4D flow magnetic resonance post-operative pulmonary stenosis assessment in patients with transposition of the great arteries repaired by arterial switch

Abstract

Patients operated for transposition of the great arteries by arterial switch defines a new population coming to adulthood with unknown long-term prognosis. The principle complication in adulthood is the pulmonary stenosis, occurring in 17% of patients and leading to re-intervention in 15% of cases. Repair of this right ventricle outflow is recommended in symptomatic patients when systolic pressure of the right ventricle is greater than 60 mmHg (velocity of tricuspid regurgitation (IT) > 3.5 m/sec). However pulmonary flow measurement cannot be always measured with transthoracic echocardiography Doppler (TTE) due to the peculiarity of the vessels anatomy.4D flow in magnetic resonance is a new imaging method, allowing analysis of blood velocity and flow in an entire volume, permitting detection, quantification and location of vascular stenosis. The objective of this study was to compare this 4D flow imaging to TTE for the diagnosis of pulmonary stenosis in adult with transposition of the great arteries corrected by arterial switch. Thirty-three patients (19 men, 14 women, mean age 25.5 years old) were prospectively included with a TTE and a MRI 4D flow examination the same day. In 16 of them (48.5%), right ventricle out flow was not correctly evaluated by TTE against 0(0%) in 4D flow. TTE detected 11 (33.3%) patients with an upper speed over 2 m/s and 2 (6%) patients with a higher speed over 3.5 m/s against 14 (42%) and 4 (12.1%) respectively with 4D flow. The peak flow velocities measurements in Doppler and 4D flow were highly correlated ( r = 0.79; P < 0.0001). Moreover, there was an highly correlation between the peak velocity and the right ventricle mass index in 4D flow which was higher than TTE ( r = 0.74; P < 0.001 against = 0.55; P = 0.02)At least, 4D flow was able to precise the location of the peak velocity: on the distal pulmonary trunk for 19 (%) patients and on the pulmonary arteries for the other 14 (54.5%) patients (40.5%) In patients with transposition of the great arteries treated by arterial switch, 4D flow MRI permits pulmonary stenosis assessment, with measurements of peak flow velocities highly correlated to TTE, and even detect more stenosis with the ability to specify their location.