Reference Ranges for the Diameter of the Right Ventricular Outflow Tract by Cardiovascular Magnetic Resonance and Comparison with Echocardiographic Measurements

Aims: To provide reference ranges for the right ventricular outflow tract (RVOT) diameter by cardiovascular magnetic resonance (CMR) in children, and compare the measurements with two-dimensional (2D) transthoracic echocardiography (TTE).

Place and duration of study: Lausanne University Hospital, between January 2014 and December 2018.

Methods: We measured the RVOT diameter in 49 children (35 male, 14 female; age range 2-18 years) with normal RVOT anatomy on balanced steady-state free precession (bSSFP) CMR images in the strict transverse and sagittal views, and on 2D TTE images in parasternal short axis (PSAX) and parasternal long-axis (PLAX) views.

Results: Based on 63 measurements, we obtained the following mean RVOT diameters and their reference ranges, indexed to body surface area: 15.2 mm/m2 (7.0 - 23.3 mm/m2) in the strict transverse view, and 14.0 mm/m2 (7.8 - 20.2 mm/m2) in the strict sagittal view. Pearson correlation showed a very strong correlation between the CMR strict transverse view and the 2D TTE PSAX view (r = 0.84; P < .001), and a strong correlation between the CMR strict sagittal view and the 2D TTE PLAX view (r = 0.78; P < .001). The Bland-Altman analysis showed poor agreement between the CMR strict transverse view and the 2D TTE PSAX view (bias -3.34 mm/m2 or -16.6%), and between the CMR strict sagittal view and the 2D TTE PLAX view (bias -3.90 mm/m2 or -19.7%).

Conclusions: There is strong correlation but poor agreement between the measurements of the RVOT diameter in the strict transverse and sagittal views by CMR and the similar PSAX and PLAX views by 2D TTE. The static bSSFP CMR images in the strict transverse and sagittal views should not be used to define RVOT dilatation in children.