72: Truncus Arteriosus

Epidemiology

• Truncus arteriosus is a rare cyanotic cardiac malformation with an incidence of 0.07 per 1000 live births (1.1 percent of all cardiac anomalies), with 40 percent of patients disclosing 22q11 deletion on genetic testing. There is also a variable phenotypic association with DiGeorge syndrome and craniofacial defects.

Morphology

• A single truncal valve usually overrides a large ventricular septal defect. The different classification schemes are based on the origin of the pulmonary arteries (PAs) (from truncus, ductus arteriosus, or descending aorta), the association of aortic arch interruption, and ventricular septal defects.

Pathophysiology

• Typically, there is intracardiac mixing (atrial and/or ventricular septal defect) with pulmonary over-circulation and, if interrupted aortic arch (IAA) is present, features of duct-dependent distal aortic perfusion. If untreated, chronic pulmonary vascular changes ensue, leading to fixed pulmonary hypertension.

Clinical features

• Presentation is in the neonatal period with pulmonary over-circulation and worsening symptoms as pulmonary vascular resistance falls. Hemodynamic collapse, acidosis, and lower body malperfusion are seen in patients with associated IAA and closure of the patent ductus arteriosus.

Diagnosis

• Echocardiography is usually all that is needed to proceed to surgical correction. Truncal anatomy, truncal valve morphology and function, location of the ventricular septal defect, and coronary anatomy are usually well defined echocardiographically. Additional diagnostic modalities include cardiac catheterization, computed tomography, and magnetic resonance imaging with three-dimensional reconstruction.

Treatment

• Complete repair in the neonatal period is standard treatment, following resuscitation and prostaglandin (PGE₁) infusion in newborns with IAA and ductal closure. Repair entails closure of the ventricular septal defect, truncal septation with reestablishment of continuity from the right ventricle (RV) to the PA with a valved conduit, and, if required, IAA and truncal valve repair. PA banding is currently very rarely performed in neonates and infants, in whom complete correction is contraindicated.

Outcomes

• In contemporary series, operative mortality ranges between 4 and 7 percent and is correlated to the reactivity of the pulmonary vascular bed and operative weight below 3 kg. Long-term prognosis is dependent on need for reintervention for truncal valve repair/replacement and structural failure of the RV-PA conduit.