Transposition of the great arteries (TGA) occurs when there is a ventriculo-arterial discordance, leading to the origin of the aorta from the right ventricle and the pulmonary artery from the left ventricle. The prevalence of TGA is approximately 5 cases per 10,000 live births, accounting for 3% of all congenital heart diseases and 20% of cyanotic lesions. The dextro-looped form (d-TGA) describes the positioning of the right ventricle to the right of the left ventricle, with the aorta positioned anteriorly and to the right of the pulmonary artery. The term “dextro” refers to the looping of the ventricles during cardiac morphogenesis, specifying the spatial relation of the right ventricle to the left. It is distinct from levo-TGA (l-TGA), also known as congenitally corrected TGA, a rarer condition characterized by both atrioventricular and ventriculo-arterial discordance. Cyanosis in l-TGA is uncommon unless associated lesions are present.

In d-TGA, the systemic and pulmonary circulations are arranged in parallel, a condition incompatible with life unless blood mixing occurs between these circuits. This mixing can happen intracardially via a patent foramen ovale, atrial or ventricular septal defects, or extra-cardiac through a patent ductus arteriosus or bronchopulmonary collateral vessels. Postnatal management aims to optimize this mixing, which is most efficient at the atrial level due to low-pressure bidirectional flows across the septum.

Despite significant advances in the management of TGA, many questions remain unanswered. What is the ideal timing for surgery? Who benefits most from balloon atrial septostomy (Rashkind procedure)? Post-discharge, what care do these patients require? What long-term issues may arise? How do neonatal decisions influence outcomes? Most studies comprise case series or single-center experiences with limited follow-up.

Today’s study provides insights into the national experience of TGA with intact septum (TGA-IS) treated with arterial switch surgery in the United Kingdom from 2000 to 2017. The study explores survival, reintervention rates, and healthcare resource utilization using data from the mandatory National Congenital Heart Disease Audit, encompassing all centers treating these patients. Complex TGA cases, alternative procedures, or deaths before surgery were excluded.

A total of 1,772 patients were identified, with a median age at surgery of 9.5 days. Ten-year mortality and reintervention rates were 3.2% and 10.7%, respectively. The median length of hospital stay after surgery was 19 days. In the first year post-surgery, patients required 7 hospital days on average, decreasing to 1 day/year after the fifth year, primarily for outpatient visits. Neither the age at surgery nor the need for balloon atrial septostomy were associated with increased mortality or reintervention rates. However, low birth weight, circulatory support, renal failure requiring therapy, and associated comorbidities were significant risk factors for mortality and reintervention. Comparisons between patients undergoing septostomy and those proceeding directly to surgery revealed no statistically significant differences.

The authors concluded that while mortality and healthcare resource utilization for this condition were low, reintervention was frequent. Early surgery was advocated, with individualized decisions regarding atrial septostomy based on patient risk factors.

COMMENTARY:

In many parts of the world, such registries are voluntary, involving selected institutions whose results may not be generalizable. The comprehensiveness of this registry is enviable, encompassing over 1,700 TGA-IS patients. The British data demonstrate exceptional survival rates exceeding 97%, reflecting the reproducibility of arterial switch surgery across centers, comparable to leading congenital heart centers globally.

However, many questions posed at the outset remain unresolved. No cases involved surgery beyond three weeks of life, suggesting that late presentations in developed settings are rare. Operating in the first week of life does not appear to offer additional benefits, aligning with recent studies advocating early surgery. The role of atrial septostomy also remains unclear due to variability in pre-existing atrial septal communication and clinical practices across centers.

One limitation of this registry is the absence of coronary anatomy data. Complex coronary patterns, such as intramural coronaries or single ostium, significantly influence hospital mortality and future reinterventions. Similarly, the relationships of great vessels and commissural alignment, which affect right ventricular outflow tract obstruction and valvular function, are not documented.

As Dr. Barron notes in his editorial, reinterventions in TGA occur at different stages. In the first year, they are predominantly coronary-related. From the second to the fifth year, they involve pulmonary branches or right ventricular outflow obstruction. A third phase, requiring over 17 years of follow-up, involves neoaortic dilation, as the neoaorta, originally pulmonary tissue, endures systemic pressure.

In conclusion, TGA will remain a topic of discussion for decades. Like tetralogy of Fallot, we must address the sequelaes of our predecessors’ successes.

REFERENCE:

Dorobantu D, Espuny Pujol F, Kostolny M, et al. Arterial Switch for Transposition of the Great Arteries. JACC Adv. 2023 Jul, 2 (5) . doi: 10.1016/j.jacadv.2023.100407