Truncus Arteriosus

PVR is the only throttle - The pulmonary arteries hang off the truncus, so nothing but PVR decides how much of each beat goes to the lungs rather than the body. Once PVR drops the lungs are flooded and systemic output suffers.

Heart failure, not cyanosis - The typical presentation in the first two weeks is poor feeding, lethargy, tachypnea, costal-sternal retractions, grunting, nasal flaring, tachycardia and hepatomegaly, with cyanosis mild or unnoticeable. Pre- and post-ductal saturations on the newborn screen sit below 95%.

Bounding pulses mean diastolic runoff - Peripheral pulses are bounding and the pulse pressure is wide because blood runs off into the pulmonary arteries during diastole. The coronaries arise from that same trunk, so a low diastolic pressure is not a benign number here.

Check the truncal valve - Regurgitation is present in about half of these patients and worsens the heart failure; stenosis also occurs, and the valve may have anywhere from one to four cusps. The echo report tells you which, and intraoperative TEE is used to follow it through repair.

Rule out an obstructed arch - Critical coarctation coexists in about 10% and can present as cardiovascular collapse or shock. Right-sided, interrupted and hypoplastic arches, abnormal coronary origins and pulmonary artery stenosis all travel with this lesion, and where there is an arch anomaly prostaglandin is used to keep the duct open.

Check the ionized calcium - Truncus arteriosus is frequently associated with 22q11.2 deletion, where failed pharyngeal pouch development leaves hypoplastic parathyroids and hypocalcemia. Get an ionized calcium before any case involving citrated blood.

Thymic hypoplasia and transfusion - The same deletion leaves the thymus hypoplastic or absent and the patient T-cell deficient with recurrent infections. Irradiation of blood products is what prevents transfusion-associated graft-versus-host disease, and line asepsis is not negotiable.

Anticipate the 22q11 airway - Pharyngeal pouch failure also affects the maxilla, mandible and palate, so cleft palate and abnormal facies are common. Look at the face and the previous anesthetic record before you promise an easy intubation.

Debubble every line - Systemic and pulmonary blood mix at the VSD, so an air bubble has a straight route into the systemic circulation.

First 48 hours post-repair - Pulmonary hypertensive crisis and low cardiac output syndrome dominate the early postoperative course. Reduced handling and mobilization lowers the rate of crises, so keep sedation and analgesia deep and cluster your interventions.

Watch the rhythm after bypass - Right bundle branch block and supraventricular tachycardia are both described after repair.

Plan for the redo - About 75% need re-intervention within ten years, most often right ventricular outflow tract reconstruction, then truncal valve repair or replacement, then relief of aortic obstruction. Many of your encounters will be repeat sternotomies, and mediastinal bleeding is a documented complication, so have blood available and checked.

Truncus arteriosus is a failure of the embryologic truncoconal septum to form, leaving a single arterial trunk that rises from both ventricles over a large ventricular septal defect (VSD) and feeds the coronary, pulmonary and systemic circulations through one common truncal valve. Systemic and pulmonary venous blood mix at the VSD, so the child is mildly cyanotic from birth.

The pulmonary arteries come straight off the truncus, which means pulmonary vascular resistance and nothing else sets pulmonary blood flow. Once PVR falls after birth that flow is usually torrential, producing overcirculation and congestive heart failure within the first two weeks and, if left alone, irreversible pulmonary vascular disease with a reversal back to right-to-left shunting. Truncal valve regurgitation is present in about half, critical coarctation in 10%, and 22q11.2 deletion is a frequent companion.