Background .– The coronary flow reserve (CFR) is progressively impaired with aortic stenosis (AS) severity, but there is a broad range of CFR in patients (pts) with severe AS, and the factors responsible for this variability are weakly characterized. Our objective was to assess the determinants of non-invasive CFR in pts with severe AS (≤ 1cm ² or ≤ 0.6 cm ² /m ² ) and preserved left ventricular ejection fraction (LVEF > 50%).

Methods .– Fifty consecutive pts (72 ± 10 years, 19 women, mean LVEF 67 ± 11%) with isolated severe AS (mean 0.77 ± 0.2 cm ² , 0.42 ± 0.12 cm ² /m ² ), no coronary artery disease, underwent prospectively transthoracic-Doppler echocardiography including CFR measurement in the distal part of the left anterior descending artery (LAD) with intravenous adenosine infusion (140 μg/kg/min over 2 min). CFR was defined as hyperemic peak LAD flow velocity divided by baseline flow velocity. Ten normal subjects matched for age and gender, served as a control group. Clinical, plasma NT-proBNP, and valvulo-arterial impedence (Z) were also assessed.

Results .– When compared to controls, pts with AS had higher baseline LAD flow velocity (37 ± 10 vs. 28 ± 9 cm/s, P < 0.05), similar hyperemic LAD flow velocity (84 20 vs. 85 ± 21, P = NS), and consequently lower CFR (2.35 ± 0.68 vs. 3.2 ± 0.8, P < 0.01). In pts with AS, there was a significant inverse correlation between CFR and age ( r = −0.33), E/Ea (early diastolic transmitral flow velocity/early diastolic mitral tissue Doppler annular velocity), LV mass/m ² , NT-proBNP ( r = −0.45), pulmonary artery systolic pressure (PASP), baseline LV rate-pressure product (LVPP) [(mean gradient + systolic blood pressure) × heart rate)], heart rate, and left atrial volume/m ² (LAV) (all, P < 0.05), and a significant positive correlation between CFR and LVEF, and deceleration time of E (all, P < 0.05). The correlation between CFR and Z was of borderline significance. Furthermore, compared to asymptomatic AS pts ( n = 10), symptomatic AS pts had a more severely impaired CFR (2.2 ± 0.6 vs. 2.76 ± 0.8, P < 0.05), higher baseline and lower hyperemic LAD flow velocities (all, P < 0.05), and higher NT-proBNP values ( P = 0.01). In multivariate analysis, after adjusting for AS severity, NT-proBNP was the main independent predictor of CFR ( P < 0.01), and among echographic variables, PASP and LVPP (all, P < 0.01). PASP was independently predicted by age, DTE and LAV (all, P ≤ 0.01).

Conclusion .– In patients with severe AS and preserved LVEF, there is a relatively wide range of CFR values. CFR is more severely impaired in symptomatic AS pts and is mainly determined by increased LV wall stress and workload, and diastolic dysfunction.