Aortopulmonary Window

An aortopulmonary window is a rare communication (about 0.1 to 0.2% of congenital heart disease) between the ascending aorta and the main pulmonary trunk, with two separate semilunar valves.

It is classified as proximal (near the valves), distal (towards the pulmonary bifurcation), or total (absence of the aortopulmonary septum).

About half have associated lesions: interrupted aortic arch, ventricular septal defect, atrial septal defect, patent ductus arteriosus, tetralogy of Fallot, coarctation, and anomalous origin of the right coronary artery from the pulmonary artery.

Pathophysiology. A large non-restrictive defect produces a large left-to-right shunt and pulmonary overcirculation. As pulmonary vascular resistance falls in the first weeks of life, heart failure develops. Diastolic run off from the aorta lowers diastolic aortic pressure and coronary perfusion.

Without early closure, pulmonary vascular disease develops within the first 1 to 2 years, leading to Eisenmenger syndrome.

• Large defect in infancy (2 to 6 weeks): tachypnoea, poor feeding, sweating, failure to thrive, recurrent chest infections. Bounding pulses with a wide pulse pressure, a hyperdynamic precordium, a systolic or continuous murmur, an apical diastolic flow murmur, and a loud pulmonary component of the second sound.
• Eisenmenger physiology: cyanosis that affects the upper and lower limbs equally, because the shunt lies proximal to the duct, with clubbing, polycythaemia and right heart failure.

Red flags.

• Heart failure in infancy with a wide pulse pressure
• Absent femoral pulses or acidosis suggesting an associated interrupted or coarcted arch
• Cyanosis with pulmonary hypertension
• Angina or ischaemic ECG changes suggesting coronary steal or anomalous coronary origin

• ECG: biventricular hypertrophy.
• Chest X-ray: cardiomegaly, plethoric lung fields and a prominent pulmonary artery.
• Transthoracic echocardiography: high parasternal short axis and long axis views show the defect between the ascending aorta and main pulmonary artery. Two separate semilunar valves are present, with left-to-right flow on colour Doppler. Assess coronary origins, arch anatomy and associated lesions.
• CT angiography or MRI: coronary origins, arch, and exact defect type.
• Cardiac catheterisation: for infants over 6 months or those with suspected pulmonary hypertension. Measure indexed pulmonary vascular resistance (PVRi) with vasodilator testing. Closure is generally feasible when PVRi is under 6 Wood units·m2 and the ratio of pulmonary to systemic resistance is under 0.3; centres differ.

Differential diagnosis.

• Truncus arteriosus (single truncal valve)
• Large patent ductus arteriosus (arises at the aortic isthmus level)
• Large ventricular septal defect
• Anomalous origin of the right coronary artery from the pulmonary artery
• Ruptured sinus of Valsalva aneurysm
• Coronary arteriovenous fistula
• Aortic regurgitation with other causes of wide pulse pressure

Diagnosis alone is an indication for closure, ideally in the first weeks to months of life, before pulmonary vascular disease. Surgical closure is on cardiopulmonary bypass by patch or by division and direct repair, with repair of associated lesions (arch reconstruction for interrupted arch, coronary reimplantation). Transcatheter device closure is limited to small restrictive defects with adequate rims from the coronary ostia and valves. Operative mortality for isolated repair is low (under 5%).

Bridging medical therapy. Furosemide in infants and children: 0.5 to 1 mg/kg intravenously every 6 to 12 hours, or 1 to 2 mg/kg orally every 6 to 12 hours, maximum 6 mg/kg daily. Monitor sodium, potassium, creatinine and weight. Avoid supplemental oxygen unless saturation falls under 90%, because it lowers pulmonary resistance and increases the shunt.

Eisenmenger syndrome (closure contraindicated).

• Bosentan 62.5 mg orally twice daily for 4 weeks, then 125 mg twice daily (62.5 mg twice daily maintenance for weight under 40 kg). Maximum 250 mg daily. Check liver enzymes monthly. Contraindicated in pregnancy (teratogenic, with reduced efficacy of hormonal contraception), moderate to severe liver impairment, and with ciclosporin or glibenclamide. Long term.
• Sildenafil 20 mg orally three times daily, 4 to 6 hours apart. Maximum 60 mg daily. Contraindicated with nitrates. Monitor blood pressure.
• Avoid dehydration, iron deficiency and intravenous air; use air filters on lines.

Special groups. Pregnancy is contraindicated in Eisenmenger physiology; maternal mortality is about 30 to 50%. Effective contraception and specialist counselling are required.

Monitoring. Early postoperative echocardiography, then at 6 to 12 months and every 1 to 2 years for residual shunt, pulmonary artery or aortic distortion, coronary flow and pulmonary pressure. In Eisenmenger syndrome, check haemoglobin, ferritin, urea, creatinine and uric acid at least annually.

Referral and escalation. Refer every infant to a paediatric cardiac surgical centre immediately. Urgent when heart failure is uncontrolled or an interrupted arch is present.