Patent Ductus Arteriosus (PDA)

Anatomy & Embryology

The ductus arteriosus is derived from the sixth aortic arch and connects the main/left pulmonary artery to the upper descending thoracic aorta, just distal to the left subclavian artery. In fetal life, ductal flow accounts for ~60% of combined ventricular output, directed from pulmonary artery → aorta (bypassing the fluid-filled lungs). At birth it measures 2–8 mm long and 4–12 mm in diameter.

Mediators of ductal tone:

Dilators (fetal)	Constrictors (postnatal)
PGE₂, PGI₂ (from placenta & lungs)	↑ PaO₂ (main stimulus)
Hypoxia	Histamine, catecholamines, bradykinin, acetylcholine

After birth, rising arterial oxygen tension is the primary trigger for smooth muscle contraction → functional closure within 10–15 hours. Anatomic obliteration by fibrosis produces the ligamentum arteriosum over the first few months of life.

Epidemiology

Incidence: ~1 in 2000 births (isolated PDA); accounts for ~7% of all congenital heart lesions
Female:Male = 2:1
Markedly increased with prematurity: up to 75% of infants at 28–30 weeks gestation
Associated with: high-altitude birth, congenital rubella, hypoxia, Down syndrome, other chromosomal abnormalities

Pathophysiology

A PDA creates a left-to-right shunt (aorta → pulmonary artery), whose magnitude depends on:

Size and length of the ductus
Ratio of pulmonary to systemic vascular resistance (PVR:SVR)

Hemodynamic consequences:

↑ Pulmonary blood flow → left atrial & left ventricular volume overload, LA/LV dilation
↓ Aortic diastolic pressure → wide pulse pressure, bounding pulses, risk of myocardial ischemia and underperfusion of systemic organs (especially gut → NEC in neonates)
Progressive pulmonary hypertension → eventual Eisenmenger syndrome (right-to-left shunt, cyanosis) in ~5% of untreated cases

Clinical Features

Symptoms by Size

PDA Size	Symptoms
Small	Usually asymptomatic; risk of infective endarteritis (~0.45%/year)
Moderate	Dyspnea, palpitations, exercise intolerance by 2nd–3rd decade
Large/unrestrictive	Heart failure, pulmonary hypertension, Eisenmenger syndrome

Classic Signs

"Machinery" murmur — continuous systolic and diastolic murmur at 1st–2nd left intercostal space below left clavicle; diastolic component shortens as pulmonary pressure rises; disappears in Eisenmenger physiology
Widened pulse pressure, bounding/collapsing pulses (Corrigan's pulse)
Hyperdynamic precordium, tachycardia, tachypnea
Differential cyanosis and clubbing (toes > fingers) in Eisenmenger — because deoxygenated pulmonary artery blood shunts into the descending aorta distal to the subclavian arteries

Diagnosis

Investigation	Findings
CXR	↑ Pulmonary vascularity, cardiomegaly, dilated ascending aorta & pulmonary artery; calcification at PDA site in older patients
ECG	LV strain, left atrial enlargement, ± RV hypertrophy
Echocardiography	Directly visualizes PDA; Doppler color flow confirms shunt; estimates shunt size — primary diagnostic tool
Cardiac catheterization	Reserved when pulmonary hypertension suspected; assesses PVR before closure

Angiography showing PDA connecting MPA to descending aorta

Angiography (RAO view) showing the conical PDA connecting the main pulmonary artery (MPA) to the descending aorta (DAo)

Treatment

The presence of a persistent PDA is an indication for closure due to increased mortality and endocarditis risk. Closure is generally contraindicated once Eisenmenger syndrome is established.

1. Pharmacologic (Premature Infants)

Indomethacin or Ibuprofen (COX inhibitors → ↓ PGE₂) — first-line in preterm neonates
Contraindicated with necrotizing enterocolitis, renal insufficiency, thrombocytopenia, or bleeding

2. Transcatheter Closure (Preferred in most children & adults)

Gianturco coils — for small ducts (<3 mm)
Amplatzer duct occluder — for moderate/large ducts
Rashkind double-umbrella device
Complications: thromboembolism, incomplete occlusion, vascular injury, endocarditis, device embolization
May not be feasible in very small premature infants (inadequate vascular access)

3. Surgical Closure

Open approach: muscle-sparing posterolateral thoracotomy, 3rd–4th intercostal space; ligation with surgical clip or suture
Must protect the recurrent laryngeal nerve (wraps around PDA)
Division + oversewing for short, broad ducts
Video-assisted thoracoscopic (VATS) clip occlusion — also used
Median sternotomy reserved for patients with concurrent cardiac lesions

Prognosis without treatment: estimated 30% mortality from isolated PDA; mortality rises to 3–4%/year by the 4th decade; two-thirds die by age 60.

PDA as a Lifesaver in Duct-Dependent Lesions

In cyanotic congenital heart disease (e.g., pulmonary atresia, critical aortic stenosis, hypoplastic left heart), ductal patency is essential to maintain pulmonary or systemic perfusion. Prostaglandin E₁ (alprostadil) is administered IV to keep the ductus open until definitive palliation or repair.

Sources: Schwartz's Principles of Surgery, 11th ed. — Goldman-Cecil Medicine — Robbins & Kumar Basic Pathology — The Developing Human (Clinically Oriented Embryology)

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