A 6-week-old infant is brought to the office due to difficulty feeding. The patient was born at 39 weeks gestation via spontaneous vaginal delivery. He is breastfeeding for 5 minutes per side every 3 hours. The patient has profuse sweating and difficulty breathing with feeds. Weight is at the 5th percentile. On examination, the patient is tachypneic. Cardiac examination shows a holosystolic murmur at the left lower sternal border; a palpable thrill is present at the left sternal border. Compared to a healthy infant, this patient likely has which of the following intracardiac pressure changes?

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11ec160b_3ca6_d381_9249_57bae3b6d33d_MD0001_00 This patient's holosystolic murmur along the lower left sternal border and a palpable thrill are consistent with a ventricular septal defect (VSD), an abnormal communication between the right ventricle (RV) and the left ventricle (LV). Although small VSDs are typically asymptomatic, large VSDs often present in early infancy with signs of heart failure (eg, poor feeding, sweating/tachypnea with feeds) and failure to thrive due to left-sided volume overload with inability to maintain adequate cardiac output. In utero, vascular resistance against left- and right-sided cardiac outflow is nearly equal. At birth, once the placenta is no longer responsible for oxygenation, pulmonary vascular resistance drops and systemic vascular resistance increases. In patients with VSD, this transition causes shunting of blood from the LV to the RV due to increased left-sided cardiac pressure relative to right-sided pressure. The unrestricted blood flow to the RV causes increased pressure in the RV (Choices B and D) and allows a large volume of blood from the LV to reenter the pulmonary circulation; this high volume of recirculating blood leads to left-sided volume overload with increased pressure in the LV and left atrium (Choices A and C). Right atrial pressure is unchanged. Educational objective: Ventricular septal defect causes left-to-right shunting with increased right ventricular pressure and, if large, left-sided volume overload with increased left ventricular and left atrial pressures. A holosystolic murmur is characteristic, and failure to thrive and signs of heart failure (eg, poor feeding, diaphoresis) can occur. __________ References: Ventricular septal defect. (http://www.ncbi.nlm.nih.gov/pubmed/29261884)

A 6-Week-Old Infant Is Brought to the Office Due to Difficulty