Persistent Truncus Arteriosus

A single arterial trunk arises from the heart, overriding a large ventricular septal defect and giving rise to the coronary, pulmonary and systemic arteries. It results from failure of the embryonic truncus to divide into aorta and pulmonary artery. About 1 to 4% of congenital heart disease, roughly 0.03 to 0.06 per 1000 live births.

• Chromosome 22q11.2 deletion is found in about one third of cases and more often when an interrupted arch coexists. A right aortic arch occurs in about 30%. The truncal valve is abnormal in about half (bicuspid, quadricuspid, thickened), with regurgitation or stenosis in about 20 to 50%.
• Types by origin of the pulmonary arteries: a short main pulmonary artery arising from the trunk and dividing into two branches; or right and left pulmonary arteries arising separately but close together from the posterior trunk; or branches arising from the lateral trunk; or no true pulmonary arteries, with pulmonary supply from collateral vessels (this variant behaves like pulmonary atresia with ventricular septal defect).
• Physiology: complete mixing of systemic and pulmonary venous blood in the trunk. As pulmonary vascular resistance falls over the first weeks of life, pulmonary blood flow rises, causing heart failure, with a falling diastolic pressure and coronary steal. Pulmonary vascular disease becomes irreversible within 3 to 6 months.
• Untreated, about half die in the first month and most within the first year.

• Mild cyanosis in the first days (with high resistance), progressing to heart failure at 1 to 4 weeks: tachypnoea, sweating, poor feeding, hepatomegaly and failure to thrive.
• Bounding pulses with wide pulse pressure, a hyperactive precordium, a single second heart sound, an ejection click, a systolic ejection murmur, and an early diastolic murmur if the truncal valve is regurgitant.
• Features of 22q11.2 deletion: cleft palate, characteristic facies, hypocalcaemic seizures (neonatal hypocalcaemia from hypoparathyroidism), recurrent infection.
• Differential diagnosis: large ventricular septal defect, aortopulmonary window, pulmonary atresia with ventricular septal defect and collaterals, patent ductus arteriosus with heart failure, atrioventricular septal defect, transposition with ventricular septal defect, total anomalous pulmonary venous return, and sepsis.
• Complications: heart failure, truncal valve regurgitation, pulmonary vascular disease, coronary ischaemia from low diastolic pressure and abnormal ostia, endocarditis, hypocalcaemic seizures, infections from T-cell deficiency, conduit obstruction after repair, and arrhythmia.

• Chest X-ray: cardiomegaly, plethora, a right aortic arch in about one third, and an absent main pulmonary artery segment. ECG: biventricular hypertrophy.
• Echocardiography: single great vessel overriding the septum, ventricular septal defect, truncal valve morphology and regurgitation, origin and size of the pulmonary arteries, coronary ostia and course, arch sidedness and any interruption or coarctation.
• CT or MR angiography or catheterisation for complex anatomy, collateral supply, or late presentation. Catheter data are essential if repair is delayed beyond about 3 to 6 months: pulmonary vascular resistance index of less than about 6 Wood units m2 is operable.
• Laboratory: ionised calcium and parathyroid hormone, full blood count with lymphocyte subsets, immunoglobulins, and a fluorescence in situ hybridisation or microarray test for 22q11.2 deletion. Renal and liver function before surgery.

• Preoperative:
  • Diuretics for heart failure: furosemide 1 to 2 mg/kg per dose orally or IV 2 to 3 times daily, and spironolactone 1 to 3 mg/kg/day.
  • Avoid supplemental oxygen unless saturation is less than 80%, because oxygen lowers pulmonary resistance and steals systemic and coronary blood flow. Aim for SpO2 of 85 to 90%.
  • Avoid hyperventilation and alkalosis. Limit enteral fluid if in failure; nutrition of 120 to 150 kcal/kg/day by tube if needed.
  • Correct hypocalcaemia: calcium gluconate 10% 0.5 to 1 mL/kg (50 to 100 mg/kg) IV slowly over 5 to 10 minutes with ECG monitoring, then calcitriol or oral calcium as advised by endocrinology.
  • For suspected 22q11.2 deletion with T-cell deficiency: give irradiated, cytomegalovirus safe blood products only, and avoid live vaccines until immune function is assessed.
• Surgical repair, ideally within the first 2 to 6 weeks of life and always before 3 months:
  • Closure of the ventricular septal defect so that the left ventricle ejects into the trunk (now the aorta), detachment of the pulmonary arteries from the trunk, and placement of a valved conduit (homograft or bovine jugular vein graft) from the right ventricle to the pulmonary arteries.
  • Truncal valve repair (or replacement) for moderate to severe regurgitation, which increases mortality; interrupted arch repair when present.
  • Operative mortality about 5 to 10%; 10-year survival about 85 to 90%, lower with severe truncal valve disease or interrupted arch.
• Postoperative care: pulmonary hypertensive crises (sedation and relaxation, oxygen, PaCO2 of 30 to 35 mmHg, inhaled nitric oxide 20 ppm, sildenafil 0.5 to 1 mg/kg per dose 6 to 8-hourly after extubation, with limited evidence in infants); inotropic support (milrinone 0.25 to 0.75 micrograms/kg/min; adrenaline 0.02 to 0.1 micrograms/kg/min).
• Late conduit problems: all conduits stenose and regurgitate as the child grows, requiring replacement every 5 to 10 years (usually 2 to 3 operations in life). Catheter balloon dilatation or stenting prolongs life, and transcatheter pulmonary valve implantation is used within suitable conduits. Indications for conduit intervention: right ventricular systolic pressure 60 to 70% of systemic or more, peak conduit gradient of 50 mmHg or more, right ventricular dilatation or dysfunction, symptoms, or severe regurgitation.
• Anticoagulation after valve replacement: warfarin to INR 2.5 to 3.5 for a mechanical truncal valve, or aspirin 3 to 5 mg/kg/day for a tissue valve.
• Endocarditis prophylaxis lifelong after conduit placement: amoxicillin 50 mg/kg (maximum 2 g) orally 30 to 60 minutes before dental procedures; clindamycin 20 mg/kg (maximum 600 mg) if allergic to penicillin.
• Special groups:
  • 22q11.2 deletion: endocrine, immune, speech, feeding and developmental follow up; monitor calcium and thyroid function.
  • Pregnancy: possible after good repair with preserved function; conduit stenosis, valve regurgitation, ventricular dysfunction and arrhythmia need assessment before conception, and the recurrence risk is about 50% if the mother carries a 22q11.2 deletion.
  • Adults: lifelong surveillance for conduit failure, aortic root dilatation and truncal valve disease.
• Red flags: tachypnoea, poor feeding, collapsing pulses, seizures, new cyanosis, exercise intolerance after repair, right heart failure, fever with murmur.
• Follow up: after repair, review at 6 weeks, 6 months and 12 months, then every 6 to 12 months in childhood and every 1 to 2 years in adulthood, with echocardiography and, periodically, cardiac MRI or CT for the conduit.