What is Patent ductus arteriosus (PDA)
Failure of the ductus arteriosus to completely close postnatally
Epidemiology of PDA
Incidence: 5–10% full-term births [41]
In premature infants: 20–60% [41]
Sex: ♀ > ♂ (2:1)
Etiology of PDA
1- Prematurity The smooth muscle of the ductus arteriosus in a preterm infant is less responsive to high O2 saturation and, therefore, less likely to constrict after birth.
2- Maternal exposure during pregnancy
Rubella infection (during the first trimester of pregnancy)
Alcohol consumption
Phenytoin use (fetal hydantoin syndrome)
Prostaglandin use
3- Respiratory distress syndrome
4- Trisomies (e.g., Down syndrome)
Pathophysiology of PDA
1- Ductus arteriosus enables the underdeveloped lungs to be bypassed by the fetal circulation (normal right-to-left shunt) and remains patent in utero via PGE and low O2 tension.
2- After birth, pulmonary vascular resistance decreases and thus allows for the reversal of the shunt from right-to-left to left-to-right.
3- Failure of the ductus arteriosus to close after birth → persistent communication between the aorta and the pulmonary artery → left-to-right shunt → volume overload of the pulmonary vessels → continuous RV (and/or LV) strain → heart failure (see also “Overview” above)
4- Eisenmenger syndrome may occur with shunt reversal and manifest with differential cyanosis.
Clinical features General of PDA
1- Small PDA: asymptomatic with normal findings on physical examination
2- Large PDA
1) Nonspecific symptoms (e.g., failure to thrive) and symptoms of heart failure in infancy
2) Bounding peripheral pulses, wide pulse pressure
3) Heaving, laterally displaced apical impulse
A sign of left ventricular volume overload
Auscultation of PDA
1) Small PDA: A murmur is sometimes heard incidentally during routine primary care visits.
2) Large PDA: Machinery murmur: loud continuous murmur heard best in the left infraclavicular region and loudest at S2
Occurs because of the constant left-to-right shunt, which follows the pressure gradient from the aorta (high pressure) to the pulmonary artery (low pressure)
As pulmonary hypertension develops (Eisenmenger syndrome), the characteristic machinery murmur decreases and ultimately disappears. This phenomenon is due to shunt reversal, which develops as soon as the pulmonary pressure exceeds the aortic pressure, thus decreasing blood flow through the PDA.
