/- 23.7 versus 183.2 +/- 50.6 mmHg x ml, p < 0.0001) in the group with SVI < 35 ml/m2. The average RWT was higher in the group with SVI < 35 ml/m2 (48.7 +/- 14.8 versus 40.0 +/- 7.5, p = 0.04). The indices of systemic arterial hemodynamics were significantly different between the groups: the SAC was lower, and the SVR and Z(va) were higher, in patients with SVI < 35 ml/m2 while FMD values were significantly greater in patients with SVI < 35 ml/m2 (11.85 +/- 6.4 versus 7.29 +/- 6.3%, p = 0.035). However, the brachial artery diameter (BAd) was smaller in the latter group, and no differences were found in the FMD x BAd index values. The PWV values were comparable in both study groups.

Conclusion: The low-flow phenomenon in severe AS with preserved LVEF is related to smaller LV dimensions, LV concentric hypertrophy, and an increased systemic arterial afterload without differences in plasma NT-proBNP levels. 'Paradoxically' higher values of FMD observed in this population may be associated with a higher proportion of females and a smaller BAd.