A 1-week-old boy is brought to the office for his first primary care visit following an uncomplicated vaginal delivery at 40 weeks gestation. The patient was born to a 30-year-old woman who took prenatal vitamins throughout the pregnancy. The nursery course was uncomplicated, and he was discharged at approximately 30 hours of life following observation of appropriate breastfeeding, voiding, and stooling. Weight, length, and head circumference are at the 50th percentile. Physical examination shows a grade II/VI harsh, holosystolic murmur best heard at the left-mid to left-lower sternal border. The rest of the examination is unremarkable. Review of medical records shows absence of the murmur at birth. This patient's findings are most likely due to which of the following embryologic events?
This patient's harsh, holosystolic murmur is characteristic of ventricular septal defect (VSD), occurring due to inadequate development of the interventricular septum. This septum is composed of muscular and membranous portions; failed fusion of any of its derivative parts results in VSD. The associated murmur may not be audible immediately after birth due to high pulmonary vascular resistance (PVR) that limits left-to-right shunting through the VSD; it typically develops over the ensuing days as PVR declines (as in this case).
Small VSDs are typically asymptomatic due to the small volume of shunted blood, but turbulent flow through this narrow connection causes a harsh, holosystolic murmur at the left-mid to left-lower sternal border. Unlike larger defects, small VSDs usually undergo spontaneous closure.
Moderate to large VSDs lead to pulmonary overcirculation and left-sided volume overload that can cause heart failure (eg, diaphoresis, failure to thrive); larger shunts increase the risk. Because of relatively unrestricted flow compared to smaller defects, auscultation typically demonstrates a softer or no murmur. Chronic left-to-right shunting can also eventually lead to pulmonary hypertension with shunt reversal and resulting cyanosis (Eisenmenger syndrome).
(Choices A and B) Atrial septal defect (ASD) can occur due to failed fusion of the septum primum and endocardial cushions (primum ASD) or to arrested growth of the septum secundum (secundum ASD); it permits left-to-right shunting. The characteristic systolic ejection murmur best heard over the second intercostal space is caused by right-sided volume overload and increased flow across the pulmonic valve.
(Choice C) Patent ductus arteriosus (PDA) occurs due to failed obliteration of the vascular connection between the pulmonary artery and aorta and allows left-to-right shunting. Like VSD, a PDA murmur typically increases in intensity as PVR declines following birth; the continuous murmur is best heard at the left upper sternal border.
(Choice E) Malalignment of the infundibular septum can cause varying degrees of right ventricular outflow tract (RVOT) obstruction, as in tetralogy of Fallot. Patients typically have a large VSD and a murmur created by flow through the partially obstructed RVOT (crescendo-decrescendo murmur best heard along the left mid to upper sternal border).
Educational objective:
Ventricular septal defect occurs due to insufficient development of the interventricular septum and commonly presents with a holosystolic murmur at the left lower sternal border as pulmonary vascular resistance declines in the neonatal period. Presentation varies from asymptomatic murmur (small defect) to heart failure (large defect).