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. Cardiovascular examination reveals a continuous murmur at the left sternal border and bounding femoral and palmar pulses. Echocardiography confirms the diagnosis. Compared to a newborn with a normal cardiovascular system, this patient most likely has which of the following changes in cardiac parameters?
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This extremely premature newborn's continuous murmur and bounding peripheral pulses are consistent with a patent ductus arteriosus (PDA). A PDA allows left ventricular (LV) output to flow from the aorta directly into the pulmonary artery; because aortic pressure is higher than pulmonary arterial pressure during both systole and diastole, left-to-right shunting occurs throughout the cardiac cycle and creates the classic continuous murmur.
The low-resistance pathway into the pulmonary circulation effectively decreases systemic vascular resistance (SVR) compared to the normal circulatory system. Pulmonary overcirculation occurs with increased blood return to the left atrium and left ventricle (ie, left-sided volume overload). The left ventricle compensates for the increased preload (increased blood return) and reduced afterload (reduced SVR) by increasing stroke volume and cardiac output, which leads to increased pulse pressure (large difference between diastolic and systolic blood pressures) and bounding pulses.
(Choices A, B, D, and E) A PDA initially manifests with an overall decrease in SVR due to shunting of aortic blood into the low-resistance pulmonary circulation. Over time, left-sided volume overload caused by a large PDA can lead to LV failure and reduced cardiac output, which may induce a reflexive increase in SVR in an effort to maintain organ and tissue perfusion. However, bounding pulses (as seen in this patient) are not expected once LV failure develops and cardiac output drops.
Educational objective:
A patent ductus arteriosus allows blood from the aorta to flow directly into the pulmonary artery, which effectively decreases systemic vascular resistance. Pulmonary overcirculation occurs with increased blood return to the left atrium and left ventricle, and the left ventricle compensates by increasing stroke volume and cardiac output.