Introduction: Low flow (LF) aortic stenosis (AS) is currently defined by a stroke volume index (SVi) ≤35mL/m2. The mechanisms of LF and its impact on the clinical outcome of patients (pts) with severe AS and preserved left ventricular ejection (LVEF) remain controversial. Moreover, data regarding the prognostic role of SVi cut-off values in this clinical setting is scarce.
Objective: We aimed to study the clinical and echocardiographic characteristics of patients with severe AS and preserved LVEF according to three transaortic flow groups: SVi <30 mL/m² (group 1), SVi 30-35 mL/ m² (group 2), and SVi >35mL/m² (group 3) and the outcome of these patients, after aortic valve replacement (AVR).
Methods: We prospectively enrolled 277 consecuti-ve pts (66±11 yrs, 56% men) with severe AS (indexed AVA ≤0.6 cm²/m²), preserved LVEF (≥50%) and no more than mild aortic or mitral regurgitation, in sinus rhythm. A complete echocardiogram was performed in all. SVi was calculated using Doppler echocardiography by multiplying the LV outflowtract (LVOT) area with the LVOT time-velocity integral. Pts that were subject to AVR were followed for 7 years (IQR 4-10). The endpoint was 5-year all-cause mortality.
Results: Most pts had normal flow (NF) (253 patients, 91%). Twenty-four (9%) patients had LF, of which 6 (25%) with SVi <30 mL/m² and 18 (75%) with SVi 30-35 mL/m². There were no significant differences in age, gender, body surface area, prevalence of hypertension, chronic kidney disease and heart failure symptoms or angina between groups (p>0.20 for all). Systolic and di-astolic blood pressure and BNP values were also simi-lar. Patients in gr. 1 had more often syncope (p=0.005) and diabetes (p=0.03) compared to those in gr. 2. Si-milar LV dimensions and parameters of systolic (inclu-ding LVEF and global longitudinal strain) and diastolic function were found in the three groups (p>0.2 for all). As compared to NF, patients with LF had smaller AVA (0.25±0.04 – gr. 1vs. 0.31±0.05 – gr. 2 vs. 0.42±0.09 cm²/m² – gr. 3, p<0.001) and higher valvulo-arterial impedance (6.8±1.3 – gr. 1 vs. 5.9±1.1 – gr. 2 vs. 4.1±0.8 Hg/mL/m² – gr. 3, p<0.001), while the aortic mean gradient (MAG) was similar (p>0.2 for all). Indexed AVA, MAG and LV afterload were similar in the two subgroups of LF. AVR was performed in 146 patients: 4 (67%) in group 1, 10 (55%) in group 2, and 132 (52%) in group 3. Five-year all-cause mortality after AVR was higher for SVi <30 mL/m² (50%) compared to SVi >35mL/m² (7%) (p=0.004), while no deaths were registered in SVi 30-35 mL/m²
Conclusions: Patients with LF had smaller AVA and a higher LV afterload than NF. Moreover, the subgroup of LF patients with SVi<30 mL/m2 had a worse outco-me after AVR than those with SVi 30-35 ml/m2. Furt-her prospective large studies are needed to test other SVi values for risk stratification and decision making in pts with low gradient AS.