What is the PDA Vessel?
The PDA (Patent Ductus Arteriosus) is a vascular connection between the aorta and the pulmonary artery that normally exists during fetal life but persists beyond the normal age of spontaneous closure after birth. 1
Anatomical Definition
- The ductus arteriosus connects the descending aorta (just distal to the left subclavian artery) to the pulmonary artery 1
- This vessel is essential for normal fetal development, allowing blood to bypass the non-functioning fetal lungs 2, 3
- Normal closure occurs within the first 3 days after birth in term infants 4
- When this vessel remains open beyond the normal closure period, it is termed "patent" ductus arteriosus 1
Epidemiology
- PDA occurs in approximately 0.3% to 0.8% of term infants 1, 5
- It is twice as common in females compared to males 1, 5
- The incidence is inversely related to gestational age—up to 80% of infants born at 25-28 weeks gestation have delayed closure 4
- PDA accounts for 5-10% of all congenital heart disease in term infants 6
Physiological Mechanism of Closure
- Postnatal closure is triggered by rising oxygen tension and withdrawal of vasodilatory mediators (prostaglandins, nitric oxide, adenosine) 2
- Vasoconstrictors including endothelin-1, catecholamines, and contractile prostanoids promote closure 2
- The process involves complex cell-matrix interactions between smooth muscle cells, endothelial cells, and extracellular matrix components 3
- In preterm infants, the normal physiologic mechanisms contributing to closure are altered due to immaturity 6
Hemodynamic Consequences
- The clinical manifestations depend on the size of the vessel and the relative systemic and pulmonary vascular resistances 1, 5
- PDA initially results in left-to-right shunting and left ventricular volume overload 1
- As pulmonary vascular resistance decreases (especially in extremely premature infants), left-to-right shunting increases, leading to pulmonary overcirculation and systemic hypoperfusion 2, 4
- Large untreated PDAs can cause congestive heart failure and pulmonary hypertension 1, 5
- In severe cases with elevated pulmonary vascular resistance, shunt reversal occurs, resulting in Eisenmenger physiology with right-to-left shunting 1, 7
Classification by Size and Hemodynamic Significance
- Trivial/silent PDA: Hemodynamically insignificant, no audible murmur 1, 8
- Small/audible PDA: Likely hemodynamically insignificant, continuous murmur present 1, 8
- Moderate to large PDA: Hemodynamically significant with left heart volume overload 1
Associated Complications
- Potential complications of hemodynamically significant PDA include prolonged ventilation, bronchopulmonary dysplasia, necrotizing enterocolitis, intraventricular hemorrhage, and death 2
- There is a risk of infective endarteritis, though this appears relatively low 1, 7
- Rare complications include aneurysm formation of the duct, which may compress the left main coronary artery 1
- Long-term morbidities include chronic lung disease, retinopathy of prematurity, and neurodevelopmental delay 4
Clinical Presentation Patterns in Adults
- Small duct with no left ventricular volume overload and normal pulmonary artery pressure (generally asymptomatic) 1
- Moderate PDA with predominant left ventricular volume overload may present with left heart failure 1, 5
- Moderate PDA with predominant pulmonary hypertension presents with pressure-overloaded right ventricle and potential right heart failure 1
- Large PDA with Eisenmenger physiology demonstrates differential hypoxemia and differential cyanosis (lower extremities cyanotic, sometimes left arm too) 1, 5