Truncus arteriosus, also known as common arterial trunk, is characterized by a single ventriculoarterial connection that links both ventricles to a single arterial trunk. This trunk provides flow to the aorta, pulmonary arteries, and coronary arteries. A singular valve, termed the truncal valve, is positioned above an outlet ventricular septal defect. With a prevalence of 1 in 10,000 pregnancies, truncus arteriosus accounts for less than 0.5% of congenital heart defects, making it one of the rarest diagnoses in this group. One in three cases is associated with 22q11.2 deletion syndrome, also referred to as DiGeorge syndrome, velocardiofacial syndrome, or CATCH22.

Embryologically, truncus arteriosus results from an aortopulmonary septation defect at three levels: great arteries, valvular, and subarterial. Several classification systems exist for truncus, from the classic Collet and Edwards system (1949), which identifies four types: Type 1 with a short pulmonary trunk, Type 2 where the pulmonary arteries emerge from the aorta, and Type 3 where the pulmonary arteries arise farther apart from the aorta. Type 4, which features no true pulmonary arteries but rather aortopulmonary collaterals, is no longer considered part of the truncus spectrum. Later, this congenital heart defect was reclassified using the Van Praagh system and its modifications. Currently, the classification proposed by Russell et al. (2011) is favored, which simplifies truncus types into two categories: aortic dominance and pulmonary dominance. This classification requires further anatomical description of the pulmonary artery branches, but it provides the best embryological and clinical correlation.

Truncus arteriosus exhibits several defining anatomical features. The subarterial outlet ventricular septal defect is often misidentified as a malalignment defect. The truncal valve, which can consist of 1 to 6 leaflets, is frequently dysplastic. Coronary arteries are anomalous by definition, as they do not originate from the aorta but from a common arterial trunk, with up to 64% of cases showing variations in origin and distribution. The neoaortic root is invariably large and grows over time, a phenomenon that remains unexplained.

The article aims to describe the natural history of truncal root dilatation following neonatal repair. This single-center, retrospective study evaluated all truncus arteriosus cases operated on at Boston Children’s Hospital from 1984 to 2018. Echocardiographic measurements were collected during follow-up, focusing on diameters and z-scores of the annulus, sinuses of Valsalva (SV), and sinotubular junction (STJ) of the neoaorta. Trends over time were analyzed using a linear mixed-effects model.

During the study period, 255 patients underwent surgery, of whom 193 (75.7%) survived and were included in the study. The median age at correction was 12 days. More than half of the patients had tricuspid valves, and a quarter had quadricuspid valves. The median follow-up was 11.6 years, during which no cases of aortic dissection were reported. Twenty percent of the cohort (38 patients) required intervention on the truncal valve or root. The mean annual growth of the annulus, SV, and STJ was 0.7 mm/year, 0.8 mm/year, and 0.9 mm/year, respectively. Z-scores, although elevated, remained stable over time. Bicuspid valves were associated with larger SV (p = .003) and STJ (p = .029) sizes, while quadricuspid valves showed larger STJ dimensions (p = .004). Over the follow-up period, patients with bicuspid and quadricuspid valves exhibited greater annular dilatation (p < .05). A high-risk group was identified: patients with truncal root growth above the 75th percentile had a higher incidence of truncal valve regurgitation (p = .019) and a greater need for reintervention (p = .002).

The authors concluded that truncal root dilatation persists beyond three decades after primary intervention. Patients with bicuspid and quadricuspid valves showed greater dilatation over time and required more frequent valve interventions, identifying them as a high-risk subgroup requiring closer follow-up.

COMMENTARY:

Truncal root dilatation is a consistent feature, progressively increasing over time, while aortic dissections remain anecdotal. The etiology of this dilatation is still unclear, whether due to altered hemodynamics from abnormal anatomy, a primary defect in the vascular wall, or a combination of both. According to clinical guidelines, replacement of the neoaorta is indicated if the diameter exceeds 55 mm. This recommendation applies equally to aortic dilatation in Fallot patients, those with transposition of the great arteries repaired by arterial switch surgery, and neoaortic dilatation in truncus arteriosus. Each condition has distinct pathophysiological substrates, yet the guideline remains the same due to the limited literature supporting individualized recommendations.

The study by Sengupta et al. explores the natural history of truncal neoaortic dilatation over a follow-up of up to 35 years, an achievement in itself. The authors demonstrate that, despite elevated z-scores, these remained stable over three decades. In a cohort of 193 patients, no cases of aortic dissection were recorded. They found that quadricuspid valves increase the likelihood of intervention on the valve or root tenfold and identify high-risk cohorts within the truncus spectrum requiring closer monitoring.

Despite being a valuable contribution, the study has limitations. It is retrospective and single-centered, analyzing a broad time frame due to the low incidence of the defect. Intraoperative data regarding truncal valve morphology, beyond leaflet count, are unavailable. Additionally, truncal annulus measurements were obtained using 2D echocardiography, providing only single-plane data despite the typically oval morphology of these annuli. Interobserver variability in echocardiographic measurements further complicates interpretation. The prevalence of 22q11.2 deletion syndrome is also unclear, as diagnostic techniques for this condition emerged in 1996.

Notably, this study still considers Type 4 truncus, which European guidelines no longer classify within the truncus spectrum.

In conclusion, this study follows the tradition of excellence from Boston Children’s Hospital, offering pertinent and relevant insights to identify high-risk patients for truncal neoaortic dilatation after repair.

REFERENCE:

Sengupta A, Gauvreau K, Shukla A, Kohlsaat K, Colan SD, Del Nido PJ, et al. Natural History of Truncal Root Dilatation and Truncal Valve Regurgitation in Truncus Arteriosus. Ann Thorac Surg. 2023 Jul;116(1):78-84. doi: 10.1016/j.athoracsur.2023.03.030.