Patent Ductus Arteriosus (PDA)

Overview

Definition

The ductus arteriosus (DA) is a fetal blood vessel connecting the left pulmonary artery to the aorta, bypassing the pulmonary circulation. Failure of the vessel to close and involute within 72 hours of birth results in a condition called patent ductus arteriosus (PDA).

Epidemiology

• Population statistics:
  • 5%–10% of all congenital heart defects (CHDs)
  • Incidence: 2 in 10,000 live term births 
  • Male:female ratio is 1:2
• Risk factors:
  • Prematurity
  • Hypoxia:
    • History of perinatal asphyxia
    • Birth at high altitude
  • Maternal factors:
    • Rubella infection
    • Phenytoin use
  • Genetic predisposition:
    • Positive family history of PDA
    • DiGeorge syndrome
    • Cri-du-chat syndrome
    • Noonan syndrome
    • CHARGE syndrome

Embryology and Pathophysiology

Embryology

• Fetal circulation:
  • In utero, lungs are fluid filled and their vasculature is vasoconstricted (oxygen comes from maternal circulation in the placenta).
  • DA shunts blood from the right (R) to left (L) in the heart, bypassing high-pressure pulmonary circulation.
• After birth, DA closure is triggered by:
  • Increased systemic oxygen (O₂) concentration → decreased pulmonary blood pressure
  • Reduced prostaglandin E2 (PGE2) levels due to separation from placenta 
• Closure starts at the pulmonary end and finishes at the aortic end:
  • Functional closure by 15 hours of life
  • Anatomical closure by 3rd week of life
• Histological changes turn ductus into ligamentum arteriosum.
• Failure or disruption of transition from fetal to extrauterine life results in the persistence of PDA.

Pathophysiology

• In PDA, the shunt reverses to L-R as pulmonary vascular resistance falls.
  • Increased end-diastolic volume in left atrium and left ventricle → volume overload → dilation → heart failure
  • Increased pressure in pulmonary artery → pulmonary hypertension → respiratory failure
• Eisenmenger’s syndrome:
  • Pulmonary hypertension → right ventricle hypertrophy→  increasing right-sided pressure
  • Shunt reverses to R-L in the prenatal period.

Clinical Presentation

The severity of symptoms depends primarily on the degree of L-R shunt, which is dictated by size and length of the defect.

Diagnosis

• Clinical findings are confirmed by echocardiogram.
• Echocardiography:
  •  Evaluates:
    • Presence of defect
    • Hemodynamics of left atrium and ventricle
    • Doppler → degree of shunt and pulmonary arterial pressure
  • All preterm infants should be screened.
• Chest X-ray:
  • Normal in small shunts
  • Large shunts may show:
    • Increased pulmonary vascularization
    • Cardiomegaly
• Electrocardiogram (ECG):
  • Biventricular or right ventricular hypertrophy in advanced cases

Management, Complications, and Prognosis

Management

• Observation indicated in smaller defects with no physiological changes:
  • Requires close follow-up
• Closure indicated in:
  • Moderate and large PDA
  • Small PDA with audible murmur
  • Presence of pulmonary hypertension
  • Heart failure
  • Respiratory compromise
  • History of infective endocarditis
• Medical therapy (pharmacological closure):
  • Decrease prostaglandin synthesis:
    • Indomethacin
    • Ibuprofen
  • Follow-up after 48 hours with echocardiography to ensure closure
  • Contraindicated in:
    • Cardiac defects where DA required to maintain perfusion for systemic circulation
    • Active bleeding
    • Suspicious or diagnosed necrotizing enterocolitis
    • Impaired renal function
• Surgical therapy:
  • Indicated when medical therapy fails and/or infant > 6 kg
  • Includes percutaneous closure or surgical ligation

Complications

• Pulmonary hypertension
• Bronchopulmonary dysplasia
• Congestive heart failure
• Infective endocarditis
• Post-surgery → paralysis of recurrent laryngeal nerve and stridor

Prognosis

• Spontaneous closure in up to 75% of infants if < 3 months of age
• Isolated PDA has an excellent prognosis (especially small defects).

Differential Diagnosis

Continuous murmur of PDA should be differentiated from:

• Venous hum: benign, common murmur secondary to forces hitting venous walls; heard in children. A continuous murmur best heard on the right side and changes with position (unlike PDA). An echocardiogram is done to confirm no pathology.
• Coronary artery fistula: congenital vascular abnormality whereby the coronary artery drains directly into chambers of heart without a capillary bed. Presentation includes a continuous murmur in the lower pericardium. An echocardiogram with Doppler will show direct drainage into the chambers.
• Aortic regurgitation: a defect of the aortic valve wherein the leaflets do not oppose perfectly, allowing blood to backflow during diastole. Patients may present with a continuous murmur and bounding pulses. Aortic regurgitation is usually seen in older patients. An echocardiogram can diagnose and quantify the severity of valvular defect.