Peripheral Pulmonary Artery Stenosis

Peripheral pulmonary artery stenosis is narrowing of the pulmonary artery branches, from the origins of the left and right pulmonary arteries to the segmental and subsegmental vessels. It may be single or multiple, unilateral or bilateral, and may accompany pulmonary valve or supravalvular stenosis.

It forms about 2 to 3% of congenital heart disease. Branch stenosis is common after surgery for tetralogy of Fallot, after the arterial switch operation, at shunt sites and at the site of a ductal ligation.

Causes are Williams, Alagille and Noonan syndromes, congenital rubella, cutis laxa, and acquired causes: Takayasu arteritis, Behçet disease, fibrosing mediastinitis, external compression, and previous surgery or stenting.

Physiological branch stenosis of the newborn is a benign flow murmur from the acute angle of the branches. It resolves by 3 to 6 months. Peripheral stenosis in Williams syndrome often improves in the first years, while in Alagille syndrome it persists.

Pathophysiology.

Narrowing raises resistance in the affected segment. Proximal pressure and right ventricular pressure rise when stenoses are bilateral or severe, because blood must cross the obstruction to reach the lungs.

Flow is diverted to unobstructed lung zones, which are overperfused and may develop pulmonary vascular changes, while obstructed zones are hypoperfused and have reduced growth. When stenoses are unilateral, the right ventricular pressure may remain normal despite marked asymmetry of flow.

Right ventricular hypertrophy and eventually failure follow persistent high pressure.

Many patients are asymptomatic. Others have exertional dyspnoea, fatigue and exercise intolerance, and, in severe bilateral disease, right heart failure. Signs are a systolic or continuous murmur radiating to the axillae and back, which is louder over the lung fields than precordially, a right ventricular heave and a loud pulmonary component of the second heart sound when pressure is raised.

• Echocardiography: right ventricular systolic pressure estimated by the tricuspid regurgitant jet, right ventricular hypertrophy, proximal branch narrowing (often only the proximal branches are seen), and associated defects.
• CT angiography or MRI with flow quantification: the extent and severity of branch narrowing, vessel diameter and relative lung flow. Lung perfusion scan quantifies flow distribution (an uneven split with one lung under 35% suggests significant unilateral obstruction).
• Cardiac catheterisation with angiography: pressure gradients across each lesion, right ventricular pressure and lesion dimensions before intervention.
• Genetic tests for 7q11.23 deletion, JAG1 variants and RASopathy genes when features suggest a syndrome. Inflammatory markers and imaging of the aorta when Takayasu arteritis is possible.

Differential diagnosis.

• Physiological branch stenosis of the newborn.
• Supravalvular and valvular pulmonary stenosis.
• Chronic thromboembolic pulmonary hypertension and pulmonary artery hypoplasia.
• Pulmonary arteritis, mediastinal compression and pulmonary vein stenosis.

Indications for intervention. Right ventricular systolic pressure over 50 mmHg, or over half of systemic pressure, with a significant (over 50%) diameter narrowing; or symptoms with a documented stenosis; or marked flow imbalance (one lung receiving under 35% of perfusion) with right ventricular dysfunction or exercise limitation. Observe mild lesions with normal right ventricular pressure.

Interventions.

• Balloon angioplasty with a high pressure non-compliant balloon (balloon to vessel ratio 1.0 to 1.5, inflated to the rated burst pressure) and cutting balloons for resistant lesions. Success rates are about 50 to 60% for peripheral lesions, which are prone to recoil.
• Stent placement across proximal and mid-branch lesions of sufficient size, using stents that can be re-dilated as the child grows. Stents give durable relief in most proximal lesions.
• Surgical patch angioplasty, with intraoperative stenting when needed, for central or complex lesions, or at the time of other cardiac surgery.
• Heparin 100 units/kg intravenously (activated clotting time over 200 seconds) and cefazolin 1 g intravenously (children 25 mg/kg, maximum 1 g) at catheterisation. After stenting, aspirin 3 to 5 mg/kg orally daily (adults 75 to 100 mg) for at least 6 months.
• Complications: vessel tear, aneurysm or rupture (1 to 2%), haemoptysis, reperfusion pulmonary oedema, stent migration, and restenosis. Reperfusion oedema: oxygen, furosemide 40 mg intravenously (children 1 mg/kg), ventilatory support when severe.

Medical therapy.

• Heart failure: furosemide 20 to 40 mg orally daily (children 1 mg/kg every 12 hours, maximum 6 mg/kg daily) and spironolactone 25 to 50 mg daily (potassium under 5.0 mmol/L and eGFR over 30; check at 1 and 4 weeks). Electrolytes and creatinine within 1 week of changes.
• Takayasu arteritis: prednisolone 0.5 to 1 mg/kg orally daily (usually 40 to 60 mg) for 4 weeks, tapered over 6 to 12 months, with methotrexate 10 to 25 mg once weekly and folic acid 5 mg weekly (avoid when eGFR is under 30 mL/min/1.73 m2; blood count and liver tests every 2 weeks for 2 months, then every 3 months), or tocilizumab 162 mg subcutaneously weekly. Delay intervention until inflammation is controlled.
• Pulmonary vasodilators have no role for isolated mechanical obstruction and may divert more flow to open segments.

Endocarditis prophylaxis. Only with prosthetic material in the first 6 months after stenting or surgery, and lifelong after previous endocarditis: amoxicillin 2 g orally (children 50 mg/kg, maximum 2 g) 30 to 60 minutes before dental procedures involving gingival manipulation.

Monitoring. Echocardiography at 6 and 12 months after intervention, then every 1 to 2 years. CT or MRI and lung perfusion at 6 to 12 months and every 3 to 5 years. Repeat catheterisation for rising right ventricular pressure. Re-dilate stents as the child grows.

Referral and escalation. Refer every confirmed lesion with raised right ventricular pressure to a congenital heart service with interventional expertise. Urgent referral for syncope, right heart failure, haemoptysis, or complications of intervention.

Special groups.

• Pregnancy: tolerated when right ventricular pressure is under half of systemic pressure and function is normal; severe bilateral disease needs intervention before conception.
• Children: re-intervention is expected as the child grows; Williams syndrome stenoses often improve spontaneously.
• Alagille syndrome: liver and renal disease affect anaesthetic risk and drug choice.
• Region specific: congenital rubella and Takayasu arteritis remain frequent causes, so test for inflammatory disease before intervention.