SUPERStudy: Patent Ductus Arteriosus (PDA)
Introduction: Patent ductus arteriosus (PDA) is a persistence of the in utero communication between the aortic and pulmonary arteries after birth causing a left-to-right shunt.
Risk factors: Maternal rubella infection; prematurity; high altitude, genetic problems such as Down syndrome
Pathophysiology: In the fetal circulation, superior vena cava blood enters the right atrium and characteristically is directed across the tricuspid valve into the RV. It is then delivered into the systemic circulation via the ductus arteriosus, which connects the left pulmonary artery to the descending aorta just distal to the insertion of the left subclavian artery. The ductus arteriosus allows oxygenated blood to bypass the lungs and go directly to the body.
After birth, normally the ductus arteriosus closes within 15 hours and seals completely at 3 weeks of age, becoming the ligamentum arteriosum. If the ductus fails to close after birth, the direction of blood flow within the ductus reverses, producing a left-to-right shunt. This left-to-right shunt results from lower pulmonary vasculature resistance as compared to systemic vasculature resistance. It leads to increased volume overload on the left side of the heart, resulting in left heart strain and congestive heart failure.
Clinical Manifestations:
Infants: Failure to thrive, respiratory infections, not gaining weight, gets short of breath and sweat when crying or playing; pulmonary hypertension with right-to-left shunting; differential cyanosis
Adults: dyspnea on exertion, chest pain, palpitations, congestive heart failure, tachyarrhythmias, pulmonary hypertension with right-to-left shunting; differential cyanosis
Acyanosis & Differential cyanosis: Initially, the patient is almost always acyanotic. When the shunt reversal happens (Eisenmenger syndrome), because the site of the PDA is distal to the left subclavian, the head and neck vessels continue to receive oxygenated blood—but the descending aorta receives the desaturated blood, with the development of differential cyanosis.Right hand is usually spared. Left hand and lower extremities may show clubbing and cyanosis. Right hand and head are always pink.
Pulse: Pulses may be collapsing with widened pulse pressure; bounding peripheral pulses with two pulse peaks in large PDA (pulsus bisferiens)
Heart murmur: A continuous “machinery” or “to-and-fro” murmur. It gradually builds to its peak in late systole, continuous through the second heart sound and wanes in diastole. It is loudest at the left upper sternal border, below the clavicle. A diastolic rumble and bounding pulses can also be present; loud S2
Complications: Left ventricular hypertrophy, heart failure, late cyanosis, and pulmonary hypertension
Diagnosis:
Echocardiography is the diagnostic test of choice; reveals direction of shunt; atrial and ventricular enlargement
ECG: normal or left atrial and ventricular hypertrophy; when pulmonary hypertension develops, it may show P-pulmonale, right-axis deviation, and evidence of RVH
Chest radiograph: normal with small shunt; in large shunts, enlarged cardiac silhouette, enlarged pulmonary artery and markings; calcification of the ductus
Cardiac catheterization: right-heart catheterization to measure the pulmonary artery pressure, peripheral vascular resistance and flow ratio.
Treatment: Indomethacin closes patent ductus arteriosus (PDA) in infants. Consider surgical or percutaneous closure in adults with large shunts or symptoms.
SUPERPoint: Patent ductus arteriosus (PDA) is a congenital heart defect characterized by the failure of the ductus arteriosus to close after birth, resulting in a continuous “machinery” murmur and a left-to-right shunt; it can lead to differential cyanosis, left heart dilation, and pulmonary hypertension, and is treatable with indomethacin or surgical ligation.
SUPERFormula: History of maternal rubella + cyanosis in only lower half of the body + continuous “machinery” murmur over left pulmonary area + closure by a prostaglandin inhibitor = Patent Ductus Arteriosus (PDA)