Acyanotic congenital heart defects: Pathology review

In a pediatric cardiology clinic, 4-year-old Tara is brought in by her parents because she has not been acting herself over the past month. The mother also mentioned that she can’t keep up with the other children when playing and often gets fatigued or short of breath. Vital signs include a temperature of 37.0 degrees Celsius or 98.6 degrees Fahrenheit, a heart rate of 100 beats per minute, a blood pressure of 110 over 70 mmHg, and a respiratory rate of 18 breaths per minute. On examination, her skin is pink, and auscultation of the heart reveals a holosystolic murmur over the left sternal border.

Ok, so Tara has some sort of congenital heart defect. Congenital heart diseases are defects in the embryological development of the heart or its major blood vessels. When the defect causes blood to move from the right to the left side, it’s called a right-to-left shunt. This is because deoxygenated blood from the right side goes to the left side, and then enters the systemic circulation. A large amount of deoxygenated blood in the systemic circulation gives the physical appearance of cyanosis, which is a bluish discoloration of the skin. Therefore, right-to-left defects are called cyanotic heart diseases. Conversely, left-to-right shunts are called acyanotic heart defects, because there is no cyanosis. In general, individuals with acyanotic congenital heart diseases could be asymptomatic or present with signs of heart failure, such as exercise intolerance, shortness of breath, and in the case of infants and young children; poor feeding and failure to thrive.

Okay, of the acyanotic congenital heart diseases, ventricular septal defect, or VSD, is the most common. The ventricular septum normally separates the left and right ventricles, and is made of a membranous component, which is the upper one-third, and a muscular component, which is the lower two-thirds. The defect most commonly occurs in the membranous portion of the septum. Ventricular septal defects are usually small and they often end up closing on their own. Individuals are asymptomatic at birth, and if symptoms develop, they usually occur a couple of weeks later or even later in life. This is a helpful clue on exams. On auscultation, a systolic murmur can be heard along the left sternal border. Bear in mind though that the smaller the defect, the more audible the murmur. That’s because when blood rushes through a more narrow opening, it produces more turbulence and therefore, more noise. In addition, because the defect allows oxygenated blood to move from the left to the right side of the heart, the oxygen saturation will be higher than normal in the right ventricle and the pulmonary artery.