Patent Ductus Arteriosus
Persistence of the fetal communication between the aorta and pulmonary artery after birth. Causes continuous left-to-right shunting with a characteristic continuous 'machinery' murmur.
Key Facts
Ductus arteriosus normally closes within 24-48 hours of birth; failure to close = PDA Continuous 'machinery' murmur best heard in the left infraclavicular region, loudest in late systole and enveloping S2 Risk factors: prematurity (most important), maternal rubella, high altitude, Down syndrome, fetal alcohol syndrome Left-to-right shunt → pulmonary overcirculation → LV volume overload → heart failure if large; Eisenmenger if untreated Medical closure: indomethacin or ibuprofen IV (inhibit prostaglandin synthesis) — effective in premature neonates Surgical/transcatheter closure: indicated for haemodynamically significant PDA; transcatheter coil/device closure is standard in older infants and children Bounding (collapsing) pulse and wide pulse pressure from aortic runoff into pulmonary artery Prostaglandin E1 (alprostadil) infusion: keeps ductus OPEN in duct-dependent congenital heart lesions (e.g., critical coarctation, TGA)
Overview
Key Facts
Patent ductus arteriosus (PDA) is the persistence of the fetal vascular connection between the descending aorta and the pulmonary artery (main PA or left PA) after birth. It normally closes functionally within 24-48 hours.
Epidemiology
- Accounts for ~5-10% of congenital heart defects
- Incidence: ~1 in 2,000 term births; much higher in premature infants (~30-40% of infants <1,500g)
- Female:male ratio ~2:1
- More common at high altitude
Aetiology
- Prematurity: most important risk factor (immature ductal wall lacks response to oxygen)
- Maternal rubella infection (first trimester)
- Genetic: Down syndrome, DiGeorge syndrome
- Fetal alcohol syndrome
- High altitude (lower PaO₂ fails to trigger ductal closure)
Pathophysiology
- In fetal life, ductus arteriosus diverts blood from PA to aorta (bypassing lungs)
- After birth, rising PaO₂ and falling prostaglandin levels trigger ductal constriction and closure
- If ductus remains patent: aortic pressure > PA pressure → left-to-right shunt
- Magnitude depends on duct size and pulmonary vascular resistance
- Large PDA → pulmonary overcirculation → LV volume overload → heart failure
- Long-term → pulmonary hypertension → Eisenmenger syndrome (shunt reversal → differential cyanosis: lower body cyanotic, upper body pink)
Clinical Presentation
Typical Presentation
- Small PDA: asymptomatic; murmur found incidentally
- Large PDA in infants: poor feeding, failure to thrive, tachypnoea, recurrent chest infections, heart failure
- Adults with unrepaired PDA: dyspnoea, palpitations (AF), heart failure
Examination Findings
- Continuous 'machinery' murmur: loudest at left infraclavicular area; peaks in late systole, continues through S2 into diastole
- Bounding (collapsing) pulse: aortic runoff through ductus
- Wide pulse pressure
- Hyperdynamic apex (LV volume overload)
- Thrill in left infraclavicular region
- In Eisenmenger PDA: differential cyanosis (lower limbs cyanosed, upper limbs pink) and differential clubbing (toes clubbed, fingers not)
Red Flags
- Heart failure in premature neonate
- Differential cyanosis (Eisenmenger)
- Failure to thrive
- Wide pulse pressure with bounding pulses in an infant
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Venous hum | Continuous murmur in neck, abolished by lying down or compressing jugular | Clinical |
| AV fistula (coronary, pulmonary) | Continuous murmur, localisation varies | Echocardiography, CT angiography |
| Aortopulmonary window | Large communication between aorta and PA, often without continuous murmur | Echo, CT |
| Ruptured sinus of Valsalva | Sudden onset continuous murmur, acute heart failure | Echocardiography |
| VSD with AR | Pansystolic + early diastolic murmur (not truly continuous) | Echocardiography |
| Innocent murmur | No thrill, no bounding pulses | Clinical + echo |
Diagnosis / Investigation
Bedside
- ECG: normal in small PDA; LVH and LA enlargement in moderate; biventricular hypertrophy if pulmonary HTN
- CXR: cardiomegaly, pulmonary plethora, prominent PA; calcified ductus in adults
- Pulse oximetry: pre-ductal (right arm) and post-ductal (foot) saturation comparison
Bloods
- BNP/NT-proBNP: elevated in significant shunt with heart failure
- Routine: FBC, U&Es, blood gas (neonates)
Imaging
- Echocardiography: visualise PDA (size, shape), shunt direction and velocity, LV dimensions, PA pressure estimation
- Cardiac MRI/CT: Qp:Qs quantification, anatomy for older patients
- Cardiac catheterisation: definitive haemodynamics; calculate Qp:Qs and PVR; may be therapeutic (device closure)
Special Tests
- Qp:Qs ratio: >1.5:1 = haemodynamically significant
Management
Non-pharmacological
- Small PDA: observe; many close spontaneously in first year
- Fluid restriction and diuretics for heart failure in premature neonates
Pharmacological
Medical closure (premature neonates):
- Indomethacin 0.1-0.25 mg/kg IV (3 doses at 12-hour intervals)
- Ibuprofen IV/oral (10 mg/kg then 5 mg/kg at 24 and 48 hours): fewer renal side effects than indomethacin
- Paracetamol IV: emerging as alternative (fewer GI/renal side effects)
- Effective in ~70-80% of premature neonates
Keep ductus OPEN (duct-dependent lesions):
- Prostaglandin E1 (alprostadil) infusion: 5-100 ng/kg/min IV
- Used in: critical coarctation, critical aortic stenosis, TGA, pulmonary atresia, hypoplastic left heart
Surgical/Interventional
- Transcatheter device/coil closure: standard for PDA in older infants, children, and adults
- High success rate (>95%); low complication rate
- Performed via femoral vein
- Surgical ligation/division: for premature neonates too small for device, or if unusual anatomy
- Via left lateral thoracotomy; low operative mortality (<1%)
- Closure contraindicated in Eisenmenger syndrome
Referral Criteria
- All haemodynamically significant PDA: paediatric cardiology referral
- Premature neonate with symptomatic PDA: neonatal consultation
- Adults with PDA: GUCH specialist
Prognosis
- Small PDA: excellent prognosis; many close spontaneously
- Post-closure: near-normal life expectancy; no long-term sequelae
- Large unrepaired PDA: Eisenmenger develops by adolescence/early adulthood
- Eisenmenger PDA: differential cyanosis; median survival ~40 years
- Surgical ligation mortality: <1%
- Transcatheter closure success: >95%
- Endocarditis risk: low but present (especially in adults with unclosed PDA)
Other Relevant Information
Duct-Dependent Lesions (Keep Ductus OPEN with PGE1)
| Lesion Type | Examples |
|---|---|
| Duct-dependent systemic flow | Critical coarctation, interrupted aortic arch, HLHS |
| Duct-dependent pulmonary flow | Pulmonary atresia, critical PS, severe ToF |
| Mixing lesions | Transposition of great arteries |
Medical Closure Options in Premature Neonates
| Drug | Dose | Notes |
|---|---|---|
| Indomethacin | 0.1-0.25 mg/kg IV x3 | COX inhibitor; renal side effects |
| Ibuprofen | 10, 5, 5 mg/kg PO/IV | Fewer renal effects |
| Paracetamol | 15 mg/kg IV QDS | Emerging alternative |