Introduction:
Aortic stenosis (AS) is considered severe when the aortic valve area (AVA) is < 1.0 cm² and the mean aortic valve gradient (mAVG) exceeds 40 mm Hg. Since many patients with AVA < 1.0 cm2 do not manifest an mAVG > 40 mm Hg, we sought to determine the AVA at which mAVG tends to exceed 40 mm Hg in a sample of subjects with varied transvalvular flow rates.

Material and methods:
Our echocardiography database was queried for subjects with native valve AS. We selected 200 subjects with an AVA < 1.0 cm². The sample was selected to include subjects with varied mean systolic flow (MSF) rates. Linear regression was performed to determine the relationship between MSF and mAVG. Since this relationship varied by AVA, the regression was stratified by AVA (critical < 0.6 cm², severe 0.6–0.79 cm², moderately severe 0.8–0.99 cm²).

Results:
The study sample was 79 ±12 years old and was 60% female. The MSF rate at which mAVG tended to exceed 40 mm Hg was 120 ml/s for critical AVA, 183 ml/s for severe AVA and 257 ml/s for moderately severe AVA. Those with moderately severe AVA rarely (8%) had an mAVG > 40 mm Hg at a wide range of MSF. In contrast, those with severe AVA typically (75%) had mAVG > 40 mm Hg when MSF was normal (> 200 ml/s). Those with critical AVA frequently (44%) had mAVG > 40 mm Hg, even when MSF was reduced.

Conclusions:
Subjects with AVA of 0.8 and 0.9 cm² rarely had mAVG > 40 mm Hg, even when the transvalvular flow rate was normal. Using current guidelines, it is not clear if such cases should be classified as severe.