A 12-day-old girl is evaluated in the neonatal intensive care unit (NICU) due to a murmur. The patient was born at 25 weeks gestation and was admitted to the NICU for respiratory support. She was born to a 21-year-old primigravida whose pregnancy was complicated by preeclampsia. Cardiac auscultation reveals a continuous murmur at the left sternal border, and bounding femoral and palmar pulses are palpable. Echocardiography confirms the diagnosis. Compared with a normal infant, this patient most likely has which of the following changes in cardiac parameters?

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11ec160b_3c9d_f9c1_9249_4ba328300152_MD0001_00 This extremely preterm infant's continuous murmur and bounding peripheral pulses are consistent with a patent ductus arteriosus (PDA). PDA allows left ventricular output to flow from the aorta into the low-resistance pulmonary circulation. Because systemic blood pressure is higher than pulmonary blood pressure during both systole and diastole, a left-to-right shunt occurs throughout the cardiac cycle and results in the classic continuous murmur. This left-to-right shunt lowers systemic vascular resistance (SVR), resulting in decreased diastolic blood pressure and bounding pulses due to the increased pressure gradient between systole and diastole. Increased blood flow into the pulmonary artery causes increased venous return to the left atrium and left ventricle. Initially, the heart compensates for the increased preload and decreased afterload (↓ SVR) by increasing left ventricular output. (Choices A and B) Large, uncorrected PDAs can result in volume overload and eventual left ventricular failure in infancy. However, this would present with symptoms of overt heart failure (eg, respiratory distress, poor capillary refill), which are not seen in this patient. (Choices D and E) A PDA initially reduces SVR due to the large run-off of arterial blood into the low pressure pulmonary circulation. Over time, increased pulmonary blood flow can cause the pulmonary vasculature to become congested and hypertrophy, resulting in increased pulmonary resistance and a reversal of the shunt to right-to-left (Eisenmenger physiology). However, this process takes years; shunt reversal typically manifests in older children and adults. Educational objective: Patent ductus arteriosus results in increased left ventricular preload (due to increased pulmonary venous return to the left atrium) and decreased systemic vascular resistance (due to the continuous left-to-right shunt). This combination of higher preload and lower afterload leads to an early increase in left ventricular cardiac output.

A 12-Day-Old Girl Is Evaluated in the Neonatal Intensive Care