Introduction:
Patients with Tetralogy of Fallot who had pulmonary valve replacement (PVR) are at risk for prosthetic valve failure that requires repeated valve replacement.
Hypothesis:
We hypothesize that the pre-operative geometry of the right ventricular outflow tract (RVOT) and the central pulmonary arteries is a predictor of future prosthetic valve dysfunction.
Methods:
In a retrospective study, using pre-operative cardiac MRI, we measured morphologic parameters including bifurcation angles, length, major and minor diameters, area, and circumference in various locations along the RVOT, pulmonary trunk (PT) and branch pulmonary arteries (BPAs) in 48 patients with Tetralogy of Fallot before they underwent PVR. Physiologic data was collected from their imaging reports (age, weight, height, body surface area (BSA), ventricular volumes and ejection fractions, valvular regurgitant fractions). All measurements were normalized by the patients’ BSA. Post-operative pulmonary valve function was assessed using Echocardiograms performed at an average of 5.5 years after the surgery. Valve dysfunction was defined as pulmonary regurgitation and/or pulmonary stenosis of at least moderate intensity. All geometric and physiologic parameters were compared between the group of patients who developed pulmonary valve dysfunction and those who did not, using a two-tailed Student t-test.
Results:
Patients who developed valve dysfunction had (1) greater RVOT circumference (p=0.038), (2) a more acute bifurcation angle between the PT and the Left Pulmonary Artery (p=0.016), and (3) smaller cross-sectional area at the distal BPAs (p=0.031, p=0.026).
Conclusions:
A dilated RVOT leading to flow vortices may increase the shear stress experienced by the valve, a sharp bifurcation angle disrupts flow patterns, adding dynamic load to the valve, and stenosis in the distal BPAs lead to increased resistance and an increased volume load to the valve - all promoting valve degeneration. Our findings are consistent with physiologic expectations and will be further explored using computational fluid dynamic simulations to elucidate how the parameters identified impact the hemodynamics around the pulmonary valve. A deeper understanding of the hemodynamic implications may ultimately reduce the incidence of valve degeneration by helping surgeons identify patients who are at high risk for valve dysfunction and guiding them to reconstruct the RVOT in specific configurations.
The Impact of Sub-valvular Apparatus Preservation on Prosthetic Valve Dysfunction During Mitral Valve Replacement
