Patent ductus arteriosus — formative SAQs

SAQ 1 (10 marks)

Question. A 4-year-old child is referred with a continuous "machinery" murmur at the upper left sternal edge, bounding pulses and a widened pulse pressure. Outline (a) the underlying anatomy and pathophysiology, (b) the key bedside and echocardiographic features that define the haemodynamic burden, and (c) the differential diagnosis. [1]

(a) Anatomy and pathophysiology. The patent ductus arteriosus is persistent postnatal patency of the fetal vessel connecting the main pulmonary artery to the descending aorta. Normally the duct closes functionally within 12 to 24 hours of birth as oxygen tension rises (closing oxygen-sensitive potassium channels, causing calcium influx and smooth-muscle contraction) and prostaglandin E2 falls, then anatomically over two to three weeks by intimal proliferation to become the ligamentum arteriosum. The congenital PDA represents failure of this closure in a structurally mature duct, and the persistent channel produces a left-to-right shunt once pulmonary vascular resistance falls below systemic resistance, the direction and magnitude of which are set by the PVR:SVR balance and the duct diameter. [1]

(b) Bedside and echocardiographic burden. The bedside signature is the continuous machinery murmur at the upper left sternal edge (it does not respect the cardiac cycle because the aorta-to-pulmonary-artery gradient persists throughout), with bounding collapsing pulses and a widened pulse pressure and low diastolic pressure reflecting diastolic run-off into the pulmonary bed. Echocardiography defines the burden by integrating the duct size and flow pattern, the peak systolic flow velocity (high velocity = restrictive duct with normal pulmonary pressure; low velocity = elevated pulmonary pressure), the left atrial to aortic root ratio (above 1.5 suggesting left-heart volume overload), and left ventricular size and pulmonary pressure estimation. [1] [6]

(c) Differential diagnosis. The continuous-murmur differentials are the coronary arteriovenous fistula, a systemic arteriovenous malformation, an aortopulmonary window and the innocent venous hum (infraclavicular, abolished by head turning or neck-vein pressure). The bounding-pulse differentials are aortic regurgitation and coarctation (bounding upper-limb pulses with weak femorals, which may coexist with a PDA and must be excluded). In the failing infant, a ventricular or atrioventricular septal defect mimics the pulmonary over-circulation and failure to thrive, and the echocardiogram resolves the differential. [1]

SAQ 2 (10 marks)

Question. Discuss the management of a patent ductus arteriosus in a child, including the indications for the different interventions, the key complications, and the contraindication to closure. [1]

The management ladder. Management matches the intervention to the haemodynamic burden. The silent or small duct with no load is observed with interval echocardiography, as most small ducts close spontaneously and the absolute endocarditis risk is too low to justify routine closure. The moderate duct with preserved pulmonary pressures in a child large enough for the delivery sheath is closed by transcatheter device occlusion with the Amplatzer Duct Occluder, the default since the Masura landmark study, with closure rates above 95% as a day-stay procedure. Surgical ligation by thoracotomy is reserved for the small infant in whom the device sheath cannot be accommodated or the device-unfriendly duct (Krichenko type B window or D complex). [1] [2]

Indications and the closure window. The clear indication is the significant left-to-right shunt with a haemodynamic burden (heart failure, failure to thrive, left-heart dilation) and preserved, reversible pulmonary vascular resistance. The central concept is the window of operability: the duct should be closed before the rising pulmonary vascular resistance becomes fixed. For the large or late-presenting duct where pulmonary vascular disease is suspected, cardiac catheterisation with vasodilator testing measures the pulmonary vascular resistance and tests reversibility before any closure. [6] [7]

Complications. From the untreated significant shunt: failure to thrive, recurrent lower-respiratory infections, pulmonary oedema, and progressive pulmonary vascular disease culminating in Eisenmenger physiology. From transcatheter closure: residual shunt with haemolysis, device embolisation, and in small infants left pulmonary artery stenosis and aortic coarctation from device protrusion. From surgical ligation: left recurrent laryngeal nerve injury with vocal-cord paralysis, chylothorax and phrenic nerve injury. [3] [4]

Contraindications and safety. Two situations define the contraindications. First, established Eisenmenger physiology with fixed, non-reactive pulmonary vascular resistance — closure removes the low-pressure pop-off and can precipitate right-heart failure, so it is withheld and pulmonary-hypertension therapy is commenced instead. Second, and before any closure is planned, a structurally normal heart must be confirmed on echocardiography to exclude a duct-dependent circulation (hypoplastic left heart, critical coarctation, pulmonary atresia), because closing such a duct is catastrophic. The AHA 2007 revision also removed routine endocarditis prophylaxis for the unrepaired PDA, removing the historical rationale for closing every silent duct. [5] [6]