Anatomy. A single arterial vessel that originates from the heart, overrides the ventricular septum (or less commonly arising exclusively from the RV), and supplies the coronary, pulmonary, and systemic circulations (in that order) from the proximal ascending vessel. The truncal valve is frequently abnormal, having between 2-4 cusps, and may be significantly regurgitant and rarely anatomically stenotic (though flow-related gradients are common). Type I: MPA present and arises just above truncal valve, commonly posteriorly. Type II: branch PAs arise separately from the truncus; MPA absent. Type III: unilateral pulmonary artery. Type IV: some form of pulmonary atresia with VSD, usually interrupted aortic arch. When PAs arise from DAo, the diagnosis is TOF/ PA, a similar diagnosis. Commonly associated with DiGeorge syndrome (and hypocalcemia).
Physiology. Truncus arteriosus is most typically repaired in the newborn period except when there is significant PA stenosis and time can be allowed for growth. Infants may develop congestive heart failure (pulmonary congestion) or shock states (e.g. NEC, renal insufficiency) as the PVR decreases in the first days of life. These clinical states may be exacerbated in the setting of moderate or severe truncal stenosis or regurgitation. Severe truncal regurgitation may result in demand coronary ischemia, an indication for urgent surgical intervention. (Recall that ECMO resuscitation in the setting of severe AI is often ineffective.)
Repair. In most cases, a biventricular repair can be performed in the newborn period. This includes a harvesting of the PAs from the truncus arteriosus and anastamosis to an RVPAC; uncommonly, the PAs may be be augmented if hypoplastic. The VSD is closed to the truncal valve, septating the circulation. When possible, intervention on the truncal valve is avoided in the newborn period, although in the setting of severe truncal regurgitation a root reduction may be performed. Rarely (as in the setting of IVH), branch PA banding can be performed as a temporizing measure.
Postoperative considerations. Biventricular repair of truncus arteriosus is corrective; the postoperative circulation should be more stable and effective than prior, even if there is some residual truncal valve disease. Rarely though there is significant post-repair truncal regurgitation or coronary ischemia which may be poorly tolerated. The primary considerations following truncus arteriosus repair include any preoperative comorbidities, truncal (i.e. aortic) regurgitation and stenosis, ventricular function, branch PA stenosis, and the presence of residual VSD. Consider restrictive ventricular physiology due to large VSD patch and RVPAC, particularly in small newborns. Risk of junctional rhythm due to VSD repair.