A newborn infant is examined 2 hours after vaginal delivery. Auscultation reveals a continuous 'machinery' murmur at the left infraclavicular area. Which of the following is the most common site of patency in persistent fetal circulation?

Explanation

## Persistent Fetal Circulation Shunts **Key Point:** The ductus arteriosus is the most common site of clinically significant patency in persistent fetal circulation, presenting with a continuous 'machinery' or 'continuous' murmur. ### Anatomical Basis The ductus arteriosus is a muscular vessel connecting the pulmonary artery to the descending aorta. In fetal life, it allows right-to-left shunting to bypass the fluid-filled, high-resistance lungs. After birth, increased systemic oxygen and decreased pulmonary vascular resistance trigger closure via smooth muscle contraction, followed by fibrosis and permanent closure (forming the ligamentum arteriosum). ### Clinical Features of Patent Ductus Arteriosus (PDA) - **Continuous 'machinery' murmur** at the left infraclavicular or left subclavicular area - **Wide pulse pressure** (bounding pulses, low diastolic pressure) - **Hyperactive precordium** - Left-to-right shunt (in most cases) leading to pulmonary overcirculation ### Frequency of Patency | Fetal Shunt | Incidence of Pathological Patency | Clinical Significance | |---|---|---| | **Ductus arteriosus** | Most common (1:2000–1:5000 live births) | High — causes hemodynamic compromise | | Foramen ovale | Common (25% adults) | Usually asymptomatic unless large | | Ductus venosus | Rare | Usually closes by 3–7 days | | Umbilical vein | Closes immediately at birth | Not a source of persistent shunt | **High-Yield:** Patent ductus arteriosus is the most common cause of a continuous murmur in a newborn and the most frequent persistent fetal shunt requiring intervention. ### Why Other Sites Are Less Common - **Foramen ovale:** Functionally closes when left atrial pressure exceeds right atrial pressure; true patency is usually probe-patent and hemodynamically insignificant unless large. - **Ductus venosus:** Closes within days; rarely persists pathologically. - **Umbilical vein:** Closes immediately after cord clamping; cannot remain patent as a functional shunt. **Clinical Pearl:** A continuous murmur in a newborn is PDA until proven otherwise. Echocardiography (2D echo with color Doppler) is the gold standard for confirmation.