What is the clinical evidence from this study?

Study design: Cross-Sectional. Population: Bicuspid aortic valve and dilated aorta (n=165). Intervention: 4D flow MRI vs. Tricuspid aortic valve and controls. Primary outcome: Average peak velocity between the left ventricle outflow tract to sino-tubular junction (p=<0.016).

September 15, 2015Open Access

Four-dimensional flow magnetic resonance imaging-based characterization of aortic morphometry and haemodynamics: impact of age, aortic diameter, and valve morphology

Q: What are the key findings of this study?

Four-dimensional flow MRI demonstrated that patients with bicuspid aortic valves had higher average peak velocity (1.3 vs 1.2 m/s; P<0.016) compared to tricuspid valves despite similar dimensions.

Key Result

Four-dimensional flow MRI demonstrated that patients with bicuspid aortic valves had higher average peak velocity (1.3 vs 1.2 m/s; P<0.016) compared to tricuspid valves despite similar dimensions.

Study Design

Type

Cross-Sectional (n=165)

Structured PICO

Does 4D flow MRI identify morphological and hemodynamic differences between patients with bicuspid aortic valves, tricuspid aortic valves with dilated aortas, and healthy controls?

Population

165 subjects including 65 controls, 50 patients with bicuspid aortic valve (BAV), and 50 patients with a dilated aorta and a tricuspid aortic valve (TAV)

Intervention

Four-dimensional (4D) flow magnetic resonance imaging (MRI)

Comparator

Comparison between BAV, TAV, and control groups

Outcome

Aorta diameter, peak systolic velocity, and normalized systolic flow displacementsurrogate

4D flow MRI demonstrates that patients with bicuspid aortic valves have altered aortic hemodynamics compared to those with tricuspid aortic valves, even when aortic dimensions are similar.

Main Result

Absolute Event Rate: 1.3% vs 1.2%

p-value: p=<0.016

Abstract

AIMS: Four-dimensional (4D) flow magnetic resonance imaging (MRI) was employed for the simultaneous assessment of morphometry and flow parameters along the thoracic aorta to investigate associations between flow, age, aorta diameter, and aortic valve morphology. METHODS AND RESULTS: One hundred and sixty-five subjects, 65 controls, 50 patients with bicuspid aortic valve (BAV), and 50 patients with a dilated aorta, and a tricuspid aortic valve (TAV) underwent 4D flow MRI. Following 3D segmentation of the aorta, a vessel centreline was calculated and used to extract aorta diameter, peak systolic velocity, and normalized systolic flow displacement. Validation of 4D flow MRI-based morphometric measurements compared with manual diameter measurements from standard contrast-enhanced MR angiography in 20 controls showed good agreement (mean difference = 0.4 mm, limits of agreement = ±1.31 mm) except at the sinus of valsalva. BAV showed significant differences in average peak velocity (PV; P < 0.016) compared with TAV and controls between the left ventricle outflow tract to sino-tubular junction (BAV: 1.3 ± 0.3 m/s; TAV: 1.2 ± 0.2 m/s; controls: 1.0 ± 0.1 m/s) and the ascending aorta for average normalized flow displacement (BAV: 0.11 ± 0.02; TAV: 0.09 ± 0.02; controls: 0.06 ± 0.01, P < 0.016) despite similar average aortic dimensions for BAV (37 ± 1 mm) and TAV (39 ± 1 mm). Multivariate linear regression showed a significant correlation of maximal aortic diameter to age, PV, and normalized flow displacement (R(2) = 0.413, P < 0.001). CONCLUSION: A single acquisition of 4D flow MRI characterized local morphological and haemodynamic differences between groups along the aorta. BAV showed altered haemodynamics when compared with TAV in spite of having similar aorta dimensions. Maximal aorta diameter was associated with age, PV, and normalized flow displacement.