Aortic stiffness in aortic stenosis assessed by cardiovascular MRI: a comparison between bicuspid and tricuspid valves

Abstract

Objectives: To compare aortic size and stiffness parameters on MRI between bicuspid aortic valve (BAV) and tricuspid aortic valve (TAV) patients with aortic stenosis (AS).

Methods: MRI was performed in 174 patients with asymptomatic moderate-severe AS (mean AVAI 0.57 ± 0.14 cm²/m²) and 23 controls on 3T scanners. Valve morphology was available/analysable in 169 patients: 63 BAV (41 type-I, 22 type-II) and 106 TAV. Aortic cross-sectional areas were measured at the level of the pulmonary artery bifurcation. The ascending and descending aorta (AA, DA) distensibility, and pulse wave velocity (PWV) around the aortic arch were calculated.

Results: The AA and DA areas were lower in the controls, with no difference in DA distensibility or PWV, but slightly lower AA distensibility than in the patient group. With increasing age, there was a decrease in distensibility and an increase in PWV. After correcting for age, the AA maximum cross-sectional area was higher in bicuspid vs. tricuspid patients (12.97 [11.10, 15.59] vs. 10.06 [8.57, 12.04] cm², p < 0.001), but there were no significant differences in AA distensibility (p = 0.099), DA distensibility (p = 0.498) or PWV (p = 0.235). Patients with BAV type-II valves demonstrated a significantly higher AA distensibility and lower PWV compared to type-I, despite a trend towards higher AA area.

Conclusions: In patients with significant AS, BAV patients do not have increased aortic stiffness compared to those with TAV despite increased ascending aortic dimensions. Those with type-II BAV have less aortic stiffness despite greater dimensions. These results demonstrate a dissociation between aortic dilatation and stiffness and suggest that altered flow patterns may play a role.

Key points: • Both cellular abnormalities secondary to genetic differences and abnormal flow patterns have been implicated in the pathophysiology of aortic dilatation and increased vascular complications associated with bicuspid aortic valves (BAV). • We demonstrate an increased ascending aortic size in patients with BAV and moderate to severe AS compared to TAV and controls, but no difference in aortic stiffness parameters, therefore suggesting a dissociation between dilatation and stiffness. • Sub-group analysis showed greater aortic size but lower stiffness parameters in those with BAV type-II AS compared to BAV type-I.

Keywords: Aorta, thoracic; Aortic valve stenosis; Aortic valve, bicuspid; Magnetic resonance imaging; Pulse wave velocity.

Fig. 1

End-diastolic (a) and end-systolic (b) frames from SSFP cine image of the ascending (top larger region) and descending (bottom smaller region) aorta, used for measurement of aortic dimensions and distensibility calculation

Fig. 2

Pulse wave velocity calculation. a Sagittal oblique cine of the aorta for measurement of Δx (average of outer and inner distance in white dashed line). b Aortic flow sequence used for calculation of Δt, i.e., the transit delay, which was estimated from the cross-correlation between the flow rate curves for the ascending (red) and descending (green) aorta (see text for details)

Fig. 3

Scatter plots showing the relationship of age with distensibility (a, b) and pulse wave velocity (c) and of distensibility with cross-sectional area in the ascending aorta (d). Units—distensibility, 10⁻³ mmHg⁻¹; PWV, m/s; AA area, mm²; age years

Fig. 4

Box plots showing the ascending aorta distensibility (a), descending aorta distensibility (b), pulse wave velocity (c), and maximum ascending aorta area (d) for patients with tricuspid, bicuspid type-I, and bicuspid type-II aortic valves. Units as in Fig. 3