Patent ductus arteriosus — viva

Examiner prompt 1 — interpretation of the stimulus

Examiner. What is the most likely diagnosis, and what physiological process explains these findings? ^[1]

Candidate. This is a long-standing large patent ductus arteriosus that has crossed into Eisenmenger physiology. The previously continuous murmur has softened and shortened because the aorta-to-pulmonary-artery pressure gradient has narrowed as the pulmonary vascular resistance has risen to equal systemic pressure. The loud pulmonary component of the second sound reflects the pulmonary hypertension, and the differential cyanosis (cyanotic toes, pink fingers) is the hallmark of shunt reversal — deoxygenated blood now flows right-to-left through the duct into the descending aorta, distal to the subclavian arteries. This is not spontaneous closure; it is the dangerous endpoint of an unrepaired large shunt. ^{[1] [4]}