Patent Ductus Arteriosus (PDA)

Anatomy & Embryology

• Functional closure: within 10-15 hours of birth, driven primarily by rising arterial oxygen tension causing smooth muscle contraction; also aided by histamines, catecholamines, bradykinin, and acetylcholine.
• Anatomic closure: fibrosis over the first few months leaves behind the ligamentum arteriosum.

Epidemiology

• Prematurity / respiratory distress syndrome (surfactant deficiency)
• Maternal rubella infection in early pregnancy
• Hypoxia (high altitude, congenital heart disease)
• Chromosomal anomalies
• Associated lesions: coarctation of the aorta, transposition of the great arteries (TGA), pulmonary stenosis/atresia (these create large pressure differentials that physically prevent ductal constriction)
• Schwartz's Principles of Surgery, 11th Ed. | The Developing Human, Clinically Oriented Embryology

Pathophysiology

1. Ductal diameter and length
2. Ratio of pulmonary to systemic vascular resistance

Hemodynamic consequences:

• Increased pulmonary blood flow → left atrial and left ventricular volume overload
• Elevated pulmonary artery pressure → right ventricular strain
• Low aortic diastolic pressure → risk of coronary and systemic hypoperfusion
• Tachycardia, tachypnea, ventricular hypertrophy via sympathetic activation

Eisenmenger syndrome (late, ~5% of isolated PDAs):

Clinical Features by PDA Size

• Untreated mortality: ~30% overall; two-thirds of patients die by age 60 if large ductus untreated. By the 4th decade, mortality rises to 3-4% per year.
• Goldman-Cecil Medicine | Schwartz's Principles of Surgery

Clinical Signs & Diagnosis

• Wide/bounding pulse pressure (due to diastolic runoff into pulmonary circulation)
• Hyperdynamic precordium
• No cyanosis in uncomplicated PDA (unless Eisenmenger develops)

• Schwartz's Principles of Surgery, 11th Ed.

Treatment

1. Pharmacological (Premature Infants Only)

• Indomethacin or ibuprofen (COX inhibitors - block prostaglandin synthesis)
• Term infants are generally unresponsive to these agents (pharmacological therapy is therefore not useful in term neonates)
• Contraindications: necrotizing enterocolitis, renal insufficiency, bleeding disorders

2. Catheter-Based (Transcatheter) Closure

• Rashkind double-umbrella device
• Gianturco coils (coil embolization)
• Occlutech/Amplatzer ductal occluder devices

• Generally preferred for older patients (>5 years) and smaller ducts (<3 mm).

3. Surgical Closure

• Open (posterior lateral thoracotomy): 3rd or 4th intercostal space, left side. Lung retracted anteriorly. PDA is ligated with a surgical clip or permanent suture. Care must be taken to protect the recurrent laryngeal nerve, which wraps around the PDA.
  • For a short, broad ductus: division between vascular clamps with oversewing of both ends.
  • CPB may rarely be needed for a very large ductus.
• Video-Assisted Thoracoscopic Surgery (VATS): Metal clips placed thoracoscopically. Offers few advantages over open approach.
• Median sternotomy: reserved for PDA combined with other lesions requiring repair.
• Preferred for preterm newborns and young children where catheter access is limited.

Key Points Summary

• Ductus arteriosus carries blood right-to-left (pulmonary artery → aorta)
• Lungs bypassed - oxygenation happens at the placenta
• ~60% of combined ventricular output flows through the ductus

• Shunt direction reverses to left-to-right (aorta → pulmonary artery)
• This happens because systemic resistance now exceeds pulmonary resistance after birth
• Results in pulmonary overcirculation and left ventricular volume overload
• Produces the classic continuous "machinery" murmur (blood flows through the ductus during both systole and diastole, since aortic pressure exceeds pulmonary artery pressure throughout the cardiac cycle)

PDA - Simple Explanation

🍼 First, understand the baby BEFORE birth

Pulmonary Artery → [Ductus Arteriosus] → Aorta
        (skipping the useless lungs)

👶 What happens AFTER birth?

❌ In PDA - the pipe DOESN'T close

• Aorta has high pressure
• Pulmonary artery has low pressure

Aorta → [Open Ductus] → Pulmonary Artery → Lungs

😰 Why is this a problem?

🔊 The famous Murmur

💊 How is it treated?

🧠 One-line memory trick

"Baby's shortcut pipe forgot to close - blood goes backwards and floods the lungs"

PDA Surgery - Simply Explained

🤔 When is surgery needed?

• Term (full-term) babies - they don't respond to indomethacin
• Premature babies where medicines are contraindicated (kidney failure, gut problems)
• Older children/adults with larger ducts

The 3 Ways to Close a PDA

🩺 Option 1: Catheter Procedure (No surgery, no big cut!)

1. A thin tube (catheter) is inserted into a leg blood vessel
2. Guided all the way up to the heart area
3. A small plug or coil is deployed through the catheter to block the ductus

Leg vein → Catheter threaded up → Plug placed inside the ductus → Done!

• No big cut, no opening chest
• Best for: older kids (>5 years), small ducts (<3 mm)
• Devices used: Gianturco coils, Rashkind double-umbrella device

🔪 Option 2: Open Surgery (The classic way)

Step-by-step:

• Baby/patient positioned on their right side (so left chest faces up)
• Cut made on the left side of the chest, entering through the 3rd or 4th gap between the ribs (intercostal space)
• This is called a posterior lateral thoracotomy

Left side cut → Enter between ribs → Access the chest

• The left lung is gently pushed forward (anteriorly) to expose the area behind it
• Now the surgeon can see the aorta, pulmonary artery, and the ductus connecting them

• The recurrent laryngeal nerve (controls voice box/speaking) wraps around the ductus arteriosus
• This is the most important danger in this surgery
• Damage it → patient gets a hoarse voice permanently

• Lung returns to normal position
• Ribs and muscles closed layer by layer
• Done! ✅

🎥 Option 3: VATS (Keyhole Surgery)

• Video-Assisted Thoracoscopic Surgery
• Small holes in the chest instead of one big cut
• Camera + instruments inserted through holes
• Metal clip applied to close the ductus
• Honest reality: offers few advantages over the open approach for PDA - so not widely preferred

Who Gets What?

⚠️ The ONE thing examiners love:

Recurrent laryngeal nerve wraps around the ductus arteriosus on the left side. During PDA ligation, this nerve is at risk. Damage = hoarseness of voice.