Truncus Arteriosus

Truncus arteriosus (TA) is a congenital heart defect characterized by the persistence of a common cardiac arterial trunk tract that fails to divide into the pulmonary artery and aorta during embryonal development. Truncus arteriosus is a rare congenital malformation with a high mortality rate within the 1st 5 weeks of life if not managed promptly. Neonates may be asymptomatic at birth but invariably develop respiratory distress and heart failure. Diagnosis is commonly made prenatally through screening ultrasounds. In the event of a missed antenatal diagnosis, TA is confirmed through an echocardiogram. Treatment involves medical stabilization immediately after birth, followed by definitive surgery. With appropriately timed management, the prognosis is excellent.

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Overview

Anatomy

  • A single common arterial trunk gives rise to pulmonary trunk and aorta: 
    • Exact location from which pulmonary arteries arise varies (see classification).
  • 1 valve associated with trunk: 
    • Semilunar valve known as truncal valve
    • Composed of variable (2–6) leaflets
    • Valve may be stenotic, regurgitant, or both.
  • Associated cardiac anomalies include:
    • Ventricular septal defect (VSD): 
      • Always present in association to TA
      • Arterial trunk overrides septal defect.
    • Coronary artery anomaly: 
      • Coronary arteries originate from abnormal location.
      • No set pattern

Embryology

  • Normal development:
    • Single truncal root gives origin to both great vessels (aorta and common pulmonary trunk).
    • Trunco-conal septum forms within truncal root to separate it into pulmonary artery and ascending aorta.
    • Trunco-conal septum also fuses with endocardial cushions and interventricular septum.
  • Abnormal development:
    • Abnormal or absent growth of trunco-conal septum causes truncal root to remain 1 single vessel.
    • Failure of trunco-conal septum to fuse with intraventricular septum results in VSD formation and associated valvular abnormalities.

Classification

  • Type 1: Posterior left side of TA gives rise to pulmonary trunk, which then branches into left and right pulmonary arteries.
  • Type 2: No true pulmonary trunk; right and left pulmonary arteries arise separately directly from posterior aspect of TA.
  • Type 3: No true pulmonary trunk; right and left pulmonary arteries arise separately directly from the lateral aspect of TA.
Truncus arteriosus classification

Truncus arteriosus (TA) classification:
Different forms of TA are classified based on how and where the pulmonary arteries arise from the outflow trunk.
In type 1, the posterior left side of TA gives rise to pulmonary trunk, which then branches into left and right pulmonary arteries.
In type 2, there is no true pulmonary trunk; right and left pulmonary arteries arise separately directly from posterior aspect of TA.
Type 3 is similar to type 2 because there is no true pulmonary trunk, but the pulmonary arteries arise from the lateral aspect of TA.

Image by Lecturio.

Epidemiology

  • Incidence: 5–15 per 100,000 live births
  • 0.7% of all forms of congenital heart defects in live-born infants
  • 4% of critical congenital heart disease

Etiology

  • Not completely understood
  • Postulated to be due to abnormal development of neural crest cells at septal region
  • Increase risk associated with:
    • Advanced maternal age
    • Maternal cigarette smoking
    • DiGeorge syndrome

Pathophysiology and Clinical Presentation

Pathophysiology

  • Single arterial trunk results in: 
    • Mixing of oxygenated and deoxygenated blood
    • Blood pumped to both systemic and pulmonary circulation at same pressure
  • Pulmonary overcirculation: 
    • Both right and left ventricle eject their cardiac output into common trunk.
    • As pulmonary vascular resistance (PVR) decreases postbirth:
      • Blood flow into pulmonary artery > blood flow into aorta
      • Left-to-right shunt through VSD increases due to the pressure differential.
      • Pulmonary congestion and heart failure ensue.
  • Eisenmenger physiology:
    • In untreated cases, prolonged pulmonary overcirculation leads to increased muscular tone of pulmonary vasculature.
    • Increased vascular tone leads to increased PVR.
    • Increased PVR leads to decreased pulmonary circulation and worsened cyanosis.
  • Truncal valve insufficiency:
    • If valve is regurgitant:
      • During diastole, blood flows back into heart.
      • Results in reduced cardiac output
      • Reduced cardiac output causes coronary artery underperfusion → myocardial infarction

Clinical presentation

Patients may be asymptomatic at birth but develop symptoms within 1st few days of life.

  • Cyanosis:
    • Mild to moderate initially
    • Worsens once PVR falls
  • Symptoms of respiratory distress and heart failure:
    • Shortness of breath
    • Grunting
    • Lethargic
    • Poor feeding
    • Diaphoresis
Cyanotic neonate

Cyanosis in a neonate due to congenital heart disease:
The infant in the image displays cyanosis due to poor perfusion caused by congenital heart disease (in this case, transposition of the great vessels, but all cyanosis due to congenital heart disease looks similar). Cyanosis can be subtle and is most clearly seen around the lips and fingertips.

