A newborn two weeks old has a thrill and a continuous machinery murmur in the left second intercostal space. Most likely diagnosis?

• A. Patent ductus arteriosus
• B. Ventricular septal defect
• C. Tetralogy of Fallot
• D. Coarctation of the aorta

Answer: (A)

A continuous, machinery-like murmur heard best in the left second intercostal space in a newborn is classic for patent ductus arteriosus. The ductus arteriosus normally closes after birth, but when it stays open there is a persistent left-to-right shunt from the aorta into the pulmonary artery that occurs throughout systole and diastole, producing a murmur that spans the whole cardiac cycle. A thrill may be present if the shunt is large, reflecting important flow through the ductus.

This lesion causes increased pulmonary blood flow and can lead to left heart volume overload; the finding at two weeks fits with a PDA that has not yet closed. Other congenital defects have different murmur patterns: a ventricular septal defect causes a holosystolic murmur at the left lower sternal border; Tetralogy of Fallot produces a harsh systolic murmur due to right ventricular outflow obstruction and often cyanosis; coarctation of the aorta typically presents with a systolic murmur and diminished leg pulses rather than a continuous murmur in the chest.