Computed tomography guided sizing for transcatheter pulmonary valve replacement

Abstract

Objective: To evaluate the predictive value of Computed Tomography Angiography (CTA) measurements of the RVOT for transcatheter valve sizing.

Background: Transcatheter pulmonary valve replacement (TPVR) provides an alternative to surgery in patients with right ventricular outflow tract (RVOT) dysfunction. We studied 18 patients who underwent catheterization for potential TPVR to determine whether CT imaging can be used to accurately predict implant size.

Methods: Cases were grouped by RVOT characteristics: native or transannular patch (n = 8), conduit (n = 5) or bioprosthetic valve (n = 5). TPVR was undertaken in 14/18 cases, after balloon-sizing was used to confirm suitability and select implant size. Retrospective CT measurements of the RVOT (circumference-derived (D_circ) and area-derived (D_area) diameters) were obtained at the level of the annulus, bioprosthesis or conduit. Using manufacturer sizing guidance, a valve size was generated and a predicted valve category assigned: (1) <18 mm, (2) 18-20 mm, (3) 22-23 mm, (4) 26-29 mm and (5) >29 mm. Predicted and implanted valves were compared for inter-rater agreement using Cohen's kappa coefficient.

Results: The median age of patients was 37 years old (IQR: 30-49); 55% were male. Diagnoses included: Tetralogy of Fallot (12/18), d-Transposition repair (3/18), congenital pulmonary stenosis (2/18) and carcinoid heart disease (1/18). Measurements of D_area (κ = 0.697, p < 0.01) and D_circ (κ = 0.540, p < 0.01) were good predictors of implanted valve size. When patients with RVOT conduits were excluded, the predictive accuracy improved for D_area (κ = 0.882, p < 0.01) and D_circ (κ = 0.882, p < 0.01).

Conclusions: CT measurement of the RVOT, using D_area or D_circ, can predict prosthetic valve sizing in TPVR. These measurements are less predictive in patients with conduits, compared to those with a native RVOT or pulmonic bioprosthesis.

Condensed abstract: We studied 18 patients who underwent catheterization for TPVR to determine whether CT imaging could be used to accurately predict implant size. Retrospective RVOT measurements were used to generate a predicted valve size, which was compared with implanted valve size for inter-rater agreement. Measurements of D_area (κ = 0.697, p < 0.01) and D_circ (κ = 0.540, p < 0.01) were good predictors of implanted valve size. When cases with RVOT conduits were excluded, the predictive accuracy improved for D_area (κ = 0.882, p < 0.01) and D_circ (κ = 0.882, p < 0.01). CT measurement of the RVOT can accurately predict prosthetic valve sizing in TPVR. These measurements are less predictive in patients with conduits.

Keywords: Darea, Area-derived Diameter; Dcirc, Circumference-derived Diameter; RVOT, Right Ventricular Outflow; TAVR, Transcatheter Aortic Valve Replacement; TPVR, Transcatheter Pulmonary Valve Replacement.

Fig. 1

Computed Tomography 3-Dimensional models of the RVOT in a selection of our patient cohort demonstrating the anatomical variation between cases where TPVR was successful.

Fig. 2

Cross-sectional measurements of area, perimeter (circumference), long-axis (D_max) and short- axis (D_min) for patient with (a) native annulus (b) valve-in-valve and (c) conduit. Note for valve-in-valve case (b), the internal diameter of the existing bioprosthesis is measured. For the conduit case (c), the outer-outer dimension of the conduit, including calcifications, have been measured.

Fig. 3

Multiplanar reformation (MPR) was used to create a double-oblique transverse plane. In this image the internal diameter of the existing bioprosthesis is manually traced, using the imaging software to calculate its cross-sectional area (mm²) and perimeter (mm). The operator then measured the minimum (D_min = 22.4 mm) and maximum (D_max = 23 mm) cross-sectional diameters.