Normal-Flow, Low-Gradient Discordance in Aortic Stenosis Severity Assessment: The Impact of Vascular Burden
Nancy Côté, Louis Simard, Anne-Sophie Zenses, Lionel Tastet, Mylène Shen, Marie-Annick Clavel
Institut universitaire de cardiologie et de pneumologie de Québec, Quebec Heart and Lung Institute, Quebec City, Canada
Background: Fifty percent of Normal-Flow, Low-Gradient (NFLG) patients (i.e. low mean gradient [MG] and small aortic valve area [AVA] ) have severe aortic valve calcification (AVC) as measured by computed tomography. However NFLG patients are considered as moderate aortic stenosis (AS) in current ACC/AHA guidelines.
Objective: The objective of this study was to evaluate the effect of hypertension and systemic arterial compliance on MG measurements.
Methods: First, in 4 sheep with experimentally induced severe and critic AS at: 1) normal aortic pressure, 2) during hypertension (HTN) induced by banding of the aorta, and 3) with reduced aortic compliance (RC) induced by a dacron prosthesis around the aorta, Doppler echocardiography was performed. Second, a comprehensive echocardiography and computed tomography were obtained in 221 patients with AS and normal flow. MG and AVC divided by the cross-sectional area of the aortic annulus (AVCd) were studied according to hypertensive (˃140 mmHg) and compliance [reduced indexed stroke volume/pulse pressure (SVi/PP) ˂ 0.8 ml/mmHg/m2] status.
Results: In sheep with severe and critic AS, HTN and RC induced a substantial decrease in MG compared to normal stage (p˂0.0001 severe AS, and p=0.03 critic AS) while the transvalvular flow remained stable (p=0.05 severe AS, and p=0.99 critic AS). HTN and RC resulted in a greater reduction of MG in critic compared to severe AS (p˂0.0001). In patients, mean age was 69±13 yr, MG 29±18 mmHg, and mean Stroke Volume index (SVi) 44±7 ml/m2. The slope of the correlation between MG and AVCd was significantly reduced in patients with HTN and RC compared to normotensive patients (p=0.009). Accordingly, the number of patients with severe AS as documented by AVCd and NFLG were more frequent in HTN and RC groups (17% and 16%, respectively) compared to the normotensive group (p=0.03). Conclusion: HTN and RC are associated with a substantial reduction in MG for similar AVC-load/AS severity, which may lead to a discordant NFLG pattern and underestimation of stenosis severity.