Aortic valve tract dynamics in normal-flow low-gradient and normal-flow high-gradient severe aortic stenosis
Authors: Yilmaz-Coskun F , Nakou E , Marvaki A , Papasozomenos G , Eskandari M , Byrne J , Dworakowski R , Baghai M , Desphande R , Wendler O , Maccarthy P , Papachristidis A 
Published: October 2024

Abstract

Introduction
Aortic stenosis (AS) is the most common valvular heart disease in developed countries. Severe AS is defined as a mean pressure gradient (MG) ≥ 40 mmHg, a maximum aortic jet velocity≥4 m/s and an aortic valve area (AVA)≤1 cm2. However, classification of AS severity may be challenging due to discordant results on echocardiography. The normal-flow low-gradient severe AS (NFLG-AS) is defined as AVA≤1 cm2, MG&lt;40 mmHg, left ventricular ejection fraction ≥ 50%, and stroke volume index (SVi) ≥ 35 ml/m2, whereas in the presence of MG &gt; 40mmHg the condition is described as normal-flow high-gradient AS (NFHG-AS).

Purpose
The purpose of this study was to seek differences in the dynamic changes of the aortic valve tract throughout the cardiac cycle between the two clinical entities: NFHG-AS (Group 1) and NFLG-AS (Group 2).

Methods
In total, 130 patients with normal flow severe AS who underwent TAVI and had 3D transoesophageal echocardiographic data sets were screened. 38 patients with NFHG-severe AS and 40 patients with NFLG-severe AS with matching clinical characteristics and aortic valve area were identified. A custom-made semi-automated application developed by SQ was used. The application allows tracking of the aortic valve tract surface throughout the cardiac cycle in 3D transoesophageal echocardiograms and provides measurements of the geometrical planes at 4 levels: left ventricular outflow tract (LVOT), aortic annulus (AoA), sinuses of Valsalva (SoV) and sinotubular junction (STJ).

Results
The echocardiographic characteristics and the dynamic changes of the aortic valve tract between the two groups are shown in Tables 1 and 2. Both groups had comparable echocardiographic characteristic apart from the mean aortic valve pressure gradient as expected. With regards to the aortic valve tract geometrical dynamic changes, the relative LVOT and AoA area changes were bigger in Group 1 (36.8±15.9% vs 29.1±11.9%; p=0.017 and 21.0±8.39% vs 17.1±6.6%; p=0.028). The SoV and STJ relative changes were similar between the two groups. The same applies to aortic stiffness parameters, namely compliance and distensibility of the ascending aorta, systemic arterial compliance, and valvulo-arterial impedance.

Conclusion
The LVOT and aortic annulus area demonstrate more prominent dynamic changes in patients with normal-flow high-gradient severe AS compared to individuals with normal-flow low-gradient severe AS. While the SoV and the STJ geometry does not change significantly through the cardiac cycle, a more elastic outflow tract allows larger expansion in systole and higher pressure gradients across the aortic valve, whereas a stiffer outflow tract and annulus result in lower pressure gradients, despite the presence of severe aortic stenosis (AVA&lt;1.0cm2). These differences in dynamic LVOT and aortic annulus changes may explain the discrepancy between aortic valve area and pressure gradients in patients with normal-flow low-gradient AS.