Truncus arteriosus and single-ventricle physiology

The thread running through this topic is mixing, and what you do about it. ^{[2] [8]} When red and blue blood cannot be kept apart, the body gets blue blood and the lungs get more blood than they can handle. Truncus arteriosus solves this with one operation that separates the circulations. Single-ventricle physiology solves it with three operations that route venous blood to the lungs without a second pump. This page covers recognition, the bedside and echocardiographic anatomy, the Collett–Edwards and Van Praagh classifications, the prostaglandin-E1-first rule, the complete neonatal repair of truncus, the staged Fontan palliation, the interstage mortality that home monitoring targets, and the lifelong burden both groups carry. It links to the ductal-dependent congenital heart disease leaf for the broader differential and to the hypoplastic left heart syndrome leaf for the detailed Norwood content.

Overview & Definition

Picture a normal heart first: two ventricles sit side by side, the right pumps blue blood to the lungs and the left pumps red blood to the body, and two separate great vessels leave through two separate valves. Truncus arteriosus collapses that design. One great artery — the truncus — leaves the heart through a single truncal valve and then branches to give off the coronaries, the aorta and the pulmonary arteries. Because a ventricular septal defect sits directly under the truncal valve, blood from both ventricles pours into the same trunk and mixes completely. The body and the lungs therefore receive the same mixed, partially blue blood. ^{[1] [2]}

Two consequences follow directly from that anatomy, and they explain everything you will see at the bedside. First, the baby is cyanosed, because the body is being fed mixed blood. Second — and this is the part candidates miss — the lungs are being fed by the same trunk with no resistance between the aorta and the pulmonary bed. After birth the pulmonary vascular resistance falls, so more and more of the mixed blood takes the easy path into the lungs. The lungs flood, the heart works harder and harder, and the baby slides into high-output heart failure over the first weeks of life. Cyanosis comes first; heart failure follows. ^[3]

Single-ventricle physiology is the other half of this topic, and it is a strategy rather than a single defect. It describes any heart in which only one ventricle is usable, because the other is hypoplastic, atretic or has no inlet or outlet. Hypoplastic left heart syndrome, tricuspid atresia, pulmonary atresia with intact septum, double-inlet left ventricle and unbalanced atrioventricular septal defect all produce it. Because there is no second pump to push blood to the lungs, you cannot simply close a hole. Instead, surgeons keep the one good ventricle as the systemic pump and route the venous return passively and directly to the lungs, in stages, until the circulations run in series. That staged pathway is called the Fontan strategy. ^{[8] [10]}

The reason these two lesions sit on one page is that both force you to think about the balance between lung blood flow and body blood flow. In truncus the balance is dangerously tipped toward the lungs. In single-ventricle physiology the entire surgical plan is about restoring a workable balance. Master that idea and the rest follows. ^{[2] [10]}

References12ShowHide

1. [1]Naimo PS; Konstantinov IE Surgery for Truncus Arteriosus: Contemporary Practice. Ann Thorac Surg, 2021.PMID 32828754
2. [2]Russell HM; Jacobs ML; Anderson RH; et al A simplified categorization for common arterial trunk. J Thorac Cardiovasc Surg, 2011.PMID 20965518
3. [3]Thompson LD; McElhinney DB; Reddy M; et al Neonatal repair of truncus arteriosus: continuing improvement in outcomes. Ann Thorac Surg, 2001.PMID 11515872
4. [4]Russell HM; Pasquali SK; Jacobs JP; et al Outcomes of repair of common arterial trunk with truncal valve surgery: a review of the society of thoracic surgeons congenital heart surgery database. Ann Thorac Surg, 2012.PMID 22088417
5. [5]Goldmuntz E 22q11.2 deletion syndrome and congenital heart disease. Am J Med Genet C Semin Med Genet, 2020.PMID 32049433
6. [6]O'Byrne ML; Yang W; Mercer-Rosa L; et al 22q11.2 Deletion syndrome is associated with increased perioperative events and more complicated postoperative course in infants undergoing infant operative correction of truncus arteriosus communis or interrupted aortic arch. J Thorac Cardiovasc Surg, 2014.PMID 24629220
7. [7]Derridj N; Villemain O; Khoshnood B; et al Outcomes after common arterial trunk repair: Impact of the surgical technique. J Thorac Cardiovasc Surg, 2021.PMID 33342576
8. [8]Fontan F; Baudet E Surgical repair of tricuspid atresia. Thorax, 1971.PMID 5089489
9. [9]Anderson PA; Sleeper LA; Mahony L; et al Contemporary outcomes after the Fontan procedure: a Pediatric Heart Network multicenter study. J Am Coll Cardiol, 2008.PMID 18598886
10. [10]Rychik J; Atz AM; Celermajer DS; et al Evaluation and Management of the Child and Adult With Fontan Circulation: A Scientific Statement From the American Heart Association. Circulation, 2019.PMID 31256636
11. [11]Sananes R; Goldberg CS; Newburger JW; et al Six-Year Neurodevelopmental Outcomes for Children With Single-Ventricle Physiology. Pediatrics, 2021.PMID 33441486
12. [12]Rudd NA; Ghanayem NS; Hill GD; et al Interstage Home Monitoring for Infants With Single Ventricle Heart Disease: Education and Management: A Scientific Statement From the American Heart Association. J Am Heart Assoc, 2020.PMID 32777961