Anatomy Thorax Abdomen · Year 1 · from Anatomy Thorax Abdomen
Case 1: Ventricular Septal Defect
Clinical Presentation
A 6-week-old infant is brought to the pediatric clinic for a routine well-child visit. The mother reports the baby feeds slowly and tires easily during breastfeeding. On examination, the infant appears small for age with mild tachypnea at rest. Cardiac auscultation reveals a grade 4/6 harsh holosystolic murmur best heard at the left lower sternal border, with a palpable thrill. There is no cyanosis.
Echocardiography demonstrates a 6 mm perimembranous ventricular septal defect (VSD) in the membranous portion of the interventricular septum with left-to-right shunting. The left atrium and left ventricle are mildly dilated due to volume overload from the shunt. Pulmonary artery pressures are mildly elevated. The infant is started on diuretic therapy to manage symptoms, with surgical repair planned at 4-6 months of age if the defect does not decrease in size.
Radiographic Findings
Image: Illustration of a ventricular septal defect showing abnormal communication between the left and right ventricles. Blood shunts from left to right due to the higher pressure in the left ventricle. Source: Wikimedia Commons, Public Domain.
Key Anatomical Points
- The interventricular septum has two components: a small membranous part superiorly (less than 1 mm thick) and a large muscular part (90% of septum)
- The membranous septum lies just below the aortic valve and is the most common site of ventricular septal defects
- The bundle of His penetrates the cardiac skeleton adjacent to the membranous septum, making this area surgically challenging
- Left ventricular pressure (120 mmHg systolic) exceeds right ventricular pressure (25 mmHg systolic), causing left-to-right shunting
Key Learning Points
- VSDs are the most common congenital heart defect, occurring in approximately 1-2 per 1000 live births
- The cardiac skeleton provides electrical insulation between atria and ventricles - the bundle of His is the only electrical connection
- Small muscular VSDs may close spontaneously as the muscular septum grows; membranous VSDs rarely close
- Understanding septal anatomy is essential for surgical repair to avoid damage to the conduction system