• Almost always associated with a VSD which is usually a large malaligned outlet VSD.  Hence often referred to as Tetralogy of Fallot with absent pulmonary valve (TOF with APV).
• The pulmonary valve is rudimentary and usually both stenotic and regurgitant.
• The pulmonary arteries are aneurysmally dilated.
• Almost always associated with absence of PDA. In fact, this may be the cause of the syndrome.
• Commonly associated with airway abnormalities which may cause respiratory failure. Abnormally branching pulmonary arteries compress bronchi.
• Rarely, IVS may be intact.
• TOF with APV constitutes 2.5% of TOF.
• 75% of APV has 22q11 deletion. This is the commonest genetic association of APV.

Embryology

• Agenesis or early closure of the ductus plays an important role in the pathogenesis.
• APV syndrome is different from TOF in pathogenesis. Even though VSD and aortic override are present in APV also, obstruction is due to pulmonary annular hypoplasia, not infundibular narrowing.

Pathology

• Pulmonary valve tissue is rudimentary.
• Pulmonary annulus is hypoplastic.
• Proximal pulmonary arteries are aneurysmally dilated. These may compress major bronchi.
• Pulmonary segmental arterioles are replaced by tufts of vessels which compress bronchi.
• Non-restrictive malaligned VSD
• RVH
• Coronary anomalies may occur- single origin, aberrant course.
• MAPCAs may be present.

Clinical presentations

• Hydrops fetalis occurs in 20%.
• Neonatal presentation-
  • Cyanosis
  • Respiratory distress- sometimes needing mechanical ventilation
  • Harsh to-and-fro murmur, single S2, prominent right ventricular impulse, hepatomegaly due to RV failure.
  • Rhonchi due to bronchial narrowing.
  • VSD like- Presentation like a large VSD.

Diagnostic findings

• ECG shows RVH and wide QRS.
• Chest X-ray shows dilated pulmonary arteries with distal attenuation of pulmonary vasculature and cardiomegaly. Right aortic arch may be present.
• Echo makes the diagnosis.
• Cardiac catheterization may be needed for ruling out AP collaterals and for their preoperative coil embolization.
• PA and RV pressures equalize in diastole due to PR. During systole there is a gradient between RV and PA suggesting PS.

Medical management

• Respiratory distress may be lessened by placing the patient prone as this suspends the pulmonary artery off the airways.
• Cyanosis is due to right to left shunt due to pulmonary stenosis, pulmonary regurgitation and abnormal distal pulmonary arteriolar bed.
• Sometimes left to right shunt can occur leading to volume overload.

Surgery

1. VSD closure.
2. Transannular incision to relieve the annular obstruction.
3. Repair of pulmonary arteries- approaches include

• Anterior plication with or without translocation of MPA and RPA anterior to the aorta OR
• Homograft insertion with excision of aneurysmal pulmonary arteries.