Assessment of Aortic Root in Tetrology of Fallot by Multislice Computed Tomography

Background: Tetralogy of fallot (TOF) is the most prevalent cyanotic congenital heart disease (CHD), affecting three out of every 10,000 births. TOF is linked to conal malseptation and lack of rotation, result in failure of the union of the conal and ventricular septa and anterior malalignment of the conal septum, producing the classic tetrad of findings. This work aimed to assess the role of ECG-gated multislice computed tomography (MSCT) in assessing conal malseptation in TOF by measuring the aortic root's clockwise angle rotation, which may serve as a predictor for the degree of conal malseptation and, consequently, the maldevelopment of the right ventricular outflow tract (RVOT).

Methods: This prospective study was performed on 30 individuals who underwent MDCT cardiac angiography of the heart and great vessels to confirm the diagnosis or to address specific anatomic questions raised by inconclusive echocardiography findings before planning the appropriate management. The examined cases were classified into two groups: Group 1 (TOF-PS) TOF with pulmonary stenosis (n=20) and Group 2 (TOF-PA) TOF with pulmonary atresia (n=10) .Using a true short-axis view of the aortic valve, the aortic root rotation was determined by drawing a line joining the interleafet anterior commissure and the middle of non-coronary sinus then measuring its angle with the interatrial septum plane. Correlation was done between the rotation angle and main pulmonary artery (MPA) diameter indexed to body surface area.

Results: All cases exhibited a rotation of the aortic root in a clockwise direction, with no instances of counterclockwise rotation. The TOF-PA group had a larger rotation angle of the root of the aorta compared to TOF-PS group with a statistical significance difference between the two groups (67.23⁰ ± 13.45⁰ vs 54.34⁰ ± 6.54⁰, P=0.028 respectively). The mean MPA diameter indexed to BSA 12.91 ± 6.05 mm/m2. The angle of aortic root rotation in a clockwise direction was negatively correlated with the indexed MPA diameter with spearman coefficient = -0.325 and p=0.162. A cut-off value of aortic angle of 56.8° was determined, above which there is a risk of pulmonary atresia (AUC=0.750, 95% CI= 0.535 – 0.965) with sensitivity 70%, specificity 65%, positive predictive value of was 50% and negative predictive value was 81.2%.

Conclusions: MSCT quantitatively assesses conal malseptation and its impact in individuals with TOF. The aortic root rotates at an angle in the clockwise direction. There is a negative correlation between the degree of aortic root rotation in a clockwise direction and the size of the proximal MPA. Patients diagnosed with TOF with pulmonary atresia (pa) exhibit a greater degree of aortic root rotation.