Abstract
The management of patients with aortic stenosis (AS) crucially depends on accurate diagnosis. The main aim of this study were to validate the four-dimensional flow (4D flow) cardiovascular magnetic resonance (CMR) methods for AS assessment. Eighteen patients with clinically severe AS were recruited. All patients had pre-valve intervention 6MWT, echocardiography and CMR with 4D flow. Of these, ten patients had a surgical valve replacement, and eight patients had successful transcatheter aortic valve implantation (TAVI). TAVI patients had invasive pressure gradient assessments. A repeat assessment was performed at 3–4 months to assess the remodelling response. The peak pressure gradient by 4D flow was comparable to an invasive pressure gradient (54 ± 26 mmHG vs 50 ± 34 mmHg, P = 0.67). However, Doppler yielded significantly higher pressure gradient compared to invasive assessment (61 ± 32 mmHG vs 50 ± 34 mmHg, P = 0.0002). 6MWT was associated with 4D flow CMR derived pressure gradient (r = −0.45, P = 0.01) and EOA (r = 0.54, P < 0.01) but only with Doppler EOA (r = 0.45, P = 0.01). Left ventricular mass regression was better associated with 4D flow derived pressure gradient change (r = 0.64, P = 0.04). 4D flow CMR offers an alternative method for non-invasive assessment of AS. In addition, 4D flow derived valve metrics have a superior association to prognostically relevant 6MWT and LV mass regression than echocardiography.
Highlights
The management of patients with aortic stenosis (AS) crucially depends on accurate diagnosis
The main aims of this study were: (1) to validate the 4D flow cardiovascular magnetic resonance (CMR) peak velocity assessment against the reference invasive pressure drop assessment, (2) to validate the 4D flow CMR velocity plane derived effective orifice area (EOA) against Doppler Transthoracic echocardiography (TTE) derived EOA, (3) investigate if 4D flow CMR aortic valve assessment offers any better association to exercise tolerance evaluated by the six-minute walk test (6MWT) when compared to Doppler TTE, and (4) in the cohort with follow-up imaging studies, evaluate which measures are associated with left ventricular (LV) remodelling
Written informed consent was obtained from all patients before participation
Summary
The management of patients with aortic stenosis (AS) crucially depends on accurate diagnosis. Transthoracic echocardiography (TTE) is the first-line test for the assessment of AS severity, left ventricular (LV) function and haemodynamics[2,3] It is well-established that TTE has limitations – the approximation of blood flow as a single streamline by continuous-wave Doppler TTE overestimates valvular pressure gradients compared to invasive measurements[4,5]. Being able to identify where the maximum velocity occurs in a three-dimensional (3D) space is a major advantage over Doppler TTE and the current standard two-dimensional (2D) phase-contrast CMR methods for AS assessment – which is recognised to underestimate velocities[10,11] It allows quantification of the EOA using the peak velocity plane, which coincides with the vena contracta, identified by an evaluation of the whole three-dimensional aortic sinus flow. It remains unclear if 4D flow CMR would offer any incremental benefit over Doppler TTE
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