A newborn girl is evaluated in the nursery for a heart murmur. The infant was born at 39 weeks gestation via spontaneous vaginal delivery following an uncomplicated pregnancy. She has been breastfeeding well and has urinated 3 times and stooled once. Approximately 1 hour after delivery, a 2/6 systolic murmur could be heard at the left upper sternal border. At age 8 hours, the murmur could be heard during both systole and diastole. Examination at age 24 hours revealed no murmur. Which of the following is most likely responsible for the disappearance of this patient's murmur?

Question

A newborn girl is evaluated in the nursery for a heart murmur.  The infant was born at 39 weeks gestation via spontaneous vaginal delivery following an uncomplicated pregnancy.  She has been breastfeeding well and has urinated 3 times and stooled once.  Approximately 1 hour after delivery, a 2/6 systolic murmur could be heard at the left upper sternal border.  At age 8 hours, the murmur could be heard during both systole and diastole.  Examination at age 24 hours revealed no murmur.  Which of the following is most likely responsible for the disappearance of this patient's murmur?

Quizplus · Accepted Answer

11ec160b_3a99_2931_9249_dbf6c4d3f44d_MD0001_00 The changes in this infant's heart murmur throughout the first day of life are most likely explained by the evolution of a patent ductus arteriosus (PDA). During fetal life, blood flows right to left through a PDA from the pulmonary artery to the aorta. This is due to high pulmonary vascular resistance (PVR) caused by the constricted pulmonary arteries and low systemic vascular resistance (SVR) caused by the low resistance of the placenta. However, after delivery, increased oxygen tension and decreased carbon dioxide tension in the lungs causes pulmonary vasodilation and reduced PVR. At the same time, umbilical cord clamping disconnects the placenta from the infant's systemic circulation, leading to increased SVR. These changes decrease pulmonary pressure and increase systemic pressure, reversing right-to-left blood flow across the PDA to left-to-right shunting. Just after birth, pulmonary diastolic pressure is still high relative to systemic diastolic pressure, so the murmur is heard best (or only) during systole. As the PVR continues to fall, systemic pressure exceeds pulmonary pressure throughout the cardiac cycle, and the classic machine-like continuous murmur is heard. When the PDA closes (usually 24-48 hr after birth), the murmur disappears. (Choices B, D, and F) After birth, right-to-left shunting (ie, Eisenmenger syndrome) may eventually develop through a PDA, an atrial septal defect (ASD), or a ventricular septal defect (VSD). However, postnatal right-to-left shunting usually causes cyanosis (not noted in this patient), and the pressure gradient is not typically large enough to cause a murmur. (Choice C) Left-to-right flow through an ASD does not typically generate a murmur itself. The characteristic murmur of ASD, a systolic murmur at the left upper sternal border, is caused by increased blood flow through the pulmonic valve. However, the murmur does not change to a continuous murmur. (Choice E) Left-to-right flow through a VSD can cause a holosystolic murmur at the left sternal border, but the murmur does not have a diastolic component. Educational objective: After birth, pulmonary vascular resistance progressively decreases and systemic vascular resistance progressively increases, resulting in decreased pulmonary pressure and increased systemic pressure. As the relative pressures in the pulmonary artery and aorta change, the patent ductus arteriosus (PDA) murmur evolves from systolic only to continuous before the PDA closes and the murmur disappears.

A Newborn Girl Is Evaluated in the Nursery for a Heart