Image: “Cyanotic neonate” by Jules Atkins. License: Public Domain

Diagnosis

Physical exam

  • Failed pulse oximetry screening test (persistently low saturation)
  • Failure to thrive
  • Heart failure:
    • Tachycardia
    • Hepatomegaly
    • Edema
  • Respiratory distress:
    • Tachypnea
    • Dyspnea
    • Grunting
    • Nasal flaring
  • Pulse:
    • Wide pulse pressure 
    • Bounding pulses
  • Murmur:
    • Single, loud S2
    • Ejection systolic murmur at apex or left sternal border
    • Truncal valve insufficiency → diastolic, high-pitched murmur at left sternal border

Imaging

  • Echocardiogram: 
    • Prenatal screening echo is usually sufficient.
    • Confirmatory in postnatal phase
    • Doppler can be used to assess truncal valve insufficiency by measuring retrograde flow through valve.
  • Chest X-ray:
    • Increased pulmonary vascular markings
    • Cardiomegaly
    • Absent thymic shadow (suggesting DiGeorge syndrome)

Other tests

  • Electrocardiogram showing:
    • Prominent P wave
    • Right and left ventricular hypertrophy
  • Arterial blood gases to determine degree of hypoxemia and acidosis in heart failure
  • Serum calcium levels (DiGeorge syndrome (hypoparathyroidism))

Management and Prognosis

Management

The initial management aims to medically stabilize the patient prior to surgical intervention.

  • Medical:
    • Treat volume overload → diuretics (e.g., furosemide)
    • Improve myocardial contractility → inotropes (e.g., dopamine)
    • Reduce afterload → ACE inhibitors
    • Treat acidosis → bicarbonate
  • Surgical:
    • Definitive management
    • Performed within 1st few weeks of life
    • Single repair procedure that consists of:
      • Closure of VSD
      • Committing common arterial trunk to left ventricle
      • Reconstructing pulmonary artery and right ventricular outflow tract (RVOT)

Prognosis

  • Untreated → 1-year survival < 15%, majority die < 5 weeks of life
  • Treated → 1-year survival is 100%
  • High cardiovascular morbidity post-op, requiring regular cardiology follow-up

Differential Diagnosis

  • Tricuspid valve atresia (TVA): congenital heart disease characterized by lack of development of tricuspid valve. Presents with cyanosis, labored breathing, hypoxic spells. Holosystolic murmur, single S2. Diagnosis made by echocardiogram and ECG.
  • Tetralogy of Fallot (TOF): congenital heart disease characterized by occurrence of 4 key cardinal features: overriding aorta, VSD, RVOT obstruction, and right ventricular hypertrophy. Patients present with cyanosis and history of tet spells (cyanosis and fainting when crying). Diagnosis is confirmed by an echocardiogram and the patient is surgically managed.
  • Transposition of the great vessels (TGV): congenital heart defect characterized by switching of great vessels, so that aorta originates from right ventricle and pulmonary artery from left. Presents with cyanosis, tachypnea, heart failure, hypoxemia unresponsive to supplemental oxygen.
  • Total anomalous pulmonary venous return (TAPVR): rare congenital cardiopathy in which pulmonary veins drain to sites other than left atrium. Presents with cyanosis from birth, heart failure, respiratory distress. Characterized by wide-split S2.
  • Ebstein anomaly (EA): congenital heart defect in which there is downward displacement of tricuspid valve leaflets causing RVOT obstruction. Presents with cyanosis, arrhythmias, failure to thrive. Diagnosed by echocardiogram.

References

  1. Kliegman, R. M., M.D., St Geme, Joseph W., MD, Blum, N. J., M.D., Shah, Samir S., M.D., M.S.C.E., Tasker, Robert C., M.B.B.S., M.D., & Wilson, Karen M., M.D., M.P.H. (2020). Cyanotic congenital heart disease: Lesions associated with increased pulmonary blood flow. In R. M. Kliegman MD, J. W. St Geme MD, N. J. Blum MD, Shah, Samir S., MD, MSCE, Tasker, Robert C., MBBS, MD & Wilson, Karen M., MD, MPH (Eds.), Nelson textbook of pediatrics (pp. 240-2420.e1). doi: http://dx.doi.org/10.1016/B978-0-323-52950-1.00458-2 Retrieved from https://www.clinicalkey.es/#!/content/3-s2.0-B9780323529501004582
  2. Brian D Soriano, David R Fulton. (2019). Truncus Arteriosus. UpToDate. Retrieved from https://www.uptodate.com/contents/truncus-arteriosus?search=truncus%20arteriosus&source=search_result&selectedTitle=1~31&usage_type=default&display_rank=1#H172309436

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