Truncus Arteriosus

Introduction

  • Truncus Arteriosus (TA, or common arterial trunk) is a rare cyanotic congenital heart defect.
  • Blood is pumped out of the heart through a single vessel, the truncal artery, which then gives rise to the pulmonary arteries and aorta.
  • Deoxygenated blood and oxygenated blood mix through this common outflow tract and provide blood to the systemic circuit, pulmonary circuit, and coronary arteries.
  • TA usually arises secondary to a failure of conotruncal separation during embryogenesis.

Epidemiology

  • TA is responsible for 0.21%-0.34 % of congenital heart defects
  • Incidence has been found to be 0.03-0.05/1,000 live births.
  • Truncus Arteriosus has been found to be associated with several risk factors:
    • Maternal cigarette smoking during gestation
    • Advanced maternal age
    • 2q11.2 deletions (DiGeorge syndrome)

Anatomy

  • The TA is located above the ventricular septum:
    • Usually has a large ventricular septal defect (VSD).
    • Usually has one valve with anywhere from 2 to 4 cusps.
  • However, the leaflets of the valve are often thickened and have inappropriate size or motion.
  • This results in an incompetent valve with either stenosis or regurgitation.

Truncus_arteriosus_1_0.jpg
https://en.wikipedia.org/wiki/Truncus_arteriosus#/media/File:Truncus_art...

  • Aortic arch abnormalities are common in TA.
            
    • These include right-sided, interrupted, and hypoplastic aortic arches.
    • In patients with interrupted and hypoplastic arches, patency of the ductus arteriosus is key for maintaining flow to the descending aorta (see “Physiology” below).
  • In patients with TA, the coronary arteries usually originate abnormally and the pattern of origin is currently unknown.
  • The sinus node and the AV node is usually in the common location in TA patients.
  • The bundles of the AV node can course through different pathways
       
    • These are often related to the location of the VSD.
  • There are several classification systems for TA (Collet and Edwards, Van Praagh, and STS modification), which describe the origin of the pulmonary arteries and the aortic arch. 

Physiology

  • The physiology of TA is largely related to the volume of blood flowing to the pulmonary circuit. This is affected by:
  1. The degree of pulmonary vascular resistance
  2. The degree of truncal valvular insufficiency
  3. The severity of any aortic arch abnormalities

Pulmonary vascular resistance

  • At birth the pulmonary vascular resistance is high enough to prevent left-to-right shunting, which restricts the amount of blood that can flow to the pulmonary system.
  • As this resistance drops more blood flows to the pulmonary system, the amount of fluid overloads the system, and heart failure begins.
  • Heart failure can begin within several weeks of birth and present by 6 months of age in patients with TA.
  • This process is similar to VSDs, but it occurs much earlier in TA.

Truncal valvular insufficiency

  • The degree of regurgitation or stenosis of the truncal valve causes additional ventricular volume.
  • The myocardium then requires greater amounts of oxygen, which leads to coronary artery ischemia and ventricular dysfunction.
  • Together, this also contributes to the onset and severity of heart failure.

Aortic arch abnormalities

  • Patients with interrupted aortic arches or coarctation require the ductus arteriosus for alleviating pressure overload in the ventricles and allowing for blood flow distally.

Clinical Manifestations

  • Cyanosis in patients with TA is due to the mixing of pulmonary and systemic blood.
  • Most patients with TA are diagnosed within one week of birth – after pulmonary vascular resistance decreases and the ductus arteriosus closes.
  • Pateints present with cyanosis and respiratory distress from pulmonary congestion and onset of heart failure.
  • Some patients also present with a murmur.
  • Pulmonary congestion and heart failure can manifest as:
    • Poor feeding
    • Letharg
    • Respiratory distress (tachypnea, subcostal retractions, nasal flaring, grunting)
    • Tachycardia
    • Hyperdynamic precordium
    • Hepatomegaly
  • On cardiac auscultation there may be a single second heart sound along with an ejection click at the apex or left sternal border and a murmur at the left sternal border.
  • If a strong clinical suspicion exists for TA, an echocardiography will confirm the diagnosis.

Differential

  • Large VSD
  • Pulmonary atresia with VSD
  • Univentricular heart
  • TA is distinguished from these with echocardiography

Treatment

  • Treatment for TA is surgical intervention.
  • Patients with TA are initially medically managed to stabilize them for surgery.
  • Medications include:
    • Diuretics to manage volume overload
    • Inotropes (e.g. dobutamine or dopamine) for cardiac contractility,
    • ACE inhibitors to reduce afterload
    • Ventilation
    • Prostaglandin E1 is given to patients with severe aortic coarctation to maintain patency of the ductus arteriosus.
  • Surgery is usually performed within 30 days of birth.
  • A typical procedure:
  1. Removes the pulmonary arteries from the truncus and reattaches them to the right ventricle
  2. Opens and repairs the truncus
  3. Closes the VSD.
  • Perioperative mortality is 10%
  • The risks of not intervening are so great that most patients undergo primary surgical repair.
  • Long-term survival:
    • 90% at 5 years after primary repair
    • 85% at 10 years 
    • 83% at 15 years 
  • Patients who undergo repair often undergo frequent re-interventions, related to factors including truncal valve dysfunction and conduit obstruction, and have diminished physical function.
  • Patients with 22q11.2 deletion tend to have longer hospital stays, more frequent re-interventions, and require more medications than patients with TA without 22q11.1 deletion.
  • After surgery, all patients with TA are followed by pediatric cardiologists.
  • Prognosis for patients with unrepaired TA is poor and patients usually do not survive without surgical intervention.
  • For patients without repair, the mean age of survival is 5 weeks and 85% do not survive to 12 months of age.

References

  1. Soriano B, Fulton DR, Triedman JK, Armsby C, “Truncus Arteriosus.” In: UpToDate, Post, TW (Ed), UpToDate, Waltham, MA, 2015.
  2. O’Byrne ML, Mercer-Rosa L, Zhao H, Zhang X, Yang W, Cassedy A, Fogel MA, Rychik J, Tanel RE, Mariano BS, Paridon S, Goldmuntz E, “Morbidity in children and adolescents after surgical correction of truncus arteriosus communis.” Am Heart J. 2013 Sept; 166(3): 512-8
  3. O’Byrne ML, Yang W, Mercer-Rosa L, Parnell AS, Oster ME, Levenbrown Y, Tanel RE, Goldmuntz E, “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 Oct; 148(4):1597-605
  4. Williams et al, “Outcomes of Persistent Truncus Ateriosus,” JACC. Vol 34, No 2, Aug 1999: 545-553

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